Local overturn of active and non-active seismic zones as a precursor of large earthquakes in the Lesser Antillean Arc
The effect of short-term activation of locally less active seismic zones simultaneously with relative quiescence of locally more active zones before strong earthquakes has been studied in the region of the Lesser Antillean Arc. This precursory pattern has been found earlier in Southern California. It takes place in the epicentral area several months before strong earthquakes. On the basis of this effect, a new preliminary prediction algorithm has been developed. The algorithm determines regions of 100 km × 100 km (approximately) in which the probability of the occurrence of strong earthquakes is increased for the period of 1 year. In the present work the algorithm is improved. A new version of the algorithm is applied retrospectively in the Lesser Antillean Arc. The results for the period 1984-June 1995 are as follows. Of the seven earthquakes with M ≥ 5, five have occurred in time-space areas of increased probability (TSIP) for strong earthquakes. The time-space volume of TSIPs is 8% of the total considered volume. Two TSIPs are false alarms. The precursory pattern can be explained by the break-up of asperities, which is reflected in activation of less active areas, corresponding to the asperities, on the background of the larger-scale quiescence.