CKI-12: Estimation of Long Period Ground Motion
This is a Group Summary following the CUREe-Kajima Meeting at Tokyoduring September 2 - 3, 1992. The subject of the present report is the long-period strong motion with periods around 8 s often observed in the Tokyo-Yokohama area. The goal of the project is to simulate the observed motions using realistic earthquake source model and three-dimensional structure of the Kanto basin. In the beginning, this goal looked too ambitious to attain in the short project period. To our surprise, we seem to have attained it, because we now have a clear, quantitative understanding of both amplitude and duration of the long-period motion in the Tokyo-Yokohama area.
This report includes the following:
LONG-PERIOD STRONG MOTION RESPONSE IN A 3D SEDIMENTARY BASIN
Professor Keiiti Aki
Professor Ta-hang Teng
Dr. Xiaofei Chen
Dr. Yoshiaki Hisada
Mr. Kenichi Kato
The understanding was achieved primarily because we used three distinctly different methods to deal with the complex wave field. They are: (1) the Gaussian Beam method for surface waves in laterally smoothly varying media, (2) the T-matrix, generalized reflection/transmission matrices method, and (3) the Boundary Element method (BEM) for laterally sharply varying media. The methods (1) and (3) were applied to the 3D basin structure, while the method (2) were restricted to the 2D case.
Chapter I - Observed Ground Motions during the 1980 Off-Izu Peninsula Earthquake
Chapter II - Waveform Simulation of Surface Waves in the Kanto Basin by the Gaussian Beam Method
Chapter III - The Effect of Sharp Boundary on the Duration of Seismic Waves
Chapter IV - 3D Seismic Response of the Kanto Basin by the BEM Based on the Greens Function of Layered Half-space and the Normal Mode Solution
Chapter V - Conclusions
Note: Chapters I and II are chiefly written by Kenichi Kato, Chapter III by Xiaofei Chen, and Chapter IV by Yoshiaki Hisada.
Part 1: Investigation of Two-Dimensional Wave Propagation in the Kanto Plain
Douglas S. Dreger and Donald V. Helmberger
and Part 2: Simulation of Long-Period Ground Motions for the 1923 Kanto Earthquake (M=8)
Minoru Takeo and Hiroo Kanamori
Several two-dimensional and one-dimensional velocity models were tested against data recorded at IRO, YKO and TKY JMA-52 sites for the 1980 Izu-Hanto-Toho-Oki earthquake to try to better understand the effects of wave propagation through the Kanto plain. The results of this analysis indicate that it is possible to explain some of the late arriving, large amplitude surface waves observed at YKO and TKY with two dimensional models. The best models include a basin structure both in the Kanto plain and the Sagami bay region (south-west of YKO). A point-source approximation was made for the earthquake and it was found that this representation causes the tangential component to be nodal, in contrast to what is observed in the data. Considering a finite source could improve the fit to the tangential components, but three-dimensional structures could also increase the amplitude of the tangential component.
Also listed as Report No.: 1992.8