The 1983 Mw 6.9 Borah Peak earthquake generated ∼36 km of surface rupture along the Thousand Springs and Warm Springs sections of the Lost River fault zone (LRFZ, Idaho, USA). Although the rupture is a well-studied example of multisegment surface faulting, ambiguity remains regarding the degree to which a bedrock ridge and branch fault at the Willow Creek Hills influenced rupture progress. To explore the 1983 rupture in the context of the structural complexity, we reconstruct the spatial distribution of surface displacements for the northern 16 km of the 1983 rupture and prehistoric ruptures in the same reach of the LRFZ using 252 vertical-separation measurements made from high-resolution (5–10-cm-pixel) digital surface models. Our results suggest the 1983 Warm Springs rupture had an average vertical displacement of ∼0.3–0.4 m and released ∼6% of the seismic moment estimated for the Borah Peak earthquake and <12% of the moment accumulated on the Warm Springs section since its last prehistoric earthquake. The 1983 Warm Springs rupture is best described as the moderate-displacement continuation of primary rupture from the Thousand Springs section into and through a zone of structural complexity. Historical and prehistoric displacements show that the Willow Creek Hills have impeded some, but not all ruptures. We speculate that rupture termination or penetration is controlled by the history of LRFZ moment release, displacement, and rupture direction. Our results inform the interpretation of paleoseismic data from near zones of normal-fault structural complexity and demonstrate that these zones may modulate rather than impede rupture displacement.

Imaging tectonic creep along active faults is critical for measuring strain accumulation and ultimately understanding the physical processes that guide creep and the potential for seismicity. We image tectonic deformation along the central creeping section of the San Andreas Fault at the Dry Lake Valley paleoseismic site (36.468°N, 121.055°W) using three data sets with varying spatial and temporal scales: (1) an Interferometric Synthetic Aperture Radar (InSAR) velocity field with an ~100‐km footprint produced from Sentinel‐1 satellite imagery, (2) light detection and ranging (lidar) and structure‐from‐motion 3‐D topographic differencing that resolves a decade of deformation over a 1‐km aperture, and (3) surface fractures that formed over the 3‐ to 4‐m wide fault zone during a drought from late 2012 to 2014. The InSAR velocity map shows that shallow deformation is localized to the San Andreas Fault. We demonstrate a novel approach for differencing airborne lidar and structure‐from‐motion topography that facilitates resolving deformation along and adjacent to the San Andreas Fault. The 40‐m resolution topographic differencing resolves a 2.5 ± 0.2 cm/yr slip rate localized to the fault. The opening‐mode fractures accommodate cm/yr of fault slip. A 90% ± 30% of the 1‐km aperture deformation is accommodated over the several meter‐wide surface trace of the San Andreas Fault. The extension direction inferred from the opening‐mode fractures and topographic differencing is 40°–48° from the local trend of the San Andreas Fault. The localization of deformation likely reflects the well‐oriented and mature fault.

Public perception and regulation of environmental hazards are important factors in the development and configuration of cities. Throughout California, probabilistic seismic hazard mapping and geologic investigations of active faults have spatially quantified earthquake hazard. In Los Angeles, these analyses have informed earthquake engineering, public awareness, the insurance industry, and the government regulation of developments near faults. Understanding the impact of natural hazards regulation on the social and built geography of cities is vital for informing future science and policy directions. We constructed a relative social vulnerability index classification for Los Angeles to examine the social condition within regions of significant seismic hazard, including areas regulated as Alquist‐Priolo (AP) Act earthquake fault zones. Despite hazard disclosures, social vulnerability is lowest withinAPregulatory zones and vulnerability increases with distance from them. Because theAPAct requires building setbacks from active faults, newer developments in these zones are bisected by parks. Parcel‐level analysis demonstrates that homes adjacent to these fault zone parks are the most valuable in their neighborhoods. At a broad scale, a Landsat‐based normalized difference vegetation index shows that greenness nearAPzones is greater than the rest of the metropolitan area. In the parks‐poor city of Los Angeles, fault zone regulation has contributed to the construction of park space within areas of earthquake hazard, thus transforming zones of natural hazard into amenities, attracting populations of relatively high social status, and demonstrating that the distribution of social vulnerability is sometimes more strongly tied to amenities than hazards.