Earth Planets Space, Vol. 63 (No. 7), pp. 773-777, 2011
Takane Hori1 and Shin'ichi Miyazaki2
1Japan Agency for Marine-Earth Science and Technology, Japan
2Kyoto University, Japan
(Received April 8, 2011; Revised June 12, 2011; Accepted June 14, 2011; Online published September 27, 2011)
We propose a generation mechanism of a giant earthquake of magnitude (M) ∼9 in subduction zones where only M = 7∼ 8 earthquakes have been identified and the surroundings of the source areas are sliding aseismically. In an M 9 event, both the M = 7 ∼ 8 source areas and the surrounding area rupture seismically and the coseismic slip amount is one order larger than that of M = 7 ∼ 8 earthquakes. To reproduce such behavior, we assume that an M 9 earthquake occurrence is the fundamental rupture mode in the subduction zone, and the M 9 source area is modeled as a large fracture energy area whose nucleation size is comparable to the size of the source area. The M = 7 ∼ 8 asperities are modeled as smaller fracture energy areas whose nucleation size is smaller than the asperity size. Based on these assumptions, we demonstrate a simple numerical simulation of earthquake generation cycles. The results are qualitatively consistent with the characteristics of the 2011 off the Pacific coast of Tohoku Earthquake and a number of phenomena observed prior to this event.
Key words: Earthquake generation cycle, hierarchical asperity model, giant earthquake, aseismic sliding, subduction zone, nucleation size, fracture energy, numerical simulation.