Australia: The Land Where Time Began

A biography of the Australian continent 

Himalayan Thrust Fault – Main Thrust Fault Unzipped by Gorkha Earthquake of 2015

According to Avouac et al. strain on faults that were previously locked is believed to be released by large earthquakes. The details of the initiation, growth and termination of earthquakes in relation to patches that have previously been locked and creeping is, however, not clear, (Schurr et al., 2014; Loveless & Meade, 2011; Yue et al., 013; Kaneko, Avouac & Lapusta, 2010). In 2015 the M_w 7.8 Gorkha earthquake in Nepal occurred close to Kathmandu in a region that has a prior pattern of faults locking which is well documented (Ader et al., 2012). In this study Avouac et al. used seismological records that had been measured at teleseismological and Synthetic Aperture Radar imagery to analyse this event. It is shown by their results that the origin of the earthquake was northwest of Kathmandu within a cluster of background seismicity fringing the bottom of the locked portion of the Main Himalayan Thrust fault (MHT). The lower edge of the locked portion of the fault was unzipped by the rupture that propagated for about 140 km. As the slip pulse propagated at about 2.8 km s^-1 along this zone of what was presumably high and heterogeneous pre-seismic stress at the seismic-aseismic transition high-frequency seismic waves radiated continuously. During the M_w 7.3 aftershock on 12 May unzipping of the fault was resumed in an eastward direction. Avouac et al. suggest that as a result of the transfer of stress to neighbouring regions during the Gorkha earthquake future rupture of the areas of MHT that are adjacent to and updip of the Gorkha earthquake rupture should have been facilitated.

Sources & Further reading

Avouac, J.-P., L. Meng, S. Wei, T. Wang and J.-P. Ampuero (2015). "Lower edge of locked Main Himalayan Thrust unzipped by the 2015 Gorkha earthquake." Nature Geosci 8(9): 708-711.