SEISMIC EVOLUTION OF THE 1989-1990 ERUPTION SEQUENCE OF REDOUBT VOLCANO, ALASKA

Citation
Ja. Power et al., SEISMIC EVOLUTION OF THE 1989-1990 ERUPTION SEQUENCE OF REDOUBT VOLCANO, ALASKA, Journal of volcanology and geothermal research, 62(1-4), 1994, pp. 69-94
Citations number
40
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Geology
ISSN journal
0377-0273
Volume
62
Issue
1-4
Year of publication
1994
Pages
69 - 94
Database
ISI
SICI code
0377-0273(1994)62:1-4<69:SEOT1E>2.0.ZU;2-N
Abstract
Redoubt Volcano in south-central Alaska erupted between December 1989 and June 1990 in a sequence of events characterized by large tephra er uptions, pyroclastic flows, lahars and debris flows, and episodes of d ome growth. The eruption was monitored by a network of five to nine se ismic stations located 1 to 22 km from the summit crater. Notable feat ures of the eruption seismicity include :(1) small long-period events beginning in September 1989 which increased slowly in number during No vember and early December; (2) an intense swarm of long-period events which preceded the initial eruptions on December 14 by 23 hours; (3) s hallow swarms (0 to 3 km) of volcano-tectonic events following each er uption on December 15; (4) a persistent cluster of deep (6 to 10 km) v olcano-tectonic earthquakes initiated by the eruptions on December 15, which continued throughout and beyond the eruption; (5) an intense sw arm of long-period events which preceded the eruptions on January 2; a nd (6) nine additional intervals of increased long-period seismicity e ach of which preceded a tephra eruption. Hypocenters of volcano-tecton ic earthquakes suggest the presence of a magma source region at 6-10 k m depth. Earthquakes at these depths were initiated by the tephra erup tions on December 15 and likely represent the readjustment of stresses in the country rock associated with the removal of magma from these d epths. The locations and time-history of these earthquakes coupled wit h the eruptive behavior of the volcano suggest this region was the sou rce of most of the erupted material during the 1989-1990 eruption. Thi s source region appears to be connected to the surface by a narrow pip e-like conduit as inferred from the hypocenters of volcano-tectonic ea rthquakes. Concentrations of shallow volcano-tectonic earthquakes foll owed each of the tephra eruptions on December 15; these shocks may rep resent stress readjustment in the wall rock related to the removal of magma and volatiles at these depths. This shallow zone was the source area of the majority of long-period seismicity through the remainder o f the eruption. The long-period seismicity likely reflects the pressur ization of the shallow portions of the magmatic system.