Magnetotelluric impedance tensor analysis for identification of transverse tectonic feature in the Wagad uplift, Kachchh, northwest India

Abstract

The 2001 Bhuj earthquake (Mw 7.7) occurred in northwestern region of Indian peninsula has reactivated a couple of transverse faults to its surroundings. Intermediate to moderate magnitude earthquakes are occurring along these faults which includes recent Dholavira earthquake (Mw 5.1, 2012) suggesting distinct tectonic scenario in the region. We present the results of magnetotelluric (MT) impedance tensors analyses of 18 sites located along a profile cutting various faults in the uplifted Wagad block of the Kachchh basin. The MT time series of 4-5 days recording duration have been processed and the earth response functions are estimated in broad frequency range (0.01-1000 s). The observed impedance tensors are analyzed by using three decomposition techniques as well as by the phase tensor method constraining with the induction arrows. The analyses suggest distinct tectonic feature within the block bounded by the South Wagad Fault (SWF) and the North Wagad Fault (NWF) particularly in the period band of 1-10 s. In the south of NWF, the telluric vectors and the major axes of the phase ellipses are aligned in the NNW-SSE to NW-SE direction where as a dominant E-W strike is obtained for northern side of the NWF. The transverse geo-electric strike coincides with the prominent clustering of seismicity after the Bhuj earthquake and trend of the Manfara transverse fault is located in close vicinity of the study area. We therefore suggest the presence NNW-SSE trending transverse structural feature in the Wagad uplift of the basin appears to play significant role in the current seismicity of the active intraplate region.

Transient Electromagnetic Investigations in a Tectonic Domain of the Kachchh Intraplate Region, Western India: A Morphotectonic Study of the Kachchh Mainland Fault

“…Pizzi and Galadini () pointed out the importance of preexisting cross‐structures in the segmentation of the active extensional belt of the Apennines. The presence of the transverse features and their role in the seismic activity of the eastern Kachchh basin is discussed by Pavan Kumar, Kumar, et al () using analyses of the magnetotelluric impedance tensors and its integration with the seismological data set. It was further opined that the Manfara structure in the close vicinity of 2001 Bhuj earthquake is originally evolved as a transverse fault linking the KMF and the SWF (Biswas & Khattri, ).…”

“…(a) General geological scenario of the Kachchh superimposed on elevation map (modified after Pavan Kumar, Kumar, et al, ). Transient electromagnetic sites are shown with magenta color symbols.…”

“…Due to its seismically active nature (Figure ), the entire Kachchh region has been assigned as the highest seismic hazard zone—zone V in seismic zoning map of India (IS:1893‐2002). Many geophysical investigations have been carried out after the 2001 earthquake to image subsurface structure of the region, its link with the seismic activity, understanding nature of the faults, and identify blind faults across the basin (Chandrasekhar et al, , ; Kayal et al, ; Mandal & Pujol, ; Naganjaneyulu et al, ; Pavan Kumar, Mahesh, et al, ; Pavan Kumar, Kumar, et al, ; Rao et al, ; Sastry et al, ). Biswas (, ) speculated a domino‐listric fault model for the Kachchh region relating lithospheric rupture and consequent melting of the subcrustal lithosphere.…”