Internal Strain Rate in Southwest Japan estimated by Block Motion Model based on Onshore and Seafloor Geodetic Observations
Abstract
Introduction
The plate motion and its interaction lead to strain accumulation both along the plate boundary and in the plate. Earthquakes occur in order to release the accumulated strain. In Japan, the seismic potential is assessed for major active faults and plate interface based on historical earthquake records(https://www.jishin.go.jp/), whereas it is not considered for the faults which are not found by geological surveys. Some previous studies have tried to assess the seismic potential using the crustal strain rate based on geodetic observations to improve the present assessment (e.g. Takahashi and Shinohara, 2015; Sagiya, 2015). They reported some problems in strain rate estimation because of, for example, interplate coupling and inelastic deformation. In this study, we estimate the internal strain rate in southwest Japan using the block motion model based on onshore and seafloor geodetic observation data to clear the problems above. Methods & Data We use the block motion model to estimate the internal strain rate. In the model, we describe the observed crustal deformation as sum of the rigid block rotation, elastic deformation due to slip deficit, and the deformation due to internal strain. The unknown parameters are coupling ratio, Euler pole vector, and internal strain rate. We use both onshore GNSS and seafloor GNSS-Acoustic observation data; the number of observation data is 887. We prepare the tectonic model which has 12 blocks. The internal strain is assumed as uniform within each block. The Observation equation is the non-linear equation; thus, we use the Markov Chain Monte Carlo (MCMC) method to obtain the Probability Density Function of each unknown parameter simultaneously. Results Overall, the internal strain is estimated as EW contraction in western blocks, whereas NW-SE contraction and NE-SW extension in eastern blocks (Figure). The largest contraction strain is estimated in the FA block in which the 2016 Kumamoto earthquake (M7.3) occurred; -11.6 nanostrain/yr with 89°E axis. The largest extension strain is estimated in the ON block; 17.4 nanostrain/yr with 23°E axis. In presentation, we discuss about the long-term earthquake assessment in southwest Japan by comparing the strain energy in each block and seismic moment on the faults evaluated in (https://www.jishin.go.jp/).- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.G51D0513K
- Keywords:
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- 9810 New fields (not classifiable under other headings);
- GENERAL OR MISCELLANEOUSDE: 1299 General or miscellaneous;
- GEODESY AND GRAVITY