Aseismic slow slip on an inland active fault triggered by a nearby shallow event, the 2008 Iwate-Miyagi Nairiku Earthquake (Mw6.8)
Abstract
Using GPS observations, we have detected an aseismic slip event on the intraplate Dedana Fault (DF) that was triggered by the Iwate-Miyagi Nairiku Earthquake (IMNE, Mw6.8, 13 Jun 2008 UTC) on a nearby but separate fault. The DF constitutes the southernmost tip of the Kitakami-Teichi-Seien Fault Zone, one of several active fault zones in the middle of the Tohoku district. There is a strain concentration zone with an EW contraction along the backbone range of northeastern Japan arc, where the volcanic front runs through. We have analyzed continuous GPS data to obtain site coordinate time series, which clearly indicate the occurrence of an aseismic slip event on the DF. We have also examined whether postseismic deformation processes other than aseismic slip on the DF are able to satisfactorily explain the observation or not. Time-dependent inversion analysis was performed to investigate where and when such slip occurred. The results exhibit three distinctive features: 1) there is no significant coseismic slip on the DF, whereas the cumulative aseismic slip reaches 29 cm following the mainshock; 2) almost no aftershocks occurred in locations where aseismic slips are large on the DF; and 3) the areas of large postseismic slip surround the region of large coseismic slip (See Figure). The static stress change caused by the mainshock can straightforwardly account for the triggering of aseismic slip. We have calculated the normal stress change and ΔCFF. A comparison of these results with the aseismic slip distribution indicates that the slip likely started in the region of positive CFF and normal stress changes. The detection of future such aseismic slip events on intraplate faults is likely to require denser geodetic networks than are currently in operation, but is important for fully characterizing the seismic hazard associated with intraplate earthquakes. Cumulative distribution of the estimated postseismic slip. The observed and calculated displacements are shown by solid and open arrows, and the contour interval is 4 cm, and the lowest contour illustrated is 8 cm. Black dots mark the aftershocks of magnitudes larger than 1.5 and a star indicates the hypocenter of the IMNE mainshock. Broken lines are depth contours of the southern and the northern fault. Solid contours represent the coseismic slip distribution.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.T13D1919I
- Keywords:
-
- 1207 GEODESY AND GRAVITY / Transient deformation;
- 1240 GEODESY AND GRAVITY / Satellite geodesy: results;
- 1242 GEODESY AND GRAVITY / Seismic cycle related deformations;
- 8118 TECTONOPHYSICS / Dynamics and mechanics of faulting