The October 9, 1995 Colima‐Jalisco, Mexico Earthquake (M_w 8): An aftershock study and a comparison of this earthquake with those of 1932

Abstract

Data from portable seismographs and a permanent local network (called RESCO) are used to locate the aftershocks of the October 9, 1995 Colima‐Jalisco earthquake (Mw 8.0). The maximum dimension of the aftershock area, which is rectangular in shape, is 170 km × 70 km. Our study shows that the mainshock nucleated ∼24 km south of Manzanillo, near the foreshock of October 6, 1995 (Mw 5.8), and propagated ∼130 km to the NW and ∼40 km to SE. The aftershock area lies offshore and is oriented parallel to the coast. The observed subsidence of the coast is a consequence of this offshore rupture area. The aftershocks reach unusually close to the trench (within 20 km). This may be due to lack of sediments with high pore pressure at shallow depth. There are some similarities between this earthquake and the two great earthquakes of 1932 (3 June, Ms 8.1; 18 June, Ms 7.8) which occurred in this region. In both cases the aftershocks were located offshore and the coastline subsided. The sum of seismic moments and the rupture lengths of the 1932 events (1.8×1021 N‐m and 280 km, respectively), however, were greater than the 1995 earthquake. Also a comparison of seismograms of 1932 and 1995 earthquakes show great differences. It seems that the 1995 event is not a repeat of either June 3 or June 18, 1932 earthquakes.

Constraints on Jalisco Block Motion and Tectonics of the Guadalajara Triple Junction from 1998–2001 Campaign GPS Data

“…MELBOURNE et al, 1997;PACHECO et al, 1997;YAGI et al, 2004). After the 1995 earthquake, GPS stations within 200 km of the rupture zone exhibited rapidly decaying transient deformation attributable to a combination of afterslip focused along areas of the subduction interface downdip from the rupture zone and viscoelastic flow of the upper mantle due to the elevated stresses from the 1995 earthquake (HUTTON et al, 2001;MARQUEZ-AZUA et al, 2002;MELBOURNE et al, 2002).…”

Source Characteristics of the 22 January 2003 M w = 7.5 Tecomán, Mexico, Earthquake: New Insights

“…The 22 January 2003 (M w = 7.5) Tecomán earthquake occurred between the rupture areas of the 9 October 1995 (M w = 8.0) Colima-Jalisco earthquake and the 30 January 1973 (M w = 7.6) Colima earthquake (see Fig. 1b) (REYES et al, 1979;PACHECO et al, 1997). The Tecomán earthquake was located by the University of Colima at 18.…”

“…Light dashed lines show the rupture area of the 1932 (M w = 8.2) earthquake (SINGH et al, 1985). Heavy dashed line is the rupture area of the 1995 (M w = 8.0) earthquake (PACHECO et al, 1997). Also shown are the aftershock areas of the 1973 (M w = 7.3) and 1986 (1980) Ensenada).…”

The elusive Rivera-Cocos plate boundary: not diffuse

“…The canyons' locations correspond to slab surface depressions: maximum depression occurs in the Armería canyon and minimum at Manzanillo canyon. Epicentral locations of the 1932 main shock (yellow diamonds) and aftershocks (purple) are shown, as well as the main shock and aftershocks of the 1995 earthquake (blue, inverted triangles, Pacheco et al 1997). The magenta square is the main shock of the 2003 Tecomán earthquake.…”

“…Singh et al (1985) already noted that for that event the break-up region occurred mostly in the Rivera plate; thus, the epicentral alignment shown here likely occurred on the margin of that plate. The second earthquake occurred in 1995 with magnitude M W 8.0 (Corboulex et al 1997;Pacheco et al 1997). In Figure 10b we plot the corresponding main shock and the aftershocks.…”