Borehole Geophysics and Rock Mechanics

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.

• Rock Physics Laboratories
  Scientists study rock properties in laboratory settings that simulate conditions deep in the earth where earthquakes occur to improve our knowledge of seismogenic faulting.
  
• The San Andreas Fault Observatory at Depth
  Scientists are proposing to drill a 4-km-deep hole into the San Andreas fault zone near Parkfield in order to learn more about the nature of stresses responsible for earthquakes. The study will address fundamental questions regarding the physical and chemical processes acting within the San Andreas and other major plate-bounding faults.