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Accurate and rapid determination of the hypocenter and magnitude is useful for an initial decision on emergency measures when large earthquakes occur. Quick determination using P wave data, which propagates faster than the principal S waves, enables an alert to be issued before a strong shock, which consequently contributes to the mitigation of hazard and socio economic damage. This project aims to develop a system that can provide real-time seismic information after the occurrence of an earthquake by processing the data from the nationwide seismographs network such as Hi-net using new algorism.  Conceptual diagram of the method for determining hypocenter using P arrival and not-arriving data When two observation sites detect P waves, the range of the hypocenter can be limited somewhere within the enclosed area in the green line (on the hyperboloid in semi-infinite medium), since the arrival time at the sites differs. At the same time, from the information that P waves have not arrived at other sites, the hypocenter can be limited within the area enclosed by the red line. From these data, it is possible to confine the location of the hypocenter on the blue line.  The next figure shows the seismic records at the time of the Tottori-ken Seibu earthquake (SW of Tottori Earthquake). The vertical lines show the time when the hypocenter was automatically determined. Each time a P wave reaches another site, the hypocenter is re-determined, giving more accurate results. Except for sites very near the epicenter, the hypocenter parameters are automatically determined before seismic waves arrive at most of the sites. Issuing earthquake warnings at this point will help damage to be mitigated.
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 National Research Institute
for Earth Science and Disaster Prevention |
) estimated by
the conventional manual method
