3D Fault Structure Inferred from a Refined Aftershock Catalog for the 2015 Gorkha Earthquake in Nepal

Abstract

In this article, we created a well-resolved aftershock catalog for the 2015 Gorkha earthquake in Nepal by processing 11 months of continuous data using an automatic onset and hypocenter determination procedure. Aftershocks were detected by the NAMASTE temporary seismic network that is densely distributed covering the rupture area and became fully operational about 50 days after the mainshock. The catalog was refined using a joint hypocenter determination technique and an optimal 1D velocity model with station correction factors determined simultaneously. We found around 15,000 aftershocks with the magnitude of completeness of ML 2. Our catalog shows that there are two large aftershock clusters along the north side of the Gorkha–Pokhara anticlinorium and smaller shallow aftershock clusters in the south. The patterns of aftershock distribution in the northern and southern clusters reflect the complex geometry of the Main Himalayan thrust. The aftershocks are located both on the slip surface and through the entire hanging wall. The 1D velocity structure obtained from this study is almost constant at a P-wave velocity (VP) of 6.0 km/s for a depth of 0–20 km, similar to VP of the shallow continental crust.

Postseismic Deformation Following the 2015 Mw7.8 Gorkha (Nepal) Earthquake: New GPS Data, Kinematic and Dynamic Models, and the Roles of Afterslip and Viscoelastic Relaxation

“…Dashed brown region: Possible stable‐sliding region in between. Gray filled circles: M≥3 aftershocks through May 2016 (Baillard et al, 2017; Yamada et al, 2020). (b) Cross section of afterslip magnitude along profile A‐A′, overlaid on estimated temperature.…”

Determination of high-frequency attenuation characteristic of coda waves in the central region of Nepal Himalaya

“…Most devastating historical mega-earthquakes have been reported around the central part of the Nepal Himalaya (Chitrakar and Pandey, 1986;Bilham, 1995;Pandey et al, 1999). Numerous seismological studies (Molnar, 1984;Pandey et al, 1999;Bollinger et al, 2004;Hubbard et al, 2016;Yamada et al, 2020) have been carried out to explore the tectonic evolution and three-dimensional geometrical fault structure beneath central Nepal.…”

“…We selected 252 well located local earthquakes (Ml ≤ 4.8, epicentral distance 15-100 Km, and focal depth ≤ 25 Km) of central Nepal from NAMASTE network, using an earthquake catalog of Yamada et al (2020) and vertical component seismograms (sampling frequency 100 Hz) of 16 different seismic stations were downloaded using BREQ_FAST request form from IRIS (https://ds.iris.edu/ds/nodes/dmc/forms/ breqfast-request/) website. It is a temporary seismic network that was installed about seven weeks after the 2015 Gorkha earthquake.…”

Orogenic Collapse and Stress Adjustments Revealed by an Intense Seismic Swarm Following the 2015 Gorkha Earthquake in Nepal

“…Monitoring of deformation in Nepal and Tibet revealed the interplay between afterslip and viscoelastic relaxation (e.g., Gualandi et al, 2017;Zhao et al, 2017;Wang and Fialko, 2018;Jiang et al, 2019;Jouanne et al, 2019;Tian et al, 2020;Liu-Zeng et al, 2020). Aftershocks are being monitored by the 21-station National Earthquake Monitoring and Research Center (NEMRC) network (Adhikari et al, 2015), continuously in operation since 1994 (Pandey et al, 1995), and temporarily complemented by local and nearby networks (Bai et al, 2016;Mendoza et al, 2019;Yamada et al, 2020). These aftershocks, still active in 2020, are mostly located in the vicinity of the rupture zone in Central Nepal, between the epicenters of the main shock and of the May 12, 2015 shock (Adhikari et al, 2015;Baillard et al, 2017).…”