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Effects of Kinematic Constraints on Teleseismic Finite-Source
Rupture Inversions: Great Peruvian Earthquakes of 23 June 2001
and 15 August 2007
Thorne Lay (Univ. California, Santa Cruz), Charles J. Ammon (The Pennsylvania State University), Alexander R. Hutko
(US Geological Survey), Hiroo Kanamori (California Institute of Technology)
The rupture processes of two great under-thrusting
earthquakes along the coast of Peru in 2001 and 2007
involve slip distributions that are distinctive from the predominantly
unilateral or bilateral rupture expansion of
many great events. Commonly used finite-source rupture
model inversion parameterizations, with specified rupture
velocity and/or short duration of slip at each grid point,
applied to the seismic recordings for these two events lead
to incorrect slip-distributions or inaccurate estimation of
rupture velocities as a result of intrinsic kinematic constraints
imposed on the model slip distributions. Guided
by large aperture array back-projections of teleseismic
broadband P-wave signals that image slip locations without
imposing a priori kinematic constraints on the rupture
process, we exploit the availability of large global
broadband body and surface wave data sets to consider
the effects of varying the kinematic constraints in teleseismic
finite-source waveform inversions. By allowing
longer than usual rupture durations at each point on the
fault using a flexible subfault source time function parameterization,
we find that the anomalous attributes of the
2001 and 2007 Peru earthquake ruptures are readily recognized
and accounted for by compound rupture models.
The great 23 June 2001 (Mw = 8.4) earthquake involved
an initial modest-size event that appears to have triggered
a much larger secondary event about 120 km away that
developed an overall slip distribution with significant slip
located back along the megathrust in the vicinity of the
initial rupture. The great 15 August 2007 (Mw = 8.0) earthquake
was also a composite event, with a modest size initial
rupture followed by a 60 sec delayed larger rupture that
initiated ~50-60 km away and spread up-dip and bilaterally.
When back-projections indicate greater rupture complexity
than captured in simple slip-pulse-type rupture
model, one should allow for possible long-subfault-slipduration
or composite triggered sequences, and not overly
constrain the earthquake slip distribution.
Maps showing the slip distribution for the preferred doublet event models for
the 2007 (top) and 2001 (bottom) Peru earthquakes. The slip region for the first
event in each pair is indicated by the orange tones. The stars indicate the USGS
epicenters and the blue circles indicate the CMT centroid.
Acknowledgements: Supported by NSF grants EAR0453884 and EAR0635570 (TL) and USGS Award Number 05HQGR0174 (CJA).
2010 IRIS Core Programs Proposal | Volume II | Earthquake Source Studies | II-61