Annual Meeting - SCEC.org

Poster Abstracts
Results of this study show that, for certain structural systems, simulated accelerograms may produce median inelastic demand
(at a collection of stations for each earthquake) different from a similar estimate using corresponding recorded motions. This
difference is especially observed in the case of degrading and evolutionary systems at high non-linearity levels, and if cyclic
response is of concern. Moreover, simulated records tend to produce nonlinear demands that are generally less heterogeneous
compared to those caused by real records. The amount of this variability reduction depends on the structural period, the nonlinearity
level and the hysteretic model used. Further investigation is needed to prove the statistical significance of these
results and identify their source.
ENGINEERING VALIDATION OF GROUND MOTION SIMULATION: PART 2. MAXIMUM INTERSTORY
DRIFT RATIO AND CRITICAL STORY SPECTRA (B-091)
C. Galasso, F. Zareian, I. Iervolino, and R.W. Graves
The study presented in this poster complement the first one addressing the issue of ground motion simulation engineering
validation in terms of elastic seismic response of multiple degrees of freedom (MDOF) systems. MDOF buildings considered
in this study are modeled as equivalent continuum structures consisting of a combination of a flexural cantilever beam
coupled with a shear cantilever beam (both with uniform mass distribution). Such models are useful tools for approximate
analysis of structures, especially those tall, ranging from moment-resisting frames to shear walls systems and for which the
higher-mode contributions may become important.
In order to study dynamic response of a wide range of buildings, a number of simplified continuum systems were selected
considering: (1) twenty oscillation periods between 0.1s and 10s; (2) three shear to flexural deformation ratios to represent
respectively shear walls structures, dual systems, and moment-resisting frames; (3) two stiffness distribution along the height
of the systems; i.e., uniform and linear. Demand spectra in term of maximum interstory drift (IDR) and critical story (i.e., the
height of maximum interstory drift) were derived for the same four historical earthquakes of the first poster; i.e., 1979 M 6.5
Imperial Valley earthquake, 1989 M 6.8 Loma Prieta earthquake, 1992 M 7.2 Landers earthquake and 1994 M 6.7 Northridge
earthquake. In addition, for same selected case study structures, the IDR distribution over the height and the modal
contributions are obtained and compared for both recorded and simulated time histories.
Some differences between median estimate of IDR demand obtained by using real records and that obtained by simulations
were observed, over a certain frequency range throughout the regions surrounding the event epicenter. These differences vary
with the considered event and the structural period while they are fairly independent of the type of structure. Moreover, the
record-to-record variability of seismic demand produced by simulated and recorded motions may be different. Further
analysis is underway to explain the effect of various ground motion simulation parameters on the discrepancy found and to
prove the statistical significance of these results.
COMPLEXITY OF THE M6.3 2009 L’AQUILA (CENTRAL ITALY) EARTHQUAKE: SLIP INVERSION AND
BROAD-BAND MODELING OF STRONG-GROUND MOTIONS (B-003)
F. Gallovic, J. Zahradnik, G. Ameri, and F. Pacor
Strong ground motion recordings of the M6.3 2009 L’Aquila (central Italy) earthquake are analyzed by a newly proposed
inversion technique. The source model consists of Multiple Finite-Extent (MuFEx) subsources. Each subsource is characterized
by an individual set of trial nucleation positions, rupture velocities and nucleation times. In addition to the best-fitting model,
grid-searching all combinations of the subsource parameters allows also the uncertainty analysis. The MuFEx model requires a
preliminary setup based on a technique free of strong constraints (constant rupture velocity over the whole fault, etc.). Here
we used two published approaches of such a type, the truncated singular value decomposition and the iterative multiplepoint
source deconvolution. Final adjustment of the MuFEX model can be performed by repeating the analysis while varying
the dimensions and locations of the subsources. Both the best-fitting model and the uncertainty analysis of the low-frequency
L’Aquila records suggest that the event consisted of two major episodes, one with the rupture propagating immediately after
the nucleation in the up-dip direction, while the other being delayed by 3-4s and characterized by the dominant propagation
towards SE along the deeper part of the fault. We point out that the data cannot distinguish between a temporal rupture arrest
and a partial slow-down of the rupture, the latter suggested in other published ‘smooth’ models. We also present broad-band
(0.1 - 10 Hz) modeling of strong ground motions constraining the source model by MuFEx inversion. The modeling allows
linking distinct features of the observed wavefield to particular source and propagation effects and provides insights on
strong-motion complexity from this moderate magnitude event. We utilize a hybrid integral-composite approach based on a
k-square kinematic rupture model, combining low-frequency coherent and high-frequency incoherent source radiation and
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