Focal parameters, depth estimation, and plane selection of the worldwide shallow seismicity with M s ! 7.0 for the period – 1900– 1976

Abstract

A worldwide seismic catalog of source parameters is an important tool in many geophysical studies. Such a kind of database is available only since 1977 with the CMT catalog. The main goal of this paper is to compile a similar catalog for the time period 1900–1976 estimating the focal parameters of shallow seismicity (depth 70 km) with Ms ! 7.0 (607 events). In particular, this new catalog (FM0076) contains strike, dip, rake, and depth estimations for 588 earthquakes in the period 1900–1976. At each estimate two reliability flags are assigned. The first is linked to the availability of data, and the second is given by comparing focal mechanism estimations and the tectonics of the epicentral area. The estimation procedure is based on the knowledge of the moment tensor of shallow earthquakes after 1977. From these data, the new concept of Weighted Cumulative Moment Tensor (WCMT), which represents such a kind of moment tensor for a mean earthquake in the epicentral area, leads to estimate the focal parameters. The estimation method is also tested by comparing out our data set for the period 1977–1989 with the CMT one (91 events). This comparison reveals a good agreement between the two methods and confirms the reliability of the catalog FM0076.