Print this pageMesoscale and microscale structure analysis of 
phase
I
and II core of the SAFOD drilling project, Parkfield, California
Rafael Almeida
Texas A & M University, Department of Geology and Geophysics
College Station, TX
To further understand the properties of damage zones of
large displacement faults in the continental crust, this project will
characterize the orientation, distribution, and timing of mesoscopic and
microscopic fracturing, and syn-faulting alteration of the damage zone of the
San Andreas Fault, Parkfield, California. These data will be acquired from 3
sections of core recovered during Phase
I and II of the SAFOD project. The data
will be analyzed in terms of the stress, strain and fluid flow history. Detailed
wrap-around maps of the lithology and mesoscopic deformation have been prepared.
In these the orientation, timing and mineral fill of different fracture sets
have been identified. FMI logs were used to orient the core. Oriented samples of
representative deformation features and lithologies have been taken for
characterization of the microscopic fracture fabric, timing, and fluid history
during faulting. Mode I microfracture densities and orientations will be
determined as a function of lithology and distance from the main fault. The
mesoscale and microscale fabric will be used to determine the paleostress field;
by determining vein mineralogy, we will determine distinct events of fluid flow.
We will try to establish if these rocks are within the damage zone of the San
Andreas Fault, and how the stress state adjacent to the fault has changed over
time as well as the possible influence of fluid flow within the damage zone. It
will be critical to establish the role these structures play in the energy
balance during the passage of a large earthquake.
AAPG Search and Discovery Article #90060©2006 AAPG Foundation Grants-in-Aid