Multiarray rupture imaging of the devastating 2015 Gorkha, Nepal, earthquake sequence

Abstract

A rapid, robust multiarray backprojection method was applied to image the rupture pattern of the 2015 Gorkha, Nepal Mw7.8 main shock and its Mw7.3 aftershock. Backprojected teleseismic P wave trains from three regional seismic arrays in Europe, Australia, and Alaska show that both earthquakes ruptured unilaterally and primarily eastward, with rupture speeds potentially decreasing with depth. The rupture of the main shock first extended ESEward at ∼3.5 km/s over ∼120 km, with later rupture propagation further downdip on the eastern segment at ∼2.1 km/s. The aftershock ruptured the fault SE of the main shock's ruptured plane. It began to rupture updipward for ∼20 km at a speed around 1.2 km/s, then it may have accelerated to 3.5 km/s for the next 50 km. The apparent depth‐dependent rupture speeds of the two earthquakes may be caused by along‐dip heterogeneities in fault strength, with a higher stress concentration on the updip part of the Nepalese Main Himalayan Thrust.

Source locations of teleseismic P, SV, and SH waves observed in microseisms recorded by a large aperture seismic array in China

“…As expected, Fig. 4 clearly shows P-wave microseisms (e.g., Vinnik, 1973) in the North Atlantic and North Pacific-regions well known for generating Pwave microseisms, especially during the northern hemisphere winter (Gerstoft et al, 2008;Koper et al, 2009;Landès et al, 2010;Zhang et al, 2010;Hillers et al, 2012;Obrebski et al, 2013;Euler et al, 2014;Reading et al, 2014;Gal et al, 2015;Pyle et al, 2015;Sheen and Shin, 2016). P amplitude is larger on the vertical component than on the radial, and no energy is observed on the transverse (Fig.…”

“…This can be achieved by using backprojection grid spacing finer than the 400 km used here, and by focusing the array beams with travel time corrections computed from 3D mantle velocity models or with empirical travel time corrections derived from earthquakes near microseism source regions. Using data from a more permanent, non-rolling array with aperture similar to or larger than WTA would also lead to better locations, as might a multi-array backprojection location approach (e.g., Roessler et al, 2010;Pyle et al, 2015;Zhang et al, 2016) and new, sophisticated methods of deconvolving array response functions such as CLEAN-PSF (Gal et al, 2016).…”

The 2015 April 25 Gorkha (Nepal) earthquake and its aftershocks: implications for lateral heterogeneity on the Main Himalayan Thrust

“…This is in close agreement with previous studies of back projection Zhang et al 2016). Distribution of high-frequency energy released during the faulting points to a multi-pulsed heterogeneous rupture process.…”

“…S3). Our results corroborate the depth dependent variation in rupture speed observed for this aftershock from the multiarray back projection study of Zhang et al (2016).…”

Coherent Seismic Arrivals in the P Wave Coda of the 2012 Mw 7.2 Sumatra Earthquake: Water Reverberations or an Early Aftershock?

“…Back‐projection is generally applied to data at epicentral distances from 30° to 90°, where the P wave Green's function is relatively uncontaminated by mantle triplications, such that simple time corrections and stacking methods can be used to extract coherent signals. The simplicity of the back‐projection method assures its robustness; for example, different groups often obtain similar back‐projection source models despite using different data sets and stacking approaches (e.g., Fan & Shearer, ; Grandin et al, ; Wang & Mori, ; Yagi & Okuwaki, ; Zhang et al, ). However, back‐projection can still suffer from imaging artifacts, depending upon the data coverage and quality, as well as details of the data processing (e.g., Kiser & Ishii, ; Meng et al, ; Xu et al, ).…”