Conjugate earthquake rupture associated with two recent intraplate strike-slip earthquakes

When any moderate to large earthquakes take place, we can now promptly learn their origin time, location, and its preliminary report on the focal mechanism [e.g., 1]. However, since those seismic data are acquired at “far-field” from epicenters, they assume a point source despite the actual earthquake rupture occurs in a finite domain. The hypocenter location inferred from seismic observation is therefore often distant from and deeper than the actual hypocenter. To overcome such issues, near-field observations are critical, and satellite-based SAR observations do play such a role. Here, we report our detection and fault source modeling of the co-seismic displacements due to the recent two moderate-sized intra-plate earthquakes at Laos (moment magnitude, Mw6.3) in May 2007 and Iran (Mw6.3) in December 2010, using ALOS/PALSAR data. Another motivation to study these earthquakes is to better understand the rupture processes of intra-plate earthquake. While intra-plate earthquakes are often smaller than those occurred at major plate boundaries, they could be even more disastrous to local residents, and they also play an important role to accommodate regional tectonic stresses driving the nearby plates. Both of the studied earthquakes were estimated to be strike-slip type. Unexpectedly, however, the observed co-seismic deformation is rather complicated in their spatial pattern. We are led to suppose two almost perpendicular (“conjugate”) fault planes to account for the observation.