Launched: October 1st, 2013
On 24th September 2013, a magnitude 7.7 earthquake occured in Pakistan.
Data: High frequency P waveforms from ~700 Hi-net stations and ~200 European stations were used in a back projection analyses of the rupture for the September 24, 2013 Pakistan earthquake (Figure 1).
Method: see Wang and Mori, 2011, EPS, and Wang and Mori, 2011, GRL.
Results: The back projection results suggest that the rupture mainly propagated to the southwest for about 150 km in space and 40 to 50 s in time (Figures 2). The located trace is not consistent with the aftershock distribution that suggests a north rupture extent. The slip model from finite waveform inversion (T. Lay, personal communication) shows that ~80% of the seismic moment were released in the north patch that is spatially correlated with the aftershock distribution. The rupture speed is very fast, ~4 km/s, which is much faster than local S wave velocity of ~3.5 km/s, suggesting another possible supershear rupture.
Another special issue for this earthquake is that an island emerged off Gwadar coast after this earthquake. Seismologists believe the formation is due to a mud volcano. But the mud volcano is 400 km from the epicenter, which is much farther than for past cases with a distance of less than 200 km. Perhaps the strong high frequency energy toward southeast as revealed by back projection account for this, but need further investigation.
(Ocean Hemisphere Research Center : Dr. Wang Dun)