Characterizing Earthquake Location Uncertainty in North America Using Source–Receiver Reciprocity and USArray

The Comprehensive Nuclear-Test-Ban Treaty community often uses calibration events with well-determined origins to improve absolute locations of nearby seismic events by accounting for the biasing effects of unknown velocity structure, but the number of these ground-truth events is limited. To provide additional constraints, source-receiver reciprocity allows us to use seismic stations as calibration events with known locations. The dense and uniform spacing of the USArray transportable array stations makes them ideal to measure the spatial coherence of mislocation vectors across North America and hence to assess how close calibration events (or stations) need to be to target events to improve locations for a given region. We use a gridsearch approach for the station"relocations," using both teleseismic earthquakes and simulated regional events. Our results show that the mislocation vectors are spatially coherent for scales up to 500 km in many regions, but that in some places, such as regions that can be associated with strong velocity anomalies in the upper mantle, mislocation vectors exhibit large changes over short distances.