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Group 2 – FARM | Poster Abstracts
Fault Rupture and Mechanics (FARM)
2-058
CORRELATION OF FAULT SEGMENTS WITH RUPTURE SEGMENTS AS A
FUNCTION OF GEOMETRICAL COMPLEXITY AND STRUCTURAL CHANGES Zielke
O, and Arrowsmith JR
Most long active faults have historically ruptured over only a part of their total length in large
earthquakes. Surface ruptures often terminate at geometric or structural discontinuities in the fault
zone, leading to speculation that faults may be portioned into consistent rupture segments along
which slip is restricted to the individual segment where it initiated. In this hypothesis, the
maximum earthquake magnitude for each segment can be estimated (via scaling relationships; e.g.,
Wells and Coppersmith, 1984), even in the absence of historic large earthquakes. This approach
requires definition of fault segments based on changes in physical properties along the fault. The
question arises then of what scale the property change (e.g., fault orientation, fault roughness,
frictional behavior, and downward extension of fault) must be to cause partial or full segmentation,
and where partial segmentation allows multi-segment rupture and full segmentation does not.
Using the numerical earthquake simulator “FIMozFric”, we investigate the effect of geometric and
structural changes of the fault zone on rupture segmentation by systematically changing
parameters that control fault segmentation (fault roughness, bends, stepovers, and gaps). The
simulator creates long (~10’s kyrs) seismic records including time, magnitude, rupture length,
rupture width, slip distribution, and surface displacement of each earthquake. While identification
of fault segments is based on fault geometry and structure, we look at the surface displacement of
individual events to identify rupture segments. Then we compare fault and rupture segments for
each record to determine their correlation as well as the probability of multi-segment rupture as a
function of geometric and structural control. At this stage, we test methods to quantify the different
geometric discontinuities based on their surface expression.
The results of this study may be applied by seismologists and paleoseismologists to define rupture
segments based on structurally-defined fault segments. The definition of rupture segments allows
estimating the maximum earthquake magnitude that may occur on an individual segment as well
as the probability of multisegment rupture –both being important in seismic hazard assessment.
2-059
INFLUENCE OF HETEROGENEOUS COUPLING ON THE SPATIAL PATTERN AND
RECURRENCE OF SEISMIC RUPTURES Kaneko Y, Avouac J, and Lapusta N
Inspired by the recent Sumatra subduction earthquake sequence (2004 - present) on the Sunda
megathrust, we explore the behavior of a simple fault model with lateral variations of frictional
properties designed to induce lateral variations of the degree of coupling (i.e., the proportion of
seismic to aseismic slip). The model consists of two velocity-weakening (potentially locked)
segments separated and surrounded by velocity-strengthening (potentially creeping) zones. The
width of the central velocity-strengthening zone and the laboratory-derived friction parameters are
adjusted so that each locked segment can be ruptured independently or the rupture can sometimes
propagate across the central creeping zone, producing a larger earthquake event. Despite its
simplicity, the model produces complex earthquake cycles with a variety of earthquake slip
patterns. The model can be used to qualitatively explain the relation of interseismic coupling to coseismic
asperities on the Sunda Megathrust. By varying the strength and width of the velocitystrengthening
region, we identify the parameter regime in which such region would act either as a
“permanent” or as a “weak” barrier to the coseismic rupture over many earthquake cycles. The
2008 SCEC Annual Meeting | 171