Investigation of Strong Ground Motion around MTL in Mikawa Area

点击翻译按钮获取中文摘要

The TASSEM,Toyohashi University of Technology Array System for Strong Earthquake Motions, has been developed around Toyohashi city to observe the strong ground motions of this area and investigate the effects of geological and topographical conditions including fault existence. The earthquake observations and their numerical analysis were conducted as remarked as below.a) The strong motion seismograph has been set up in Shinshiro city (called site 2 in outer zone) and Gamagori city (called site 3 in inner zone) in 1995, in addition to old observation points (called site 1 around TUT) established in 1989. All these observation location are distributed around the Median Tectonic Line (MTL) and installed on the basement in engineering meaning. In total, five earthquake records were observed, four of which occurred in outer zone and one in inner.b) Based on the analysis of such recorded acceleration, unsteady properties of wave propagation due to the scattering within MTL are obvious, that … More are involved with the ratation of principal propagating direction and the occurrence of additional surface wave and different frequency distribution within inner zone and outer zone.c) On the amplification and attenuation of ground motions, even though some records showed trend to amplify the high frequency components when the seismic wave propagated over the MTL,it is difficult to assert such results only from MTL effect, because we need to separate the local site effect of topographical conditions besidea near field soil condition. On the other hand, the amplification in seaside area were always observed both in inner zone and outer zone, which is considered due to the effects of thick alluvium.d) The coherency functions of different observation sites showed various value with respect to different focal region. It is considered that both MTL and site effects on ground motions behaved associated with seismic wave propagating routes.e)The theoretical analysis on ground motion indicated that the amplification due to local site conditions was significant, but the Q value in both side of MTL,as an index of attenuation of wave propagation, showed no much difference. More accurate simulations have to be experimented to imterpret the MTL effects. Less