[Geysers] Seismic Activity

[Randall Marrett]

I'm not a seismologist and I don't know specific details about this 
swarm, but....

The most common earthquake swarm follows on the heels of a larger 
earthquake, in the form of aftershocks.  Swarms without a main shock 
commonly occur in areas of active volcanism, and are thought to be a 
consequence of magma movement.  The movement can be sudden flow of 
magma into a crack, resulting in a dike.  The magma movement 
alternatively can induce indirect deformation of rock surrounding a 
larger magma body, such as a magma chamber.  With large enough quakes 
from dike inflation, the interpretation can be corroborated by focal 
mechanisms (the pattern of seismic energy radiation is different for 
shear motion along a fault vs opening motion along a dike).

No doubt, Bob Smith of Univ Utah could provide more authoritative 
answers.  He's a seismologist, and has been working on Yellowstone 
for decades.

http://www.seis.utah.edu/EQCENTER/PRESS/yell_press.htm#12292008


At 8:00 AM -0800 12/30/08, Jack Ashe wrote:
>Recent reports in the press about small quakes in Yellowstone.
>Does anyone know what the geologist perception of this swarm tends 
>to suggest in Yellowstone? Not looking for prediction, just 
>prevailing interpretation of this sort of seimic activity might mean 
>in Yellowstone-- does it represent small movements along a single 
>fault, multiple fractures at multiple sites, expansion, 
>contraction,shearing parallel to surface, etc.?
>
>Jack Ashe

-- 

Randall Marrett
Professor

Department of Geological Sciences
Jackson School of Geosciences
University of Texas at Austin
1 University Station C1100
Austin, Texas  78712-0254

phone:   (512) 471-2113
fax:      (512) 471-9425
e-mail:  marrett at mail.utexas.edu

web:      http://www.geo.utexas.edu/faculty/marrett/