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Revised world seismicity catalog (1950-1997) for strong (Ms 6) shallow (h 70 km) earthquakes

Department of Earth Sciences Simón Bolívar University, Caracas, Venezuela

Abstract

Using the standard earthquake catalogs provided by the International Seismological Centre (ISC), its predecessor the International Seismological Summary (ISS), and the National Earthquake Information Center (NEIC), I analyze the worldwide consistency of teleseismic reporting, completeness of the seismicity record, and homogeneity of magnitude determination, for strong shallow earthquakes (surface-wave magnitude, Ms 6; depth, h 70 km) for the period 1950 to 1997. Under the postulates that the rate of earthquake occurrence for the entire world is constant on a time scale of decades and that well after the installation of the World-Wide Standardized Seismograph Network in the middle 1960s the earthquake catalog for strong (Ms 6) shocks is complete, and the seismicity rates are typical of all periods in the century, we find that, due to the use of different formulations and criteria to calculate the parameter magnitude, the Ms of moderate (6 Ms < 7) events during the period 1950 to 1963 was systematically overestimated by as much as 0.5 magnitude unit, relative to the Ms assigned to shocks occurring after 1963. When this correction is taken into account, the new catalog of events with Ms (corrected) 6 in the period 1950 to 1997 becomes largely homogeneous in Ms. Under the foregoing postulates, this new catalog is shown to list nearly all and only the strong shocks [Ms (corrected) 6; h 70 km] that occurred in the Earth during the period, a notable exception being the time span from 1964 to 1968. The revised catalog, including the scalar moment and moment magnitude for each event, is listed on the worldwide web page http://www.ldc.usb.ve/~ojperez/catalog.