Seismic velocity structure in the source region of the 2016 Kumamoto earthquake sequence, Japan

Azusa Shito, Satoshi Matsumoto, Hiroshi Shimizu, Takahiro Ohkura, Hiroaki Takahashi, Shinichi Sakai, Tomomi Okada, Hiroki Miyamachi, Masahiro Kosuga, Yuta Maeda, Masayuki Yoshimi, Youichi Asano, Makoto Okubo

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Abstract

We investigate seismic wave velocity structure and spatial distribution of the seismicity in the source region of the 2016 Kumamoto earthquake sequence. A one-dimensional mean velocity shows that the seismogenic zone has a high-velocity and low-Vp/Vs ratio relative to the average velocity structure of Kyushu Island. This indicates that the crust is relatively strong, capable of sustaining sufficiently high strain energy to facilitate two large (Mj > 6.5) earthquakes in close proximity to one another in rapid succession. Three-dimensional tomography of the seismogenic zone around the source of the 2016 Kumamoto earthquake sequence yields Vp = 6 km/s and Vs = 3.5 km/s. Most large-displacement areas (asperities) of the Mj 7.3 event overlap with the seismogenic zone and the overlying surface layer. Aftershock seismicity is distributed deeper than the conventional seismogenic zone, which suggests decreased strength due to fluids or increased stress, both caused by coseismic slip.

Original languageEnglish
Pages (from-to)7766-7772
Number of pages7
JournalGeophysical Research Letters
Volume44
Issue number15
DOIs
Publication statusPublished - Aug 16 2017

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All Science Journal Classification (ASJC) codes

  • Geophysics
  • Earth and Planetary Sciences(all)

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