Reinvestigation of the 1989 Mammoth Mountain, California seismic swarm and dike intrusion

Hughes, Gwyneth

doi:10.1016/j.jvolgeores.2011.07.001

Cited by 4 publications

(1 citation statement)

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“…The upward movement triggered large amounts of trapped CO 2 gas to leak through the paths provided by the fault zones to the surface. Hughes (2011) incorporated the 1-D earthquake relocations by Prejean et al (2003) and an infl ation model to constrain the size of the intruded dike. The Hughes (2011) model shows preference for a shallower dike than the one fi xed at 9 km depth when allowing the dike's vertical extent to vary over the entire upper crust, although the resulting overpressure is unrealistically high.…”

Section: Discussionmentioning

confidence: 99%

Seismic investigation of magmatic unrest beneath Mammoth Mountain, California, USA

Lin

2013

Geology

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I present a reinvestigation of the seismic activity during an 11-mo-long seismic swarm between 1989 and 1990 beneath Mammoth Mountain in eastern California (United States). This swarm, believed to be the result of a shallow intrusion of magma beneath Mammoth Mountain, was followed by the emission of magmatic CO 2 gas, resulting in tree die-off in 1990 and posing a signifi cant human health risk around Mammoth Mountain. In this study, I apply a state-of-the-art approach to estimate the ratio of compressional-to shear-wave velocity (Vp/Vs) within similar event clusters using differential times from waveform crosscorrelation. A high-resolution three-dimensional seismic velocity model and a precise earthquake location catalog are obtained to complement the analysis of the in situ Vp/Vs ratios. The majority of the relocated seismicity below sea level is distributed in an anomalous body with low Vp and high Vp/Vs, consistent with the seismic expression of the magma body that triggered the seismic swarm. Abrupt changes in Vp/Vs ratios, with lower values for the shallow depths, are observed near sea level, indicating the source of the 1989 CO 2 fl ux is a shallow CO 2 reservoir instead of the hypothesized basaltic magma at mid-crustal depths of 10-25 km. From sea level to the surface, low Vp/Vs ratios in a near-vertical zone suggest involvement of fl uid in the upward-migration of the seismicity.

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Section: Discussionmentioning

confidence: 99%