Bulletin of the Seismological Society of America; August 2007; v. 97; no. 4;
p. 1221-1232; DOI: 10.1785/0120060080
© 2007 Seismological Society of America
Macroseismic Study of the Mw 7.5 21 January 2003 Colima, México, Across-Trench Earthquake
Vyacheslav M. Zobin1 and
Jaime A. Pizano-Silva1
1 Observatorio Vulcanológico
Universidad de Colima
Colima, 28045, México
vzobin{at}cgic.ucol.mx
A field investigation of residential house damage in 83 localities of the
Occidental part of México allowed construction of a macroseismic map of
the moment magnitude 7.5 2003 Colima earthquake. The 12-grade modified Mercalli
(MM) scale and the 7-grade damage scale of
Whitman (1988) were used for
estimating the earthquake intensities. The macroseismic effects of this
earthquake were unexpected for the Occidental part of México. The
earthquake occurred within the across-trench structure of the El Gordo Graben
and was characterized by the down-dip across- trench directivity of its rupture,
as reconstructed from seismic-waveform modeling. It was a reason for the severe
damage to buildings in the localities situated at distances where usual
along-trench rupturing subduction earthquakes of the same magnitude do not
produce any significant damage. The macroseismic map of the 2003 earthquake
shows that the narrow (30 km wide) MM VII zone was elongated (up to
60 km) in the northeast direction toward the continental part of Colima
state. As a result, the intensity in Colima city was 1.5 grades larger than
would be expected for this magnitude according to the proposed attenuation of
intensity with distance relationship for earthquakes from the Mexican subduction
zone.
Copyright © 2009 by Seismological Society of America