An Experimental Study on Engineering Characteristics of Spatial Correlation of Earthquake Ground Motion

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In spite of its engineering importance, spatial correlation of earthquake ground motion over a distance of several hundreds of meters has not been studied in detail. In order to experimentally examine the abovementioned properties from the engineering point of view, the following observation system has been constructed in the Chiba Experiment Station of the University of Tokyo.1) By installing eight 3-component acceleration-type seismographs on and in the ground (-1m and -20m, respectively), the previously existing dense array network has been expanded to a system of 44 seismographs with a total number of 132 components within a triangular area with sides of about 300m. By this expansion, spatial correlation characteristics of ground motions over distances of 300m, 150m, 120m, 30m, 15m, 10m and 5m can be investigated based on actually observed seismograms.2) A JMA (Japan Meteorological Agency) displacement-type seismograph (2 horiz. and 1 vert. components) and three velocity-type seism … More ographs(2 horiz. and 1 vert.) with wide dynamic range have been installed together with a borehole acceleration-type seismograph (2 horiz. and 1 vert. components) at the same place to examine the reliability of displacement time-histories obtained by integration of the records of acceleration- type seismograph.Since the total observation system began to operate only in December, 1985, complete sets of satisfactory records are yet to be obtained. However, some interesting findings have been made by using the data so far recorded.1) The displacement waveform computed by double integration of accelero gram was found to agree with that recorded by the JMA displacement-type seismograph for the components of waves in the period range of 2 - 13s.2) Agreement between ground motions recorded by acceleration-type and velocity-type seismographs was found satisfactory at least for the components of waves with periods longer than 4s.3) From the two of the strongest array records so far obtained, the peak acceleration on the ground surface was found to vary with a coefficient of variation of 20% within the 300m triangular area whose geological conditions are almost uniform. This seems to indicate an important direction of future research related to the spatial correlation of ground motion. Less