Annual Meeting - SCEC.org

Report | SCEC Research Accomplishments
Shearer, P., E. Hauksson, and G. Lin, Southern California hypocenter relocation with waveform cross correlation: Part 2.
Results using source-specific station terms and cluster analysis, Bull. Seismol. Soc. Am., 95, 904-915, doi:
10.1785/0120040168, 2005.
Stephenson, W. J., J. K. Odum, R. A.Williams, and M. L. Anderson, 2002, Delineation of faulting and basin geometry along a
seismic reflection transect in urbanized San Bernardino valley, California, Bull. Seismol. Soc. Am. 92, 2504–2520.
Süss, M. P., and J. H. Shaw, 2003, P-wave seismic velocity structure derived from sonic logs and industry reflection data in the
Los Angeles basin, California, Journal of Geophysical
Research, 108/B3.
Tape, C., Q. Liu, A. Maggi, and J. Tromp, 2010, Seismic
tomography of the southern California crust based on
spectral-element and adjoint methods, Geophys. J. Int.,
180, 433–462.
Tape, C., Q. Liu, A. Maggi, and J. Tromp, 2009, Adjoint
tomography of southern California, Science, vol 325, p.
988-992.
Fault and Rupture Mechanics
The primary mission of the Fault and Rupture Mechanics
Focus Group is to develop physics-based models of the
nucleation, propagation, and arrest of dynamic rupture to
understand earthquakes in Southern California. Specific
research goals of FARM are to investigate the relative
importance of different dynamic weakening mechanisms,
characterize the constitutive behavior of faults and
develop a capability to incorporate the behavior into
dynamic rupture models, discover the relation of fault
zone structure and earthquake mechanics at all scales, and
determine the extent and causes of rupture directivity.
Over the past year a large number of funded projects have
addressed the research priorities of FARM using a variety
of techniques. For the purpose of reporting research
accomplishments, the projects are loosely categorized into
the themes of fault-slip behavior, the micromechanics of
faulting, the constitutive behavior of fault materials,
advanced dynamic rupture modeling, and the
characteristics of fault-slip and fault structure through
observational studies in the field and laboratory. This
section provides a brief summary of some
accomplishments and research-related activities reported
in March of 2011. Additional accomplishments are
reviewed in other sections of this report. For a complete
review of all FARM-related activities please see the annual
reports for the individual projects posted on the SCEC
website.
Mechanics-based Analysis of Fault Slip
Behavior
Building off of earlier work of Shearer et al. (2005), Bird
recomputed Brune-type stress drops of magnitude 1.5-3.1
earthquakes occurring in southern California from 1989 to
2001 to test hypotheses relating stress drops to hypocentral
56 | Southern California Earthquake Center
Figure 18. Interpreted stress-drop regimes, based on temperature- and
depth-systematics (from Fig. 3 in SCEC Report #10025). Dotted lines
show steady-state geotherms for various heat-flows, based on the
assumed crustal conductivity and radioactivity. Long-dashed curves
show model brittle/ductile transition conditions (for strain rates varying
over 4 orders of magnitude) in the homogeneous crustal rheology
assumed by Liu & Bird [2002], whose models used the same thermal
parameters and map of of heat flow.
Figure 19. (a) The profiles of coseismic displacement on the Earth
surface for the elastic simulation, a plastic simulation, an elastic
prediction for the simulated slip distribution shown in panel b, and the
best fitting model to the plastic response in the inversion. (b) The slip
distribution in the plastic simulation and slip inversions of the surface
displacements. The blue curve is the inverted slip of the surface
displacement of the elastic prediction. The red curve is the inverted slip
of the surface displacement of the simulated plastic response. (c)
Difference between the inverted slip distributions shown in panel b,
indicating that 10% (0.5 m) of the coseismic slip at 3-4 km depths is
due to an artifact of the inversion that is based on the elastic model.