Integrated interpretation of geophysical data from Zagros mountain belt (Iran)

Abstract

Fluid composition and distribution, the key factors determining geoelectric structure in a seismically active region, are controlled by local and regional stresses and rheological contrasts. Two closely located magnetotelluric and seismic velocity profiles are jointly interpreted to recover more accurately the structural boundaries and fluid distribution within the crust in the central Zagros collision zone, one of the world’s most seismically active mountain belt. A multi-site and multi-frequency approach was used for the strike analysis of regional structure and decomposition of distortion effects on magnetotelluric data. Distortion corrected magnetotelluric data were then used for two-dimensional inversion modeling. The results indicate distinct conductive structures within the crust: (i) a thick conductive overburden in the southwest of the profile, (ii) high conductivities attributed to the fault zone conductors (FZCs) and (iii) an almost concave conductor extending from middle to lower crust in the central-eastern portion of the mountain belt, beneath the High Zagros (HZ). Comparison with the already available S-wave velocity structure, obtained by joint inversion of P-wave receiver functions and surface wave dispersion data shows that these main conductive features are spatially correlated with a low-velocity layer representative of the sedimentary cover overlying the Arabian platform and a velocity contrast bounded by the main Zagros thrust (MZT) fault, indicating the presence of fault zone fluids. The joint interpretation of magnetotelluric inverse modeling and seismicity data also shed light on fluid generation influencing rock deformation and seismicity in this region. It suggests that beneath the HZ, deep crustal fluids generated through metamorphism may promote aseismic deformations before high stresses are builtup and cause the north-eastern part of the Zagros Fold and Thrust Belt (ZFTB) to be seismically inactive compared to its southwestern part.