Complexity of the Mw 6.3 2009 L'Aquila (central Italy) earthquake:
1. Multiple finite-extent source inversion
Journal of Geophysical Research, 117 (B4):
B04307+ (Apr 19, 2012)DOI: 10.1029/2011JB008709
Abstract
Strong ground motion recordings of the Mw6.3 2009 L'Aquila earthquake
are analyzed by a newly proposed slip inversion technique. The source
model consists of Multiple Finite-Extent (MuFEx) subsources. The
slip amplitude, rupture velocity, rake and rise time are assumed
constant within each subsource. The size and location of the MuFEx
subsources have to be inferred independently from other methods,
preferably those free of strong constraints (such as constant rupture
velocity over the whole fault, etc); here we use two published approaches
satisfying such requirement: the truncated singular value decomposition
and the iterative multiple-point source deconvolution. Each MuFEx
subsource is characterized by an individual set of trial nucleation
points, rupture velocities and nucleation times, which are grid-searched.
For each combination of these parameters, the subsources' slip is
determined by the least-squares approach. This procedure thus provides
not only the best-fitting model, but also a whole range of acceptable
models, allowing for the uncertainty analysis. The method is demonstrated
on three synthetic tests. When applied to the L'Aquila data, both
the best-fitting model and the uncertainty analysis suggest that
the event consisted of two major episodes, one with the rupture propagating
immediately after the nucleation in the up-dip direction, the other
being delayed by 3-4s with dominant propagation towards the SE along
the deeper part of the fault. The retrieved complexity of the rupture
propagation warns against attempts to stabilize inversions by the
use of a constant rupture velocity over the whole fault.