The World Under The Ground

Sunday, March 25, 2012

2D inversion of magnetotelluric data (Mahallat)

2D inversion of the magnetotelluric data from Mahallat geothermal field in Iran using finite element approach

M.Darijani¹, B.Oskooi¹

¹Institute of Geophysics, University of Tehran, Iran.

Accepted to Arabian Journal of Geosciences [Springer] (ISI). Feb. 2013.
Accepted to Istanbul International Geophysical Conference, September 2012, Oral.

Abstract

A magnetotelluric (MT) survey was conducted on Mahalat geothermal field located in west central Iran. The region of Mahalat is a popular tourist spot due to the occurrence of hot water springs and one of the greatest geothermal fields in Iran. The purpose of the first MT survey in this area is to provide more information on the geoelectrical structure of this important geothermal reservoir. MT is widely utilized for surveying geothermal areas such as Mahalat. In thermal areas, the electrical resistivity is substantially different form and generally lower than in areas with colder subsurface temperature. The selected MT profiles in the region cross over the hydrothermally altered zones and different geological structures. Data were acquired along two profiles crossing the Mahalat hot springs with a total of 28 MT stations in a frequency range of 8000 Hz to 0.008 Hz. Spacing between stations was kept 500 m for a better resolution. We have used the code MT2DInvMATLAB for inversion using the method of ﬁnite elements (FEM) for forward modeling. Apparent resistivity and phase data of TE, TM and TE+TM modes along each profile were modeled. The geothermal fluid reservoir is resolved at 1000 to 3000 m depth and the geothermal resource is estimated to be located at 7000 m or deeper.

Leia Mais…

2D inversion of magnetotelluric data (Markazi)

Investigation of the electrical resistivity and geological structures on the hot springs in Markazi province of Iran using magnetotelluric method

(Derived from my Thesis)

M. Darijani¹,B. Oskooi¹, M. Mirzaei²

¹Institute of Geophysics, University of Tehran

²Department of Physics, Faculty of Sciences, Arak University

Submitted to Bollettino di Geofisica Teorica e Applicata (ISI). Oct. 2012.

Abstract

Markazi geothermal field is a potential geothermal system in Iran. In this paper the 12 MT stations of 2011 MT data set with elevation from 1657 to 1891 m were used along one profile. This paper detects the main features of the conductivity structures of this area. For subsurface mapping purpose, the long period natural-field MT method proved very useful. 2D inversions are conducted to resolve the conductive structures. We performed a code from Pedersen (2004) for the 1D inversion and a code from Siripunvaraporn and Egbert (2000) for the 2D inversion of DET-mode data. The MT survey has improved our understanding of the geological structure around the hot springs. The conductive layer at the surface can clearly be interpreted as the flow of the fluids in the fractures of the rocks and the top soil which saturated with penetrated water. The 2D model significantly illustrates the geothermal structures including cap rock (from 100 to 600m), reservoir (from 500 to 2000 m) and source (from 1000 m to depth). This study demonstrates how MT data can provide information about deep structure which cannot always be achieved using other geophysics techniques. MT surveys are potentially a tool for mapping geological structure beneath travertine cover around the hot springs. The faults that most likely represent active hydrothermal zones enhance the probability of conditions favorable for Enhanced Geothermal Systems. The results of our study indicate that an alteration zone is present beneath the surface; this suggests that a hydrothermal fluid circulation exists at depth.

Leia Mais…

2D inversion of magnetic data (Shahmirzad)

2D modeling and inversion of the magnetic data in Shahmirzad area, Semnan, Iran, for depth and shape determination of the iron-ore body
M.Darijani¹, B.Oskooi¹

¹Institute of Geophysics, University of Tehran, Iran

Accepted to the 8^th Iranian Student Conference of Mining Engineering, November 2011, oral.

Accepted to the Iranian Journal of Geophysics. May 2012.

Abstract

In this study, we had a method for magnetic data inversion to make 2D susceptibility models of an area with a suitable potential of Iron-ore. We made use of a 2D inversion method to study the magnetic data of Shahmirzad located in Semnan province, to evaluate the hematite mineralization in the area. After data acquisition and processing, we apply an automatic 2D inversion for two profiles. This algorithm is based on physical parameter distribution method. The subsurface beneath the studied profile is divided to a great number of infinitely long horizontal prisms with unknown susceptibility. Solving an underdetermined system of equation in MATLAB will result in magnetic susceptibility distribution inside the earth which is related to hematite content of rocks. Inversion results on selected profiles, has detected some anomaly sources trending E-W. After the modeling and inversion and using mask signal method for two profiles of the Shahmirzad magnetic data, finally, the models show a steep anomaly in this region with the average thickness of 10 m and approximately 5m to 25m in depth with 100m along. This iron-ore contains hematite mineral with susceptibility of 0.05, located on the middle of the area of study between igneous intrusive masses and limestone.

Leia Mais…

3D inversion of magnetic data (Mahallat)

Studying of the geothermal structure of Mahalat hot springs in Iran using the 3D inversion of magnetic data

M. Mohammadzadeh¹, M. Darijani¹, M. Mirzaei², B. Oskooi¹*

¹Institute of Geophysics, University of Tehran

²Department of Physics, Faculty of Sciences, Arak University

Accepted to the 4^th Iranian National Conference of Economical Geology, March 2012.

Abstract

Existence of many hot springs in Mahalat and also its special geology show a probable deep geothermal system. In order to delineate susceptible area with geothermal potentials accurately, ground magnetometery was performed around hot springs of Mahalat. Total magnetic field data was collected along 10 profiles of 16 km, with station distance of 40 m and profile distance of 1.5 km. During this survey, measurements were performed on over 4000 stations. This paper evaluates application of 3D inversion of geomagnetic data for estimating depth and shape of geothermal structure. For this purpose, we used Mag3D software. This software determines the best depth bodies with an iterative approach. Existence of magnetic anomaly was interpreted as a source of geothermal reservoir, with probable depth of more than 3000 m. Presence of thick alluvial travertine in the area implies high antiquity of this geothermal reservoir. Preliminary results of the interpretation showed a reliable agreement with those resulted from aeromagnetic data and also with the geological and hydrological evidence of the hot springs in the area.

* I am corresponding author because of working by software, interpretation and writing the paper.