Real-time earthquake magnitude assessment from statistical analysis of strong-motion data

Gunnar Grecksch1, Hans-Joachim Kümpel2
University of Bonn, Geological Institute, Section of Applied Geophysics, Nussallee 8, D-53115 Bonn, Germany.
Tel. : +49-228-739308, Fax: +49-228-732584,
E-mail: 1grecksch@geo.uni-bonn.de, 2kuempel@geo.uni-bonn.de

To provide a short-term warning of ground shaking from strong earthquakes, the source parameters have to be determined rapidly and sufficiently reliable. To mitigate the damage, various actions could be initiated automatically, but only if the seismic source parameters are determined rapidly. Location and origin time of an earthquake can be assessed rather well. One major problem of an early warning system seems to be the real-time estimation of the earthquake’s size. Based on a data set provided by the U.S. Geological Survey in 1992, we investigated digitised strong-motion accelerograms from nearly 250 earthquakes in North- and Central America between 1940 and 1986 to find out, whether their initial portions reflect the size of the ongoing earthquake. Applying conventional methods of time series analysis we calculated various signal parameters from the first second of each accelerogram and describe their variability in relation to epicentral distance, magnitude and peak acceleration. Multilinear regression analyses, based on an empirical relation, show that the magnitude of an ongoing earthquake can be predicted from the first second of a single accelerogram within ±1.36 magnitude units with 95% statistical probability. The uncertainty can be reduced to about ± 0.5 magnitude units by computing an average magnitude estimate from initial portions of a larger number of accelerograms recorded by a dense network of seismic stations.