The interrelationship between electrical resistivity and VP/VS ratio: A novel approach to constrain the subsurface resistivity structure in data gap areas in a seismogenic zone

Abstract

Large man-made water reservoirs promote fluid diffusion and cause critically stressed fault zones underneath to trigger earthquakes. Electrical resistivity is a crucial property to investigate such fluid-filled fault zones. Therefore, we carry out magnetotelluric (MT) investigation to explore an intraplate earthquake zone, which is related to artificial reservoir-triggered seismicity. However, due to surface access restrictions, our data set has a gap in coverage in the middle part of the study area. This data gap region coincides with the earthquake hypocenter distribution in that intraplate earthquake zone. Therefore, it is vital to fill the data gap to obtain the electrical signature of the active seismic zone. To compensate for the data gap, we have developed a relation that connects resistivity with the ratio of seismic P- to S-wave velocity ([Formula: see text]). Using this relation, we estimate a priori resistivity distribution in the data gap region from known [Formula: see text] values during the inversion to compensate for the data gap. A comparison study of the root-mean-square misfits of inversion outputs (with and without data gap filled) proves the effectiveness of the established relation. The inversion output obtained using the established relation brings out fault signatures in the data gap region. To examine the reliability and accuracy of these fault signatures, we occupy a portion of the data gap with new MT sites. We compare the inversion output from this new setup with the inversion output obtained from the established relation and observe that the electrical signatures in both outputs are spatially correlated. Furthermore, a synthetic test on a similar earth model establishes the credibility and robustness of the derived relation.