Study of magnitudes, seismicity, and earthquake detectability using a global network

Abstract

Abstract Based on 10 yr of observations reported in the International Seismological Centre bulletins (1971-1980), m b magnitudes for about 70,000 earthquakes have been recomputed using a maximum-likelihood estimation technique. Reportings from a network of 115 globally distributed stations were used in these calculations. Comparison to conventional m b estimates show that the network magnitude bias problem is quite significant at low and intermediate magnitudes. Recurrence statistics based on the revised m b estimates give b values consistent with those obtained from LASA and NORSAR data, and indicate that the number of earthquakes worldwide of m b ≧ 4.0 averages about 7,500 annually. This number is much lower than previous estimates. The teleseismic detection capability of the network (requiring at least four detecting stations) has been evaluated based on recurrence statistics. The estimated 90 per cent incremental m b threshold ranges from 3.9 to 4.5 in the northern hemisphere and from 4.2 to 4.8 in the southern hemisphere. This is consistent with results obtained by the “Networth” approach.