Japan Geoscience Union Meeting 2016

Presentation information

International Session (Oral)

Symbol S (Solid Earth Sciences) » S-CG Complex & General

[S-CG20] Intermediate-depth and deep earthquakes: their origins and material properties of subducting slabs

Tue. May 24, 2016 9:00 AM - 10:30 AM 201A (2F)

Convener:*Keiko Kuge(Department of Geophysics, Graduate School of Science, Kyoto University), Saeko Kita(National Research Institute for Earth Science and Disaster Prevention), Alexandre Schubnel(CNRS), Geoffrey Abers(Cornell University, Department of Earth and Atmospheric Sciences, New York, USA), Chair:Keiko Kuge(Department of Geophysics, Graduate School of Science, Kyoto University), 国立研究開発法人 防災科学技術研究所

9:30 AM - 9:45 AM

[SCG20-03] Rupture initiation of deep-focus earthquakes

★Invited papers

*Zhongwen Zhan1 (1.California Institute of Technology)

Keywords:deep-focus earthquakes, rupture initiation

As part of the deep-focus earthquake mechanism puzzle, the initiation mechanism, which needs to be spontaneous, is particularly important and enigmatic. Once rupture is initiated, various feedback mechanisms, such as shear heating/melting, can potentially be triggered and promote further slip. However, accurate characterization of the initiation phase is difficult due to the limited data resolution and complex high-frequency Green’s functions. Here we develop a new method to jointly invert teleseismic and regional P waveforms for a Haskell-style model, assuming unilateral rupture with constant rupture speed. Small aftershocks’ waveforms are used as Empirical Green’s functions when available. We apply this method to large deep-focus earthquakes to zoom in on their first 2~3 seconds of rupture. We found that their initiation phases often show relatively high, sometimes supershear rupture speeds, depending the fracture modes. For example, the 2015 M7.9 Bonin Islands earthquake shows a supershear initiation, and the 1994 M8.2 Bolivia earthquake’s initial rupture speed is also higher than its later stages. The observed high-speed initial ruptures may suggest a more efficient initiation mechanism than the later rupture propagation mechanism(s).