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Group 1 – CDM | Poster Abstracts
1-109
CREEP EPISODES ON THE SUPERSTITION HILLS FAULT: A SILENT M5.0 EVENT
OCTOBER 3-6, 2006 Wei M, Sandwell DT, and Fialko Y
During October of 2006, the 20-km long Superstition Hills fault in Salton Trough, Southern
California, slipped aseismically producing maximum offset of 27 mm as recorded by a creep meter.
We investigate this creep event as well as the spatial and temporal variations in slip history since
1992 using ERS-1, ERS-2, and Envisat Satellites data. During this 15-year period, quasi-steady creep
is punctuated by at least three events. The first two events are associated with the 1992 Landers and
1999 Hector Mine earthquakes suggesting the creep events were dynamically triggered. In contrast,
there is no obvious triggering mechanism for the October 2006 event. Field measurements of fault
offset after the 1999 and 2006 events are in good agreement with the InSAR data suggesting the
creep is highly localized. A dislocation model of the 2006 creep event shows that the slip is
concentrated in the upper 500 m with a maximum depth of 2-3 km. The moment released during
this event is equivalent to a Mw5.1 earthquake; it is surprising that such a significant event
produced no detectable aftershocks and was not recorded by the continuous GPS stations in the
area. Modeling of the long-term creep (1992 to 2000) using stacked ERS interferograms also shows
a maximum creep depth of 2-3 km with slip concentrated in the upper 500 m. This is shallower that
the basement depth of 3-5 km suggesting that the creep depth is unrelated to sediment thickness.
1-110
MULTI-SCALE BLOCK MODELING OF THE PACIFIC-NORTH AMERICA PLATE
BOUNDARY ZONE Meade BJ, and Loveless JP
To understand geodetic constraints on both regional tectonics and seismic hazard we present
results from a block model for southern California that is consistent with the kinematics of the
western United States (including Pacific-North America-Juan de Fuca plate motions). At the
synoptic scale of southern California, we use the rectilinear Community Fault Model and at the
scale of the Los Angeles basin we model the Puente Hills thrust system, and Parkfield segment of
the San Andreas fault using triangulated fault surfaces as defined in the Community Fault Model.
By embedding locally high-resolution fault geometry within a regionally consistent model we can
simultaneously analyze regions of complex faulting and estimate plate motions at larger scales. The
block modeling technique accounts for the effects of local block rotations, elastic strain
accumulation, and a parameterization of deformation that can be effectively represented as internal
block strain. Estimates of internal block strain allow us to determine; 1) whether or not we have
failed to include structures that accommodate significant deformation, 2) are there particular
regions of internal blocks strain that are correlated with macroscopic parameters such as heat flow
or rock type?, and 3) the fraction of deformation (in terms of geometric moment) accommodated on
structures explicitly represented in our model. We use ~1500 GPS stations to estimate kinematically
consistent fault slip rates in southern California and estimate spatially variable slip on the the
individual sections of the Puente Hills thrust. This analysis allows for an assessment of how similar
the present day pattern of deformation is to geologic estimates.
1-111
THREE-DIMENSIONAL MODELS OF ELASTO-STATIC DEFORMATION IN
HETEROGENEOUS MEDIA: APPLICATION TO THE EAST CALIFORNIA SHEAR
ZONE Barbot S, Fialko Y, and Sandwell DT
The static displacements accompanying the 1992 Mw 7.3 Landers and the 1999 Mw 7.1 Hector
Mine earthquakes in the East California Shear Zone (ECSZ) exhibit localized strain along the trace
of nearby active faults, as revealed by anomalous line-of-sight (LOS) displacements in radar
2008 SCEC Annual Meeting | 127