STATISTICAL-ANALYSIS OF STRONG-MOTION ACCELEROGRAMS AND ITS APPLICATION TO EARTHQUAKE EARLY-WARNING SYSTEMS

In view of increasing damage due to earthquakes, and the current probl ems of earthquake prediction, real-time warning of strong ground motio n is attracting more interest. In principle, it allows short-term warn ing of earthquakes while they are occurring. With warning times of up to tens of seconds it is possible to send alerts to potential areas of strong shaking before the arrival of the seismic waves and to mitigat e the damage, but only if the seismic source parameters are determined rapidly. The major problem of an early-warning system is the real-tim e estimation of the earthquake's size. We investigated digitized stron g-motion accelerograms from 244 earthquakes that occurred in North and Central America between 1940 and 1986 to find out whether their initi al portions reflected the size of the ongoing earthquake. Applying con ventional methods of time-series analyses we calculate appropriate sig nal parameters and describe their uncertainties in relation to the mag nitude and epicentral distance. The study reveals that the magnitude o f an earthquake can be predicted from the first second of a single acc elerogram within +/- 1.36 magnitude units. The uncertainty can be redu ced to about +/-0.5 magnitude units if a larger number (greater than o r equal to 8) of accelerograms are available, which requires a dense n etwork of seismic stations in areas of high seismic risk.