Velocities of Pn-Waves in the Taiwan Strait and Its Surrounding Area from Regional Earthquakes

由區域地震推求臺灣海峽及其鄰近地區之Pn波速

黃柏壽(B. S. Huang) ； 陳國誠(K. C. Chen) ； 王凱魯(K. L Wang) ； 顏宏元(H. Y. Yen)

《Terrestrial, Atmospheric and Oceanic Sciences》 9卷3期 (1998/09) Pp. 473-486

並列摘要

Seismogenic conditions associated with the plate interface in the southernmost Ryukyu arc-Taiwan region is studied in four different aspects.From the history of large and great earthquakes,it is inconclusive whetherM(subscript w)≥8 events have ever occurred along the plate interface,but there seemsto be no doubt that at least a few earthquakes with M(subscript w)≥7.0-7.5 have occurred in the region since the turn of this century.Earthquake focal mechanisms show the co-existence of extensional earthquakes in the vicinity oftrench and within the subducted lithosphere,suggesting no patterns of aseismic cycle due to strong interface coupling.The lack of”transitionalthrust”earthquakes near the lower portion of the interface further supports that the interface is not strongly coupled.The maximum M(subscript w)of aninterface earthquake is estimated to be 7.6-7.7,as inferred from the geometric configuration of the interface.The average slip obliquity of interface earthquakes is 35° while the convergence obliquity is 70°.Such a pattern of slip partitioning indicates that the rheological behavior of the Ryukyufore-arc in this region is not completely elastic,thus is unlikely to generateM(subscript w)＞8 subduction earthquakes.However,there is strong evidence in focalmechanisms to indicate interactions among different tectonic stress regimes.Although such interactions may not necessarily mean a bigger earthquake,they are possible to increase the frequency of earthquake occurrence because the combined stress regime would reach the failure criteria of geological materials more effectively.Given that NE Taiwan is the most likelyplace that interactions among various stress regimes could take place,it issuggested the seismicity there to be closely monitored.From the seismichazard point of view,the potential threat from frequent occurrences of M(subscript w)＞7 events in the region cannot be ignored.Due to the short distances fromNE Taiwan to the three largest metropolitan areas on the island,improvingand strictly enforcing building code and careful planning of major industrial facilities are probably the most effective measures to prevent the potential devastation due to earthquakes.

並列關鍵字

Taiwan Strait ； Pn Velocities ； Uppermost Mantle Velocity ； Kinman Island