The 2003 Armeria, Mexico Earthquake (Mw 7.4): Mainshock and Early Aftershocks

Abstract

On 22 January 2003 an earthquake of Mw 7.4 occurred off the Pacific coast of the state of Colima, Mexico, near the town of Armeria. The damage pattern and effects of this earthquake in the nearby areas of Colima and Jalisco were different and more severe than those from recent previous big earthquakes in this region. The mainshock and its aftershocks were recorded by local seismic networks. The Jalisco region is one of the most active seismic regions in Mexico and is characterized by complex seismotectonics. The largest earthquake ( M 8.2) of the twentieth century in Mexico occurred in 1932 in this region, followed fifteen days later by another large event ( M 7.8). Singh et al. (1985) studied these earthquakes and concluded that their composite rupture area extended along the whole coast of Jalisco and Colima; they also proposed a recurrence time of 77 years for this region. In 1995, a Mw 8.0 earthquake occurred near Manzanillo but did not rupture the whole 1932 rupture area, leaving unruptured regions in the north, the Vallarta gap, and to the south, the Colima gap (Figure 1). In spite of the occurrence of these large earthquakes and the high hazard associated with the seismic activity in the region, only one permanent station—at Chamela (CJIG), from the Mexican Seismic Network (SSN)—and the Red Sismica Telemetrica de Colima (RESCO)—an analog, 1 Hz vertical sensor network—were sited on the Colima graben to monitor seismicity in that area and at the Colima volcano (Figure 1). By the end of 2001 the Jalisco Civil Defense and the Centro de Sismologia y Volcanologia de Occidente had begun to deploy the Red Sismica Digital Telemetrica de Jalisco (RESJAL) (Nunez-Cornu et al. , 2001). Currently, RESJAL operates six telemetered and five autonomous stations, all with 24-bit data loggers and …