On the relevance of the foreshocks in forecasting seismic mainshocks

Abstract

We analyze the usefulness of the foreshocks in forecasting seismic mainshocks. The analysis is based on possible correlations which may exist between foreshocks and mainshocks. Such correlations are expressed by a previously established time-magnitude relationship, which indicates the presence of an abrupt magnitude-decreasing sequence of correlated foreshocks in the proximity of a mainshock. By fitting this formula, we are able to derive the occurrence time of a possible mainshock. Also, we can estimate the magnitude of the mainshock, providing we know the parameters of the background seismicity of the seismic region. We report here on the application of this procedure to three Vrancea (Romania) mainshocks, the l’Aquila (Italy), Yangbi (Yunnan, China) and Izmit (Turkey) earthquakes. The limitations of the procedure are discussed. Also, a discussion is included regarding the so-called temporal variability of the Gutenberg-Richter parameter in the proximity of a mainshock, as resulting from time-magnitude and time-time correlations.