Interplate Coupling Weakening Before the 2011 Tohoku Earthquake Accompanied by the Periodic Variation
Abstract
Recently, Uchida et al. [2016, Science] revealed the periodic changes in the interplate coupling in the northeast Japan subduction zone based primarily on the activity of small repeating earthquakes. They found that slow slip on the plate interface has occurred repeatedly at intervals of from 2 to 6 years, depending on the location. They also used the horizontal displacement gradient time series of the 1-year sub-time-window to estimate the recurrence interval and concluded that the recurrence intervals based on the seismic and geodetic data analyses are mutually corresponding. Meanwhile, studies based on GNSS observations revealed that the interplate coupling at the shallow and intermediate plate interfaces became weak before the Tohoku-oki earthquake [Ozawa et al., 2012; Mavrommatis et al., 2014; Yokota and Koketsu, 2015}. In this study, I estimated the spatio-temporal change in the interplate coupling along the plate boundary in NE Japan based on the spatial gradient of the surface displacement rates in each belt-like region configured along the direction normal to the Japan Trench for time windows such as 0.5, one, two, three, and five years being shifted by one week. The gradient of the horizontal velocities is negative and has a large magnitude when the interplate coupling at the shallow and intermediate part. The spatio-temporal variation in the horizontal displacement rate gradients for a 1-year sub-time-window reveals that the decrease in the negative gradients at off Ibaraki to Miyagi prefectures did not occur monotonically. The decreases occurred around 1997, 2001, 2005, and 2009, and the northern limit of the fluctuating profiles advanced northward. It indicates the semi-periodic occurrence of slow slip events and the expansion of the area of slow slip events before the 2011 Tohoku-oki Earthquake (M9.0) approaching the hypocenter of the Tohoku-oki earthquake.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFM.G42A..05I
- Keywords:
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- 1207 Transient deformation;
- GEODESY AND GRAVITY;
- 1211 Non-tectonic deformation;
- GEODESY AND GRAVITY;
- 8159 Rheology: crust and lithosphere;
- TECTONOPHYSICS;
- 8163 Rheology and friction of fault zones;
- TECTONOPHYSICS