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 period2000-2018 with the goal of determining their moment tensor solutions. Because oflarge number of events, we automatize the process based on a set criteria. Usingepicentral location and magnitude of each earthquake reported by the SSN, a setof 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. Toexpedite calculations a pre-computed library of Green functions is used. Through a linear inversion, for three-station combinations, the observed data andthe corresponding Green functions are used to determine the seismic momenttensor (with null isotropic component). To reduce a possible bias related to thestation distribution, each solution is weightened as a function of the azimuthalcoverage of the stations used. After the automatic process solutions of only8,000 earthquakes could be obtained; other events were rejected because ofincomplete length of the data segment and/or its integrity. The solution quality is measured by the variance reduction value (VR). Astatistical analysis of quality allows us to establish a VR value of ≥ 50% asreasonable 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 matchesthe areas of higher density of seismologic stations, and the limits of tectonicplates as well. A comparison between the catalog here obtained and the GlobalCentroid Moment Tensor (GCMT) catalog shows similarities. However, the magnitudereported in our catalog is systematically smaller than those reported byGCMT. 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 ofthis kind is presented.