Revisiting the 1992 Landers earthquake: a Bayesian exploration of co-seismic slip and off-fault damage

Abstract

S U M M A R YExisting models for the distribution of subsurface fault slip associated with the 1992 Landers, CA, earthquake (M w = 7.3) show significant dissimilarities. In particular, they exhibit different amounts of slip at shallow depths (<5 km). These discrepancies can be primarily attributed to the ill-posed nature of the slip inversion problem and to the use of physically unjustifiable smoothing or regularization constraints. In this study, we propose a new coseismic model obtained from the joint inversion of multiple observations in a relatively unregularized and fully Bayesian framework. We use a comprehensive data set including GPS, terrestrial geodesy, multiple SAR interferograms and co-seismic offsets from correlation of aerial images. These observations provide dense coverage of both near-and far-field deformation. To limit the impact of modelling uncertainties, we develop a 3-D fault geometry designed from field observations, co-seismic offsets and the distribution of aftershocks. In addition, we account for uncertainty in the assumed elastic structure used to compute the Green's functions. Our solution includes the ensemble of all plausible models that are consistent with our prior information and fit the available observations within data and prediction uncertainties. Using near-fault high-resolution ground deformation measurements and the density of aftershocks, we investigate the properties of the damage zone and its impact on the inferred slip at depth. We attribute a part of the inferred slip deficit at shallow depth to our models not including the impact of a damage zone associated with a reduction of shear modulus in the vicinity of the fault.

Landers 1992 "reloaded": Integrative dynamic earthquake rupture modeling

“…Numerous studies estimated the on-fault slip distribution of the Landers earthquake [e.g., Campillo and Archuleta, 1993;Wald and Heaton, 1994;Cohee and Beroza, 1994;Cotton and Campillo, 1995;Fialko, 2004a;Milliner et al, 2015;Gombert et al, 2018]. While theses studies are based on different source inversion approaches and datasets, they overall agree that the largest slip is encountered on the HVF.…”

“…Recent coseismic slip models derived by a Bayesian approach suggest that the overall SSD for the Landers event is about 40%, but might vary between fault segments [Gombert et al, 2018].…”

“…Let us compare the resulting slip distribution of our dynamic rupture model (on a segmented fault system and including off-fault plasticity) to inversion results of Gombert et al [2018] and to numerical simulations on a single planar fault plane [Roten et al, 2017]. Recall from Sec.…”

“…Recent advances in processing high-resolution aerial photographs of near-fault deformation patterns reveal that off-fault deformation primarily correlates with fault complexity [Milliner et al, 2015]. A significant slip reduction towards the shallow part of the faults is inferred, known as shallow slip deficit (SSD), which is often attributed to plastic deformation [Fialko et al, 2005;Kaneko and Fialko, 2011;Milliner et al, 2015;Gombert et al, 2018]. Simulations on a single, planar fault plane reveal that purely elastic simulations underpredict the SSD [Roten et al, 2017] as well as ground motions [Roten et al, 2014[Roten et al, , 2015.…”

“…3. We compare the ratio of shallow near-surface slip and deep slip (within the seismogenic zone) to recent inversion results based on a Bayesian approach [Gombert et al, 2018], as well as the modeled off-fault plastic strain distribution with near-field observations of fault zone width [Milliner et al, 2015]. Analyzing ground motions in terms of spatial distribution and shaking levels (e.g.…”