Kinematic source analysis of the 2003 Tecomán, México, earthquake (Mw 7.6) using teleseismic body waves

Resumen

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.