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Comparative characteristics of the 1997–1998 seismic swarms preceding the November 1998 eruption of Volcán de Colima, México

2002; Elsevier BV; Volume: 117; Issue: 1-2 Linguagem: Inglês

10.1016/s0377-0273(02)00234-2

1872-6097

Vyacheslav M. Zobin, Miguel González Amezcua, G. Á. Reyes Davila, T. Domı́nguez, J.C Cerda Chacón, J Montes Álvarez,

Geological and Geochemical Analysis

The recent eruption of Volcán de Colima, México, began on 20 November 1998 and was preceded by a 12-month period of seismic activity that included five swarms of microearthquakes. The swarm activity occurred mainly within the southern part of Colima Volcanic Complex. We located about 600 events of magnitude Mw from −0.5 to 2.7 within a 50 km2 area including the active crater of Volcán de Colima and the region between it and the Pleistocene volcano Nevado de Colima 5.5 km to the north. The majority of hypocenters within this area did not exceed 5 km depth below sea level (BSL) and were mainly distributed within the volcanic edifices of Volcán de Colima and Nevado de Colima. We investigated the spatial distribution and spectral properties of events that occurred during three main seismic swarms: in November–December 1997, June–July 1998 and October–November 1998. We identified a temporal change in the depths of events from November–December 1997 and June–July 1998 (from 4 km BSL to 4 km above sea level (ASL)) to October–November 1998 (from 0 to 4 km ASL). Two groups of events with mean P-wave corner frequencies of 5 Hz (LF) and 10 Hz (HF) were distinguished. HF events dominated during the first swarm whereas the LF events were dominant during the June–July 1998 swarm. During October–November 1998, the numbers of HF and LF events were comparable, but very low-frequency low-stress drop events disappeared two days before the eruption. We consider the LF events to have resulted from fracturing along two systems of local faults, whereas the HF events could have been produced by dike movement along these same faults. We propose a model for construction of a magma passageway by the opening of two systems of local faults triggered by magma intrusion.