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| Titel |
Extended fault inversion with random slipmaps: A resolution test for the 2012 Mw 7.6 Nicoya, Costa Rica earthquake from a Popperian inversion strategy. |
| VerfasserIn |
José Ángel López Comino, Daniel Stich, Ana M. G. Ferreira, José Morales Soto |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250102328
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| Publikation (Nr.) |
 EGU/EGU2015-1639.pdf |
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| Zusammenfassung |
| The inversion of seismic data for extended fault slip distributions provides us detailed models
of earthquake sources. The validity of the solutions depends on the fit between observed and
synthetic seismograms generated with the source model. However, there may exist more than
one model that fit the data in a similar way, leading to a multiplicity of solutions. This
underdetermined problem has been analyzed and studied by several authors, who agree that
inverting for a single best model may become overly dependent on the details of the
procedure. We have addressed this resolution problem by using a global search that scans the
solutions domain using random slipmaps, applying a Popperian inversion strategy that
involves the generation of a representative set of slip distributions. The proposed technique
solves the forward problem for a large set of models calculating their corresponding
synthetic seismograms. Then, we propose to perform extended fault inversion through
falsification, that is, falsify inappropriate trial models that do not reproduce the
data within a reasonable level of mismodelling. The remainder of surviving trial
models forms our set of coequal solutions. Thereby the ambiguities that might
exist can be detected by taking a look at the solutions, allowing for an efficient
assessment of the resolution. The solution set may contain only members with
similar slip distributions, or else uncover some fundamental ambiguity like, for
example, different patterns of main slip patches or different patterns of rupture
propagation. For a feasibility study, the proposed resolution test has been evaluated using
teleseismic body wave recordings from the September 5th 2012 Nicoya, Costa
Rica earthquake. Note that the inversion strategy can be applied to any type of
seismic, geodetic or tsunami data for which we can handle the forward problem. A
2D von Karman distribution is used to describe the spectrum of heterogeneity in
slipmaps, and we generate possible models by spectral synthesis for random phase,
keeping the rake angle, rupture velocity and slip velocity function fixed. The 2012
Nicoya earthquake turns out to be relatively well constrained from 50 teleseismic
waveforms. The solution set contains 252 out of 10.000 trial models with normalized
L1-fit within 5 percent from the global minimum. The set includes only similar
solutions –a single centred slip patch- with minor differences. Uncertainties are
related to the details of the slip maximum, including the amount of peak slip (2m to
3.5m), as well as the characteristics of peripheral slip below 1 m. Synthetic tests
suggest that slip patterns like Nicoya may be a fortunate case, while it may be more
difficult to unambiguously reconstruct more distributed slip from teleseismic data. |
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