A deep outer-rise reverse-fault earthquake immediately triggered a shallow normal-fault earthquake: The 7 December 2012 off-Sanriku earthquake (M W 7.3)

Abstract

Teleseismic body wave analysis revealed that the 7 December 2012 off-Sanriku earthquake (MW 7.3) at the outer rise of Japan Trench consisted of two successive subevents. The first subevent with reverse-fault mechanism (Event 1, MW 7.1) at 56 km depth was followed by, approximately 20 s later, the second subevent with normal-fault mechanism (Event 2, MW 7.2) at 6 km depth. Finite-fault slip models show that the slip of Event 1 was concentrated around the initial rupture point with the maximum of 2.7 m and that Event 2 had two asperities with the maximum of 4.5 m at both sides of the initial rupture point. The static Coulomb Failure Function analyses suggested that Event 1 triggered Event 2 and that both subevents were promoted by the 2011 Tohoku earthquake (MW 9.1). Key Points The 2012 Off-Sanriku event consisted of reverse- and normal-fault sub-events The reverse-fault sub-event immediately triggered normal-fault sub-event The 2011 Tohoku earthquake promoted both sub-events The 2012 Off-Sanriku event consisted of reverse- and normal-fault sub-events The reverse-fault sub-event immediately triggered normal-fault sub-event The 2011 Tohoku earthquake promoted both sub-events. © 2013. American Geophysical Union. All Rights Reserved.