Quantifying near‐field and off‐fault deformation patterns of the 1992 M_w 7.3 Landers earthquake

Abstract

Coseismic surface deformation in large earthquakes is typically measured using field mapping and with a range of geodetic methods (e.g., InSAR, lidar differencing, and GPS). Current methods, however, either fail to capture patterns of near-field coseismic surface deformation or lack preevent data. Consequently, the characteristics of off-fault deformation and the parameters that control it remain poorly understood. We develop a standardized method to fully measure the surface, near-field, coseismic deformation patterns at high resolution using the COSI-Corr program by correlating pairs of aerial photographs taken before and after the 1992 M w 7.3 Landers earthquake. COSI-Corr offers the advantage of measuring displacement across the entire zone of surface deformation and over a wider aperture than that available to field geologists. For the Landers earthquake, our measured displacements are systematically larger than the field measurements, indicating the presence of off-fault deformation. We show that 46% of the total surface displacement occurred as off-fault deformation, over a mean deformation width of 154 m. The magnitude and width of off-fault deformation along the rupture is primarily controlled by the macroscopic structural complexity of the fault system, with a weak correlation with the type of near-surface materials through which the rupture propagated. Both the magnitude and width of distributed deformation are largest in stepovers, bends, and at the southern termination of the surface rupture. We find that slip along the surface rupture exhibits a consistent degree of variability at all observable length scales and that the slip distribution is self-affine fractal with dimension of 1.56.

Landers 1992 "reloaded": Integrative dynamic earthquake rupture modeling

“…The SSD is frequently observed in geodetic slip inversions for major strike-slip earthquakes, including the 1992 Landers event [e.g., Fialko, 2004a;Milliner et al, 2015]. We show that an along-strike variability of the SSD is possible, even for laterally constant rock cohesion and bulk friction.…”

“…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.…”

“…The SSD of the Landers earthquake is estimated to be of the order of 30-60% [e.g., Cohee and Beroza, 1994;Fialko, 2004a;Milliner et al, 2015]. 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].…”

“…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.…”