An EPIC Tikhonov Regularization: Application to Quasi‐Static Fault Slip Inversion

Ortega‐Culaciati, Francisco; Simons, M.; Ruiz, J. A.; Rivera, Luis; Díaz-Salazar, N.

doi:10.1029/2020jb021141

Cited by 16 publications

(13 citation statements)

References 61 publications

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“…This means that target cannot be predicted by the uncertainties. We attribute this to the fact that in these shallow areas, the sensitivity is very low, as other works have observed (e.g., Ortega‐Culaciati et al., 2021), that is, if we change the amplitude of a parameter, it is not strongly affected in the data. Which means that the areas near the trench intrinsically have poor resolution in their solution.…”

Section: Discussionsupporting

confidence: 59%

Plate‐Locking, Uncertainty Estimation and Spatial Correlations Revealed With a Bayesian Model Selection Method: Application to the Central Chile Subduction Zone

et al. 2022

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Inversions of geodetic data are regularly used to estimate interseismic locking in subduction zones. However, the ill‐posed nature of these problems motivates us to include prior information, physically consistent with processes of the subduction seismic cycle. To deal with model instabilities, we present an inversion method to estimate both plate‐locking and model uncertainties by inverting Global Navigation Satellite System derived velocities based on a Bayesian model selection scheme. Our method allows us to impose positivity constraints via a multivariate folded‐normal distribution, with a specified covariance matrix. Model spatial correlations are explored and ranked to find models that best explain the observed data and for a better understanding of locking models. This approach searches for hyperparameters of the prior joint multivariate probability density function (PDF) of model parameters that minimize the Akaike Bayesian Information Criterion (ABIC). To validate our approach, we invert synthetic displacements from analytic models, yielding satisfactory results. We then apply the method to estimate the plate‐locking in Central Chile (28°–39°S) and its relation to the coseismic slip distribution of earthquakes with magnitudes Mw > 8.0, on the subduction zone since 2010. We also search among different prior PDFs for a single ductile‐fragile limit depth. Our results confirms a spatial correlation between locked asperities and the 2010 Mw 8.8 Maule and 2015 Mw 8.3 Illapel earthquake rupture zones. The robustness of our locking model shows potential to improve future seismic and tsunami hazard estimations.

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Section: Discussionsupporting

confidence: 59%

Plate‐Locking, Uncertainty Estimation and Spatial Correlations Revealed With a Bayesian Model Selection Method: Application to the Central Chile Subduction Zone

et al. 2022

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“…(2020). We attribute such disagreements to methodological differences, as we additionally estimate surface regional strain rates, account for epistemic uncertainties, and use the spatially variable EPIC Tikhonov regularization that improves the along dip resolution of the inferred back‐slip distribution (Ortega‐Culaciati et al., 2021).…”

Section: Discussionmentioning

confidence: 99%

“…Here, we set prior information on a quantity h = Hm representing some characteristics of back‐slip and regional motion model parameters, constraining the values of h to be close to h o = 0 with covariance matrix C h . We use the EPIC Tikhonov regularization to define a spatially variable smoothing prior for back‐slip, improving stability, resolution and interpretability of slip estimates, particularly along the dip direction (Ortega‐Culaciati et al., 2021). The EPIC counterbalances the spatial heterogeneity of the constraints on back‐slip provided by GNSS observations, by determining variances of prior information ( C h ) based on a chosen form of the structure of the posterior covariance matrix

\left({\tilde{\mathbf{C}}}_{\mathbf{m}}\right)

.…”

Section: Methodsmentioning

confidence: 99%

“…The standard deviation of inferred coupling is σ c = 0.096 across the modeled portion of the megathrust -or σ t = 6.4 mm/year for back-slip -as determined using the evidence (Figure S1 in Supporting Information S1). From the posterior covariance matrix, we compute a spatial correlation length for coupling at each subfault, that we use as a proxy for spatial resolution, as it defines the size of coupling features that can be resolved (Figure 2, Figure S15 in Supporting Information S1, Ortega-Culaciati et al, 2021). As EPIC Tikhonov applies a stronger smoothing for fault regions less constrained by data, the correlation length becomes larger at those regions.…”

Section: Coupling Degreementioning

confidence: 99%

“…In contrast, we represent surface velocities by incorporating crustal strain, in addition to standard rigid block motion and interplate coupling. Moreover, we account for observational and epistemic uncertainties and take advantage of a recently developed spatially variable Equal Posterior Information Condition (EPIC) Tikhonov regularization (Ortega‐Culaciati et al., 2021).…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Interplate Coupling and Seismic Potential in the Atacama Seismic Gap (Chile): Dismissing a Rigid Andean Sliver

Yáñez-Cuadra

Ortega‐Culaciati

Moreno

et al. 2022

Geophysical Research Letters

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Geodetically constrained interseismic interplate coupling has been widely used to assess seismic potential in subduction zones. Modeling interseismic deformation is challenging, as it involves interplate coupling and often ignores continental internal deformation processes. We present a novel methodology to jointly estimate interplate coupling along with upper plate rigid motion and surface strain, constrained by GNSS‐derived velocities. We use a least squares inversion with a spatially variable Equal Posterior Information Condition Tikhonov regularization, accounting for observational and elastic structure uncertainties. Our modeling reveals three megathrust regions with high tsunamigenic earthquake potential located within the Atacama Seismic Gap (Chile). This study indicates the presence of a downdip segmentation located just above the 1995 (Mw8.0) Antofagasta earthquake rupture, raising concerns for the potential of tsunamigenic earthquake occurrence at shallower depths. Additionally, we show that surface motion is dominated by strain, with rather negligible rigid motion, dismissing the rigid Andean microplate model typically assumed in previous studies.

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A secondary zone of uplift measured after megathrust earthquakes: caused by early downdip afterslip?

Ragon

Simons

2022

Preprint

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A secondary zone of surface uplift (SZU), located ˜300 kilometers from the trench, has been measured after several megathrust earthquakes. The SZU reached a few centimeters hours after the 2011 Mw 9.1 Tohoku (Japan) earthquake. Less than a day after the 2010 Mw 8.8 Maule (Chile) earthquake, it peaked at 12 cm. Published coseismic finite-fault models for these events do not reproduce the measured SZU. One interpretation is that this SZU is universal, driven by volume deformation around the slab interface (van Dinther et al. 2019). In contrast, with synthetic tests and an investigation of the Maule event, we demonstrate the SZU may instead result from slip on the slab interface. Further, we suggest that slip occurs as rapid postseismic afterslip. We can reproduce the SZU with fault slip if elastic heterogeneities associated with the subducting slab are accounted for, as opposed to assuming homogeneous or layered elastic lithospheric structures.

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An EPIC Tikhonov Regularization: Application to Quasi‐Static Fault Slip Inversion

Cited by 16 publications

References 61 publications

Plate‐Locking, Uncertainty Estimation and Spatial Correlations Revealed With a Bayesian Model Selection Method: Application to the Central Chile Subduction Zone

Plate‐Locking, Uncertainty Estimation and Spatial Correlations Revealed With a Bayesian Model Selection Method: Application to the Central Chile Subduction Zone

Interplate Coupling and Seismic Potential in the Atacama Seismic Gap (Chile): Dismissing a Rigid Andean Sliver

A secondary zone of uplift measured after megathrust earthquakes: caused by early downdip afterslip?

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