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Poster Abstracts
of a ‘weight vector’ which quantifies the hierarchy of importance of various ground motion intensity measures. A simple
method allows an estimation of bias in seismic response analysis results due to improper ground motion selection. The
methodology has been implemented in the open-source software OpenSHA to improve uptake in practice. The theoretical
foundation of the methodology leads to the consistent computation of the seismic demand hazard, irrespective of the adopted
conditioning intensity measure.
STRONG GROUND MOTIONS OBSERVED IN THE 22 FEBRUARY 2011 CHRISTCHURCH EARTHQUAKE (B-
055)
B.A. Bradley and M. Cubrinovski
On 22 February 2011 at 12:51pm local time, a moment magnitude M_w6.3 earthquake occurred beneath the city of
Christchurch, New Zealand, causing an unparalleled level of damage and human causalities in the country’s history.
Compared to the preceding 4th September 2010 M_w 7.1 Darfield earthquake, which occurred approximately 30km to the
west of Christchurch, the close proximity of the 22 February event lead to ground motions of significantly higher amplitude in
the densely populated regions of Christchurch. As a result of these significantly larger ground motions, structures in general,
and commercial structures in the central business district in particular, were subjected to severe seismic demands and,
combined with the event timing (12:51pm), structural collapses accounted for the majority of the 181 causalities.
A preliminary assessment of the near-source ground motions recorded in the Christchurch region is conducted. Particular
attention is given to the observed spatial distribution of ground motions which is interpreted based on source, path and site
effects. Comparison is also made of the observed ground motion response spectra with those of the 4 September 2010 Darfield
earthquake and those used in seismic design in order to emphasise the amplitude of the ground shaking and also elucidate the
importance of local geotechnical and deep geologic structure on surface ground motions.
EARTHQUAKE NUCLEATION MECHANISMS AND DAMAGE IN HETEROGENEOUS FAULT ZONES,
PROBED WITH PERIODIC LOADINGS (IN MODELS AND EXPERIMENTS). (B-041)
B.W. Brinkman, Y. Ben-Zion, J.T. Uhl, and K.A. Dahmen
We study the response to stress oscillations of different periods and amplitudes in models and experiments, in order to
improve the understanding of nucleation processes and evolving seismicity. The basic question is whether monitoring
changes in observed seismicity can be used to identify the operative nucleation mechanism (or combination of mechanisms).
We use a simple earthquake model (Ben-Zion 2008; Dahmen et al., 2009) to explain the frequency and amplitude dependence
of slip nucleations seen in acoustic emission experiments on sheared rocks (Lockner 1999, Beeler 2003). We show comparisons
of analytical results, numerics, and experiments. The results suggest new ways to estimate the rate at which frictional slips or
earthquakes are nucleated. The application to earthquake faults suggests that seasonal stresses may be more likely to trigger
large earthquakes than tidal stresses.
References:
Beeler, N.M., D.A. Lockner (2003). „Why earthquakes correlate weakly with the solid Earth tides: effects of periodic stress on
the rate and probability of earthquake occurrence.” J. Geophys. Res.-Solid Earth 108.
Ben-Zion, Y. (2008). Collective Behavior of Earthquakes and Faults: Continuum-Discrete Transitions, Evolutionary Changes
and Corresponding Dynamic Regimes, Rev. Geophysics, 46, RG4006, doi:10.1029/2008RG000260.
Dahmen, K.A., Y. Ben-Zion, and J.T. Uhl (2009). A micromechanical model for the deformation in solids with universal
predictions for stress-strain curves and slip avalanches, Phys. Rev. Lett. 102, 175501.
Lockner, David A. and Nick M. Beeler (1999). Premonitory slip and tidal triggering of earthquakes, J. Geophys. Res. 104,
20,133-20,151.
LOWER CRUSTAL ANISOTROPY IN THE MOJAVE DESERT REGION FROM ELECTRON BACKSCATTER
DIFFRACTION (EBSD) MEASUREMENTS OF CRYSTAL PREFERRED ORIENTATION (CPO) (B-138)
S.J. Brownlee, K. Wagner, and B.R. Hacker
Seismic anisotropy is commonly used to infer flow directions in the mantle, but anisotropy in the mid and lower crust can be
much more difficult to measure and to interpret. By measuring the crystal preferred orientations (CPOs) of minerals in lower
crustal rocks we can calculate the anisotropic seismic properties of the aggregate using mineral single-crystal elastic constants
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