![](https://webarchive.library.unt.edu/eot2008/20090109022802im_/http://quake.wr.usgs.gov/research/physics/images/cores.jpg) |
USGS scientist Dave Lockner using a
diamond core drill to prepare sandstone samples for lab
testing. See Rock Physics Laboratories (below) for more
information on lab studies. |
The initiation and propagation of earthquake ruptures depend
upon the mechanical behavior of fault rocks and fluids at
depths of several kilometers or more. Using borehole geophysical
measurements in conjunction with laboratory studies, USGS
scientists determine the temperature, stress, and fluid-pressure
conditions at the depths where earthquakes occur and characterize
the mechanical behavior of fault-zone materials at realistic
in-situ conditions. This knowledge is combined with surface-based
geophysical observations, measurements of tectonic strain
accumulation, and other information to yield improved models
of the earthquake cycle.
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