Annual Meeting - SCEC.org

Poster Abstracts
RUPTURE PATTERN OF THE 1892 LAGUNA SALADA EARTHQUAKE: A PRECURSOR TO 2010 EL MAYOR-
CUCAPAH (A-122)
K. Mueller, T. Rockwell, O. Teran, J. Fletcher, S. Akciz, and P. Patton
As part of the SCEC response effort and analysis of surface deformation produced by the 2010 El Mayor-Cucapah earthquake,
we measured fault displacement and larger-scale rupture patterns from the 1892 Mw 7.2 Laguna Salada precursor earthquake.
Our goal was to understand the interaction between rupture segmentation in 1892 and 2010 and its implications for
connectivity between the two fault zones. Comparison between the 1892 and 2010 ruptures suggests that both earthquakes
activated distinct fault segments separated by 1-3 km gaps except for the much larger Puerta accommodation zone in 2010.
Interestingly, the 9 km-wide Puerta gap ruptured previously in 1892 as part of a longer segment on the Laguna Salada fault. In
contrast, this pattern is not apparent where another transfer zone further north at Paso Superior behaved similarly in both
1891 and 2010. The greatest difference between the 1892 and 2010 ruptures is the sense of slip at the rupture endpoints. While
both 1892 and 2010 fed oblique slip into pure dextral offset towards their respective northern and southern endpoints, the
Laguna Salada fault terminated abruptly at the rapidly slipping Canon Rojo normal fault. The proportion of dextral to normal
slip, or slip budget along 1892 rupture segments is not necessarily consistent with fault strike except across the right angle
bend at Canon Rojo. We postulate the difference is due to strain release at longer timescales than is apparent from just the 2010
and 1892 events.
SLIP DEFICITS, RELEASE AND TRANSIENTS ALONG THE CENTRAL SAF FROM REPEATING
MICROEARTHQUAKES (A-102)
R.M. Nadeau, R.C. Turner, and R. Burgmann
To better understand interactions between seismic and aseismic deformation at seismogenic depths, deep aseismic fault slip
rates (Vd) from characteristically repeating microearthquake seqeunces (CSs) along the central San Andreas Fault (SAF) are
compiled and analyzed. Using repeating CS data, spatial and temporal variations in Vd can be resolved over large contiguous
regions, in diverse tectonic settings, and back in time to well before the advent of satalite based geodesy (e.g., GPS, InSAR).
Previous studies have also revealed systematics in Vd indicative of slip transients associated with post-seismic deformation,
slow-slip events, quasi-periodic slip pulsing, and regions of slip-deficit accumulation. We present results of Vd from 343 CSs
(~3000 repeated microearthquakes) along a 200 km stretch of the SAF in central California occurring over a 27+ year period
between 1984 and mid-2011. The spatio-temporal mapping of CS inferred Vd covers the section of the SAF between the the
1989 M6.9 Loma Prieta (LP) earthquake and the inferred northern terminus of the 1857 M7.8 Ft. Tejon (FT) earthquake. This
mapping includes pre- and post- seismic periods of the LP and 2004 M6.0 Parkfield earthquakes. In the study zone we find
large (several 100%), broadly distriubted (several 10s of kms), and systematic variations in Vd associated with the occurrence
of moderate to large earthquakes (i.e., low preseismic rates and large postseismic transients) and in the SAF creeping section
(e.g., quasi-periodic slow-slips) where moderate to large events did not occur. We also show that the a slip deficit that had
accumulated in the Parkfield area was fully released northwest of Parkfield in the 2004 M6 mainshock, but was only partially
released to the southeast adjacent to the locked Cholame segment of the SAF.
SITE RESPONSE IN THE BÍOBÍO REGION, CHILE USING THE Κ METHOD (B-052)
C. Neighbors, E.J. Liao, E.S. Cochran, A.I. Chung, J.F. Lawrence, A. Belmonte, M. Miller, H.H. Sepulveda, and C.
Christensen
We assess local site response in the Bíobío region of Chile utilizing seismograms recorded by the Quake-Catcher Network
(QCN) micro-electro-mechanical system (MEMS) accelerometers during the aftershock sequence that followed the February 27,
2010 Mw 8.8 Maule earthquake. The earthquakes were captured by over 70 QCN low-resolution (10, 12, and 14-bit)
seismometers from March 1 to June 1, 2010. Site effects are caused by the local amplification of seismic energy due to
subsurface structures and geologic materials, which often result in spatially variable patterns of surface damage following an
earthquake.
In this study we estimate kappa, κ, which models the decay of the acceleration spectra to characterize strong ground motion at
high frequencies (> 1 Hz). We calculated the Fourier spectra and κ for each station following the method of Douglas et al.
(2010). During the aftershock deployment, the QCN network recorded over 229 earthquakes of magnitude 4.5 and greater. Of
these recordings, we determine that 57 earthquakes (25%) have sufficient signal-to-noise quality for use in site response
analysis, as determined by visual inspection. Preliminary results indicate κ values between 0.03 and 0.06 s. These values
suggest that the Bíobío region of Chile is sharply attenuating and likely consists of less competent rock, as expected.
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