Papers in Meteorology and Geophysics

We developed an X-window program for estimating seismic moments and fault parameters of small earthquakes by waveform fitting. The graphical interface was adopted for operational convenience in routine processing. Manual parameter searching was implemented in the tool as well as waveform inversion. Body wave data recorded at stations within 100 kilometers of hypocenters are compared with synthetic records. Frequency components slightly lower than the corner frequency are used to estimate source parameters. Time for calculating synthetic records was reduced by preparing Green's functions beforehand. Source parameters were estimated by the tool for the earthquakes of Mw from 3.5 to 6.1 in the southern Kanto area.

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The dispersion effect is not negligible in the numerical simulation of far-field tsunamis propagating through deep oceans. Imamura et al. (1990) introduced a technique in which the discretization error in the finite difference equation of the linear long wave equation was used to approximate the physical dispersion term. The technique is widely accepted to compute trans-Pacific tsunamis caused by great earthquakes (Mw> 8). However, the technique has never been applied to compute tsunamis caused by smaller earthquakes (Mw< 7) because the approximation may break down. In order to compute the tsunami caused by the 1998 Papua New Guinea earthquake (Mw 7.1), we numerically solve the linear Boussinesq equation, which includes the physical dispersion term, using an implicit scheme. For comparison, we also compute the tsunami using Imamura's technique. The comparison of the computed waveforms at the ocean bottom pressure gauge off Boso (BS3-OBP) from the two numerical simulations indicates that the linear Boussinesq equation should be used to simulate the tsunami waveform more accurately, especially the later phase of tsunami waveforms. We also found that the observed tsunami that was originally generated by the 1998 Papua New Guinea earthquake and recorded at BS3-OBP was a ridge wave. The ridge wave was enhanced by the shallow water region around the Izu-Bonin Islands.

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