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Tectonic motion across the Los Angeles region is distributed across an intricate network of strike-slip and thrust faults that will be released in destructive earthquakes similar to or larger than the 1933 M6.4 Long Beach and 1994 M6.7 Northridge events. Here we show that Los Angeles regional thrust, strike-slip, and oblique faults are connected and move concurrently with measurable surface deformation, even in moderate magnitude earthquakes, as part of a fault system that accommodates north-south shortening and westerly tectonic escape of northern Los Angeles. The 28 March 2014 M5.1 La Habra earthquake occurred on a northeast striking, northwest dipping left-lateral oblique thrust fault northeast of Los Angeles. We present crustal deformation observation spanning the earthquake showing that concurrent deformation occurred on several structures in the shallow crust. The seismic moment of the earthquake is 82% of the total geodetic moment released. Slip within the unconsolidated upper sedimentary layer may reflect shallow release of accumulated strain on still-locked deeper structures. A future M6.1-6.3 earthquake would account for the accumulated strain. Such an event could occur on any one or several of these faults, which may not have been identified by geologic surface mapping.

Reproducibility of results from scientific studies is rarely demonstrated outside the laboratory. Measurements of fault slip rate underpin scientific models of active faulting and seismic hazard assessments widely used for policymaking and risk mitigation. We replicated a highly referenced study that measured the slip rate as 33.9 ± 2.9 mm/year along the San Andreas fault over the past ~3,700 years at Wallace Creek in the Carrizo Plain National Monument, USA. Our results provide a slip rate of slip 36 ± 1 mm/year since ~3,500 CalBP. We find that the late Holocene slip rate of the San Andreas fault, a key indicator of seismic hazard, is reproducible within measurement uncertainty. Geologic slip rate determinations are relatively insensitive to short‐term fluctuations and thus should be reproducible if the time interval of measurement is much greater than the average rupture interval. Plain Language Summary: We have replicated a keystone San Andreas fault slip rate measurement from the 1980s and showed that fault slip rate is reproducible if measured over the same geologic time interval and if the time interval is much greater than the average time interval between surface rupturing earthquakes. Key Points: Slip rate of the San Andreas fault was measured at a keystone site in the 1980s and remeasured in 2011‐2017 with newer methodsWithin measurement uncertainty, the 3,700‐year slip rate published in 1984 agrees with this 2019 slip rate measurementGenerally, fault slip rate is reproducible within measurement uncertainty if the time interval of measurement is much greater than the average rupture interval [ABSTRACT FROM AUTHOR]