ONE MINUTE AFTER - STRONG-MOTION MAP, EFFECTIVE EPICENTER, AND EFFECTIVE MAGNITUDE

This article reports the recent progress on real-time seismic monitori ng in Taiwan, particularly the real-time strong-motion monitoring by t he Taiwan Central Weather Bureau's telemetered seismic network (CWBSN) , which is presently aiming at rapid reporting immediately after a lar ge earthquake occurrence. If rapid reporting can be achieved before th e arrival of the strong shaking, earthquake early warning will become possible. CWBSN has achieved the generation of the intensity map, epic enter, and magnitude within 1 min of the occurrence of a large earthqu ake. Both rapid reporting and early warning are principally applied to large (M much greater than 5) events; the requirement of on-scale wav eform recording prompted CWBSN in 1995 to integrate strong-motion sens ors (e.g., force-balance accelerometers) into its telemetered seismic monitoring system. Time-domain recursive processing is applied to the multi-channel incoming seismic signals by a group of networked persona l computers to generate the intensity map. From the isoseismal contour s, an effective epicenter is immediately identified that resides in th e middle of the largest (usually the 100-gal) contour curve of the int ensity map. An effective magnitude is also defined that can be derived immediately from the surface area covered by the largest (usually the 100-gal) contour curve. For a large event with a finite rupture surfa ce, the epicenter and magnitude so derived are more adequate estimates of the source location and of the strength of destruction. The effect ive epicenter gives the center of the damage area; it stands in contra st with the conventional epicenter location, which only gives the init ial point of rupture nucleation. The effective magnitude reflects more closely the earthquake damage potential, instead of the classical mag nitude definition that emphasizes the total energy release. The CWBSN has achieved in obtaining the above crucial source information well wi thin I min. This time can further be reduced to better than 30 sec, as illustrated by the example in this article, showing that earth quake early warning is indeed an achievable goal. The rapid reporting and ea rly warning information is electronically transmitted to users to allo w rapid response actions, with or without further human intervention.