Since tide-gauge records are available as far back as the 1850s, use of them will provide unique and important information on long-term global seismicity.Ībe, K.: 1979, Size of great earthquakes of 1837–1974 inferred from tsunami data, J. Such estimates are possible only using tsunami records. The 1944 Tonankai and 1946 Nankaido earthquakes are examined as examples of old events, and slip distributions are obtained. For old earthquakes, many tide gauge records exist with quality comparable to modern records, while there are only a few good quality seismic records.
Waveform modeling of this event shows that part of the abnormal size of this tsunami is due to the propagation effect along the shallow ridge system.
The 1984 Torishima earthquake caused unusually large tsunamis for its earthquake size. The use of tsunami waveforms is more useful for the study of unusual or old earthquakes. Both events show nonuniform slip distributions very similar to those obtained from seismic wave analyses. Two recent earthquakes, the 1968 Tokachi-oki and 1983 Japan Sea earthquakes, are examined for calibration purposes. This method has been applied to several earthquakes around Japan.
Using waveform inversion techniques, we can estimate the spatial distribution of coseismic slip on the fault plane from tsunami waveforms. The tsunami propagation can be accurately evaluated, since bathymetry is much better known than seismic velocity structure in the Earth. Tsunami waveforms recorded on tide gauges, like seismic waves recorded on seismograms, can be used to study earthquake source processes.
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