IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS008 Poster presentation 2009
1-D AND 2-D interpretation of bam fault CSTMT data
Mr. Davood Moghadas
Institute of Geophysics student IAGA
Saeid Hashemi Tabatabaei
In recent years, EM methods are widely used for detection and producing detailed subsurface resistivity
structure of faults. One such study of faults is reported here. We experienced Controlled Source Tensor
Magnetotelluric (CSTMT) method to recognize a fault zone in Bam area (South-eastern of Iran). The
CSTMT is an electromagnetic method used for shallow studies. It aims at mapping of shallow subsurface
resistivity structures. Depending on the porosity, fluids and clay minerals there in, geological structures
have different responses to the electromagnetic waves. Fault zones have resistivity contrast particularly
when water and other fluids flow through them; therefore they can be recognized easily by
electromagnetic methods. The tensor RMT technique (CSTMT) has additional high resolution capabilities
because at every point along the profile, a detailed tensor sounding is performed. Bam lies within the
western of two north-south, strike-slip fault systems located on each side of the aseismic Lut desert,
which together accommodate the relative motion between central Iran and Afghanistan, part of the
Eurasian plate. An earthquake devastated the town of Bam on December 26, 2003. Surface
displacements reveal that over 2 m of slip occurred at depth on a fault that had not previously been
identified. This fault located in south of bam is a strike slip fault which extends from the centre of Bam
southwards for about 12 km. The region is an almost flat, featureless and sloping gently east. The
CSTMT survey was carried out in summer 2006 using EnviroMT system from Uppsala University,
Sweden. Data were collected along a profile with 19 stations and with an approximately W-E direction
which was perpendicular to the fault. The frequency range used in this method is from 1-25 KHz. 1-D
inversion approach presented by Pedersen (2004) was applied on the determinant, TE and TM mode
data. We also obtained 2-D models using inversion algorithm proposed by Siripunvaraporn and Egbert
(2000). We assumed 0.05 error floor on the impedance elements. In this essay, we discuss inversion
and interpretation of CSTMT data collected from bam south fault. Two dimensional inversion results
agree well with data sections and regional geology. The CSTMT field measurements resolved well the
resistivity contrasts along the profile.
Keywords: cstmt, fault, 2d inversion