Nowcast earthquake information and its application to early earthquake alarm system

摘要

The earthquake disaster may be reduced if the information on the arrival and the intensity of principal motion of a large earthquake is issued before its arrival. The Japan Meteorological Agency (JMA) has been planning to issue this kind of information, called the Nowcast earthquake information, in the near future. This paper describes the outline of this project, and presents the basic idea and the prototype system of the application of this information to an early earthquake alarm system of railways. In the paper, we present new method of estimating the hypocenter and magnitude in a short time after the detection of P waves, which are called the B-DELTA method, territory method and grid search method. The B-DELTA method uses seismic records of a single observation station to estimate the epicenter. The territory method uses the one-or two-station records and the grid search method uses the P-wave data of more than two stations. The estimation of the hypocenter becomes more accurate, but it takes more time in order of the B-DELTA method, territory method and grid search method. JMA has developed the data processing system in cooperation with the Railway Technical Research Institute and is planning to test the system by issuing the information experimentally in 2003.