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Abstract:
Seismic network optimization for Earthquake Early Warning (EEW) differs from the more general mission of regional monitoring. A network designed for EEW must prioritize speed of detection, the magnitude and rate of occurrence of likely earthquakes, and the location of seismic sources relative to population centers. A recent analysis by Böse et al. combines these elements in an end-to-end analysis for EEW monitoring in Switzerland. They sample from the combined instrumental and historical catalog for the region to evaluate hazard and losses. We have developed a similar approach based on gridded USGS National Seismic Hazard Map (NSHM) inputs. Hazard maps include catalog and historical seismicity, but also synthesize geologic and geodetic slip rates, geophysical inputs and paleoseismic event information. They are also extensively reviewed. The US NSHM maps are extrapolated from hazard curves calculated on a grid. We extract from the hazard curves the return time at a given shaking intensity, e.g. PGA=0.1 g, as a proxy for how often a station at that location will contribute to EEW detection from nearby earthquakes. The ground motion intensity corresponds to an approximate magnitude and location distribution that can be used in a forward calculation with attenuation to find impact on population centers. Stations near active faults generally minimize detection time and maximize warning time. Stations with shorter return times contribute more often and are generally near larger earthquakes. The best station distribution will give the greatest number of people the most useful warning.
