Ground Electrical and Electromagnetic Studies in Koyna-Warna Region, India

Abstract

In this paper, we present results of the Ground Electrical and Electromagnetic (GEE) studies (MT, CSAMT, DRS) carried out in the Koyna-Warna zone since 1976 and discuss their relevance in understanding the seismicity of the Koyna-Warna seismic zone. Though there were not many GEE studies carried out in this region, the existing ones provided a vital information, in particular, on the subsurface crustal structure, the Deccan Trap thickness and its variation and also the nature of the basement in this region. The GEE studies rule out the presence of any subtrappean sediments in this region. An interesting feature that has been identified from MT studies is the presence of a well-defined crustal block structure, characterized by high resistive blocks interspersed with moderately conductive features. All these structural features clearly point out to the intensity of tectonic disturbance that the region was subjected to in the geological past. The conductive features are correlatable with some of the known seismogenic structural features, for e.g., the Konya Fault Zone, the west coast fault, the Donachiwada fault. The moderately resistive zone sitting over the high resistive blocks as seen both in MT& DRS models is inferred to be related to the generally fractured nature of the shallow crustal column. The conductive linear features bordering the resistive blocks represent fluid filled fracture/fault zones. It is inferred that because of the NE to NS oriented compressive stress regime in the Indian shield, due to the Himalayan collision tectonics, some of these structural features may become the locales of stress accumulation which may get released due to fluid filling of these zones under the influence of nearby reservoirs, resulting in triggering of seismicity. Results from different GEE studies conducted in the study area are found to be highly consistent with each other as well as with the Rasati bore hole data, thus bringing significant validity to the subsurface model derived. Further, the 3D modelling of the MT data acquired in the Koyna-Warna region together with airborne gravity gradient and magnetic studies carried out under the Deep drilling program would open up new gate ways to accomplish multi-parametric three dimensional modeling, that will provide still more detailed and relevant subsurface image of this important RTS zone.

Delineation of Damage Zones From 3 km Downhole Geophysical Logs in the Koyna Seismogenic Zone, Western India

“…The activity includes the 1967 M6.3 Koyna earthquake, over 20 earthquakes of M5–5.9, ~200 earthquakes of M ≥ 4, and thousands of smaller earthquakes, which are located in the depth range 2–10 km within the granite‐gneiss basement below the Deccan traps (Gupta et al, ). Previous geophysical studies including seismic, gravity, and magnetotelluric as well as seismological investigations indicate the presence of zones of low velocity, density, resistivity, and high Poisson's ratio at multiple depths in the granitic basement (Catchings et al, ; Dixit et al, ; Krishna, ; Patro et al, ; Tiwari et al, ). However, resolution of such data sets is inadequate to delineate small‐scale faults and damage zones that are likely associated with the occurrence of a large number of low magnitude earthquakes in the area.…”

Gravity-induced seismicity modulation on planetary bodies and their natural satellites

“…Gravity-induced resonance destabilization model appears to be in better agreement with the contrast/diversity in seismicity modulation on the Earth, Moon, and Mars. We acknowledge that the presence of anomalous crustal fluid 66 – 68 , variation in frictional parameters 69 , 70 , critical triggering thresholds 71 – 73 , fault geometry and rheology 69 , 74 , fault gauge accumulation 70 , etc., can make the seismic triggering/modulation phenomenon extremely complex and non-linear. Nevertheless, our robust observations and gravity-induced resonant destabilization model clearly demonstrate diversity in seismicity modulations of the solar system objects in an integrated approach.…”

Tectonics of the Deccan Trap: Focus on Indian geoscientists’ contribution in last four years

“…Kumar and Dixit (2017), based on local earthquake tomography document a ~ 5 km wide and 3-7 km deep seismic cluster south of the Warna region. Patro et al (2017), based on ground electrical and electromagnetic studies, deduce the thickness variation of the Deccan trap lava around the Koyna region. A similar approach by Patro et al (2018) reveals the same in other parts of the western Ghat as well.…”