Magnitude Dependent Seismic Quiescence of 2008 Wenchuan Earthquake

Abstract:

The change in seismicity leading to the Wenchuan Earthquake in 2008 (Mw 7.9) has been studied by various authors based on statistics and/or pattern recognitions (Huang, 2008; Yan et al., 2009; Chen and Wang, 2010; Yi et al., 2011). We show, in particular, that the magnitude-dependent seismic quiescence is observed for the Wenchuan earthquake and that it adds to other similar observations. Such studies on seismic quiescence prior to major earthquakes include 1982 Urakawa-Oki earthquake (M 7.1) (Taylor et al., 1992), 1994 Hokkaido-Toho-Oki earthquake (Mw=8.2) (Takanami et al., 1996), 2011 Tohoku earthquake (Mw=9.0) (Katsumata, 2011). Smith and Sacks (2013) proposed a magnitude-dependent quiescence based on a physical earthquake model (Rydelek and Sacks, 1995) and demonstrated the quiescence can be reproduced by the introduction of “asperities” (dilantacy hardened zones). Actual observations indicate the change occurs in a broader area than the eventual earthquake fault zone. In order to accept the explanation, we need to verify the model as the model predicts somewhat controversial features of earthquakes such as the magnitude dependent stress drop at lower magnitude range or the dynamically appearing asperities and repeating slips in some parts of the rupture zone. We show supportive observations. We will also need to verify the dilatancy diffusion to be taking place. So far, we only seem to have indirect evidences, which need to be more quantitatively substantiated.