---

Coseismic Electromagnetic Signals as Pseudo-Seismogramsfor Mapping of Upper Crustal Seismic Velocity Structure:An Example from the Ganga Basin Using Magnetotelluric Time Series of the 3 November 2023 Western Nepal Earthquake.

Manglik A, Gupta S.

JOURNAL OF THE GEOLOGICAL SOCIETY OF INDIA

https://doi.org/10.17491/jgsi/2025/174165 

Seismic wave propagation induces electromagnetic perturbations in the ground, produced mainly by the electrokinetic and/or seismic-dynamo processes. These coseismic-electromagnetic (CoSEM) signals closely resemble seismic traces at recording stations with distinct onsets of different seismic phases. We have modeled the time series of these CoSEM perturbations for surface wave dispersion, treating these as pseudo-seismograms, for the 2023-11-03 western Nepal earthquake (M 6.4). Our results suggest that CoSEM signals can be gainfully utilized to delineate the seismic velocity structure and to analyze the petrophysical properties of the medium in a sedimentary environment.

(A) Map showing epicenters of the western Nepal Himalaya earthquake of 2023-11-03 (red star), its main aftershock (orange star), other aftershocks of magnitude ≥ 3 (cyan and green stars), and LMT sites (green triangles) along the Bhind – Sharda Deep (BSD) profile. (B) 1-D shear wave velocity models obtained by inversion of fundamental mode Rayleigh wave group velocity dispersion data, and resistivity image along the same profile showing conductivity variation beneath the sites.

(a) One-dimensional shear wave velocity models obtained by inversion of the fundamental mode Rayleigh wave group velocity dispersion data. Site numbers are written at the bottom of each model. Different layers of sediments with varying shear wave velocities are marked on the models. The grey dashed line marks an intermediate layer with a decrease in the shear wave velocity. (b) Resistivity image along the same profile (Suresh et al., 2023) showing conductivity variation beneath the sites. The semi-transparent rectangle in “b” marks the seismic velocity depth section as shown in “a”.

---