Abstract
Accurate kinematic models are fundamental to enhance our knowledge of
the seismic cycle as well as to improve surface ground motion
prediction. However, the solution of the ill-posed kinematic inverse
problem is non-unique (e.g., Cohee & Beroza, 1994; Wald & Heaton,
1994; Cotton & Campillo, 1995 and Minson et al., 2013) and, according
to current acquisition systems surrounding active faults, this problem
is highly underdetermined, in spite of its rather simple formulation as
a linear inverse problem. Non-linear formulations of the problem, based
on model reduction strategies, alleviate the underdetermination of the
problem. However, non-linear formulations imply drastic assumptions on
the rupture history and they complicate the use of linear algebra tools
to assess the uncertainties of results. Regardless of the assumed
inverse formulation, the incorporation of physical constrains and prior
information into the inverse problem is necessary to provide more robust
and plausible solutions. In this work (Sanchez-Reyes et al. 2018), we
present a new hierarchical linear time domain kinematic source inversion
method able to assimilate data traces through evolutive time windows.
This progressive approach, both on the data and model spaces, does
require mild assumptions based on prior knowledge or preconditioning
strategies on the slip rate local gradient estimations. Contrary to
similar approaches (Fan et al., 2014), this strategy benefits from the
sparsity and causality of the seismic rupture while still ensuring the
positivity of the solution. While standard regularization terms are used
for stabilizing the inversion, strategies based on parameter reduction
leading to a non-linear relationship between the source history and the
observed seismograms are avoided. Rise time, rupture velocity and other
attributes can be extracted later on from the slip-rate inversion we
perform. . Satisfactory results are obtained on synthetic benchmarks
proposed by the Source Inversion Validation project (Mai et al. 2016)
and for the 2016 M$_w$7.0 Kumamoto mainshock. Our specific
formulation combined with simple prior information, as well as numerical
results obtained so far, yields interesting perspectives for a
quasi-real-time implementation and to ease the uncertainty
quantification of such ill-conditioned problem.