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Poster Abstracts
Previous models of the Landers rupture process have included multiple nonplanar fault segments, but the off-fault response
was assumed to be ideally elastic. Our prior studies of dynamic ruptures on idealized nonplanar faults have highlighted the
importance of accounting for inelastic deformation to bound otherwise unreasonable stress concentrations that develop
around structural complexities. Building on that modeling framework, we present a dynamic rupture model of the Landers
earthquake that incorporates plastic deformation in addition to the realistic nonplanar geometry. Simulations show that a
rupture cannot jump over one kilometer without the presence of a linking fault, at least for the specific geometries and
parameters we studied. Since the main segments of the complex Landers fault system are almost 5 kilometers apart, we
speculate that minor connecting faults must play a key role in rupture propagation spanning multiple segments.
To gain more insight, we have studied three typical but simplified fault geometries: parallel (two faults 5 km apart with no
overlap), overlapping, and linked (two overlapping faults connected by a linking fault). The linked geometry was the only one
of the three tested geometries that allowed the rupture to jump from the first fault to the second. This confirms our speculation,
and brings attention to the often-neglected linking faults in complex fault systems. We expect that our findings will help
seismologists better understand both the physics behind and the probability of multifault rupture on large, complex fault
systems.
MODELING GROUND MOTION OF A M7+ EARTHQUAKE ON THE SAN ANDREAS FAULT USING THE
VIRTUAL EARTHQUAKE APPROACH (B-007)
M. Denolle, G.C. Beroza, E.M. Dunham, and G. Prieto
The utility of empirical ground motion prediction equations is limited by the scarcity of large events. Physics-based
simulations provide an important way to overcome this data scarcity, provided they accurately take into account the
complexity of the source, the crustal elastic and anelastic structure and the local site effects. Our incomplete knowledge on
crustal structure is an important source of uncertainty in ground motion simulations. We use the ambient seismic field to
validate ground motion predictions at long periods. We compute the impulse responses of the Earth in between specific
seismic station pairs with ambient seismic field analysis. Comparison of impulse responses with earthquake records from
moderate earthquakes confirms that this process preserves relative amplitude. The distribution of the noise sources is not
homogeneous, however, and this has the potential to bias amplitude variations.
We can achieve a better control on the source of seismic energy with the coda-wave interferometry. We use the aftershocks of
the April 4th, 2010, M7.2, El Mayor-Cucapah earthquake and southern California earthquakes with magnitudes exceeding 4. If
the direction of the microseism and the earthquakes are complementary in some directions and improve the stability of the
amplitude, they also improve the quality of the asymmetric impulse responses. We then correct the impulse responses with
simple analysis on the dispersion of the surface waves to account for the depth-dependence of excitation as well as radiation
pattern of a double couple point source and directivity effects of an extended finite source. We use a spectral collocation
method using Chebyshev polynomials to evaluate the depth-dependence of the fundamental mode surface-wave excitation
for complex crustal structure. After validating this technique with moderate Californian earthquakes, we apply our approach
to a temporary seismic network that was deployed along the southern segment of the San Andreas Fault (SAVELA
experiment). To simulate an extended finite source and capture directivity effects, we superimpose the impulse responses
from all the station sources that represent parts of the fault. As predicted by large-scale computer simulations strong ground
motion amplification in the Los Angeles sedimentary basin is clearly observed in the scenarios we study for a large M7+
strike-slip earthquake on the reach of the San Andreas Fault near San Gorgonio Pass.
GPS NETWORK OPERATIONS AT USGS PASADENA (A-067)
D. Determan, A. Aspiotes, K. Hudnut, N. King, and K. Stark
The US Geological Survey Pasadena field office operates 104 permanent, continuously-operating Global Positioning System
(GPS) stations in southern California. These stations are primarily located throughout the urban Los Angeles area and along
the southern San Andreas fault. The construction and in159s159t159a159l159l159a159t159i159o159n159 159o159f159
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