Seismicity associated with renewed dome building at Mount St. Helens, 2004-2005

Seth C. Morgan; Stephen D. Malone; Anthony I. Qamar; Weston A. Thelen; Amy K. Wright; Jacqueline Caplan-Auerbach

doi:10.3133/pp17502

Seismicity associated with renewed dome building at Mount St. Helens, 2004-2005: Chapter 2 in A volcano rekindled: the renewed eruption of Mount St. Helens, 2004-2006

Professional Paper 1750-2

This report is Chapter 2 in A volcano rekindled: the renewed eruption of Mount St. Helens, 2004-2006. For more information, see: Professional Paper 1750

By: Seth C. Morgan, Stephen D. Malone, Anthony I. Qamar, Weston A. Thelen, Amy K. Wright, and Jacqueline Caplan-Auerbach

Edited by: David R. Sherrod, William E. Scott, and Peter H. Stauffer

https://doi.org/10.3133/pp17502

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Abstract

The reawakening of Mount St. Helens after 17 years and 11 months of slumber was heralded by a swarm of shallow (depth <2 km) volcano-tectonic earthquakes on September 23, 2004. After an initial decline on September 25, seismicity rapidly intensified; by September 29, M_d >2 earthquakes were occurring at a rate of ~1 per minute. A gradual transition from volcano-tectonic to hybrid and low-frequency events occurred along with this intensification, a characteristic of many precursory swarms at Mount St. Helens before dome-building eruptions in the 1980s. The first explosion occurred October 1, 2004, 8.5 days after the first earthquakes, and was followed by three other explosions over the next four days. Seismicity declined after each explosion and after two energetic noneruptive tremor episodes on October 2 and 3. Following the last explosion of this series, on October 5, seismicity declined significantly. Over the next ten days seismicity was dominated by several event families; by October 16, spacing between events had become so regular that we dubbed the earthquakes “drumbeats.” Through the end of 2005 seismicity was dominated by these drumbeats, although occasional larger earthquakes (M_d 2.0-3.4) dominated seismic energy release. Over time there were significant variations in drumbeat size, spacing, and spectra that correlated with changes in the style of extrusion at the surface. Changes in drumbeat character did not correspond to variations in magma flux at the conduit, indicating that drumbeat size and spacing may be more a function of the mechanics of extrusion than of the extrusion rate.

Suggested Citation

Morgan, S.C., Malone, S.D., Qamar, A.I., Thelen, W.A., Wright, A.K., Caplan-Auerbach, J., 2008, Seismicity associated with renewed dome building at Mount St. Helens, 2004-2005: U.S. Geological Survey Professional Paper 1750-2, 34 p., https://doi.org/10.3133/pp17502.

ISSN: 2330-7102 (online)

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Additional publication details
Publication type	Report
Publication Subtype	USGS Numbered Series
Title	Seismicity associated with renewed dome building at Mount St. Helens, 2004-2005
Series title	Professional Paper
Series number	1750-2
DOI	10.3133/pp17502
Year Published	2008
Language	English
Publisher	U.S. Geological Survey
Publisher location	Reston, VA
Contributing office(s)	Volcano Hazards Program
Description	34 p.
Larger Work Type	Report
Larger Work Subtype	USGS Numbered Series
Larger Work Title	A volcano rekindled: the renewed eruption of Mount St. Helens, 2004-2006 (Professional Paper 1750)
First page	27
Last page	60
Country	United States
State	Washington
Other Geospatial	Mount St. Helens