Moment Tensor Catalog for Mexican Earthquakes: Almost Two Decades of Seismicity

Abstract

In this work we used waveforms and the catalog of National Seismological Service (SSN) to analyze more than 20,000 events with M>= 4.0 for the period 2000-2018 with the goal of determining their moment tensor solutions. Because of large number of events, we automatize the process based on a set criteria. Using epicentral location and magnitude of each earthquake reported by the SSN, a set of valid stations to be used for the moment solution, the length of time series, and the filter band for data and synthetics are automatically selected. To expedite calculations a pre-computed library of Green functions is used. Through a linear inversion, for three-station combinations, the observed data and the corresponding Green functions are used to determine the seismic moment tensor (with null isotropic component). To reduce a possible bias related to the station distribution, each solution is weightened as a function of the azimuthal coverage of the stations used. After the automatic process solutions of only 8,000 earthquakes could be obtained; other events were rejected because of incomplete length of the data segment and/or its integrity. The solution quality is measured by the variance reduction value (VR). A statistical analysis of quality allows us to establish a VR value of ? 50% as reasonable threshold for reliable solutions. With these criteria a catalog of ~ 1,500 events have been compiled, including some small events (Mw < 4.0). There is evidence that show that the location of the well-solved events matches the areas of higher density of seismologic stations, and the limits of tectonic plates as well. A comparison between the catalog here obtained and the Global Centroid Moment Tensor (GCMT) catalog shows similarities. However, the magnitude reported in our catalog is systematically smaller than those reported by GCMT. The moment tensor solution catalog is available online in a public database (132.248.6.13/~cmt). This work is the first in Mexico in which a database of this kind is presented.