mohammad fahim avish

In the recent decade, there has been an increasing interest in developing various resources of renewable energy as an alternative to fossil fuels in Iran. Geothermal energy is one of the promising reservoirs and exploration of geothermal favorability has become one of the main research interests in most parts of the country. Some reconnaissance studies have shown that the Kerman Province can be one of the geothermal potential regions in Iran. Different studies are being performed to prepare the geothermal favorability map for Kerman Province. The aim of this study is to estimate the Curie point depth (CPD), heat flow and geothermal gradient from spectral analysis of aeromagnetic data for reconnaissance exploration of geothermal resources in the east of Kerman Province, southeast of Iran. This area is selected because it is characterized by thermal manifestations such as several hot springs with temperatures between 20–73°C, faults, and igneous rocks in the southern and southwestern parts. Aeromagnetic data were first processed for removing the geomagnetic main field (using the International Geomagnetic Reference Field (IGRF)), reduced to pole (RTP) and band-pass filter. Then, we used spectral analysis technique to estimate the top and bottom boundaries of the magnetized crust. Comparison of magnetic map with geologic map shows a good correlation between the exposed geological units and magnetic signatures. Strong variations in magnetic intensity suggest a variety of magnetic properties. Bandpass filtered data were produced from the RTP aeromagnetic anomalies to isolate near surface and undesired deep effects. Then, the map was divided into thirty blocks, each having 50% of overlap with the adjacent block. A first-order trend was removed from each block, and grids were expanded by 10% using the maximum entropy method to make the edges continuous. Then, each block was analyzed using the spectral centroid method to obtain the depths to the top, centroid and bottom of magnetic sources. First, we calculated the radially averaged log power spectrum of each block. To compute the spectrum of the data, the magnetic anomaly of the area was transformed by 2D Fourier to obtain the average Curie depth. From the slope of the very long wavelength part of the spectrum, the centroid depth (Z0) was estimated, while the average depth to the top (Zt) was estimated from the second longest wavelength part of the spectrum. Using the values obtained for Z0 and Zt, the depth to the bottom (Zb) was calculated for each block using the equation Zb=2Z0−Zt. The depths obtained for the bottom of the magnetized crust are assumed to correspond to Curie point depths where the magnetization of the layer disappears. Variations of the Curie isotherm level can correlate to some indices of geothermal activity (e.g., geothermal gradient and near-surface heat flow) in the study area. The results showed that Curie point depth in the study area varies from 8.5km to 18.2km, and accordingly, the geothermal gradient ranges between 31-67°C/km. The heat flow was estimated in the range 139-294mW/m2 in the study area. The results showed the shallowest Curie depths occurring in the southern part of the area. This is the zone which mainly hosts volcanic rocks and hot springs.

Summary: In this study, satellite images, and aeromagnetic and ground magnetic data were analyzed to explore the geothermal potential in Sirch-Golbaf area in Kerman province. Thermal anomalies and apparent thermal inertia images were studied using MODIS, Landsat and ASTER images. As a result, two thermal anomalies were obtained; one in the southeastern part of the study area and the other one in Jooshan location. Magnetic investigations also detected two anomalies; a deep magnetic anomaly in the southern part of the area and another magnetic anomaly near Jooshan hot spring in the northeastern part. These magnetic anomalies were correlated with thermal anomalies.
Remote sensing techniques are helpful reconnaissance tools for detecting surface temperature anomalies and identifying geothermal indicators (Calvin et al., 2005). Lu et al. (2008) used Landsat ETM thermal images to detect thermal anomalies strongly correlated with faults in certain scales in the Jiangshan-Shaoxing fault in the Zhejiang Province, China. They defined thermal anomalies as areas having temperatures higher than the temperature of the spatial background. In a geothermal resource exploration in Akita and Iwate prefectures, northern Japan, Noorollahi et al. (2007) showed that 95% of the production wells were located in a zone within 6000 m to the active faults and 4000 m to hot springs. Magnetic measurements are also generally used in geothermal exploration programs to locate hidden intrusive bodies and possibly estimate their depths. Moreover, they can be used to trace buried dykes and faults, and also to detect areas of reduced magnetization due to thermal activity (Georgeson, 2009). A variety of magnetic studies in geothermal exploration projects having different objectives can be found in the literature (e.g. Hojat et al., 2016; Gailler et al., 2014; Georgsson, 2009; Hunt, 1989; Palmason, 1975). The aim of this study is to analyze remote sensing and magnetic data (airborne and ground measurements) for evaluating the geothermal potential zones in an area east of Kerman Province.
Methodology and Approaches: The input data in this research include MODIS, MOD11_L2 005 (day and night) reflectance and LST products, for the year 2015, ASTER L1T night-time image on November 10, 2015, Landsat ETM day-time image on November 14, 2015, aeromagnetic data collected by Houston Texas Co., USA, in 1975-1977, and geomagnetic total intensity contour map of Gowk area having 1:50000 scale, which surveyed by Atomic Energy Organization of Iran. Ground magnetic survey is also carried out in an area around Joshan hot spring. A comparison of the day-time and night-time images can reveal surface thermal differences for detecting geothermal anomalies. Land surface temperature was calculated using generalized split-window algorithm for MODIS sensor (Wan and Dozier, 1996), emissivity normalization method for ASTER (Coll et al., 2007; Banerjee et al., 2014), and LST calculation method for Landsat sensor (Barsi et al., 2003; Barsi et al., 2005; Coll et al., 2010). Apparent thermal inertia of the three sensors was calculated using albedo and LST difference of day and night (Sabol et al., 2006; Scheidt et al., 2010; Chang et al., 2012; Qin et al., 2013). After removal of noise from the observed magnetic data, processing steps including main field removal using IGRF model of the proper period, reduction to the pole, and upward continuation were applied on the magnetic data. The processed magnetic data were finally interpreted in order to locate the hidden intrusive bodies and faults.
Results and Two thermal anomalies were detected on the maps and charts obtained for the average temperature difference (day and night) and apparent thermal inertia. One anomaly was located in the Jooshan area and the other one was situated in the western part of Gowk fault and continues along it to the southeastern side. Gowk fault is an active fault with Jooshan (45 C) hot spring, and most earthquakes larger than magnitude 5 have occurred in this part. These might be evidences of a thermal anomaly. The results of magnetic interpretations confirmed thermal anomalies showing a deep magnetic anomaly in the southern part of the study area and another magnetic anomaly in the Jooshan hot spring.