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Stress conditions and seismic activity around the rupture zone of the 2016 Kumamoto earthquake in Kyushu, southwest Japan
  • Michiharu Ikeda,
  • Kozo Onishi,
  • Naoki Nishizaka
Michiharu Ikeda
Shikoku Research Institute Incorporated

Corresponding Author:m-ikeda@ssken.co.jp

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Kozo Onishi
Shikoku Electric Power Co. Inc.
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Naoki Nishizaka
Shikoku Electric Power Company Incorporated
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The main events of the 2016 Kumamoto earthquake in Kyushu were a foreshock (Mw 6.2) on 14 April and the main shock (Mw 7.0) on 16 April 2016, both of which were caused by fault ruptures near the intersection of the Futagawa and Hinagu fault zones. However, not all sections of the two fault zones were ruptured during the earthquake. In particular, the northernmost (Takano-Shirahata) section of the Hinagu fault zone ruptured, but the rupture did not propagate to southern sections of the fault zone. We examined fault geometry and paleoseismological data of the fault zones, and furthermore used numerical analyses to investigate rupture conditions around the source faults of the earthquake, which together allowed us to consider the potential for future earthquakes in the region. Fault geometry, slip tendencies, and fault rupture history indicated that the rupture potential on the source faults was high before the earthquake. Seismicity and rupture propagation during the earthquake sequence were probably controlled by geological heterogeneities of the fault zones. Coulomb stress change analysis indicated that stress transfer from the source faults to the Hinagu section during the earthquakes was smooth, and that most of that section received a positive stress change. This stress change and the high slip tendencies we calculated for the Hinagu section indicate that it has high potential for a future rupture. These results provide crucial information for preparation for disaster mitigation of future earthquakes around the rupture zone of the 2016 Kumamoto earthquake.