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Absolute and relative locations of earthquakes at Mount St. Helens, Washington, using continuous data: implications for magmatic processes: Chapter 4 in A volcano rekindled: the renewed eruption of Mount St. Helens, 2004-2006

Professional Paper 1750-4

This report is Chapter 4 in A volcano rekindled: the renewed eruption of Mount St. Helens, 2004-2006. For more information, see: Professional Paper 1750
By:
, ,
Edited by:
David R. Sherrod, William E. Scott, Peter H. Stauffer

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Abstract

This study uses a combination of absolute and relative locations from earthquake multiplets to investigate the seismicity associated with the eruptive sequence at Mount St. Helens between September 23, 2004, and November 20, 2004. Multiplets, a prominent feature of seismicity during this time period, occurred as volcano-tectonic, hybrid, and low-frequency earthquakes spanning a large range of magnitudes and lifespans. Absolute locations were improved through the use of a new one-dimensional velocity model with excellent shallow constraints on P-wave velocities. We used jackknife tests to minimize possible biases in absolute and relative locations resulting from station outages and changing station configurations. In this paper, we show that earthquake hypocenters shallowed before the October 1 explosion along a north-dipping structure under the 1980-86 dome. Relative relocations of multiplets during the initial seismic unrest and ensuing eruption showed rather small source volumes before the October 1 explosion and larger tabular source volumes after October 5. All multiplets possess absolute locations very close to each other. However, the highly dissimilar waveforms displayed by each of the multiplets analyzed suggest that different sources and mechanisms were present within a very small source volume. We suggest that multiplets were related to pressurization of the conduit system that produced a stationary source that was highly stable over long time periods. On the basis of their response to explosions occurring in October 2004, earthquakes not associated with multiplets also appeared to be pressure dependent. The pressure source for these earthquakes appeared, however, to be different from the pressure source of the multiplets.

Geospatial Extents

Additional Publication Details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Absolute and relative locations of earthquakes at Mount St. Helens, Washington, using continuous data: implications for magmatic processes: Chapter 4 in A volcano rekindled: the renewed eruption of Mount St. Helens, 2004-2006
Series title:
Professional Paper
Series number:
1750-4
Year Published:
2008
Language:
English
Publisher:
U.S. Geological Survey
Publisher location:
Reston, VA
Contributing office(s):
Volcano Hazards Program
Description:
25 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:
71
Last page:
95
Number of Pages:
25
Country:
United States
State:
Washington
Other Geospatial:
Mount St. Helens