[SIO GP Seminars] FRIDAY 3PM: Seth Moran, CVO, USGS

[Robin Matoza]

Geophysics Seminar Announcement-

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Friday, May 4th, 3:00 PM
   (refreshments served at 2:45 PM)
   Munk Conference Room

Seth Moran, Cascades Volcano Observatory (CVO), USGS

"Seismogenesis during the 2004-2007 eruption of Mount St. Helens"

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ABSTRACT
The ongoing eruption of Mount St. Helens (MSH) has been highly  
seismogenic but remarkably benign, with only six explosions  
accompanying the continuous extrusion of a lava dome. The lack of  
explosions, coupled with development of platforms for remotely  
deploying instruments, has made it reasonably safe for scientists to  
deploy seismometers, cameras, GPS receivers, tiltmeters, and other  
instruments at short distances from the vent, in some cases as close  
as 100m. One phenomenon that has motivated much research is the  
extrusion of a fault-gouge-covered lava dome, a fact that has lead to  
speculation that much of the seismicity accompanying the eruption has  
been generated by stick-slip processes along the conduit walls  
(Iverson and others, 2006; Harrington and Brodsky, 2007). This  
speculation has been bolstered by observations of earthquakes  
occurring in conjunction with 10-minute-long tilt events, suggesting  
that at least a subset are responding to stresses caused by  
extrusion. Deployments of time-lapse cameras at various locations  
within 500m of the vent have been primarily designed to capture sub- 
cm-level motion of the extruding lava dome to investigate the  
relationship between dome motion and earthquake occurrence. The close- 
in cameras have so far failed to capture individual slips, however,  
and recent results from a temporary broadband deployment indicate  
that a significant fraction of MSH earthquakes may be generated by a  
collapsing crack (Waite and others, 2007). However, more distant  
cameras placed on the crater rim have recorded whole-scale slumping  
of the dome following larger earthquakes and, in one remarkable  
several-day-long sequence, the sticking-and-slipping of a large  
segment of the lava dome in association with several M > 3  
earthquakes (this sequence motivated an earthquake prediction that  
proved successful, although the methodology is unfortunately not  
exportable outside the MSH crater). Thus at this stage there is no  
single model that can adequately relate all geophysical and geologic  
observations to the problem of seismogenesis at MSH.


References:

Iverson, R.M., Dzurisin, D., Gardner, C.A., Gerlach, T.M., Lahusen,  
R.G., Lisowski, M., Major, J.J., Malone, S.D., Messerich, J.A.,  
Moran, S.C., Pallister, J.S., Qamar, A.I., Schilling, S.P., and  
Vallance, J.W., 2006, Dynamics of seismogenic volcanic extrusion at  
Mount St. Helens in 2004-2005: Nature, v. 444, p. 439-443.

Harrington, R.M., and Brodsky, E.E., 2007, Volcanic hybrid  
earthquakes that are brittle-failure events: Geophysical Research  
Letters, v. 34, no. L06308, p. 4.

Waite, G.P., Chouet, B., and Dawson, P.B., 2007, Eruption dynamics at  
Mount St. Helens imaged from inversion of broadband waveforms:  
Interaction of the shallow magmatic and hydrothermal systems (abs),  
Seismological Research Letters, v. 78 (2), p. 245..
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