Reproducibility of spatial and temporal distribution of aseismic slips in Hyuga-nada of southwest Japan
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SPECIAL ISSUE PAPER
Reproducibility of spatial and temporal distribution of aseismic slips in Hyuga-nada of southwest Japan Ryoko Nakata • Shin’ichi Miyazaki Mamoru Hyodo • Takane Hori
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Received: 30 May 2013 / Accepted: 27 September 2013 Ó Springer Science+Business Media Dordrecht 2013
Abstract The Hyuga-nada region of southwest Japan, which is located off the east coast of Kyushu Island, may have the potential to generate great interplate earthquakes along the Nankai trough in the future. In this area, thrust earthquakes of M = 6.7–7.2 have occurred with recurrence intervals of approximately 30 years. In association with these earthquakes, possible local heterogeneities of plate coupling may be expected within 100 km from the coast in the Hyuga-nada region. We investigate numerical experiments to determine the spatial and temporal resolution of slip on the plate interface beneath the Hyuga-nada offshore region. For this purpose, we calculated synthetic displacement data from the result of numerical simulation conducted for the afterslip following an Mw 6.8 earthquake, for existing global positioning system stations on land and planned ocean floor seismic network stations. The spatial and temporal distribution of fault slip is then estimated using a Kalman filter-based inversion. The slip distribution estimated by using ocean floor stations demonstrates that the heterogeneity of plate coupling is resolved approximately within 50 km from the coastal area. This heterogeneity corresponds to the coseismic area of an Mw 6.8 earthquake with a radius of 10 km. Our study quantitatively evaluates the spatial resolution of aseismic slip in the
R. Nakata (&) M. Hyodo T. Hori Earthquake and Tsunami Research Project for Disaster Prevention, Japan Agency for Marine-Earth Science and Technology, 3173-25, Showa-machi, Kanazawa-ku, Yokohama 236-0001, Japan e-mail: [email protected] S. Miyazaki Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University, Kitashirakawaoiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan
Hyuga-nada region. Analysis based on continuous ocean floor data is useful for resolving the spatial variations of heterogeneities in plate couplings. Keywords Ocean floor observation network Afterslip Inversion Plate coupling
Introduction The Nankai trough is known to experience great interplate earthquakes (M = 8–8.7) with a recurrence interval of approximately 100–200 years. These mega-thrust earthquakes result from the subduction of the Philippine Sea plate beneath southwestern Japan. The western edge of the hypocentral area is located offshore of Shikoku Island (Fig. 1a). Geological investigations of the tsunami-inundated Ryujin Lake in Kyushu indicate that future Nankai trough earthquakes may extend farther westward into the Hyuga-nada region than previously suggested (Furumura et al. 2011). Furthermore, we cannot rule out the possibility of M [ 9 earthquakes that may occur as a result of rupturing by Nankai trough earthquakes toward the Ryukyu trench, which lies southwest
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