Boletín de la Sociedad Geológica Mexicana


Volumen 62, núm. 2, 2010, p. 249-262

http://dx.doi.org/10.18268/BSGM2010v62n2a5

Juan Martín Gómez-González1,*, Carlos Mendoza1, Anthony Sladen2, Marco Guzmán Speziale1

1Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Blvd. Juriquilla 3001, 76230 Querétaro,Qro., México.
2 Tectonics Observatory, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA.

*This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

We analyze the Tecomán, Colima, earthquake (Mw 7.6) of January 22, 2003, one of the major seismic events that has occurred in the Colima-Jalisco region, México, during the last 100 years. We describe its rupture process by a classical waveform modeling of teleseismic body waves. A point source inversion indicates a shallow underthrust event (25 km); its fault plane is defined by a strike of 278°, a dip of 27º, and a rake of 78º. The source time function (STF) has a total duration of about 22 s and shows a relatively simple time history. The main moment release is preceded by a small onset of about 6.6 sec, located 17 km south of the main moment release. This precursor is associated with an initial rupture velocity of about 2.6 km/s. Slight azimuthal variations of relative source time functions (RSTF) indicate a weak directivity, probably produced by a bilateral asymmetrical rupture oriented NNE-SSW. The RSTFs confirm that the Tecomán earthquake is composed of three subevents that mainly ruptured down-dip. A finite line-source analysis along the strike and dip also confirms the orientation of the rupture propagation and shows the wide range of apparent rupture velocities along the fault. The Tecomán earthquake is an interesting case of a well-recorded event, with good quality data, but with results that are poorly constrained, which affects the uncertainty of several parameters, like directivity and hypocenter depth.

Keywords: Body waves, earthquake-source mechanism, fault plane solution, seismology, source time function, waveform analysis.