IAG-IASPEI 2017

Presentation information

Poster

IASPEI Symposia » S01. Open session

[S01-P] Poster

Tue. Aug 1, 2017 3:30 PM - 4:30 PM Event Hall (The KOBE Chamber of Commerce and Industry, 2F)

3:30 PM - 4:30 PM

[S01-P-20] Distribution of deep earthquakes in the subducting Pacific slab beneath Japan

Ayako Tsuchiyama1, Junichi Nakajima1, Toru Matsuzawa2 (1.Tokyo Institute of Technology, Tokyo, Japan, 2.Tohoku University, Miyagi, Japan)

Generally, the number of earthquakes in slabs decreases with depth. However, the seismicity increases again in a depth range of 400–500 km. The mechanism of this phenomenon remains poorly understood, even though many hypotheses for the genesis of deep earthquakes have been proposed, which include dehydration-embrittlement hypothesis, transformational faulting, and shear instability. In this study, we analyzed 93 deep earthquakes (M≥3.0) that occurred at depths of >300 km beneath Tokai area in Japan to understand factors that control the high seismic activity in the mantle transition zone.
First, we read P-wave polarities and determined focal mechanism solutions of earthquakes. Then, we picked arrival times of both P and S waves and relocated hypocenters by using double-difference earthquake relocation algorithm (Waldhauser and Ellsworth, 2000). The relocated hypocenters do not show a double-planed seismicity as is observed in Iidaka and Furukawa (1994). In the next step, we will relocate hypocenters with differential travel-time data derived from waveform cross correlations and constrain hypocenter locations with high accuracy. We will present detailed hypocenter distributions together with focal mechanism solutions, and discuss a plausible mechanism that facilitates deep earthquakes in the mantle transition zone.