Rupture processes of the 2010 Canterbury earthquake and the 2011 Christchurch earthquake inferred from InSAR, strong motion and teleseismic datasets

Abstract:

The September 4, 2010, Canterbury earthquake with a moment magnitude (M_w) of 7.1 is a crustal earthquake in the South Island, New Zealand. The February 22, 2011, Christchurch earthquake (M_w=6.3) is the biggest aftershock of the 2010 Canterbury earthquake that is located at about 50 km to the east of the mainshock. Both earthquakes occurred on previously unrecognized faults.

Field observations indicate that the rupture of the 2010 Canterbury earthquake reached the surface; the surface rupture with a length of about 30 km is located about 4 km south of the epicenter. Also various data including the aftershock distribution and strong motion seismograms suggest a very complex rupture process. For these reasons it is useful to investigate the complex rupture process using multiple data with various sensitivities to the rupture process. While previously published source models are based on one or two datasets, here we infer the rupture process with three datasets, InSAR, strong-motion, and teleseismic data.

We first performed point source inversions to derive the focal mechanism of the 2010 Canterbury earthquake. Based on the focal mechanism, the aftershock distribution, the surface fault traces and the SAR interferograms, we assigned several source faults. We then performed the joint inversion to determine the rupture process of the 2010 Canterbury earthquake most suitable for reproducing all the datasets. The obtained slip distribution is in good agreement with the surface fault traces.

We also performed similar inversions to reveal the rupture process of the 2011 Christchurch earthquake. Our result indicates steep dip and large up-dip slip. This reveals the observed large vertical ground motion around the source region is due to the rupture process, rather than the local subsurface structure.

To investigate the effects of the 3-D velocity structure on characteristic strong motion seismograms of the two earthquakes, we plan to perform the inversion taking 3-D velocity structure of this region into account.