Detailed one-dimensional seismic velocity profiles beneath the Himalayan collision zone: evidence for a double Moho?

摘要

Seismicity in the Himalaya indicates that relatively deep earthquakes (focal depth 40∼100 km) occur in specific regions beneath the High Himalaya and Nepal. This study focuses on these specific regions to estimate the detailed velocity structure of the lower crust and upper mantle. We selected 202 earthquakes from the Himalaya Nepal Tibet Seismic Experiment (HIMNT) and relocated these earthquakes accurately by applying a genetic algorithm locator, GA-MHYPO (Kim et al., 2006). The detailed onedimensional P-velocity structure is estimated based on travel-time inversion using hypocentral parameters determined by GA-MHYPO. Computational results show two velocity anomalies exhibiting upper-mantle velocities at depth of about 45–50 and 60 km, respectively, beneath the High Himalayan region, whereas a single Moho exists at about 55 km depth beneath Nepal. To validate the stability of these results, a bootstrapping method was used for the inversion.