Physics
Scientific paper
Apr 1991
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991pepi...66..214y&link_type=abstract
Physics of the Earth and Planetary Interiors, Volume 66, Issue 3-4, p. 214-243.
Physics
16
Scientific paper
The interplate coupling and stress accumulation process associated with the subduction of the Philippine Sea plate beneath the Eurasian plate along the Nankai trough, where large earthquakes have occurred periodically, have been investigated in detail, taking into account the three-dimensional complicated structure of the Philippine Sea plate and its motion relative to the Eurasian plate. For this purpose, we mainly used extensive geodetic data in southwest Japan, such as levelling, tide gauge and trilateration, which presumably are effective means of revealing coupling properties, and applied a three-dimensional finite element method. Here, two seismic periods associated with the 1944 Tonankai and 1946 Nankaido earthquakes were considered-interseismic and pre-seismic stages. Comparing the coupled regions obtained for the two cases, a possible explanation of its temporal change was proposed: it might gradually spread from a shallower to deeper portion, with transition from the interseismic to pre-seismic stage. A comparison of the coupling properties between southwest Japan and northeast Japan reveals the following properties. In southwest Japan, the coupling is generally strong, and its region is limited in a relatively shallow portion. The pre-seismic coupled regions coincide with the co-seismic and post-seismic fault zone, suggesting that the accumulated stress is released at the time of a large earthquake. In northeast Japan, on the other hand, the coupling is weak and its extent appears to reach a depth of about 100 km, and the co-seismic and post-seismic regions are limited to the upper half of the coupled region. The weakly coupled region in southwest Japan seems to correspond well to the region with high seismic activity, a high dip angle subducting slab and the possible existence of seamounts, in contrast to the strongly coupled region correlated with low seismicity, low dip angle subduction and no seamounts. On the western coupled region off Shikoku, an anomalously strongly coupled region, corresponding to a convergence rate of 7-8 cm year-1, was identified. This may be caused by geomorphological properties, such as the low dip angle of the subducting plate and smooth plate boundary, resulting in a large amount of stress concentration there. The stress field associated with the interplate coupling was also calculated. There is fair agreement between the observations and calculations near the plate boundary beneath the southern Kii peninsula and Shikoku. Although the effects of the interplate coupling may have some influence on strike-slip faulting with the N-S compressive axes beneath Shikoku, other earthquake generating stress, such as a two-layered double-buckling, would be dominant there.
Present address: Department of Earth and Planetary Physics, Faculty of Science, Tokyo University, Bunkyo-ku, Tokyo 113, Japan.
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