Source mechanisms of persistent shallow earthquakes during eruptive and non-eruptive periods between 1981 and 2011 at Mount St. Helens, Washington
Journal of Volcanology and Geothermal Research
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Abstract
Shallow seismicity between 0 and 3-km depth has persisted at Mount St. Helens, Washington (MSH) during both eruptive and non-eruptive periods for at least the past thirty years. In this study we investigate the source mechanisms of shallow volcano-tectonic (VT) earthquakes at MSH by calculating high-quality hypocenter locations and fault plane solutions (FPS) for all VT events recorded during two eruptive periods (1981–1986 and 2004–2008) and two non-eruptive periods (1987–2004 and 2008–2011). FPS show a mixture of normal, reverse, and strike-slip faulting during all periods, with a sharp increase in strike-slip faulting observed in 1987–1997 and an increase in normal faulting in 1998–2004. FPS P-axis orientations show a ~ 90° rotation with respect to regional σ1 (N23°E) during 1981–1986 and 2004–2008, bimodal orientations (~ N-S and ~ E-W) during 1987–2004, and bimodal orientations at ~ N-E and ~ S-W from 2008–2011. We interpret these orientations to likely be due to pressurization accompanying the shallow intrusion and subsequent eruption of magma as domes during 1981–1986 and 2004–2008 and the buildup of pore pressure beneath a seismogenic volume (located at 0–1 km) with a smaller component due to the buildup of tectonic forces during 1987–2004 and 2008–2011.
Suggested Citation
Lehto, H.L., Roman, D., Moran, S.C., 2013, Source mechanisms of persistent shallow earthquakes during eruptive and non-eruptive periods between 1981 and 2011 at Mount St. Helens, Washington: Journal of Volcanology and Geothermal Research, v. 256, p. 1-15, https://doi.org/10.1016/j.jvolgeores.2013.02.005.
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Source mechanisms of persistent shallow earthquakes during eruptive and non-eruptive periods between 1981 and 2011 at Mount St. Helens, Washington |
| Series title | Journal of Volcanology and Geothermal Research |
| DOI | 10.1016/j.jvolgeores.2013.02.005 |
| Volume | 256 |
| Year Published | 2013 |
| Language | English |
| Publisher | Elsevier |
| Contributing office(s) | Volcano Science Center |
| Description | 15 p. |
| Larger Work Type | Article |
| Larger Work Subtype | Journal Article |
| Larger Work Title | Journal of Volcanology and Geothermal Research |
| First page | 1 |
| Last page | 15 |
| Country | United States |
| State | Washington |
| Other Geospatial | Mount St. Helens |