TERRAPUB Earth, Planets and Space

Earth Planets Space, Vol. 64 (No. 8), pp. 693-702, 2012

Migration process of very low-frequency events based on a chain-reaction model and its application to the detection of preseismic slip for megathrust earthquakes

Keisuke Ariyoshi1, Toru Matsuzawa2, Jean-Paul Ampuero3, Ryoko Nakata1, Takane Hori1, Yoshiyuki Kaneda1, Ryota Hino2, and Akira Hasegawa2

1Earthquake and Tsunami Research Project for Disaster Prevention, Japan Agency for Marine-Earth Science and Technology, Yokohama 236-0001, Japan
2Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
3Seismological Laboratory, California Institute of Technology, Pasadena, California 91125-2100, USA

(Received March 29, 2010; Revised September 29, 2010; Accepted September 30, 2010; Online published August 27, 2012)

Abstract: In order to reproduce slow earthquakes with short duration such as very low frequency events (VLFs) migrating along the trench direction as swarms, we apply a 3-D subduction plate boundary model based on the slowness law of rate- and state-dependent friction, introducing close-set numerous small asperities (rate-weakening regions) at a depth of 30 km under high pore pressure condition, in addition to a large asperity. Our simulation indicates that swarms of slip events occur repeatedly at the small asperities, and these events are similar to the observed slow earthquake group, especially to VLF, on the basis of the relation between characteristic duration and seismic moment. No slip events occur there without the small asperities, which mean that the close-set numerous small asperities may be one of the necessary conditions for generating the short-duration slow earthquakes such as VLFs. In the preseismic stage of the megathrust earthquakes that occur at the large asperity, the swarms of VLFs have higher migration speeds and higher moment release rate as well as shorter recurrence interval. Thus, monitoring the migration of slow earthquakes may be useful in imaging the preseismic slip of megathrust earthquakes.
Key words: Numerical simulation, friction law, slow earthquake, low-frequency tremor, preseismic change.

Corresponding author E-mail: ariyoshi@jamstec.go.jp

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