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Poster Abstracts
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SEISMOGRAM-BASED ASSESSMENT OF THE SOUTHERN CALIFORNIA SEISMIC VELOCITY MODEL
CVM-H 11.9 WITH 234 REFERENCE EARTHQUAKES (B-127)
C. Tape, E. Casarotti, A. Plesch, and J.H. Shaw
Pervasive moderate earthquakes (M > 3) in southern California provide an excellent means for independently testing seismic
velocity models of the crust and uppermost mantle. It is possible to obtain a seismic data set that is potentially sensitive to all
details in a complex structural setting by using a large number of earthquakes, considering the full length of three-component
seismograms, and examining different period ranges. We quantitatively assess the crustal and upper mantle model CVM-H
11.9 by performing seismic wavefield simulations based on unstructured hexahedral meshing (GEOCUBIT) and the spectralelement
method (SPECFEM3D). We generate a database of synthetic seismograms for 234 reference earthquakes in southern
California. These synthetic seismograms are filtered over different period ranges and then compared with observed
seismograms using a variety of misfit functions. The misfit analysis provides an earthquake-based perspective of the quality of
CVM-H 11.9, and it can be used to improve future model versions.
THE EFFECT OF BARRIERS ON SLIP PARTITIONING IN AN UPWARD BRANCHING FAULT SYSTEM (A-
076)
J. Tarnowski, D. Oglesby, and D. Bowman
The finite element method and slip-weakening friction are employed to investigate dynamic rupture propagation on a
branched fault system. The system consists of an oblique-normal fault at depth connected to vertical and dipping fault
branches 5km from the surface. The branches accommodate predominately strike-slip and dip-slip motion, respectively. When
rupture is nucleated on the oblique fault at depth, dynamic unclamping favors rupture propagation to the vertical fault, with
no rupture on the dipping fault. However, when a zone of doubled normal stress, referred to as a barrier, is located on the
vertical fault, rupture is delayed on the vertical fault, causing shear stress to increase and normal stress to decrease along the
corresponding area of the dipping fault. Consequently, the dynamic nature of the stresses facilitates slip on both segments.
There is a correlation between barrier area and the ease with which an earthquake at depth propagates to both upper branches,
suggesting a critical patch size for nucleation on the dipping fault. Increasing the slip-weakening distance by a factor of √2
necessitates the use of a critical barrier area that is increased by a factor of ~2, which is consistent with the critical patch size
relationship suggested by Day (1982). Further numerical models show that the behavior above is relatively general, and does
not require finely-tuned stress and frictional parameters.
CRUSTAL THICKENING AND STRIKE-SLIP CONTROLLED GROWTH OF THE NORTHERN COLOMBIAN
ANDES (A-153)
M.H. Taylor, G. Veloza, and A. Mora
Neotectonic field mapping, seismic reflection profiles, and cosmogenic nuclide surface exposure dating aid in estimating the
style and rate of recent shortening across the eastern foothills of the Colombian Andes. Active structures include the eastdirected
Guicarimo thrust fault that folds Cretaceous, Paleogene, Neogene and Quaternary sediments, and the east-directed
Cusiana thrust fault – both structures are seismically active and are considered to sole at depth into a common decollement.
Uplifted, folded and entrenched Quaternary alluvium are cut by active thrust faults with resulting entrenchment mainly
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