فهرست مطالب

فصلنامه فیزیک زمین و فضا
سال چهل و چهارم شماره 3 (پاییز 1397)

  • تاریخ انتشار: 1397/08/06
  • تعداد عناوین: 15
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  • امین رشیدی، ظاهر حسین شمالی*، ناصر کشاورز فرج خواه صفحات 495-508

    درحالی که توجه جهانی به سمت پدیده سونامی به خصوص در مناطق شرقی اقیانوس هند در نزدیکی اندونزی افزایش یافته، مکران غربی که در شمال غرب اقیانوس هند و در دریای عمان واقع است به عنوان یک ناحیه دارای پتانسیل خطر سونامی کمتر مورد توجه واقع شده است. عدم رخداد زمین لرزه طی سالیان طولانی در این ناحیه احتمال قفل شدگی مکران غربی را افزایش داده که در این صورت می توان انتظار داشت که خطر سونامی بالقوه ای در آینده سواحل مکران و دریای عمان را تهدید خواهد کرد. هدف این مطالعه شبیه سازی عددی فرآیند تولید سونامی محتمل در منطقه مکران غربی با هدف محاسبه شرایط اولیه برای انتشار سونامی می باشد. برای این منظور با در نظر گرفتن یک سناریو با پارامترهای مشخص در دریای عمان میدان دگرشکلی حاصل از این چشمه سونامی با استفاده از الگوریتم اکادا محاسبه شد. نتایج حاصل از این مطالعه الگوی مقطع اولیه سونامی را که شامل بالاآمدگی و فروافتادگی است در سرتاسر ناحیه مورد مطالعه نشان می دهد. خروجی حاصل از این مدل سازی به عنوان ورودی مدل سازی انتشار سونامی استفاده می شود.

    کلیدواژگان: سونامی، مکران غربی، دریای عمان، شبیه سازی عددی، تولید سونامی
  • امین رشیدی، ظاهر حسین شمالی*، ناصر کشاورز فرج خواه صفحات 509-521

    باتوجه به ابهاماتی که در مورد خطرپذیری و پتانسیل خطر وقوع سونامی در سواحل جنوبی ایران وجود دارد، برای درک بهتر خطر سونامی و آمادگی در مقابله با وقوع آن به خصوص برای منطقه مکران غربی مدل سازی سونامی امری ضروری و لازم می باشد. هدف این مطالعه شبیه سازی عددی فازهای انتشار امواج سونامی در دریای عمان و شمال اقیانوس هند و بالاروی آن به هنگام رسیدن به سواحل مکران غربی در ایران می باشد. در این مطالعه، مدل سازی هیدرودینامیکی برای شبیه سازی انتشار سونامی در دریای عمان و شمال اقیانوس هند و بالاروی و گسترش سونامی در سواحل جنوب شرق ایران مورد استفاده قرار گرفت. در این مطالعه به منظور شبیه سازی انتشار و بالاروی سونامی از یک شبکه تودرتو استفاده شد. مدل سازی بالاروی سونامی در منطقه مکران غربی به ترتیب به غرب، میانه و شرق سواحل مکران در ایران تقسیم شد و برای هر منطقه به صورت جداگانه مدل سازی عددی بالاروی و سیل سونامی انجام شد. چگونگی گسترش و انتشار امواج سونامی، بیشینه ارتفاع موج، بالاروی و سیل امواج و سری زمانی سونامی در نقاطی خاص از جمله نتایج به دست آمده از این مطالعه می باشند.

    کلیدواژگان: سونامی، مکران غربی، ایران، شبیه سازی عددی، انتشار و بالاروی سونامی
  • محسن فیضی، مهدی روفیان نایینی صفحات 523-534
    در این مقاله با استفاده از مشاهدات گرانی سنجی هوایی برداری در منطقه ای از کشور تانزانیا، مدل سازی محلی میدان گرانش با استفاده از دو روش مختلف و برمبنای بسط به توابع هارمونیک محلی صورت می گیرد. بدین منظور، در روش اول، جواب مساله مقدار مرزی دیرخله برای معادله لاپلاس، با مقادیر مرزی تعریف شده در محدوده یک کلاهک کروی حل می شود. در این حالت جواب معادله لاپلاس بر مبنای ترکیب خطی توابع لژاندر وابسته از مرتبه صحیح و درجه غیرصحیح بیان می شود، که به توابع هارمونیک کلاه کروی معروف هستند. درروش دوم، معادله لاپلاس در سیستم مختصات کارتزین محلی حل می شود و مقادیر مرزی در این حالت در یک محدوده مسطح از سطح زمین در نظر گرفته می شوند. در این روش، جواب معادله لاپلاس، برحسب ترکیب توابع مثلثاتی به عنوان توابع پایه بیان می شود، که به آنها، هارمونیک های مستطیلی گفته می شود. به منظور بررسی کارایی هر یک از روش های ذکر شده، از مشاهدات گرانی سنجی هوایی برداری بر فراز منطقه ای در تانزانیا جهت برآورد پارامترهای هر مدل (ضرایب هارمونیک هر مدل) استفاده شده است. کمترین مقدار اختلافات بین مدل هارمونیک مستطیلی و نقاط کنترل برای درجه ی80 (به عنوان درجه ی بهینه ی بسط) در مناطق داخلی حدود 2 تا 3 میلی گال و برای مناطق لبه ای بین 8 تا 9 میلی گال حاصل شد. کمترین مقدار اختلافات بین مدل هارمونیک کلاه کروی و نقاط کنترل برای درجه 100 (به عنوان درجه بهینه بسط) در مناطق داخلی کمتر از یک میلی گال و حدود 3 میلی گال برای مناطق لبه ای به‎ دست آمد.
    کلیدواژگان: آنالیز هارمونیک کلاه کروی، آنالیز هارمونیک مستطیلی، میدان گرانش محلی، گرانی سنجی هوایی، مدل ژئوپتانسیل
  • مهدی فلاح صفری، محمدکاظم حفیظی ، رضا قناتی صفحات 535-555
    روش سونداژ تشدید مغناطیسی تنها روش ژئوفیزیکی است که به طور مستقیم به مولکول های آب زیرسطحی حساس می باشد. با استفاده از وارون سازی داده های سونداژ تشدید مغناطیسی می توان اطلاعات مهمی از قبیل ضخامت و عمق لایه آبخوان، محتوای آب و در شرایطی مناسب، میزان رسانندگی هیدرولیکی لایه آبدار را به دست آورد. این روش به شدت به اندازه و نوع نوفه حساس است؛ لذا تخمین پارامترهای سیگنال و نیز وارون سازی آن حساسیت بالایی دارد. وارون سازی داده های سونداژ تشدید مغناطیسی یک مساله بدوضع می باشد و نمی توان با استفاده از روش های مستقیم آن را حل کرد. به همین دلیل استفاده از روش های منظم سازی در وارون سازی سونداژ تشدید مغناطیسی امری اجتناب ناپذیر است. روش های متعددی جهت حل مساله وارون سونداژ تشدید مغناطیسی پیشنهاد شده است. رهیافت هندسه ثابت و رهیافت هندسه متغیر، همراه با بهره گیری از روش های مختلف بهینه سازی تابع هدف از جمله این روش ها است. در این مقاله از رهیافت هندسه ثابت و اعمال منظم سازی تیخنوف همراه با قیدهای مناسب، جهت وارون سازی و مدل سازی پیشرو استفاده شده است. خروجی حاصل از داده های مصنوعی، و داده هایی از ایران و آلمان به عنوان داده های کم آب و پرآب، نتایج قابل قبولی از تغییرات محتوای آب نسبت به عمق و به کار گیری روش ارائه شده نشان می دهد.
    کلیدواژگان: تنظیم تیخنوف، سونداژ تشدید مغناطیسی، محتوای آب، وارون سازی
  • تکتم زند، حمیدرضا سیاه کوهی *، علی غلامی صفحات 557-573

    مهاجرت به روش کیرشهف یکی از ساده ترین و رایج ترین الگوریتم های مهاجرت داده های لرزه ای است. از آنجا که عملگر مهاجرت کیرشهف، الحاقی عملگر مدل سازی است، قادر به بازسازی درست دامنه بازتاب ها نبوده و تصویر نهایی مهاجرت یافته دارای وضوح کافی نخواهد بود. مهاجرت کمترین مربعات برای رفع این مشکل و بازسازی صحیح دامنه معرفی شد اما بخاطر ابعاد بزرگ ماتریس ها، حل مساله به صورت تکراری انجام می شود که زمان بر است. اگرچه در مقایسه با حل الحاقی، حل کمترین مربعات موجب بهبود دامنه می شود، ولی تصویر حاصل کماکان وضوح کافی نخواهد داشت. در این مقاله با منظم سازی نرم-1 برای تزریق تنکی به جواب کمترین مربعات کیرشهف یک روش مهاجرت با تفکیک پذیری بالا ارائه می شود. در اینجا مهاجرت لرزه ای به شکل یک مساله بهینه سازی با قید تنکی فرمول بندی و با الگوریتم شکافت عملگری برگمن حل می شود. از خصوصیات مطلوب این الگوریتم همگرایی بالا و حل مسائل مقید بدون نیاز به محاسبات وارون ماتریس و تنها با استفاده از عملگرهای مهاجرت و مدل سازی است. نتایج حاصل از داده های شبیه سازی شده عملکرد بسیار بهتر الگوریتم پیشنهادی به لحاظ تفکیک پذیری در قیاس با الگوریتم مرسوم مهاجرت کیرشهف را نشان می دهند. مهاجرت کمترین مربعات قادر به کاهش اثرات ناشی از ناقص بودن داده در تصویر مهاجرت یافته می باشد. لذا روش پیشنهادی نیز با افزایش کیفیت تصویر حاصل از مهاجرت کمترین مربعات، تصویری مهاجرت یافته از یک داده ناقص با تفکیک پذیری بالاتری تولید خواهد کرد. نتایج حاصل از اعمال روش بر روی داده مصنوعی و واقعی عملکرد مطلوب آن را نشان می دهد.

    کلیدواژگان: مهاجرت کیرشهف، مهاجرت کمترین مربعات، تفکیک پذیری، منظم سازی نرم-1، تنکی، بهینه سازی تنک، شکافت عملگری برگمن
  • میثم مقدسی، علی نجاتی کلاته ، محمد رضایی صفحات 575-583
    مدل سازی وارون داده های گرانی، یکی از موثرترین ابزارهای عددی به منظور به دست آوردن تصاویر سه بعدی از ساختار های زمین شناسی است. یکی از پارامترهای موثر برای تولید مدلی مناسب در مدل سازی معکوس داده های گرانی همانند اغلب روش های مدلسازی معکوس داده های ژئوفیزیکی پارامتر منظم سازی است. روش‏های مختلفی برای این پارامتر در وارون‏سازی داده‏های گرانی مورد استفاده بوده است. در این مقاله از روش متعادل سازی قید فعال (ACB) به عنوان روشی جدید برای تخمین مناسب این پارامتر در وارون سازی دوبعدی داده های گرانی سنجی پرداخته می شود. برای این منظور الگوریتم طراحی شده بر روی یک مدل مصنوعی و یک مجموعه داده های واقعی گرانی سنجی مربوط به ذخیره کرومیت در منطقه ماتانزاس در کشور کوبا مورد مطالعه قرار گرفته است. نتایج حاصل از وارون سازی دو بعدی در این منطقه با حفاری های موجود سازگاری دارند و نشان می دهد که الگوریتم پیشنهادی می تواند تخمین مناسبی از توزیع چگالی و ساختارهای زیر سطحی ماده معدنی ارائه کند.
    کلیدواژگان: وارون سازی، داده گرانی، پارامتر منظم سازی، روش (ACB)
  • مهسا افرا ، تقی شیرزاد صفحات 585-594
    مطالعه و بررسی رویدادهای پس لرزه می تواند ابزاری بسیار قدرتمند برای تعیین توابع گرین بین جفت رویدادها و به تبع آن مطالعه ساختار درونی زمین را فراهم آورد. با استفاده از این رویدادها، یکی از پس لرزه ها به عنوان چشمه ی لرزه ای، و پس لرزه دیگر به عنوان گیرنده مجازی در نظر گرفته می شود. پس از زمین لرزه 29 آذر 1389 (MW 6. 5) در بخش پنهان گسل کهورک در منطقه ریگان در جنوب شرق ایران، پس لرزه ها در پهنه صفحه گسلی توزیع گردید. این مطالعه، بازسازی توابع گرین بین جفت رویداد پس لرزه و انتشار آن را در بخش پنهان صفحه گسل کهورک بررسی می نماید. لذا با استفاده از شروطی، نظیر مقدار بزرگی پس لرزه ها (M>2) ، عمق یکسان پس لرزه ها و نسبت سیگنال به نوفه شکل موج آنها (SNR≥4) ، جفت رویداد 031-163 گزینش و تابع گرین مرتبط با آن بازسازی گردید. همچنین مدل سازی مصنوعی یک بعدی و دوبعدی علاوه بر آن که بازسازی این تابع گرین را تصدیق می نماید، انتشار این سیگنال را برصفحه گسل تایید می کند.
    کلیدواژگان: تابع گرین، گیرنده مجازی، تداخل سنجی، صفحه گسل، ریگان
  • مهدی گلی صفحات 595-606
    اثر جاذبی توپوگرافی یکی از مولفه های مهم میدان گرانی است که سهم مهمی در مطالعات ژئوفیزیک و ژئودتیکی را ایفا می کند. برای تفاسیر ژئوفیزیکی لازم است اثر توپوگرافی به عنوان عامل مزاحم از داده های جاذبی اندازه گیری شده حذف شود. در حل مسائل مقدار مرزی ژئودتیکی توپوگرافی مانعی برای هارمونیک بودن فضا است. این مطالعه به نحوه محاسبه اثر توپوگرافی اجرام نزدیک تا فاصله 1. 5 درجه (برابر 167 کیلومتر) موسوم به زون هایفورد-بووی می پردازد. رابطه ریاضی برای این منظور مشتق ارتفاعی انتگرال نیوتن و داده های مورد استفاده مدل های رقومی ارتفاعی است. کارایی چهار روش مبتنی بر المان تسرویید با روش منشور مقایسه می شود. این روش ها شامل: انتگرال گیری عددی با قاعده نمایی مضاعف موسوم به روش فوکوشیما، انتگرال گیری عددی بروش مارتینک-ونیچک، بسط سری تیلور موسوم به هک-سویتز و روش نقطه مادی همگی دارای تقریب کروی هستند. برای آزمون صحت نتایج روش های مختلف، از یک مدل تحلیلی (توپوگرافی مصنوعی حاصل از یک کلاهک کروی با ارتفاع 1000متر) با اثر توپوگرافی معلوم استفاده شده است. گسسته سازی این مدل تحلیلی با شبکه های با ابعاد مختلف و در نواحی بسیار نزدیک، نزدیک و دور انجام شد. نتایج عددی حاکی از موفقیت روش منشور برای مدل سازی اثر توپوگرافی برای اجرام نزدیک (ناحیه تا شعاع 18 کیلومتر) نسبت به روش های بر مبنای تسرویید است. در این ناحیه، انتگرال گیری با مدل ارتفاعی با گام بهتر از 30 متر برای تامین دقت 10 میکروگال لازم است. در نواحی 18 کیلومتر تا 167 کیلومتر نتایج عددی همه روش های تعیین اثر توپوگرافی یکسان است.
    کلیدواژگان: اثر توپوگرافی، آنومالی جاذبه، تسرویید، انتگرال گیری عددی، منشور
  • رضا برهانی، فرهنگ احمدی گیوی *، سرمد قادر، علیرضا محب الحجه صفحات 607-624

    هدف این پژوهش مطالعه فراوانی و توزیع جهانی رخداد تاشدگی وردایست، با تاکید بر منطقه جنوب غرب آسیا، و همچنین تغییرات فصلی آن در فاصله سال های 2013 تا 2015 است. بدین منظور میدان های اولیه از قبیل باد، دما و ارتفاع ژئوپتانسیلی از داده های بازتحلیل Interim) ECMWF (ERA- اخذ و میدان های ثانویه مانند تاوایی پتانسیلی (PV) و دمای بالقوه (θ) محاسبه شده است. تشخیص تاشدگی وردایست دینامیکی بر اساس الگوریتم توسعه یافته روش اسپرنگر و همکاران (2003) و گری (2003) و با استفاده از نیمرخ قائم در هر یک از نقاط شبکه انجام شده است. توزیع زمانی- مکانی تاشدگی ها نشان می دهد که فراوانی تاشدگی در عرض های جنب حاره ای و میانی (بین 20 تا 40 درجه) در هر دو نیم کره شمالی و جنوبی بیشتر است و در نیم کره زمستانه نیز این تاشدگی ها از فراوانی بیشتری برخوردارند. منطقه جنوب غرب آسیا در تمام طول سال دارای بی هنجاری مثبت فراوانی تاشدگی نسبت به مقدار میانگین نیم کره شمالی است. میزان بی هنجاری یاد شده در این منطقه طی فصل های مختلف سال متفاوت است و در فصل تابستان هم زمان با شکل گیری واچرخند موسمی بر روی عرض های جنب حاره ای اقیانوس هند، فراوانی تاشدگی وردایست به شدت افزایش می یابد. بیشترین بی هنجاری مثبت در ماه ژوئن و در دو کانون، یکی بر روی ایران-افغانستان و دیگری در شرق مدیترانه اتفاق می افتد. مطالعه موردی انجام شده در ژوئن 2015 تشکیل دو هسته جریان جتی قوی در منطقه را نشان می دهد و بررسی نقشه های نیمرخ قائم میدان های باد افقی، دمای بالقوه و PV مربوط به این ماه نیز وجود دو ناحیه اصلی تاشدگی وردایست واقع در غرب این دو هسته جریان جتی و در زیر آن و همچنین وجود دو ناحیه کژفشاری بارز (طبق توازن باد گرمایی) در محل تشکیل تاشدگی ها را به خوبی تایید می کند.

    کلیدواژگان: تاشدگی وردایست، تاوایی پتانسیلی، دمای بالقوه، جنوب غرب آسیا، موسمی، ناپایداری کژفشار
  • رضا دوستان صفحات 625-640
    دورپیوندهای جهانی با تغییر آرایش گردش جو، با اقلیم مناطق دورتر مرتبط هستند. مهم ترین این پدیده ها برای اقلیم ایران کدامند؟ رابطه دورپیوندهای منطقه ای و جهانی، با استفاده از سری زمانی ماهانه 61 سال (1950 تا 2010) در دوره سرد سال و روش همبستگی پیرسون تعیین شد. نتایج حاکی از آن است که مهم ترین پدیده های جهانی در سطوح میانی جو، دورپیوند دریای شمال- خزر (NCP) و نوسان اطلس شمالی (NAO) است. در فاز مثبت این دو دورپیوند، مرتبط با دورپیوند منطقه ای اروپای غربی-خزر شمالی، کاهش دما و افزایش بارش و در فاز منفی، افزایش دما و کاهش بارش در ایران حادث می شود. همچنین دورپیوندهای جهانی مهم در سطح زمین، نوسان قطبی (AO) ، اسکاندیناوی (SCAN) ، اطلس شرقی- روسیه غربی (EA-WR) و اطلس شرقی (EA) ، مرتبط با دورپیوندهای منطقه ای اروپای شمالی، سیبری شمالی و آسیای مرکزی می باشند که با فاز منفی نوسان قطبی، اسکاندیناوی و فاز مثبت اطلس شرقی- روسیه غربی و اطلس شرقی، کاهش دما و افزایش بارش و در فاز متفاوت، دورپیوندهای فوق با افزایش دما و کاهش بارش در ایران همراه اند. این شش دورپیوند جهانی در مطالعات اقلیمی، پیش بینی و تغییرات اقلیمی برای ایران، مهم ترین پدیده های جهانی دوره سرد سال می باشند.
    کلیدواژگان: دورپيوند جهاني، دورپيوند منطقه اي، دوره سرد، اقليم ايران
  • سحر تاج بخش ، امیرحسین نیک فال صفحات 641-658
    بهمن یکی از مهم ترین مخاطرات وضع هوا در مناطق کوهستانی و برف گیر است و پیش بینی صحیح آن در افزایش ایمنی جاده های کوهستانی نقش موثری دارد. از این رو در این تحقیق کوشش شده است ضمن بررسی شرایط همدیدی رخداد بهمن در یک مطالعه موردی، مهم ترین شاخص های پیش بینی پتانسیل رخداد بهمن با استفاده از یک مدل پیش بینی عددی برآورد و احتمال رخداد بهمن بر اساس یکی روش های کاربردی موجود بررسی شود. مطالعه موردی به گونه ای انتخاب شده که شرایط جوی قابل توجهی برای رخداد بهمن در منطقه دیده نمی شود و تنها یک مورد سقوط بهمن در طول 24 ساعت در منطقه شهرستانک جاده چالوس گزارش شده است. مهم ترین نتایج این بررسی نشان می دهد که الگوهای پیش بینی همدیدی وضع هوا در این مطالعه، با شرایط جوی واقعی همخوانی دارد و ویژگی مشخصی برای وقوع بهمن در این الگوها دیده نمی شود. آستانه های معرفی شده برای پتانسیل وقوع بهمن با رخداد واقعی در این مطالعه همخوانی خوبی دارد. وزش باد کمتر از m/s 9، بارش برف کمتر از 30 سانتی متر در 24 ساعت، افزایش دما کمتر از C° 8 در 12 ساعت، عدم ماندگاری دما در محدوده 4- تا C° 10- و آسمان نیمه ابری در طول روز بدون بار باران، شرایطی است که بر احتمال رخداد بهمن و نه قطعیت آن (پتانسیل نامشخص وقوع بهمن) تاکید دارد و برای پیش بینی پتانسیل بالای وقوع بهمن، آستانه های جوی باید بالاتر از مقادیر یاد شده باشند.
    کلیدواژگان: بسته برف، ضخامت برف، آب معادل برف، بهمن و مدل پیش بینی عددی WRF
  • محمد فرمان آرا، حسین ملکوتی ، اسماعیل حسن زاده صفحات 659-670
    در این تحقیق با استفاده از مدل شبیه سازی پیچک بزرگ موازی سازی شده (PALM) ، ویژگی های لایه اکمن کف خلیج فارس در تابستان و پاییز مطالعه شده است. برای این منظور سه آزمایش عددی با تاکید بر تاثیر چینه بندی بر لایه اکمن طراحی شد. یک آزمایش مرجع بدون گرادیان دما و شوری و دو آزمایش با گرادیان دما و شوری متناسب با شرایط تجربی تابستان و پاییز خلیج فارس پیاده سازی و اجرا شد. نتایج نشان داد هنگامی که چینه بندی در خلیج فارس قوی باشد، لایه اکمن تنها به لایه آمیخته کف محدود می شود و مولفه های سرعت اکمن نمی توانند به لایه های بالایی نفوذ کنند. در پاییز پهنای لایه پیکنوکلاین کمتر است و به 20 متر می رسد؛ درنتیجه مارپیچ اکمن پهن تر و بزرگی مولفه سرعت عمود بر جریان زمینگرد حدود 25% بیشتر می شود. نتایج نشان می دهد که اگر شار گرمایی در کف یا سطح وجود نداشته باشد، با گذر زمان در مرز بین لایه چینه بندی و لایه آمیخته، یک لایه پیکنوکلاین شدید به پهنای حدود 4 متر به وجود می آید که باعث افزایش پایداری شاره و درنتیجه مانع نفوذ جریان های تلاطمی می شود. چینه بندی تاثیری روی انرژی جنبشی تلاطمی و تنش کف ندارد؛ اما باعث می شود که تلاطم سریع تر شکل بگیرد. مشاهده شد که در مرز بین لایه چینه بندی و لایه آمیخته تنش برشی افزایش می یابد.
    کلیدواژگان: لایه اکمن، لایه آمیخته کف، شبیه سازی پیچک بزرگ، مدل پالم، خلیج فارس
  • الناز امیرخانلو، احسان توابی، سیما ضیغمی صفحات 671-677
    خورشید به طور مداوم ذرات یونیزه را به بیرون از اتمسفر پرتاب می کند که سبب باد های خورشیدی می شوند. برای درک اینکه منشا این بادها کجاست 50 سال است که تحقیقات گوناگون در شید سپهر، تاج و رنگین سپهر انجام می شود. حفره های تاجی در مقیاس بزرگ معمولا مناطقی هستند که به طور قطعی به عنوان منشا بادهای خورشیدی پذیرفته شده اند. با این حال هنوز تحقیق و پژوهش در مناطق دیگر انجام می شود. جت های شبکه ای یکی ازپدیده هایی هستند که به عنوان منشا بادهای خورشیدی مطرح می باشند. هدف ما بررسی توزیع میدان سرعت درون آنها و پی بردن به ساختار این نوع جت ها و نقش آن در جریان های پلاسمایی می باشد. نوسانات و جابه جایی عرضی محور جت ها را می توان به دلیل وجود امواج عرضی در امتداد محور آنها تعبیر نمود. دو نوع موج که مسئول این نوسانات هستند عبارتند از امواج مگنتواکوستیکی و امواج آلفون. در این مقاله با استفاده از تصاویر تلسکوپ IRISبا کمک الگوریتم FLCT تحت برنامه نویسی IDL توزیع میدان سرعت جریان پلاسما را در پایه جت های رنگین سپهر مورد مطالعه قرار دادیم.
    کلیدواژگان: پلاسما، جت رنگین سپهر، سرعت ظاهری، امواج آلفونی
  • سحر تاج بخش ، فروغ مومن پور، حسین عابد، سمانه نگاه، نیما فرید مجتهدی صفحات 679-695
    هدف از این پژوهش، تعیین ضرایب رابطه مارشال-پالمر برای بازتابش رادار هواشناسی گیلان با استفاده از شدت بارش دیدبانی شده است. به همین منظور، ابتدا وایازش توانی داده های بارش رادار هواشناسی (با استفاده از ضرایب پیش فرض در رابطه مارشال-پالمر) بر حسب داده های باران سنج ایستگاه خودکار فرودگاه رشت استان گیلان در یک بازه سه ساله (2012-2015) انجام و ضرایب جدید شناسایی شدند. سپس، با اعمال ضرایب جدید، شدت بارش رادار دوباره محاسبه و مقادیر به دست آمده شدت بارش در هر دو حالت (با ضرایب پیش فرض و جدید) ، با استفاده از آماره ریشه مجذور مربعات، با داده های دیدبانی باران سنج ایستگاه هواشناسی رشت مقایسه شدند. این مقایسه یک مرتبه بر اساس فصل های مختلف و مرتبه دیگر بر اساس شدت بارش ها انجام شد. نتایج بررسی های فصلی نشان از بهبود نسبی برآورد شدت بارش رادار پس از تصحیح ضرایب دارد به گونه ای که برآورد شدت بارش در ماه های مارس تا می (بهار) ، 38 درصد و ماه های دسامبر تا فوریه (زمستان) 22 درصد اصلاح شد. طی ماه های ژوئیه تا نوامبر (تابستان و پاییز) تغییر قابل توجهی در برآورد شدت بارش دیده نشد. نتایج به دست آمده برای شدت بارش (بدون در نظر گرفتن فصل ها) نشان داد که پس از اعمال ضرایب جدید، بارش های متوسط و شدید به ترتیب 25 و 47 درصد بهبود داشته اند. این در حالی است که برای بارش با شدت ملایم، تغییری در نتایج بر اساس روش به کاررفته مشاهده نشد. به نظر می رسد تصحیح ضرایب برای بارش های شدید تر کاربرد بیشتری دارد.
    کلیدواژگان: رابطه مارشال-پالمر، شدت بازتاب رادار هواشناسی، ایستگاه خودکار هواشناسی، وایازش
  • ابراهیم عسگری، اباذر اسمعلی عوری ، رئوف مصطفی زاده، غلامرضا احمدزاده صفحات 697-713
    تعدد عوامل موثر در خصوصیات حوزه آبخیز منجر به تغییرات مکانی و زمانی در فرآیندهای تولید رواناب و رسوب می شود. پژوهش حاضر با هدف ارزیابی تغییرات مکانی مقادیر رواناب، رسوب و آستانه شروع رواناب با استفاده از داده های شبیه سازی بارش در حوزه آبخیز قره شیران اردبیل انجام گرفت. شبیه سازی بارش با استفاده از دستگاه باران ساز در 45 نقطه در سازندهای مختلف زمین شناسی حوزه آبخیز انجام و پس از اندازه گیری مقدار رواناب و رسوب در هر نمونه متغیرهای مورد مطالعه با روش کریجینگ درون یابی و تغییرات مکانی ارزیابی و ارتباط مکانی مقادیر این متغیرها مورد بررسی قرار گرفت. نتایج نقشه های درون یابی نشان داد که سازندهای بخش های بالادست حوزه آبخیز (گدازه های داسیتی و تراکیتی) در آستانه های پایین (17/3-99/1 دقیقه) رواناب تولید می شود و به سمت سازندهای بخش های پایین دست (مانند پادگانه های آبرفتی قدیمی) آستانه تولید رواناب (25/7-13/6 دقیقه) افزایش می یابد. مقدار رواناب در بالادست حوزه (گدازه های داسیتی و تراکیتی) ، زیاد (25/7-07/6 لیتر بر مترمربع) ولی مقدار رسوب کم (66/1-25/1 گرم بر لیتر) و در پایین دست حوزه (مانند پادگانه های آبرفتی قدیمی) مقدار رواناب تولیدی کم (50/3-20/2 لیتر بر مترمربع) و مقدار رسوب تولید شده بیشتر (5/3-25/2 گرم بر لیتر) می باشد. نتایج ارتباط بین مقادیر تغییرات رسوب، رواناب و آستانه شروع رواناب در نرم افزار Surfer نشان داد که در آستانه های بالای 4 دقیقه و رواناب های بین 5/5-5/2 لیتر، مقدار رسوب بیشتر از حدود 2 گرم بر لیتر می باشد و به طور کلی می توان گفت که در آستانه های پایین اثر تولید رواناب بر تولید رسوب در حوزه بیشتر است و در آستانه های بالا اثر تولید رواناب کاهش می یابد.
    کلیدواژگان: تغییرات مکانی، شبیه ساز باران، آستانه شروع رواناب، سازند زمین شناسی، آبخیز قره شیران
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  • Amin Rashidi, Zaher Hossein Shomali, Nasser Keshavarz Farajkhah Pages 495-508


    Tsunami is an oceanic gravity wave generated by the displacement of huge volumes of water. There are three main types of disturbances: underwater earthquakes, submarine landslides and sudden earth surface movements adjacent to the ocean (volcanoes, meteorites, rock falls, sub-aerial landslides and ship sinking). Most tsunamis are caused by large shallow earthquakes in subduction zones (Satake and Tanioka, 1999). Sumatra–Andaman (2004) and Honshu, Japan (2011) tsunami events and following widespread damages and tragic consequences demonstrated the need of worldwide attention, awareness and preparedness for tsunami hazard mitigation. While the world draws its attention to tsunamis in the Indian Ocean, further attention is increased in the eastern areas of the Indian Ocean near Indonesia. Western Makran is located in the northwestern Indian Ocean basin. It has received less attention as a potential tsunamigenic zone. The Makran region is a 1000-km section of the Eurasian-Arabian plate boundary and located offshore Pakistan in the northwestern Indian Ocean where the oceanic crust of Arabian plate is being subducted beneath Eurasian plate since the Early Cretaceous along a north dipping subduction zone (Byrne et al., 1992; Smith et al., 2013). Following the great earthquake in Pasni-Ormara on 1945.11.27, Mw=8.1 (Byrne et aL, 1992), the coastline uplifted by about 2 m (Page et al., 1979). This event was accompanied by a significant regional tsunami, with run-up in the 5–10 m range which caused about 4000 deaths along the very sparsely populated Makran coast (Heck, 1947; Ambraseys and Melville, 1982; Okal and Synolakis, 2008). The Makran may be seismically segmented along its length into a western and an eastern segment, distinguished by different levels of seismicity (lower in the west). Moderate to large magnitude earthquakes are either related to the down going slab at intermediate depths or superficial in the eastern Makran (e.g. 1765, 1851 and 1945 earthquakes), while western Makran is marked with almost no seismicity in the coastal area at present but might have experienced a strong earthquake in 1483 (Byrne et al., 1992; Zarifi, 2006).
    The lack of earthquakes for many years has increased the possibility of locking the western Makran segment. This means that, it could generate a potential tsunami event in the future that can threat the Gulf of Oman and the Makran coastlines. Because of the tsunamigenic potential of Makran subduction zone, also importance of strategic geographic location, financial role of Makran coast in Iran, accessibility to international waters, ability to communicate with other countries and its cultural, natural and historical tourism potential along with the establishment of ports and coastal and offshore installations in the region, tsunami can be a real threat. Consequently, it is indispensable to have accurate studies and estimates for tsunami risk mitigation. The aim of this study is to simulate tsunami generation in western Makran numerically for estimating the initial condition for tsunami propagation. Tsunami generation mechanism should be modeled as the first step in the process of tsunami modeling. The generation modeling problem should be studied geophysically and geologically, therefore it is a very important and vital stage in tsunami simulation. To estimate the static uplift of seafloor, we can use the fault models e.g., Okada (1985) and Mansinha and Smylie (1971) which are the analytical solution of deformation field caused by instantaneous rupture on an elastic finite fault plane. The theory was proposed originally by Mansinha and Smylie (1971) and then improved by Okada (1985). We need the fault parameters (Hypocenter (Latitude, Longitude and Depth), Length and Width of Fault Plane, Dislocation (Slip), Strike direction, Dip angle and Rake (slip) angle) to compute the deformation. A tsunami scenario with defined source parameters was constructed in the Gulf of Oman to compute the deformation field based on the Okada algorithm. The source model was based on Okal and Synolakis (2008) and Smith et al. (2013) with a length of 450 km, a width of 100 km and a dislocation of 10 m which has a moment magnitude (Mw) of 8.7. The result of this study represents the initial profile of the tsunami while including the uplift and subsidence in the study area. The earthquake scenario predicted maximum seafloor uplift of 3.5 m and maximum subsidence of 2.4 m. The deformation field covered an area from 23.5° N to 27.5° N and from 56° E to 63° E. The southern coastal areas of Iran and Pakistan experienced subsidence and the northern coastlines of Oman experienced uplift. The outcome can be used as the input in the simulation of tsunami propagation

    Keywords: Tsunami, western Makran, Gulf of Oman, numerical simulation, tsunami generation
  • Amin Rashidi, Zaher Hossein Shomali, Nasser Keshavarz Farajkhah Pages 509-521

    Tsunami numerical modeling is a mathematical description of tsunami life cycle circle including generation, propagation and run-up. Numerical simulation is a powerful tool to understand the impacts of past and future events. It is critical to use the results of tsunami simulation such as tsunami waves propagation patterns, time series, amplitudes and run-up along coastlines to mitigate tsunami hazard of possible future events. Tsunami waves propagate with a velocity up to 700 to 950 km/h in the ocean without losing a lot of energy. As they reach shallow waters, their amplitude grows larger in the wave shoaling process. Nonlinear shallow water equations are often used to model tsunami wave propagation and run-up.
    The aim of this study is simulation of tsunami wave propagation and run-up in the western Makran for a tsunamigenic scenario capable of generating a Mw 8.7 magnitude. The initial condition to of model the tsunami propagation is computed using the Okada's algorithm. The COMCOT hydrodynamic model is used for the numerical tsunami simulation. The COMCOT is capable of solving non-linear shallow water equations in both Spherical and Cartesian coordinates using explicit staggered leap-frog finite difference schemes and a nested grid configuration.
    Tsunami propagation is highly influenced by the bathymetry. A three level nested grid system with different resolutions is used for tsunami simulation in this study. Configuring a nested grid system in tsunami modeling is necessary to compute tsunami run-up and inundation on dry land. The simulation is then performed for a total run time of 90 minutes with a time step of 0.5 min for the parent grid and 0.0625 min for the finest grid. Numerical modeling of tsunami run-up and inundation is performed for the western (C1), central (C2) and eastern (C3) parts of the Makran coastline in the south of Iran.
    The trapping of tsunami waves inside the Gulf of Oman causes more impacts on the coastlines of Iran and Oman in comparison to the other areas. To investigate the time histories of tsunami waves after the generation by the tsunmigenic scenario, we put 18 virtual gauges near and along the southeastern coastline of Iran. Generally, it takes about 20 minutes for maximum tsunami wave amplitudes to be observed at the southeastern coastlines of Iran. The maximum tsunami wave heights computed for the gauges near Jask and Chabahar are 2/8 and 3/3 m respectively. The entire southeastern coastline of Iran is impacted by such tsunami waves. The maximum computed tsunami wave height along the southeastern coastline of Iran is 11m.
    The maximum tsunami wave field exhibits a significant local hazard field inside the Gulf of Oman posed to the shores of Iran and Oman. The maximum tsunami amplitude reaches up to 11 m and 6 m inside the Gulf of Oman the Arabian Sea Basins, respectively. The results of run-up modeling show that the maximum computed run-up for the C1, C2 and C3 areas are 10, 17 and 19 m. The maximum tsunami inundation distance for those areas are 6, 6 and 4 km, respectively. The considerable values of inundation distance are due to low elevation topography of the affected coasts. Computing the tsunami inundation distance can be used in choosing evacuation lines during the possible future tsunamis and finding safer locations along the coastal areas. Accurate tsunami simulations are required to develop a tsunami early warning system and estimate the tsunami inundation on dry land. To perform more accurate simulations, high resolution local bathymetric/topographic maps are required, especially for the major ports in southeastern Iran

    Keywords: Tsunami, western Makran, Iran, numerical simulation, tsunami propagation, run-up
  • mohsen Feizi, Mehdi Raoofian Naeeni Pages 523-534
    Many different methods for gravity field modelling have been investigated, among which, the harmonic expansion has been widely used due to harmonic nature of gravity potential field that satisfies Laplace equation in an empty space. This method, however, cannot reach to a high resolution in a gravity field, and suffers from omitting the high frequency gravity signals and therefore it is not appropriate for local gravity field modelling. To overcome this drawback and recover high frequency features of gravity field, appropriate basis functions with local support should be used. One of the methods for local gravity field modeling based on local harmonic function is spherical cap harmonic analysis. In this method, the Dirikhlet boundary value problem for Laplace equation is solved for boundary conditions on the surface of a spherical cap which results in Eigen expansion of the solution in terms of the associated Legendre function of non-integer degree and integer order. Another method that can be used for local gravity field modeling is rectangular harmonic analysis. In this method, Laplace equation is solved in a local Cartesian coordinate system and boundary conditions are applied on a plane area which. In this approach, trigonometric functions are used as basis functions.
    In this study, the problem of local gravity field modeling based on both spherical cap, and rectangular harmonic expansion is investigated. Also, a numerical study is conducted to show the performance of each method for local gravity field modeling. To do so the observations of vector airborne gravimetry in the northwest of Tanzania in Highland region are used to derive the coefficients of each model. The low-frequency part of observed gravity field is removed from the data using EGM2008 geo-potential model, and the resulting residual gravity field is considered for local modelling. Since the governing equations for determination of the coefficients suffer from an ill-conditioning problem, it is necessary to apply some regularization schemes to find the optimum solution. Here, the Tikhonov regularization method is utilized to obtain the regular solution. In this study, the edge effect for each model is also analyzed. To show this effect, the results of models are compared with the observations of gravity at some control points distributed both within the study area and its margin. It should be noted that the maximum degree of expansion in harmonic series, plays an important role in appropriate fitting of local gravity field models to the gravity data and it has significant effects on the computational task of determining the coefficients of each model. For this purpose, local gravity field modelling is calculated with different value of maximum degree of expansion and then regarding to the result (accuracy of local gravity model by comparing with control points), appropriate value of maximum degree of expansion for each model is determined.
    Finally the results of two models are compared to each other to show the performance of each models in local gravity field modeling. The results of this study reveal that ASHA has the ability to model local gravity with accuracy of about 1 mGal, and RHA method in the best situation can just achieve to a 3 mGal accuracy, although the convergence rate in RHA model is faster than ASHA model. Also by comparing the edge effect on each models, it is seen that the edge effect in two models and in all directions occurred but in a Z direction of RHA model that are more significant than the other directions in two models and one may conclude that the edge effect of RHA are much larger than that of ASHA. Finally, the result obtained shows that ASHA model can have better results for local gravity modelling
    Keywords: Local gravity field modeling, Adjusted spherical cap harmonic, rectangular harmonic analysis, airborne gravimetry
  • Mahdi Fallah Safari, Mohammad Kazem Hafizi, Reza Ghanati Pages 535-555
    Magnetic resonance sounding (MRS) is a relatively new approach and is the only geophysical method which is directly sensitive to the underground water molecules. MRS is based on the principal of Nuclear Magnetic Resonance (NMR). A wire loop with different diameter depending on the depth of aquifers, is laid out on the ground. The wire loop is used for both transmission of the oscillating magnetic field and reception of the MRS signal. This method proved to be sufficiently accurate and to have a high resolving capability. In the geophysical application of Magnetic Resonance, the groundwater is the target of investigation. Inverting MRS data provides significant information regarding depth and thickness of the aquifer, distribution of water content and, under favorable conditions, hydraulic conductivity. In this method water content is defined based on the portion of the total volume of subsurface occupied by the free water which is unattached to grain walls and can be extracted from the rock and signal of bounded water which is captured by grains is not included. That is to say that signals related to the bounded water which is absorbed by the grains of the medium is excluded from the calculation process. This method is sensitive to the noise level so estimation of signal parameters and inversion plays an important role. The inverse problem of MRS is ill-posed meaning that the solution is not unique. On the other hand, within a certain depth range, two layers with different thickness and water content but with the same product could return the same theoretical sounding curve. The inversion of this method is carried out according to the well-known Tikhonov method. Solution of MRS inversion like other inverse problems in geophysics is not a continuous function of the data in which there are a small perturbation of the input data that can cause a large perturbation of the model parameters. Consequently, regularization methods should be employed to tackle possible instabilities in solution process. Moreover defining the kind of regularization a proper choice of the regularization parameter is essential. There are various methods available. In this paper the L-Curve is used. From model space point of view, there are various schemes for inverting MRS data including fixed geometry and variable geometry approaches in conjunction with using different methods of the objective function optimization. In fixed geometry approach, the model is assumed to have fixed layers with increasing layer thickness in depth, in fact the water content is allowed to vary; and in variable geometry approach it assumes a small number of layers, where both water content and layer thickness can vary. To numerically demonstrate the performance of the proposed inversion algorithm, we used a seven-layer model consisting of three horizontal, homogeneous, by 30% water content. In this paper, stable and unique solution is sought through the fixed geometry approach and imposing Tikonov regularization with constraints. After the test of inversion algorithm on synthetic data, Iran and Germany data were used to illustrate algorithm field use and to verify model results. Estimation of water content of synthetic data, Iran and Germany data shows a reasonable efficiency of the proposed strategy.
    Keywords: Tikonov regularization, magnetic resonance sounding, water content, Inversion
  • Toktam Zand, Hamid Reza Siahkoohi, Ali Gholami Pages 557-573


    For decades Kirchhoff migration has been one of the simplest migration algorithms and also the most frequently used method of migration in industry. This is due to its relatively low computational cost and its flexibility in handling acquisition and topography irregularities. The standard seismic migration operator can be regarded as the adjoint of a seismic forward modeling operator, which acts on a set of subsurface parameters to generate the observed data. Such adjoint operators are able to provide an approximate inverse of the forward modeling operator and only recover the time of the events (Claerbout, 1992). They cannot retrieve the amplitude of reflections, thus leading to a decrease in the resolution of the final migrated image. The standard seismic migration (adjoint) operators can be modified to better approximate the inverse operators. Least-squares migration (LSM) techniques have been developed to fully inverse the forward modeling procedures by minimizing the difference between observed and modeled data in a least-squares sense. An LSM is able to reduce the (Kirchhoff) migration artifacts, enhance the resolution and retrieve seismic amplitudes. Although implementing LSM instead of conventional migration, leads to resolution enhancement. It also brings some new numerical and computational challenges which need to be addressed properly. Due to the ill-conditioned nature of the inverse operator and also incompleteness of the data, the method generates unavoidable artifacts which severely degrade the resolution of the migrated image obtained by the non-regularized LSM method. The instability of LSM methods suggests developing a regularized algorithm capable of including reasonable physical constraints. Including the seismic wavelet into the migration operator, migration will generate the earth reflectivity image which can be considered as a sparse image, so applying the sparseness constraint, e.g., via the minimization of the 1-norm of reflectivity model, can help to regularize the model and prevent it from getting noisy artifacts (Gholami and Sacchi, 2013).
    In this article, based on the Bregmanized operator splitting (BOS), we propose a high resolution migration algorithm by applying sparseness constraints to the solution of least-squares Kirchhoff migration (LSKM). The Bregmanized operator splitting is employed as a solver of the generated sparsity-promoting LSKM for its simplicity, efficiency, stability and fast convergence. Independence of matrix inversion and fast convergence rate are two main properties of the proposed algorithm. Numerical results from field and synthetic seismic data show that migrated sections generated by this 1-norm regularized Kirchhoff migration method are more focused than those generated by the conventional Kirchhoff/LS migration.
    Regular spatial sampling of the data at Nyquist rate is another major challenge which may not be achieved in practice due to the coarse source-receiver distributions and presence of possible gaps in the recording lines. The proposed model-based migration algorithm is able to handle the incompleteness issues and is stable in the presence of noise in the data. In this article, we tested the performance of our proposed method on synthetic data in the presence of coarse sampling and also acquisition gaps. The results confirmed that the proposed sparsity-promoting migration is able to generate accurate migrated images from incomplete and inaccurate data

    Keywords: Kirchhoff migration, Inverse operator, Least-squares, Bregmanized operator splitting, Sparsity-constrained, Incomplete data
  • Meysam Moghadasi, Ali Nejati Kalateh, Mohammad Rezaie Pages 575-583
    Inversion method is very common in the interpretation of practical gravity data. The goal of 3D inversion is to estimate density distribution of an unknown subsurface model from a set of known gravity observations measured on the surface. The regularization parameter is one of the effective parameters for obtaining optimal model in inversion of the gravity data for similar inversion of other geophysical data. For estimation of the optimum regularization parameter the statistical criterion of Akaike’s Bayesian Information Criterion (ABIC) usually used. This parameter is experimentally estimated in most inversion methods. The choice of the regularization parameter, which balances the minimization of the data misfit and model roughness, may be a critical procedure to achieve both resolution and stability. In this paper the Active Constraint Balancing (ACB) as a new method is used for estimating the regularization parameter in two- dimensional (2-D) inversion of gravity data. This technique is supported by smoothness-constrained least-squares inversion. We call this procedure “active constraint balancing” (ACB). Introducing the Lagrangian multiplier as a spatially-dependent variable in the regularization term, we can balance the regularizations used in the inversion. Spatially varying Lagrangian multipliers (regularization parameters) are obtained by a parameter resolution matrix and Backus-Gilbert spread function analysis. For estimation of regularization parameter by ACB method use must computed the resolution matrix R. The parameter resolution matrix R can be obtained in the inversion process with pseudo-inverse multiplied by the kernel G.
    (1)
    The spread function, which accounts for the inherent degree of how much the ith model parameter is not resolvable, defined as: (2)
    where M is the total number of inversion parameters, is a weighting factor defined by the spatial distance between the ith and jth model parameters, and is a factor which accounts for whether the constraint or regularization is imposed on the ith parameter and its neighboring parameters. In other words, the spread function defined here is the sum of the squared spatially weighted spread of the ith model parameter with respect to all of the model parameters excluding ones upon which a smoothness constraint is imposed. In this approach, the regularization parameter λ(x,z) is set by a value from log-linear interpolation.
    (3)
    where and are the minimum and maximum values of spread function , respectively, and the and are minimum and maximum values of the regularization parameter λ(x,z), which must be provided by the user. With this method, we can automatically set a smaller value λ(x,z) of the regularization parameter to the highly resolvable model parameter, which corresponds to a smaller value of the spread function in the inversion process and vice versa. Users can choose these minimum and maximum regularization parameters by setting variables LambdaMin and LambdaMax. For getting the target an algorithm is developed that estimates this parameter. The validity of the proposed algorithm has been evaluated by gravity data acquired from a synthetic model. Then the algorithm used for inversion of real gravity data from Matanzas Cr deposit. The result obtained from 2D inversion of gravity data from this mine shows that this algorithm can provide good estimates of density anomalous structures within the subsurface
    Keywords: Inversion, Gravity data, Regularization parameter, ACB method
  • Taghi Shirzad, Mahsa Afra Pages 585-594
    Analysis of earthquake events provides an efficient tool to extract the empirical Green's function (EGF) between pairs of earthquakes by interferometry approach. Because of sparse distribution of stations or low seismicity, many classical seismic studies (earthquake-receiver systems, ambient seismic noise and etc.), may yield a poor or noisy calculation of the tomographic result maps. However, inter-event EGFs between two earthquake locations can be retrieved by virtual stations, first outlined by Curtis et al. (2009). These EGFs are equivalent to the waveform produced as an impulse at one receiver location and that recorded by another receiver. Several researchers (e.g. Hong and Menke, 2006; Curtis et al., 2009) used a source-receiver reciprocity theorem, to indicate that inter-event EGFs could be retrieved when their waveforms are recorded by a set of receivers surrounding the events. According to this theorem, the stacked cross-correlations of event-pair (between a pair of earthquake event) waveforms recorded by these set of receivers, are equivalent to the estimated EGFs (Curtis et al., 2009). This technique can, therefore, provide new insight and useful tool to study fault planes and Earth's interior where real receivers can not be installed. However, the fault plane where earthquake ruptures occur at depth is often interpreted as being a transitional zone which is characterized by asperities and barriers (Aki, 1984). Thus the aftershock events interferometry approach could be applied to study fault plane by retrieving accurate, stable and reliable inter-event EGFs. After the Rigan earthquake occurred on 20 December 2010 (Mw 6.5) in Kerman province (southeastern Iran), aftershock events extended along the hidden part of the Kahurak Fault. In this paper, the cross-correlation of aftershock events was applied to retrieve the inter-event EGF on the hidden part of the Kahurak Fault plane in the Rigan area. This event-pair example was selected based on some criteria that the most important of these conditions is the similar (approximately) depth of events due to the ease of operation and processing. Aftershock event-pair projection and data processing is similar to that explained in detail by Bensen et al. (2007). The mean and trend were removed and the data were decimated to 10 sps. Time and frequency domain normalizations were then applied to suppress the influence of instrument irregularities and high energy events. After cross-correlation and stacking procedure, event-pair EGF signal was extracted. Then, 1D and 2D synthetic signals were generated using computer program in seismology (Herrmann and Ammon, 2013) and SPECFEM , respectively. Horizontal velocity result at depth of ~4 km, which is calculated by Shirzad et al. (2017), was applied for both 1D and 2D synthetic input modeling. Comparison between inter-event EGF and synthetic signals indicates that the inter-event EGF is in agreement with the synthetic models. Also, inter-event EGF signal propagates on the hidden part of the Kahurak fault plane. The correlation coefficient of 1D and 2D synthetic inter-event 031-163 EGF signals are of the order of ~75% and 80% within the signal window. In conclusion, these inter-event EGFs can be used for investigating the laterally varying the 2D mapping of surface wave group and/or phase velocities.
    Keywords: Green function, virtual seismometer, interferometry, fault plane, Rigan
  • Mehdi Goli Pages 595-606
    The gravitational effect of topographical masses is one of the important component of the gravity field, which plays a key role in geophysical and geodetic studies. For geophysical interpretations, it is necessary to eliminate the effect of topography as a disturbing factor from the observed gravity data. In geodetic applications, the solution of geodetic boundary problem such as Stokes requires mass free space above the geoid. In present study efficiency of different tesseroid based methods are compared with well-known rectangular prism to evaluate the gravimetric terrain corrections up to distance of 1.5 arc-degree known as the Hayford-Bowie zone. For this purpose, the mathematical formula: the vertical derivative of Newton integral and the digital elevation model (DEM) are used as data. In computing the topographic effect, we are involved with the two factors: 1- the integral element (point, line, plane, rectangular prism, tesseroid, etc.) and 2- geometry of topography (planar, spherical and ellipsoidal), which causes some difficulties to understand the subject. Finite element method is a general and standard method for estimating the terrain correction. In this method, the gravitational topographic effect is evaluated as the total gravitational effect of the smaller elements.
    Tesseroid is the geometrical body bounded by two concentric spheres. This element uses the spherical geometry of topography which introduces relative error of about 1% (Novak and Grafarend, 2005). By choosing this element, the Newton integral and its radial derivatives do not have an analytic solution, and numerical integration must be applied. The rectangular prism element, has been used frequently to compute terrain correction in various studies. It uses planar geometry and has an analytical solution for Newton's integral and its derivatives. Recently many studies investigated tesseroid based method to compute the potential and attraction of topographic masses, see, [Fukushima, 2017; Grombein et al., 2013; Heck and Seitz, 2007; Uieda et al., 2016]. Fukushima's method utilizes the 3D numerical double-exponential integration method, HS's method uses the Tylor series up to term 2 and the PM method is the zero term approximation of HS method. The simulation studies demonstrated the higher accuracy of tesseroid based methods compared to the method of prism in the literature. However, their performance is not tested for gravimetric terrain correction. The main goal of this study is the investigation of efficiency, in terms of speed and accuracy, of four tesseroid
    methods
    Fukushima, Martinec-Vanicek (MV), Heck-Seitz (HS), point mass (PM) compared with prism in Hayford-Bowie zone.
    To investigate the computation accuracy, we used bounded spherical shell with constant thinness and density for which the analytical exact solution exists. The thinness of the shell have been chosen 1000 meter and the computation point is located on the origin of bounded spherical shell on the equator in the spherical coordinate (0,0,1000). The computation of terrain correction are discretized in different zones: innermost, inner and outer correspond respectively to , and and with different sizes. The contribution of innermost zone is over 75% of total effect. Numerical results indicate the success of the prism for topographic effect in all three zones, especially for masses in neighborhoods of computation points, than those methods based on tesseroid. To overcome the effect of Earth's curvature, the elevation of computation point is corrected using a simple formula. Also, our calculations show that, in innermost zone, the topography should be discretized in 30 meter elements to achieve 10 Gal level of accuracy
    Keywords: terrain correction, gravity anomaly, tesseroid, numeric integration, prism
  • Reza Borhani, Farhang Ahmadi, Givi, Sarmad Ghader, Alireza Mohebalhojeh Pages 607-624

    This research is aimed to study the global distribution of tropopause folding frequency and its seasonal changes, emphasizing the ones over the Southwest Asia, for a 3-year period from Jan. 2013 up to Dec. 2015. For this purpose, the European Centre for Medium-Range Weather Forecasts (ECMWF) (ERA- Interim) reanalysis data set including wind, temperature and geopotential height were used. The horizontal resolution of the initial fields is 1×1 degrees in longitudinal and latitudinal directions prepared operationally every six hours at 60 levels. Applying the initial fields, the secondary fields, such as potential vorticity and potential temperature were calculated. From the 60 vertical levels, about 19 levels extending from 600 to 100 hPa cover the depth of all tropopause folding events studied here. In this research, we define the 2PVU potential vorticity surface as the dynamical tropopause (1PVU corresponds to 10-6 m2s-1Kkg-1). Identification of tropopause folding is based on the algorithm developed by Sprenger et al. (2003) and Gray (2003) and refined by Škerlak et al. (2014) using pseudosoundings in each of the grid points. A 3-D labeling algorithm is used to distinguish between stratospheric and tropospheric air masses and labeling them according the PV values. After labeling, the tropopause folds are identified at every grid points from the vertical profiles of the label field as areas of multiple crossings of dynamical tropopause. The frequency of folds at each grid point over a chosen period is calculated from the number of folding divided by the total 6-hourly instances corresponding to the season, and finally expressed as a percentage. According to this algorithm, tropopause folds are classified into three categories as shallow, medium and deep.
    The analysis of spatio–temporal distributions of tropopause folds shows that the frequency of folding events over subtropical and mid latitude regions (between 20° to 40° north and south latitudes) is higher than the other latitudes in both the Northern and Southern Hemispheres and their frequency is increased remarkably in the winter season. Tropopause foldings in the Northern Hemisphere winter are seen as a relatively narrow band located in the subtropical latitude that surrounds zonally the whole Hemisphere, while in the summer season, foldings are concentrated in the subtropical region of the Eastern Hemisphere. Also, tropopause foldings occur mainly as shallow type in the subtropical region but as medium or deep ones in higher latitudes. Foldings in high latitudes are attributed to large-scale deformation fields, as noted by Holton and Hakim (2013), that are confirmed with water vapor satellite images, while the ageostrophic frontal circulations affect the tropopause deformation in mid latitudes.
    The other noticeable point is that the Southwest Asia region has positive anomalous values of tropopause folding frequency annually, relative to the Northern Hemisphere mean. This can be partly due to the Rossby wave breaking as pointed out by Martius et al. (2007) and Gabriel and Peters (2008). These anomalous values of folding frequency change in different seasons and obtain their maximum amounts in the summer time. Two regions with the maximum value of the folding frequency more than 5 times the Northern Hemisphere mean, seen over Iran–Afghanistan and the eastern of the Mediterranean Sea that occurred in June. The increase of folding frequency in the Southwest Asia during the summer season can be related mainly to the formation and existence of the monsoon anticyclone over the subtropical region of the Indian Ocean (Tyrlis et al., 2013) and partly to the baroclinic instability events. Results of the case study relevant to tropopause foldings in June 2015 show the existence of two strong jet streams in the aforementioned regions. Also, in the meridional cross-sections of wind and PV fields two principal areas of tropopause folding are seen in the west and downward of the jet streams locations. As expected, the potential temperature maps indicate the existence of marked baroclinic regions associated with the tropopause foldings.

    Keywords: tropopause folding, potential vorticity, potential temperature, Southwest of Asia, monsoon, baroclinic instability
  • reza Doostan Pages 625-640
    Teleconnection is defined as a meaningful relationship of time variations of two meteorological patterns that are far from each other and teleconnection is an important principle in climate for the explanation of meterologic phenomena. The term was used for the first time in climate studies by Angstrom (1935). Later Wallace and Gautzler (1981) defined the concept as a meaningful correlation between the time series of a month or longer of the climate parameters in distant locations. Teleconnections are associated with the anomaly of atmospheric large scale and hemisphere circulation. Therefore, it is important to recognize teleconnections affecting the regional climate. In this regard the question is: What are the most important global teleconnections for the cold seasons in Iran? To find an appropriate answer, the monthly time series of teleconnections close to Iran and the world from 1950 to 2010 were selected and the Pearson correlation method was used. The correlations indicated that global phenomena associated with regional teleconnection are established in the North Atlantic, Europe and Western Siberia, while the Pacific Oceanographic centers have a weak connection with the regional teleconnection in the cold period. The most important phenomena in the middle layers of the atmosphere are the North Sea - Caspian Pattern (NCP), and the North Atlantic Oscillation (NAO) associated with regional teleconnection of the Western Europe - North Caspian. In the positive phase of the North Atlantic Oscillation and the North Sea - Caspian Pattern, the precipitation increases and the temperature decreases while in the negative phase, the temperature increases and precipitation decreases in Iran. These two phenomena are important and reliable predictors in Iran. At ground level, the Arctic Oscillation (AO), Scandinavia (SCAND), Eastern Atlantic - Western Russia (EA-WR) and East Atlantic (EA) related to regional teleconnection of Northern Europe, Northern Siberia, and Central Asia are the most important phenomena on the surface for the climate of Iran. In the negative phase of the Arctic Oscillation, Scandinavia, the precipitation increases and temperature decreases for the climate of Iran, and in the positive phase of these two, the climate of Iran experiences dries conditions. Also in the positive phase of the Eastern Atlantic and Eastern Atlantic - western Russia, the temperature decreases and the precipitation increases, and in the negative phase, the temperature increases and the precipitation decreases. It appears the global and regional teleconnections in Eurasia and the Northern Atlantic are not completely separated. Therefore, the global teleconnection associated with the climate of Iran are: the North Atlantic Oscillation, the North Sea - Caspian Pattern, Arctic Oscillation, Scandinavia, Eastern Atlantic - Western Russia and Eastern Atlantic. Often, teleconnections of the cold seasons of Iran are related to meridional westerlies along the blocking and cut-off low that are established in Western Europe, Central and Western Siberia to lower and higher latitudes in the same geographic locations. In climate studies one should not ignore the role of geographic featues on the surface of the earth, while considering the above-mentioned issue.
    Keywords: World teleconnection, Regional teleconnection, Cold period, Climate of Iran
  • sahar Tajbakhsh, Amirhosein Nikfal Pages 641-658
    Avalanches are likely to happen in winter time mountainous regions of Iran, and its timely prediction can help to improve the road traffic safety. The aim of this study is to provide the avalanche first guess using Numerical Weather Prediction (NWP) model outputs. Since the meteorological observations in mountainous areas are very scarce, access to snow data in ground measurements is not feasible; it seems that making use of numerical models to simulate the associated data and predicting the avalanche first guess may be a reliable method. For this purpose, three avalanche events which occurred in Chalous Road (Kanduan-Gachsar) were investigated synoptically as the case studies. Then the precipitation (water equivalent to snow, snow thickness), temperature and wind outputs of Weather Research and Forecasting (WRF) model were analysed based on the Spangler classification tables in order to determine the potential of avalanche events.
    Snow density, snow water equivalent and snow depth are the most important factors of snow cover that have fundamental applications in predicting avalanche and flood events. The predictions in this study are based on the WRF model numerical simulations. Spangler et al. (2009) presented a model for estimating the avalanche potential based on the three components of the region’s climatic conditions, present weather survey and forecasting avalanche indices. For verification of the model, the threshold values for precipitation, temperature and wind were calculated in Colorado. In the present study, only the third part of the Spengler method (prediction of avalanche occurrence potential) was applied to make the first guess of avalanche potential occurrence in the mountainous regions of the country. The period 26 -29 December 2016 for heavy snow conditions with multiple avalanche was considered as a case study. The area under study is the Shahrestanak (36, 10 °N and 51.31° E) on the Chalous road, which experienced more than 10 avalanche events during winter 2016. Its elevation is about 2230 to 2240 meters and is located in Alborz Province. There are similar climatic conditions in the two regions of Colorado and Alborz based on the Gutten climate classification but their temperature and type of snowpack are different according to the Sturm snowpack classification. The type of snowpack in the Colorado area is prairie (thin and moderate cold snow covering with substantial wind drifting, with the maximum depth of about 1 meter),while the type of snowpack in Alborz area is ephemeral (thin and warm snow that melts down soon and its depth is between zero to 50 cm). Hence, it seems that the thresholds of the meteorological indicators related to avalanche potential in Alborz region could be slightly lower than its thresholds in Colorado area. The synoptic study was done using the mean daily ERA-Intrim data. In the present study, the patterns of sea level pressure, thickness of 500/1000 hPa, geopotential heights and temperature with relative vorticity of 500 hPa, vertical velocity at 700 hPa, as well as relative humidity and winds of 850 hPa were studied in order to identify the weather conditions during the avalanche period. Also, using the WRF meso-scale model (ver. 3.9), the simulation of atmospheric condition is conducted for 4 days (26-29 December 2016). Temperature, wind, cloudiness, snow thickness, snow water equivalent and snow cover (the most important indicators of avalanche) were determined using the WRF numerical prediction model. Then the potential of avalanches’ occurrence was investigated according to the Spengler model.
    Here, we attempt to investigate the potential of avalanche event in a case study using a NWP model and determine the probability of occurrence of avalanche based on one of the existing methods. The case study was selected in such a way that no significant atmospheric conditions were observed in the area. There was only one case of avalanche over 24 hours in the Chalous Road, Shahrestanak position. The results showed that the patterns of weather forecasting in this study are in agreement with actual weather conditions and there is no specific feature for avalanche occurrence in these patterns. The presented thresholds for the avalanche potential have good match in this case study. Winds of less than 9 m/s, snow depth of less than 30 cm in 24 hours, temperature of less than 8 °C in 12 hours, unstable temperature in the range of -4 to -10°C, and cloudy sky during the day without rain emphasize the probability of avalanche and not its certainty. To predict the high potential for avalanche, the atmospheric thresholds should be higher than these values
    Keywords: Snowpack, Snow depth, Snow water equivalent, Avalanche, WRF numerical weather prediction
  • Mohammad Farmanara, Hossein Malakooti, Smaeyl Hassanzadeh Pages 659-670
    In this study, the turbulent properties of the bottom Ekman layer of the Persian Gulf is studied, using a Parallelized Large-Eddy Simulation Model (PALM). Three numerical experiments were carried out with emphasis on stratification effects. A reference experiments (EXP C) without vertical gradients of the potential temperature and salinity and two experiments with vertical gradient of the potential temperature and salinity. The initial values of the surface potential temperature and salinity and their vertical gradients, provided from in situ data, were chosen according to August (EXP A) and November (EXP N) condition of the Persian Gulf. The eastern part of the Iranian coastal area of the Persian Gulf near the Hormuz Strait was chosen because there is a considerable western current during the year in this area. Also, the sea is deep enough to observe a distinctive pycnocline layer which separates surface and bottom mixed layer. The domain size is 200m×200m×100m in x, y and z directions respectively. A pycnocline layer with 40m and 20m deep was considered for August and November, respectively. A Geostrophic current with 0.15m s^(-1) speed is supposed to flow in x direction over the rough sea bed. The bottom boundary condition of the momentum flux was set to Dirichlet in order to create a no-slip condition at the sea bed. The simulations were carried out for 48h to include at least two inertial periods and avoid inertial oscillations. The results showed that the stratification limits the bottom Ekman layer depth and it does not grow with time. While in EXP C, where the fluid is neutral, a rapid growth of the bottom Ekman layer is obvious during the first 20h and its maximum depth reaches 60m. The Ekman cross-stream current component cannot entrain into pycnocline layer and it vanished at the bottom of the pycnocline layer. In autumn in which the pycnocline layer is thinner, the Ekman spiral is broadened and the magnitude of the Ekman cross-stream current component is 25% larger in compare to summer. The maximum value of the Ekman cross-stream current component is about 0.04m s^(-1) in EXP C and EXP A while it is about 0.05m s^(-1) in EXP N. The hodograph of the horizontal velocity in EXP C is more similar to Ekman theoretical solution. The stream-wise component of the horizontal velocity decrease with the same rate near the sea bed in all experiments which implies that the stratification does not have much effect on bottom stress. It is concluded that when an intense pycnocline exists and the bottom mixed layer is thin, less time is needed to trigger the turbulence. The bulk turbulent kinetic energy in all experiments is the same. Since the bottom boundary is assumed adiabatic and there is no heat flux from the bottom, the heat budget in the neutral BBL is approximately conserved (molecular diffusion is not considerable compared). Then a pycnocline is necessary to maintain heat conservation after the formation of a mixed layer. These intensified pycnocline can be observed as distinctive peaks in vertical profiles of the buoyancy frequencies near the top and bottom of the stratified layer. The thickness of the intensified pycnocline grows with time and at the end of simulation reaches about few meters. These intensified pycnocline layers in November is thicker than that of August. Also at the bottom interface of the stratified, the shear stress increases.
    Keywords: Ekman layer, Bottom Mixed layer, Large Eddy Simulation, PALM model, Persian Gulf
  • Elnaz Amirkhanlou, Ehsan Tavabi, Sima Zeighami Pages 671-677
    The sun is constantly throwing ionized particles out of its surface and causing solar storms. Various investigations have been carried out for finding out the origin of these storms for 50 years, in the photosphere, corona, and chromosphere. Large-scale coronal holes are usually areas that are definitely accepted for origin of the storms. However, research is still being done in other areas. Network jets are one of the issues that we have tried to investigate the distribution of their velocity field and their structures and also their role in plasma flows. Oscillations and transverse displacement of the jet axis can be interpreted as the presence of transverse waves along their axis. The two types of waves responsible for these fluctuations are magneto-hydrodynamic waves and alfvenic waves. In this paper, we studied the transverse displacement of the network jet axis, with the FLCT algorithm under IDL. The FLCT method is widely used to obtain the speed of moving features. The observed area is so large that we can identify many of the network jets. After choosing the coordinates of the item using the FLCT algorithm, we intend to obtain the Alfven velocity of the desired coordinates. The FLCT algorithm is a mathematical program used to construct a two-dimensional velocity field of connected images. The calculation of speed in this method depends on three factors: 1. Isolate the point on the image, 2- Calculation of correlation function between two images, 3. Peak location of the mutual correlation function, calculated for each pixel of the velocity. The FLCT algorithm uses interpolation to eliminate the complexity of the fixed angle on the center of the images. In results we can see the images analyzed in the IDL program, using MATLAB software to show the speed vectors that are torsional and indicate the speed of the alphabet. The images are in pixels and each pixel are is 0.3 sec. We estimated the chromosphere mass velocity of about 20 kms-1 using FLCT. Some of the network jets in the images seem to be other than the second type solar spicules sticks. However, we noticed that the speed of the jets is generally twice as large as the second type of sticks, which indicates the high contribution of these jets to the mass and energy of the solar atmosphere. We have noticed that network jets are important regardless of their relationship with second-generation sticks. A bunch of network jets is considered as an example of a jet. The network jet mechanism demonstrates the dynamics of the jets with high speeds (close to the speed of the Alfven in the interface area), which allows magnetic reconnection between the small magnetic rings and the background. Based on observational findings, several theoretical models and numerical simulations have been developed to describe the mechanism of these structures. Of course, unlike the remarkable improvements created by very accurate observations and the expansion of numerical theories and simulations, it is still unclear and their mutual relationship, their physical parameters, the definition of their formation mechanism and their possible role in the solar corona heat is unknown. These ambiguities are mainly due to the difference in the appearance of these phenomena when viewed in a variety of spectral lines.
    Keywords: Plasma, chromospheric jets, velocity, Alfven waves
  • sahar Tajbakhsh, Furugh Momenpoor, hossein Abed, samaneh Negah, Nima Farid Mojtahedi Pages 679-695
    Radar is a remote sensing instrument that sends electromagnetic waves with specific power to atmosphere and evaluates the amount of return power. It can then measure the difference between the send and retune powers and detect atmospheric phenomena as clouds. Using this tool, there is a wide, continuous and integrated monitoring of atmospheric phenomena. Like any remote sensing device that has, data of weather radars can also have errors. One of the most important measures to eliminate or minimize the radar data errors is calibration, and correction of radar index coefficients. The purpose of this paper is to extract an appropriate relationship for precipitation intensity related to radar reflectivity in Gilan. The Gilan ground based radar installed at the Kiashahr Port is a German-made GEMATRONIK MTEOR1600C type operating in the dual-polarization Doppler radar frequency band (c-band). In general, in order to calibrate the weather radars, “a” and “b” coefficients are required to modify in the Marshall Palmer initial formula for the target area. For this purpose, we tried to estimate the coefficients of this relationship (the relationship between precipitation intensity and radar reflection intensity) in a three years period (2012-2015) and to find new coefficients. In this study, the Doppler filter method (IIR Doppler Filter) was used to remove clutters. This filter was installed in the signal processor. In order to calibrate the Gilan radar, the rain gauge data of the Rasht airport synoptic station was compared with radar data. In this way, the precipitation statistics of the meteorological station were extracted using available meteorological and scdata software in the selected period and were separated based on two views of the season and precipitation severity.
    Then the precipitation intensity was calculated based on radar data. Due to the large amount of raw data in Rainbow software, the data format was converted from binary to text. In the next step, the power regression is made between meteorological radar data ( ) and the automatic rain gauge (in mm / h), based on the existing default coefficients. Then, the new coefficient (a’ and b’) were determine by introducing the linear equation, a (a') and a new b (b'). In the third step, the precipitation intensity was re-calculated by applying new coefficients in radar measuremets. Now, there are 2 precipitation intensity values which are obtained by default and new coefficients. The intensity precipitation values were compared with observation of meteorological data using root mean square error in different seasons regardless of intensity. The same process was performed for the severity of observed precipitation and calculated precipitation by the radar regardless of seasons. The most important results of this study are relative improvement of radar estimation from precipitation intensity after correction of coefficients, which was 38% in March to May (spring) and 22% in December to February (winter). During the months of July to November (summer and autumn), there was almost no improvement. Also, based on precipitation intensity (regardless of seasons), average accuracy of precipitation was increased by 25% and severe precipitation by 47%. While in gentle precipitation, this method did not work and there was no improvement
    Keywords: Marshall-Palmer relation, radar-reflector severity, automated meteorological station, regression
  • Ebrahim Asgari, Abazar Esmali, Ouri, Raoof Mostafazadeh, Gholamreza Ahmadzadeh Pages 697-713
    Diverse factors affect the characteristics of the watershed that lead to spatial and temporal variations in the runoff and sediment production processes. Runoff and sediment are the main important elements in the hydrological cycle, and their changes directly affect river systems and sedimentary environments; and their spatial and temporal variations change the morphology of the rivers. Due to differences in soil characteristics, source materials and geological formations, vegetation and slope in different parts of a region, the amount of runoff and sediment produced in these areas can vary with spatial variations. The purpose of this study is to evaluate the spatial variations of runoff and sediment and runoff threshold using rainfall simulation data in the Gharehshiran watershed in Ardebil Province. Considering the importance of spatial distribution of sampling points across the catchment area, the locations of the samples were determined, taking into account the access path to the points, as well as sampling in different formations through determining the boundaries of the study area.
    The field experiments and simulation of precipitation were carried out using a 1×1m rainfall simulator in 45 points in different geologic formations of the watershed area. The amount of runoff and sediment were measured in each experiment along with recording the threshold time of runoff generation. The measured variables were mapped and interpolated by using Kriging method over the study area. To assess the accuracy of the interpolation results, 7 samples were selected randomly and the Root Mean Square Error (RMSE), Mean Absolute Error (MAE) and Mean Bias Error (MBE) statistical measures were calculated by comparing observational and estimated values. Then, the correlation between the studied variables in various geological formations was evaluated using Pearson correlation analysis. The relationship between sediment and runoff amount, and runoff threshold time were also evaluated using a triple diagram model.
    The results of the interpolated maps showed that the lowest values of runoff time threshold (1.99-3.17 min) were observed in the geological formations of upper part of the watershed having dacite and tracite igneous, volcanic rocks. While the runoff time thresholds were increased (6.13-7.25 min) in the low land areas with the old alluvial terraces. The amount of generated runoff in the upper hillslopes of the watershed with dacite and tracite rocks was estimated as (6.07-7.25 lit/m2), and the amount of sediment was low (1.25-1.66 g/l). Meanwhile, in the lower parts of old alluvial terraces, the amount of runoff production was low (2.20-3.50 lit/m2) and the amount of produced sediment was higher with values of (2.25-3.5 g/l). The results of correlation analysis showed that the correlation coefficients between runoff threshold and runoff volume were significant at 0.01 significant level (r = -0.802). Also, a significant negative correlation (r = -0.672), were observed between runoff and sediment values.
    The relationship between the runoff time threshold and the sediment content was positive at significant level of 0.01 (r = 0.900). The results of interdependency between the sediment, runoff and runoff time threshold values using triple diagram models showed that the sediment amount was about 2g/l at high runoff time thresholds of 4 minutes with 2.5-5.5 lit/m2 runoff amounts.
    In general, it can be said that the sediment production in the study area is strongly under the effects of runoff amounts in lower time thresholds of runoff. As a remark, the results pointed out that the internal relationship of runoff and sediment production are affected by a variety of effective factors which requires comprehensive studies to reach a final conclusion
    Keywords: Spatial Variation, Rainfall simulator, Runoff threshold, Geologic Formations, Gharehshiran watershed