Tearing the terroir: Details and implications of surface rupture and deformation from the 24 August 2014 M 6.0 South Napa earthquake, California

The M w 6.0 South Napa earthquake of 24 August 2014 caused slip on several active fault strands within the West Napa Fault Zone (WNFZ). Field mapping identified 12.5 km of surface rupture. These field observations, near‐field geodesy and space geodesy, together provide evidence for more than ~30 km of surface deformation with a relatively complex distribution across a number of subparallel lineaments. Along a ~7 km section north of the epicenter, the surface rupture is confined to a single trace that cuts alluvial deposits, reoccupying a low‐slope scarp. The rupture continued northward onto at least four other traces through subparallel ridges and valleys. Postseismic slip exceeded coseismic slip along much of the southern part of the main rupture trace with total slip 1 year postevent approaching 0.5 m at locations where only a few centimeters were measured the day of the earthquake. Analysis of airborne interferometric synthetic aperture radar data provides slip distributions along fault traces, indicates connectivity and extent of secondary traces, and confirms that postseismic slip only occurred on the main trace of the fault, perhaps indicating secondary structures ruptured as coseismic triggered slip. Previous mapping identified the WNFZ as a zone of distributed faulting, and this was generally borne out by the complex 2014 rupture pattern. Implications for hazard analysis in similar settings include the need to consider the possibility of complex surface rupture in areas of complex topography, especially where multiple potentially Quaternary‐active fault strands can be mapped. This paper summarizes the field observations of surface rupture following the 2014 South Napa Earthquake in northern California, USA. It also describes how repeat radar measurements from an aircraft operated by NASA enhance our understanding of this earthquake. Though geologists mapped 12.5 kilometers of surface rupture in the field, the airborne survey provided information that indicates that over 30 km of ground surface was deformed by the earthquake. We also compare the patterns of surface rupture to previous geological and hazard mapping and find that this earthquake followed several mapped fault traces but also ruptured across fault zones that were previously unmapped. The 24 August 2014 South Napa earthquake ruptured the Earth's surface in a complex manner both spatially and temporally Advanced remote sensing techniques enhanced field measurements made to map and quanti