Was the 2011 Tohoku-Oki earthquake preceded by aseismic preslip? Examination of seafloor vertical deformation data near
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Was the 2011 Tohoku-Oki earthquake preceded by aseismic preslip? Examination of seafloor vertical deformation data near the epicenter R. Hino • D. Inazu • Y. Ohta • Y. Ito • S. Suzuki • T. Iinuma • Y. Osada • M. Kido H. Fujimoto • Y. Kaneda
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Received: 2 July 2013 / Accepted: 23 November 2013 Ó The Author(s) 2013. This article is published with open access at Springerlink.com
Abstract Ocean-bottom pressure records obtained near the epicenter of the 2011 Tohoku-Oki earthquake were examined to test whether the earthquake was preceded by substantial precursory crustal deformation. The seafloor data enabled us to search for small-scale preslip near the epicenter that would be difficult to identify from terrestrial geodetic data. After treating the data to reduce nontectonic fluctuations, we obtained a time series of seafloor vertical deformation in the epicentral region with a noise level of 2–4 cm. No significant crustal deformation related to preslip was detected in the period of roughly a day before the mainshock, whereas postseismic deformation associated with the largest foreshock 2 days before the mainshock was apparent. From our quantitative estimate of the sensitivity of the seafloor network in detecting slip on the plate interface, we conclude that the Tohoku-Oki earthquake was not preceded by preslip with moment release greater than moment magnitude (Mw) 6.2 in the vicinity of the hypocenter or greater than Mw 6.0 along the subduction interface near the trench.
R. Hino (&) T. Iinuma Y. Osada M. Kido H. Fujimoto International Research Institute of Disaster Science, Tohoku University, Sendai, Japan e-mail: [email protected] D. Inazu National Research Institute for Earth Science and Disaster Prevention, Yokohama, Japan Y. Ohta Y. Ito S. Suzuki Graduate School of Science, Tohoku University, Sendai, Japan Y. Kaneda Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan
Keywords Precursory slip Interplate megathrust earthquake Seafloor vertical deformation Ocean-bottom pressure monitoring
Introduction Temporal changes in aseismic crustal deformation precursory to the occurrence of earthquakes have been investigated for many large earthquakes. If they can be detected successfully, changes in deformation rates may facilitate warnings of imminent earthquakes. One possible cause of pre-earthquake deformation rate changes is a quasi-static aseismic slip associated with a transitional process before a fault rupture reaches high-speed seismic slip (e.g. Scholz 2002). Observations of preseismic deformation, therefore, are also important for understanding earthquake generation. However, a comprehensive review by Roeloffs (2006) found few credible published accounts of preseismic crustal deformation events. In subduction environments, it appears that deformation events can be categorized into two groups according to their lead time before the mainshock: those with a lead time of less than about a month and those with a lead time longer than that. The former g
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