Does a focal region of shallow slow earthquake become a source area of tsunami? -Approach of geophysical and geological survey for a large historical earthquake-
Abstract
In Hyuga-nada region, located in the western part of Nankai Trough, Japan, is one of the most active areas of the shallow slow earthquakes. The shallow slow earthquakes will be the key to understand the occurrence of the megathrust earthquake and tsunami adjacent trench region. Recent offshore geophysical observation has shown that the shallow low-frequency tremor associated with migration repeatedly occurred at the shallow part of the plate interface (5-15 km deep) in this region. In 1662, a large historical earthquake occurred in the Hyuga-nada region and large tsunami estimated at least 4-5 m struck the east coast of Kyushu Island, that was unusually large tsunami caused by a usual M7-class interplate earthquake in this area. However, the detail of the 1662 earthquake is unclear because the tsunami deposit survey still hasn't been occurred in this region.
In this study, we hypothesized that the unusual large tsunami of the 1662 earthquake was caused by the coseismically slipping of focal region of shallow slow earthquakes (i.e., focal area of shallow slow earthquakes also became a tsunami source area), which is similar to the 2011 Tohoku earthquake. To verify this hypothesis, we started a new study using both geophysical and geological methods. For clarifying to scale and recurrence of the 1662 tsunami, we started the tsunami deposit survey along the coastline of southeast Kyushu area. A preliminary survey was performed at 32 points along 60 km of coastline. Several sandy event deposits, which is similar to modern shoreline deposits, can be found at some surveyed points. From geophysics, the detail of characteristics of shallow tremor activity were documented such as the distribution of spatial frequency and radiated source energy [Watanabe et al., this meeting], and tidal response [Katakami et al., 2017], which may be an indicator of friction characteristics at the shallow plate interface. For the next, the fault model of the 1662 earthquake is constructed based on the recent result of geophysical observation, and numerical simulation of the tsunami is carried out. Eventually, we compare the simulation result and data of tsunami deposits, and update the model in a trial and error. Acknowledgments: This work was supported by JSPS KAKENHI Grant Numbers JP17K01328, JP16H06473.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T33F0472Y
- Keywords:
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- 1242 Seismic cycle related deformations;
- GEODESY AND GRAVITYDE: 7230 Seismicity and tectonics;
- SEISMOLOGYDE: 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICSDE: 8163 Rheology and friction of fault zones;
- TECTONOPHYSICS