Magnetotelluric evidence for trapped fluids beneath the seismogenic zone of the Mw6.0 Anjar earthquake, Kachchh intraplate region, Northwest India

Abstract

Lithospheric rheological heterogeneities across a rift play a significant role in intraplate deformation and seismic activity. The Kachchh rift in the northwestern part of the India has not only experienced lithospheric stretching but also witnessed large magnitude devastating earthquakes. Here, we present the results of a magnetotelluric (MT) investigation carried out in the southeastern part of the Kachchh intraplate region illuminating the seismogenic zone of the 1956 Anjar earthquake (Mw 6.0). The two-dimensional geoelectrical model derived from the MT data acquired at 21 sites along a NE-SW profile reveals assemblage of conductive and resistive zones in the upper and the mid crustal depths in the close vicinity of the major fault zones and the hypocentral depths. The results reveal a very high conductive zone near the Moho, affirming the presence of an upper mantle fluidized zone. Unlike the South Wagad Fault, the Kachchh Mainland Fault and the Katrol Hill Fault do not have a downward lower crustal extension, and terminate at the mid crustal depths. We suggest that the presence of trapped fluids in the brittle-ductile transition zone (12–15 km) and their seepage to the resistive plutons might be a possible mechanism for triggering the 1956 event as well as the current seismic activity in the region.