Publication Date:
2013-11-22
Description:
Using the Japan Meteorological Agency earthquake catalog since 1923, we investigated the seismic activity prior to the 2011 M w 9.0 Tohoku-Oki earthquake with reference to the slip distribution, which is characterized by two high-slip (≥20 m) patches separated by a zone of relatively low slip. The peak of the northern high-slip patch is located near the trench while the peak of the southern high-slip patch is situated about 40 km southeast of the mainshock epicenter, about 70 km away from the trench. It is estimated that the mainshock ruptured the southern high-slip patch first and then extended to a larger adjacent region, including the northern high-slip patch. The epicenters of foreshock activity that started two days before the mainshock are distributed in the western edge of the northern high-slip patch where other prominent activity, such as the 1981 event, occurred during the past 90 years. Based on the spatiotemporal seismicity pattern around the two high-slip patches, we infer that the foreshock activity triggered the 2011 Tohoku-Oki earthquake because the increased stress from the foreshock activity was able to overcome the strength of the southern high-slip patch, which had been sufficiently weakened by a series of large surrounding earthquakes since 2003. Other prominent activity, such as the 1981 event, failed to trigger such a great earthquake because similar stress condition had not been established at those times. The doughnut-shaped seismicity pattern that formed around the peak of the southern high-slip patch suggests the existence of an extremely strong patch that had not been ruptured by the surrounding large earthquakes for a long period of time.
Print ISSN:
0037-1106
Electronic ISSN:
1943-3573
Topics:
Geosciences
,
Physics
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