Seismic Velocity Recovery in the Subsurface: Transient Damage and Groundwater Drainage Following the 2015 Gorkha Earthquake, Nepal

Abstract

Following the passage of seismic waves, a wide range of transient effects have been observed near the Earth's surface, including increased landslide rates (Marc et al., 2015), enhanced permeability (Manga et al., 2012;Xue et al., 2013), and perturbations of frictional properties in fault zones (Pei et al., 2019). These observations suggest that earthquakes induce a lingering effect in the properties of near-surface rocks that may be linked to non-linear mesoscopic elasticity (NLME, e.g., Gassenmeier et al., 2016;Marc et al., 2021). This phenomenon is generally expressed by a drop in elastic moduli after a dynamic or static strain perturbation that is followed by a non-instantaneous recovery of these moduli. This recovery phase, also called relaxation or slow dynamics, is linear on a logarithmic time scale (Snieder et al., 2017) and can last anywhere from a few seconds (Shokouhi et al., 2017)

The Seismic Signature of California's Earthquakes, Droughts, and Floods

“…We also find that the spatial difference in time scales can be explained by the spatial variations in crustal and mantle viscosity. We have not coupled the hydrological terms with the tectonic signals as did Illien et al (2022). Our approximation may be valid in the cases of southern California earthquakes, given the low water table and occurrence during dry periods.…”

SAR and optical images correlation illuminates post-seismic landslide motion after the Mw 7.8 Gorkha earthquake (Nepal)

“…This configuration can’t therefore explain the long temporal diffusion (several days) of water-flow excess through water transport in the rivers. However, coseismic damage 11 , 46 allows the subvertical draining of water and subsequently the recharge of deep aquifers 16 . The subvertical draining can be caused by the co-seismic shaking and fracturing of the bedrock.…”

The Seismic Signature of California's Earthquakes, Droughts, and Floods

“…We also find that the spatial difference in time scales can be explained by the spatial variations in crustal and mantle viscosity. We have not coupled the hydrological terms with the tectonic signals as did Illien et al (2022).…”

“…Coupling among these terms is possible and would invalidate the linear decomposition of equation 5. Earthquake damage often opens cracks in the near-surface and allows for increased groundwater flow (Rojstaczer et al, 1995;Brodsky, 2003;Illien et al, 2022), which temporarily alters the hydrological parameters (increased permeability) that we often assume fixed through time. Sens-Schönfelder and Eulenfeld (2019) models the coupling between tidal and thermoelastic strains.…”