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
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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, Md
>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 (Md
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.
Study Area
| 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 |
| Google Analytic Metrics | Metrics page |