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پژوهش های ژئوفیزیک کاربردی - سال سوم شماره 2 (پیاپی 6، پاییز و زمستان 1396)

نشریه پژوهش های ژئوفیزیک کاربردی
سال سوم شماره 2 (پیاپی 6، پاییز و زمستان 1396)

  • تاریخ انتشار: 1396/06/06
  • تعداد عناوین: 8
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  • محمد رضایی*، علی مرادزاده، علی نجاتی کلاته، حمید آقاجانی صفحات 145-154
    وارون سازی داده های مغناطیسی از اهمیت زیادی در تفسیر داده های اکتشافی برخوردار است. در این روش تخمین توزیع مغناطیس پذیری مدل زیرسطحی از طریق داده های اندازه گیری شده سطحی صورت می گیرد. یکی از نکات کلیدی در حل مسائل وارون داده های ژئوفیزیکی تعیین مقدار بهینه پارامتر منظم سازی است. برای این منظور روش های مختلفی در وارون سازی سه بعدی داده های مغناطیسی وجود دارد. در مطالعه حاضر از روش تخمینگر نااریب ریسک احتمالی (UPRE) برای تعیین مقدار بهینه پارامتر منظم سازی جهت وارون سازی سه بعدی مقید داده های مغناطیسی با روش نمایش گرادیان تعدیل شده نیوتن (GPRN) استفاده شد. جهت نیل به این هدف الگوریتمی تهیه گردید؛ که مقدار پارامتر منظم سازی برای وارون سازی تخمین زده می شود. برای بررسی چگونگی عملکرد و تعیین اعتبار الگوریتم تهیه شده، ابتدا از داده های مغناطیسی حاصل از یک مدل مصنوعی و داده های واقعی مغناطیسی مربوط به کانسار آهن الله آباد استان یزد استفاده شد. نتایج مدل سازی وارون سه بعدی داده های مغناطیسی در این منطقه نشان می دهد که عمق کانی سازی در این منطقه کمتر از 100 متر است. نتایج به دست آمده در مقایسه با داده های حاصل از حفاری نشان می دهد که به کارگیری این الگوریتم، می تواند تخمین مناسبی از توزیع مغناطیس پذیری و ساختارهای زیرسطحی ماده معدنی ارائه کند.
    کلیدواژگان: وارون سازی سه بعدی، داده مغناطیسی، پارامتر منظم سازی، روش UPRE، روش GPRN، پارامتر مدل، کانسار الله آباد
  • اکبر حیدری، تکتم زند*، علی غلامی صفحات 155-166
    واهمامیخت یکی از مراحل مهم پردازش سیگنال های لرزه ای برای به دست آوردن تصاویر با تفکیک پذیری بالا از زیر سطح زمین از جمله تصاویر مخازن هیدروکربن است. در این مقاله فرآیند واهمامیخت ناپایا به منظور تخمین دامنه و زمان ضرایب غیر صفر سری بازتاب و همچنین تخمین فاکتور کیفیت لایه ها با فرض وجود محیط میرا کننده برای انتشار موجک چشمه با استفاده از روشی آماری انجام شده است. بازیابی محل دقیق بازتاب ها و حذف اثر میرایی زمین با استفاده از الگوریتم تبلور شبیه سازی شده صورت گرفته و فاکتور کیفیت برای هر لایه تخمین زده می شود. همچنین دامنه سری ضرایب بازتاب نیز با روش کمترین مربعات به دقت به دست می آید. در روش پیشنهادی، هر سه پارامتر دامنه، زمان ضرایب و فاکتور کیفیت مربوط به هر لایه به صورت هم زمان تخمین زده می شود که می توان آن را مزیتی نسبت به سایر روش ها بیان کرد. از الگوریتم تبلور شبیه سازی شده که الگوریتمی آماری و بر پایه ی تکرار است؛ برای حل مسئله ی مورد نظر استفاده شده است. نتایج حاصل از پیاده سازی این الگوریتم بر داده های مصنوعی و میدانی، دقت عملکرد آن را به خوبی نشان می دهد.
    کلیدواژگان: واهمامیخت ناپایا، سری ضرایب بازتاب، فاکتور کیفیت لرزه ای، فیلتر میرایی، الگوریتم تبلور شبیه سازی شده
  • نسترن حیدرآبادی پور، آزاده حجت *، حجت الله رنجبر، سعید کریمی نسب صفحات 167-176
    با توجه به قرار گرفتن کشور ایران در کمربند ماگمایی جهانی و وجود چشمه های آب گرم فراوان و کوه های آتش فشانی، ایران از جمله مناطق دارای پتانسیل قابل توجه منابع زمین گرمایی به حساب می آید. اگرچه برخی اکتشافات مقدماتی، وجود پتانسیل های زمین گرمایی در استان کرمان را شناسایی کرده، اما تاکنون مطالعات جامعی به منظور اکتشاف دقیق تر این ذخایر انجام نشده است. در این تحقیق، محاسبه عمق نقطه کوری به منظور تعیین پتانسیل زمین گرمایی در منطقه واقع بین طول های شرقی 30 و °56 تا 30 و °58 و عرض های شمالی 30 و°28 تا 30 و °29 با وسعت 22010 کیلومترمربع در محدوده مرکزی استان کرمان (واقع در شمال شهر جیرفت و شرق شهر بافت) مورد توجه قرار گرفت. بدین منظور، اطلاعات زمین شناسی منطقه و داده های مغناطیسی هوابرد، به عنوان داده های اصلی تحقیق، مورد استفاده قرار گرفت. بعد از حذف میدان مغناطیسی اصلی از داده های مغناطیسی (با استفاده از مدل میدان IGRF) و پس از اعمال فیلترهای RTP و میان گذر، بلوک بندی منطقه جهت استفاده از روش تحلیل طیفی انجام شد. بعد از انتخاب اندازه بهینه ابعاد بلوک بندی، با استفاده از شیب نمودار طیف توان، عمق بالا و عمق مرکز توده مغناطیسی برای تمام بلوک ها محاسبه و در نهایت، نقشه عمق کوری منطقه مورد مطالعه تهیه شد. عمق کوری در منطقه مورد مطالعه، در محدوده 9 تا 9/9 کیلومتر متغیر است و کمترین مقادیر آن مربوط به ناحیه جنوب شرقی منطقه است. اطلاعات زمین شناسی منطقه حاکی از وجود شواهد دیگری چون چشمه های آب گرم، توده های نفوذی و توده های آتش فشانی در قسمت جنوب شرقی منطقه است. محدوده مذکور، به عنوان محتمل ترین ناحیه جهت انجام مطالعات اکتشاف تفصیلی منابع زمین گرمایی در محدوده مورد مطالعه معرفی می شود.
    کلیدواژگان: مغناطیس هوابرد، زمین گرمایی، عمق نقطه کوری، طیف توان، کرمان
  • مهرداد خلیل طهماسبی، امین روشندل کاهو *، علی نجاتی کلاته صفحات 177-188
    تضعیف نوفه یکی از مراحل مهم پردازش داده های لرزه ای بازتابی است. عدم تضعیف نوفه در مراحل ابتدایی پردازش می تواند بر روی مراحل بعدی پردازش و تفسیر تاثیر مخرب داشته باشد و باعث افت کیفیت مقاطع و تصاویر لرزه ای نهایی شود. دسته مهمی از نوفه های داده های لرزه ای، نوفه های همدوس هستند؛ که از یک ردلرزه به ردلرزه دیگر دارای روند می باشند. یکی از مهم ترین نوفه های همدوس، نوفه زمین غلت است؛ که دارای محدوده فرکانسی پایین، دامنه بالا و سرعت انتشار پایین می باشند. روش های مختلفی نظیر فیلتر های فرکانسی بالا گذر، میان گذر و فیلتر فرکانس-عدد موج (f-k) برای تضعیف آن ها به کار می رود؛ که هرکدام از آن ها معایبی دارند. در این مقاله از روش تجزیه مد متغیر برای تضعیف نوفه زمین غلت استفاده شده است. تجزیه مد متغیر بر خلاف سایر روش های تجزیه مانند روش تجزیه مد تجربی دارای پایداری بسیار بهتری در مقابل نوفه است. در این روش سیگنال حاوی نوفه به مولفه های نوسانی به نام مد، تجزیه می شود. هر مد از حوزه زمان به حوزه زمان-فرکانس انتقال داده می شود و سپس فیلتر طراحی شده بر روی آن اعمال می گردد و به حوزه زمان برگردانده می شود. ردلرزه نوفه زدا شده از حاصل جمع مدهای فیلتر شده به دست می آید. روش تضعیف نوفه زمین غلت با استفاده از تجزیه مد متغیر بر روی داده های لرزه ای مصنوعی و واقعی اعمال گردید و نتایج آن با نتایج حاصل از روش متداول f-k مقایسه شد. مقایسه نتایج نشان داد که روش مبتنی بر تجزیه مد متغیر بر خلاف روش متداول f-k بدون آسیب رساندن به سیگنال بازتابی، به خوبی نوفه زمین غلت را تضعیف نماید و می تواند به عنوان یک روش مناسب برای تضعیف نوفه زمین غلت مورد استفاده قرار گیرد.
    کلیدواژگان: لرزه نگاری بازتابی، تجزیه مد متغیر، صفحه زمان- فرکانس، امواج زمین غلت
  • بهمن صادقی عزیزلو *، وحید ابراهیم زاده اردستانی صفحات 189-201
    برای تعیین موقعیت افقی اجسام زیرسطحی از روی نقشه های میدان پتانسیل، روش های تعیین مرز مورد استفاده قرار می گیرند. در این روش ها عمدتا از مشتقات میدان پتانسیل استفاده می شود. از رایج ترین این روش ها می توان به سیگنال تحلیلی، زاویه تمایل، مشتق افقی کل زاویه تمایل و مشتق افقی کل نرمال شده اشاره کرد؛ که در تفسیرهای ژئوفیزیکی مورد استفاده قرار می گیرند. در این مقاله، قابلیت روش واریانس ناهمسانگردی نرمال شده در تعیین مرز آنومالی های گرانی بررسی و با روش های ذکرشده مقایسه شده است. عدم استفاده مستقیم از مشتقات درجات بالا و مشتق قائم در محاسبات، از مزایای این روش است؛ که موجب شده نتایج به دست آمده برای داده های همراه با نوفه از پایداری بیشتری برخوردار باشند. یکی از پارامترهای تاثیرگذار در محاسبات مربوط به این روش، عدد پنجره است. این عدد برای داده های بدون نوفه مقدار بهینه سه در نظر گرفته شده است و برای داده های حاوی نوفه، این مقدار بهینه از طریق محاسبه تغییرات بیشینه های واریانس ناهمسانگردی نرمال شده برحسب عدد پنجره های مختلف انجام گرفته است. به منظور بررسی کارایی این روش در تعیین مرز توده های گرانی و مقایسه نتایج آن با نتایج سایر فیلترهای ذکرشده، از مدل های مکعبی در دو حالت مختلف استفاده شده است. در حالت اول از مکعب های در کنار هم و در حالت دوم از دو مکعب هم مرکز که با یک فاصله عمودی روی یکدیگر قرار دارند، بهره گرفته شده است. فیلترهای عنوان شده قادر به شناسایی مرز مکعب ها در حالت دوم نبوده اند. این در صورتی است که مرز مکعب ها در هر دو حالت توسط روش واریانس ناهمسانگردی نرمال شده به خوبی آشکارسازی شده است. همچنین، قابلیت این روش در حالتی که داده ها همراه نوفه هستند؛ نیز بررسی شده است. درنهایت، این روش بر روی داده های واقعی معدن منگنز صفو اعمال شده است؛ که نتایج قابل قبولی به دست آمده است.
    کلیدواژگان: تعیین مرز، میدان پتانسیل، گرادیان افقی و قائم، واریانس ناهمسانگردی نرمال شده، معدن منگنز صفو
  • سارا ایازی، علیرضا گودرزی*، میثم کورکی صفحات 203-215
    امروزه روش های مختلفی برای آنالیز سرعتی داده های لرزه ای به کار می رود؛ که از آن جمله روش های مبتنی بر همدوسی است؛ که در تخمین سرعت برانبارش بسیار راهگشاست. از آنجا که همه روش های مطرح شده در حوزه زمان پیاده سازی شده اند؛ سعی بر آن است با معرفی حوزه موجک گسسته غیرکاهشی ارتقای آنالیز سرعتی نشان داده شود. وجود نوفه و همچنین تضعیف سیگنال ها در اثر جذب فرکانس باعث می شود که سیگنال طی زمان و عبور از لایه های مختلف دچار اعوجاج شده و به تدریج در حیطه زمانی با از دست دادن فرکانس هایش پهن تر شود. از دست دادن فرکانس های بالاتر و حضور نوفه می تواند منجر به خطا در تخمین دقیق سرعت شده و نهایتا تصویرسازی لرزه ای را دچار خطا کند. در این مقاله ابتدا داده ها توسط یک موجک مادر که در اینجا دابیچی2 انتخاب شده است؛ تجزیه شده و به فضای موجک گسسته غیر کاهشی برده می شود. سپس آنالیز سرعتی در هر کدام از مقیاس ها به طور جداگانه صورت می پذیرد. توجه شود که هر ردلرزه به صورت مجزا تجزیه می شود و روش تبدیل موجک گسسته غیرکاهشی به فرم یک بعدی اعمال می گردد. سپس مقیاس های یکسان از همه ردلرزه ها در یک مقیاس تجمیع شده و آنالیز سرعتی انجام می شود. در انتها طیف های سرعتی مقیاس ها با وزن یکسان یکپارچه شده و آنالیز سرعتی چند تفکیکی را ارائه می دهند. نتایج حاصل از داده های مصنوعی و واقعی مبین افزایش چشم گیر دقت آنالیز سرعتی چند تفکیکی نسبت به آنالیز سرعتی در حوزه زمان است. همچنین حضور نوفه همدوس و اتفاقی تاثیر کمتری در ایجاد خطا در روش پیشنهادی داشته است.
    کلیدواژگان: تحلیل سرعت، طیف سرعت، همدوسی، تبدیل موجک گسسته غیرکاهشی
  • سمیه کریمی زاده، نرگس افسری*، فتانه تقی زاده فرهمند صفحات 217-227
    کمربند چین خورده- راندگی زاگرس در نتیجه برخورد صفحه عربستان با پوسته قاره ای ایران مرکزی استو به عنوان یک مثال از یک کمربند جوان برخورد قاره- قاره در نظر گرفته می شود. در این مطالعه تحلیل تابع گیرنده P برای تعیین ضخامت پوسته و نسبت Vp/Vs در شمال غرب زاگرس استفاده شده است. به همین منظور از داده های زمین لرزه هایی که توسطایستگاه هایلرزه نگاری کوتاه دوره و باند پهن سه مولفه ای شبکه های کرمانشاه و خرم آباد در فاصله رومرکز ̊95>D> ̊30 و با بزرگای 5/5≤mbکهطی سال های 2010 تا 2015 ثبت شده اند؛استفاده شده است. ابتدابااستفادهازتاخیرزمانیبینفاز تبدیل یافته Ps از موهو نسبت به رسید مستقیم P، متوسط عمق موهو برای منطقه برآورد شد. سپسبااستفادهازروشبرآوردهمزمانعمقونسبت Vp/Vs پوسته وبهکمکبازتاب هایچندگانهپوسته (PpPs،PpSs + PsPs) مقدارمتوسط ضخامت پوستهونسبت Vp/Vs با روش زو و کاناموریمحاسبه شد. با استفاده از این روش متوسط عمق موهو در شمال غرب زاگرس 44 کیلومتر به دست آمد؛ که از 36 کیلومتر تا 55 کیلومتر تغییر می کند. در بخش شمالی منطقه ضخامت پوستهبه طور متوسط 38 کیلومتر بوده و با عبور به سمت قسمت مرکزو جنوب منطقه؛ پوسته ضخیم تر می شود. نتایج نشان می دهد ناپیوستگی موهو در زیر منطقه مورد مطالعه تخت نیست. نسبت Vp/Vs برای پوسته شمال غرب زاگرس به طور متوسط 74/1 به دست آمد؛ که از 66/1 تا 86/1 تغییر می کند.
    کلیدواژگان: زاگرس، تابع گیرنده P، ناپیوستگی موهو، نسبت Vp-Vs، بازتاب های چندگانه
  • شاهین شعبانی، کیوان کیانفر*، مهدی محمدی ویژه صفحات 229-243
    عریان شدگی از جمله خرابی های رایج است که در اغلب روسازی های آسفالتی به وقوع می پیوندد. منشا این خرابی از رطوبت است. به نحوی که در اکثر مطالعات «عریان شدگی» و «آسیب رطوبتی» معمولا به جای هم استفاده می شود. روش متداول برای شناخت این خرابی، مغزه گیری از نقاط مشکوک در سطح راه و انجام آزمایش های مخرب بر روی مغزه به دست آمده است. از جمله رایج ترین آزمایش ها، چگالی واقعی آسفالت، مقایسه نسبت تنش کششی غیرمستقیم نمونه ها در حالت اشباع به خشک و به دست آوردن میزان درصد فضای خالی آسفالت است؛ اما این قبیل از آزمایش ها، مخرب اند و چاله های به وجود آمده از مغزه گیری در سطح راه باید مرمت و وصله شوند. همچنین انجام این کار دشوار و دستیابی به نتایج حاصل از آزمایش های مخرب اغلب وقت گیر هستند. روش ارزیابی با رادار نفوذی به زمین Ground Penetration Radar (GPR) از جمله روش های غیر مخرب است، که امروزه کاربرد آن در مهندسی راه رو به افزایش است. در این پژوهش قطعاتی از مسیر شبکه راه های استان تهران، با انتخاب نقاطی از مسیر، پس از ارزیابی غیر مخرب، مغزه گیری شد و نتایج حاصل از تحلیل رادار با پارامترهای آزمایش های مخرب مقایسه شد. به طوری که با کاهش درصد فضای خالی کمتر از 7 درصد، افزایش چگالی واقعی آسفالت، افزایش مقدار نسبت تنش کششی غیرمستقیم نمونه ها در حالت اشباع به خشک به بیش از 8/0 و در نهایت افزایش مقدار ثابت دی الکتریک ناشی از ارزیابی غیر مخرب مشاهده شد. در این پژوهش عدد ثابت دی الکتریک کمتر از 10/5، عریان شده و بیشتر از آن آسفالت سالم در عمق 5 سانتی متر از سطح آسفالت و در سطوح زیرین آسفالت (از عمق 5 تا عمق 10 سانتی متری) ثابت دی الکتریک کمتر از 40/5 منطبق بر نواحی عریان شده و بالاتر از این مقدار منطبق بر آسفالت سالم است.
    کلیدواژگان: عریان شدگی، رادار نفوذی به زمین، مغزه گیری، آزمایش های مخرب
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  • Mohammad Rezaie *, Ali Moradzadeh, Ali Nejati Kalateh, Hamid Aghajani Pages 145-154
    Summary Inversion of magnetic data is one of the important steps in the interpretation of practical magnetic data. The inversion result can be obtained by minimization of Tikhonov objective function. The determination of an optimal regularization parameter is highly important in magnetic data inversion. In this paper, an attempt has been made to use unbiased predictive risk estimator (UPRE) method in selecting the best regularization parameter for 3D constrained inversion of magnetic data using gradient projection reduced Newton (GPRN) algorithm. To achieve this goal, an algorithm has been developed to estimate this parameter. The validity of the proposed algorithm has been evaluated by magnetic data acquired from a synthetic model. The results have been compared with the results of generalized cross validation (GCV) method. The GCV method failed to estimate the regularization parameter, but the UPRE method could find the best regularization parameter. Then, the algorithm was used for inversion of real magnetic data obtained from Allah Abad iron deposit. The results of three-dimensional (3-D) inversion of magnetic data from this iron deposit show that the GPRN algorithm can provide an adequate estimate of magnetic susceptibility and geometry of subsurface structures of mineral deposits. A comparison of the inversion results with drilling data clearly indicate that the proposed algorithm can be used for 3-D inversion of magnetic data to estimate precisely the magnetic susceptibility and geometry of magnetized ore bodies.
    Introduction Inversion of magnetic data is one of the most important steps in the interpretation of practical magnetic data. The goal of 3-D inversion is to estimate magnetic susceptibility distribution of an unknown subsurface model from a set of known magnetic observations measured on the surface. Inversion of magnetic data is an underdetermined and ill-posed problem. In addition, the non-uniqueness of the solution is the main issue of the inversion. One way to achieve a suitable model result in the inversion is to carry out the inversion with smoothness and smallness constraint. The solution can then be obtained by minimization of an objective function that consists of a misfit function and one of Tikhonov regularization functions. Regularization parameter makes a trade-off between misfit and regularization function. The determination of an optimal regularization parameter is highly important in magnetic data inversion. There are different methods for automatic estimation of regularization parameter in 3-D inversion. The GCV method is one of the most popular methods for choosing optimal regularization parameter in inversion of magnetic data. This method sometimes fails to find optimal regularization parameter. Therefore, it is suggested to use other methods. In this paper, we have applied the UPRE method to choose the best regularization parameter for 3-D constrained inversion of magnetic data using the GPRN algorithm.
    Methodology and Approaches The UPRE method has been adapted for the solution of inverse problems. The UPRE method is based on a statistical estimator of the mean squared norm of predictive value. In this method, the optimal regularization parameter minimizes the UPRE function. We have developed an algorithm for 3-D inversion of magnetic data that uses the UPRE method for choosing optimal regularization parameter, and then, the inverse problem is solved by the GPRN algorithm under flatness and positivity constraints. To evaluate the reliability of the introduced method, the magnetic data of a synthetic model contaminated by 3 percent random noise have been inverted using the developed method. The GCV method is also applied for comparison of its results with the UPRE results. The obtained results indicate that the GCV method fails to choose regularization parameter but the UPRE method finds a unique optimal regularization parameter. Finally, The introduced algorithm has been used for 3-D inversion of magnetic data from Allah Abad iron deposit. The results are consistent with borehole information.
    Results and Conclusions In this paper, the UPRE method has been developed for choosing optimal regularization parameter in 3-D constrained inversion of magnetic data using the GPRN algorithm. Data from synthetic model have been inverted using the introduced algorithm and acceptable results have been obtained. Geometrical parameters of synthetic model have been obtained from the constrained inversion process with acceptable accuracy. After validation of the algorithm performance on synthetic model, it has been applied for 3-D inversion of magnetic data from Allah Abad iron deposit. The results of drilling boreholes in the area confirm the results of the 3-D inversion.
    Keywords: 3D inversion, Magnetic data, Regularization parameter, UPRE method, GPRN method, Model parameter, Allah Abad iron deposit
  • Akbar Heidari, Toktam Zand *, Ali Gholami Pages 155-166
    Summary Deconvolution is one of the significant steps in seismic signal processing for obtaining high resolution images of subsurface. In this paper, a new nonstationary deconvolution is developed to retrieve the impulse response of the earth and remove the earth attenuation effects from it via a simulated annealing (SA) optimization. The time location of each spike and the corresponding quality factor is estimated by the SA method and its amplitude is calculated using a least-squares method. All three parameters of the reflection coefficient, time lag, and the quality factor for each layer are estimated simultaneously. Available information from well-logs can also be incorporated as a priori information. Numerical examples from simulated and field seismic data show high performance of the proposed algorithm for estimating the reflectivity structure and the model of the quality factor. Numerical examples confirm promising applicability of the new method for processing and interpretation of seismic data. The goal of non-stationary deconvolution is to remove the effects of the source wavelet and the attenuation filter from the data to retrieve the earth impulse response with an enhanced temporal resolution.
    Introduction High resolution images of subsurface, obtained from seismic studies, can serve an important role in the oil and gas exploration industry. One of the main steps in seismic signal processing is deconvolution to increase the temporal resolution of the data. Beside the blurring effect of the source generated pulse, the inhomogeneity and anelasticity of the earth causes a decrease in the resolution of the acquired data due to the absorption and dispersion mechanisms. While propagation, the absorption decreases the strength of the pulse and dispersion leads to a gradual change in its shape. These effects deteriorate the resolution of the subsurface images and need appropriate processing tools for compensating their effects. Simultaneous compensation of these effects is a non-linear and ill-posed problem. In this paper, based on SA, a new algorithm is developed for this task. The performance of the method is tested via numerical examples.
    Methodology and Approaches Many approaches have been proposed for solving non-linear optimization problems such as the hill climbing, the genetic algorithm and the SA methods. One of the advantages of these methods in comparison with the gradient based solvers is their ability to find the global minimizer. Here, we employ the SA method for solving the non-stationary seismic deconvolution. This method escape from trapping in local minima by adding random amounts to the solution space. Most of the algorithms avoid approaching false solutions which may cause trapping in local minima. The SA method, however, prefers evaluating possibly incorrect solutions and calculating its correctness using a probability distribution function based on the amount of the cost function. The other advantage of the SA method is that the uncertainty of the parameters can also be calculated by applying the algorithm several times for searching the whole model space in order to obtain a set of solutions, which fit the data and satisfy the constraints.
    Results and Conclusions In this paper, a stochastic SA-based algorithm, was proposed to solvinge the non-stationary seismic deconvolution problem for simultaneous compensation of the blurring effect of the wavelet and the Q-filtering effects of the earth. The Q-model of the earth is also estimated during the deconvolution. Numerical examples of synthetic and field data confirmed high-performance of the proposed algorithm.
    Keywords: Non-Stationary Deconvolution, Reflectivity, Seismic Quality Factor, Attenuation Filter, Simulated Annealing Algorithm
  • Nastaran Heydarabadi Pour, Azadeh Hojat*, Hojjatollah Ranjbar, Saeed Karimi Nasab Pages 167-176
    Summary To optimize the widespread use of fossil fuels in Iran, different resources of renewable energy can be considered as promising challenges. The everincreasing energy demands of the country can be satisfied by the very rich resources of renewable energy such as wind, solar, biomass, and geothermal energies. This paper presents the results of Curie point depth calculations from spectral analysis of aeromagnetic data for preliminary exploration of geothermal resources in central region of Kerman Province. The calculations were performed for an area of 22010 km2 located north of Jiroft city and east of Baft city. RTP correction and band pass filtering were first applied to the data. Then, the block dimension of 80×80 km with an overlap of 50% was selected for the spectral analysis. The spectral power was calculated for all the blocks and the Curie depth map was obtained for the study area. The results showed that the shallowest Curie depths are about 9 km observed in the southeastern part of the study area. Different information layers including geological and surface information layers were, then, onvestigated in the ArcMap software. Concentration of several hot springs and presence of faults, intrusive structures, and volcanic rocks prove a high probability of geothermal anomaly in the area of shallowest Curie depth.
    Introduction Although there are evidences of rich geothermal potential regions in Iran, very few exploration studies have been carried out so far, especially in the eastern and central regions of the country. Geothermal heat flux is one of the main parameters to be investigated in geothermal exploration programs but few direct heat flux measurements are available in Iran. Given the proved relation between Curie depths and heat flux, we can use magnetic data to calculate the Curie depths in areas where few or no direct heat flow measurements are available. Hojat et al. (2016) used an iterative forward modeling approach to calculate the Curie depth of Kerman province from satellite magnetic data. The obtained Curie map revealed an area with very shallow Curie depth in the southeastern region of Kerman province. Their finding was confirmed by geological evidence for the probability of a geothermal potential zone. In this paper, aeromagnetic data are used to calculate the Curie depth map for an area of 22010 km2 located in the central region of Kerman Province, part of which overlaps with the probable geothermal zone revealed from the previous study.
    Methodology and Approaches The aeromagnetic data have first been processed in the Oasis Montaj software. The IGRF model has been used to remove the main field from the observations. RTP and Bandpass filtering have then been applied to the data. The block dimension of 80×80 km with the overlap of 50% has been selected for the spectral analysis method. After calculating the Curie depth map of the study area, different information layers including hot springs, faults, intrusive bodies, and volcanic structures have been combined in the ArcMap software to validate the interpretation of the results.
    Results and Conclusions 1. Curie depth values were obtained in the range of 9-9.9 km. 2. The shallowest Curie depths occurred in the southeastern part of the study area. 3. The main concentration of hot springs, intrusive bodies, and volcanic structures was in the area with the shallowest Curie depths. 4. It is suggested to perform detailed land surveys in the most probable area detected in this study.
    Keywords: Aeromagnetic Data, Geothermal Resources, Curie Point Depth, Power Spectrum, Kerman
  • Mehrdad Khalil Tahmasebi, Amin Roshandel Kahoo*, Ali Nejati Kalateh Pages 177-188
    Summary Seismic imaging is highly dependent on the quality of seismic data. Structural and stratigraphic interpretation of seismic sections that contain the least amount of noise is much easier. Reflection seismic data are often associated with noise. Coherent noise is a major category of noise that accompanies seismic data, and has the same trend in different seismic traces of the data. Ground roll is one of the main coherent noises that has a low frequency, high amplitude and low velocity. Various methods, such as frequency filters and frequency-wavenumber filter, have been used for ground-roll attenuation. Different advantages and disadvantages are mentioned for each of the methods. In this paper, we have used time – frequency transform and variational mode decomposition to attenuate the ground-roll.
    Introduction Generally, seismic noises are divided into two categories: coherent and incoherent. Coherent noise attenuation has always been a serious challenge for seismic data processors. Ground-roll is the main type of coherent noise in seismic data and is characterized by dispersive wave, low frequency, high amplitude relative to other events of interest in land seismic surveys, and propagates along and near the surface of the earth and obscures useful information in seismic exploration. The ground-roll noise often masks the shallow reflections at near offset and deep reflections at far offset and must be attenuated before the succeeding processing procedure. Therefore, ground-roll removal is an essential part of land seismic data processing. There have been many researches about eliminating ground-roll noise published in literature, and many authors have introduced various methods for handling the ground-roll noise problem. A most straightforward and commonly used method for suppressing the ground-roll noise is band-pass filtering. In many cases, ground-roll has significant amplitudes only at frequencies lower than the signal. In such cases, a simple frequency band-pass filter will provide suitable noise removal. In the case of the frequency overlap of primary reflections and ground-roll, the band-pass frequency filter either fails to attenuate all the ground-roll noise or removes much useful reflection energy. Dip filtering also known as f-k filtering, which is based on the 2D Fourier transform, is another commonly used technique to attenuate ground-roll. In the 2D Fourier transform of a seismic pre-stack gather, there is no a clear separation border between signal and noise region, consequently it leads to signal distortion. Radon, tau-p, and radial trace transforms have also been applied to ground-roll removal. Another widely used method to remove ground-roll noise from seismic data is singular value decomposition (SVD)-based method. Nevertheless, all of the above-mentioned approaches disagree with seismic data natural behavior because of stationary signal assumptions. Several methods have been introduced that consider the non-stationary nature of seismic data. The time-frequency denoising algorithm is an effective method for handling noise problems. A high resolution time-frequency map can be very helpful in unwanted energy filtering in time-frequency domain. In this paper, we have used variational mode decomposition method to create a high resolution time-frequency map of seismic trace and ground-roll attenuation.
    Methodology and Approaches The goal of variational mode decomposition method is to decompose a real input signal,   xt, into a number of modes that have specific sparsity properties while each being band-limited about a center frequency, k 
    , and reproducing the
    input. Each intrinsic mode function,   k ut, can be calculated by solving an optimization problem as:         2 , 2 s.t. min                  k kk jt tk u k k k j t u t e t u t x t     Time-frequency filter has been widely used to attenuate the ground roll components. Based on the time-frequency map obtained from the variotional mode decomposition of seismic data and instantaneous frequency,   i ft, and instantaneous bandwidth,   i bt, of seismic data, an effective time-frequency filter can be designed based on the difference between seismic signals and ground roll in time-frequency map as:  
            1 , , 22 0 otherwise             ii ii b t b t f f t f t H t f The de-noised seismic trace can be obtained by applying the above time-frequency filter on time-frequency map of seismic trace and transfer back the filtered time-frequency map to time domain.
    Results and Conclusions The proposed algorithm has been tested on a real seismic shot gather and the results have been compared to the results of applying frequency–wavenumber method on the seismic data. The obtained results show that the proposed method attenuates the ground-roll effectively while minimal harm to the reflected signal incurs. Hence, it can be an excellent alternative technique to attenuate the ground-roll noise.
    Keywords: Reflection Seismic, Variational Mode Decomposition, Time-Frequency Map, Ground-Roll Waves
  • Bahman Sadeghi-Azizloo*, Vahid Ebrahimzadeh Ardestani Pages 189-201
    Summary To determine the location of subsurface objects from the potential field maps, edge detection methods are used. This methods are mainly derivatives of potential field. For edge detection, several methods or filters such as analytic signal, tilt angle, total horizontal derivative of tilt angle and normalized total horizontal derivative are commenly used in geophysical interpretation. In this regard, the method of normalized anisotropy variance (NAV) for edge detection is investigated in this paper. This filter directly do not use high-order derivatives, and also, vertical derivative in calculations, thus, stability of noisy data is preserved in this method. One of the effective parameters in the calculation of this method is the optimal window number that is obtained by maximum of variation of normalized anisotropy variance and window number. In order to assess performance of the NAV-method in the edge detection of gravity anomalies, cubic models used with positive and negative density contrast and different depth, and the NAV-method and also the above-mentioned filters were applied to synthetic models and real gravity data of Safo Manganese mine. Consequently, acceptable results from applying the NAV method for edge detection of gravity anomalies were obtained.
    Introduction A variety of techniques based on horizontal and vertical derivatives of potential field data have been developed as effective tools for the edge detection of potential field anomalies. Location of maximum horizontal derivative can be used an indicator of the location of the anomaly’s edges. The first vertical derivative (FVD) is positive over the source, zero-crossing value of FVD over the edge, and outside of a vertical sided source is negative. The peaks of the horizontal derivatives indicate the edges and zero over the body. One of the most important problems in using derivative-based edge detection techniques is that the noise in the potential field data increases during the process. Analytic signal is one of the filters that employs both horizontal and vertical derivatives to determine the boundary of the anomalies. Local phase filters are set of filters based on horizontal and vertical derivatives of potential field data that are used in geophysical interpretation. Tilt angle, total horizontal derivative of tilt angle and normalized total horizontal derivative (TDX) are conventional local phase filters that are sensitive to noise. To achieve the best result for edge detection of gravity anomalies, we introduce normalized anisotropy variance or NAV method that reduces sensitivity to noise.
    Methodology and Approaches To determine the edge of subsurface bodies, NAV edge detection filter has been applied to gravity data. The NAV method has been investigated as a tool to detect the edge of anomalies.In this regard, its ability to determine the edge of synthetic models from gravity data, in a noisy and free-noise state has been demonstrated in this paper. Anisotropy scale and window number are two important parameters on the value of the NAV. The anisotropy scale in anomalies separation in the vicinity of each other, is an effective parameter. An empirical approach to select these parameters has been applied. Window number (M) is associated with data quality, for noise-free data M=3 is acceptable. For data that are contaminated with noise, the value of M is determined by variation of the maximum value of NAV with window number. Since the NAV does not use any of higher-order derivatives directly, it is less sensitive to noise than the other methods. In MATLAB platform, a computer program has been prepared and its outputs are extracted.
    Results and Conclusions In this research, capability of NAV method in estimating boundaries of synthetic and real potential field anomalies has been investigated. Vertical derivative that creates complexity for the interpretation, has not been used in this method; hence this method or filter for deep resources is more stable. Similar to tilt angle filter, the zero value of NAV corresponds to the edges of anomalies. The value of the NAV filter is positive over the body and negative out of it; therefore, area of the body can be detected from other parts. The results also show that this method is less sensitive to noise and the boundaries that are determined for the model, are in good accordance with reality. For the model that a small prism superposed on a big prism, the NAV could detect the edges of the superposed prism with high accuracy.
    Keywords: Edge Deteectin, Potential Field, Horizontal, Vertical Gradient, Normalized Anisotropy Variance, Safo Manganese Mine
  • Sara Ayazi, Alireza Goudarzi *, Meisam Kourki Pages 203-215
    Summary Different methods are used for seismic velocity analysis, including spectral analysis based on semblance, which is a reliable way to estimate the stacking velocity. The proposed method in this research is superior over other seismic velocity analysis methods because in the proposed method, the wave due to the absorption of the earth makes a reduction of the frequency content of the source in time, and results in poor temporal resolution. In this paper, the velocity analysis performed in the wavelet domain using undecimated discrete wavelet transform (UDWT). Random noise is often placed in high-frequency sub-bands and their effect leads to a reduction in coherency than other sub-bands. In this way, data analyses to high-pass and low-pass sub-bands and velocity analysis at any scale are performed using discrete wavelet transform and scaling filters. A Comparison of the obtained results showed that the spectral analysis of the velocity in the wavelet domain increases the accuracy of the velocity analysis in each band of frequencies.
    Introduction One of the valuable information that can be obtained using seismic waves is the velocity of the earth layers, which can be useful for identifying the properties and petrophysical parameters of the layers. The velocity information is usually estimated when processing of seismic reflection data using the CMP velocity analysis is made. Velocity analysis is a powerful tool for detecting reflections and determines the stacking velocity of seismic data. Different methods are presented for analysis of seismic velocity. The UDWT method for signal decomposition has been introduced by Guo (1995).
    Methodology and Approaches For a flat layer, the shape of the move out curve is defined by the hyperbolic relationship between the zero offset time and the velocity. Several methods of velocity analysis have been used in the past, but today, most velocities are selected interactively using combined displays on the processing workstations. Nevertheless, velocity analysis is still one of the most time-consuming parts of seismic processing. This is also the most critical step since velocity analysis is an initial interpretation of the data and it is important as the seismic interpreter is involved in the analysis and quality control steps. Velocity analysis is often performed several times during processing, which results in an iterative improvement in velocity estimation. The velocity spectrum display is calculated by determining how a given hyperbolic event matches actual events on the central CMP gather. These represent much more velocity trials than can be done using CVS or FVS analysis. The maximum coherence amplitude is expected when the hyperbola corresponds best fits to a given large amplitude seismic event. The coherence measurement most often used is called semblance, which is robust to noise, spatial aliasing, and lateral amplitude variations. There are various methods of displaying semblance. The average of too many gathers would increase computation time and could begin to filter geological variations. Wider peaks in the deeper part of the section indicate reduced resolution. The velocity spectrum is also good for identification of multiple reflections.
    Results and Conclusions In this research, an improvement for the analysis of seismic velocity was made. In this paper, we have investigated the coherence technique based on discrete wavelet transform. We conclude that the cumulative spectrum in the UDWT domain gives a precise velocity spectrum.
    Keywords: Velocity Analysis, Spectrum, Coherency, Undecimated Discrete Wavelet, Transform (UDWT)
  • Somayeh Karimi Zadeh, Nargaes Afsari *, Fataneh Taghizadeh-Farahmand Pages 217-227
    Summary The Zagros fold and thrust belt (ZFTB) is resulted from the collision of the Arabian Plate with the continental crust of Central Iran and is considered as an example of a young continent–continent collision belt. In this study, we have used P receiver function technique to determine the crustal thickness and Vp/Vs ratio in northwest of Zagros. Our dataset includes teleseismic data (with magnitude Mb ≥ 5.5, epicentral distance  from 30◦ to 95◦) that have been recorded at 11 three component short-period and broadband stations of Kermanshah and Khoramabad telemetry seismic networks from 2010 to 2015. First, the differential travel time between the incident P wave and S converted wave (delay time) is used for computation of crustal thickness. Then, we have used the arrival times of crustal multiples (PpPs, PpSs PsPs) to determine crustal thickness (H) and Vp/Vs ratio using Zhu and Kanamori method. Applying this method, the average Moho depth is determined that is 44 km in northwest of Zagros and varies between 36 km and 55 km. In northern part of the region, the average thickness of the crust is about 38 km, and toward the center and south of the region is going to be thicker. The average Vp/Vs ratio in the crust of northwest of Zagros is about 1.74 and varies from 1.66 to 1.86.
    Introduction Investigation of crust and upper mantle structures below the surface of the Earth is one of the important objectives of geophysics. Receiver functions are widely employed to detect P-to-S converted waves and are especially useful to image seismic discontinuities in the crust. This study intends to improve our knowledge on crustal thickness in northwest of Zagros. The region, which is referred as northwest of Zagros in Iran, includes the area located between 45°-49° longitude and 33°-36° latitude.
    Methodology and Approaches Teleseismic events with relatively high signal-to-noise ratio (>4) have been carefully selected at each station. We have considered a time window of 120 s, starting 20 s before the P-onset arrival time. Firstly, to broaden the response of short-period and broad band instruments into a more useful teleseismic frequency band, the instrument response is denconvolved from the original records. The three components in the coordinate system ZNE are then rotated into the local ray coordinate system LQT using theoretical back azimuth and incidence angle. To isolate the P-to-S conversions on the Q component, the L component is deconvolved from the Q component. They are stacked after move out correction for reference slowness of 6.4 s/°. P-RFs are sorted by increasing back azimuth. Moho depths are obtained by using the model presented by Afsari et al. (2011) (Vp=6.4 km/s, Vp/Vs=1.78). Then, we obtain the depths using Zhu and Kanamori method, which performs a grid search through the H and Vp/Vs space, and searches for the largest amplitudes at the predicted times of direct conversions and multiples. In this regard, we have used the weight factors of 0.5 and 0.25 for the Moho conversion and multiples, respectively.
    Results and Conclusions By applying Zhu and Kanamori method in northwest of Zagros reveals that the average Moho depth ia about 44 km, which is in good agreement with the results obtained by P receiver function analysis (~ 42 km). Our results also are in accordance with those obtained from other studies in ZFTB. Beneath the central part of Kermanshah region, a significant crustal thickening to a depth of approximately 51 km (station Kermanshah) has been observed. It may show a local effect beneath this part of region that has previously been reported in earlier studies. A local overthrusting system just beneath this station including dipping Moho boundary could be an alternative explanation for the observed feature. The results show that the Moho discontinuity in the study region is not flat.
    Keywords: Zagros, P Receiver Function, Moho Discontinuity, Vp-Vs Ratio, Multiples
  • Shahin Shabani, Keyvan Kianfar *, Mehdi Mohammadi Vizeh Pages 229-243
    Summary Stripping is a common distress occurring on asphalt pavements. The source of this stress comes from moisture, thus, stripping and moisture damage are often used interchangeably. A common way to identify these failures is drilling and coring from road surfaces, and doing destructive tests. The most commonly used tests are bulk density, comparing indirect tensile stress in saturated to dry condition (TSR) , and finding air void percentage .These tests are destructive, and take time more than usual. In addition, we must repair and patch the asphalt pavements where drilled and cored. Ground penetrating radar (GPR) is a method, which is not only a non-destructive method but it also evaluates the roads continuously and provides us with results much quicker than the common destructive tests. In this study, parts of the road networks in Tehran are evaluated using GPR, then several points of the road surface are drilled and cored. Finally, the results of the GPR measurements and destructive tests are analyzed and compared with each other.
    Introduction Moisture damage is a common distress that occurs in asphalt pavements. In this phenomenon, adhesion between bitumen and aggregates is ruined. It usually happens where the level of underground water is high, and it is seen along the wheel paths. Stripping starts at the sub base layer, and moves to the upper layer until it appears on the surface. This problem often occurs in the moisture condition when the pavement temperature increases. Cracks appear where traffic is heavier. Finally, it causes holing and showing.
    Methodology and Approaches In this study, parts of the road network in Tehran (namely,Amir Kabir Boulevard) were evaluated using GPR, and then, several points of the road surface were drilled and cored. The cores were tested, and as a result, bulk density, TSR, and air void percentage were obtained. Finally, the analysis results of the GPR and destructive tests in different depths were compared.
    Results and Conclusions As the amount of asphalt bulk density increases, the air void percentage decreases to less than 7%, and the TSR reaches over 0.8. Stripping is observed where dielectric constant becomes less than 5.10 in the upper 5 centimeters of asphalt depth, and also, stripping happens in the upper 10 centimeters of asphalt depth where dielectric constant reduces to less than 5.40.
    Keywords: Stripping, Ground Penetrating Radar (GPR), Coring, Destructive Tests