Applying True Source Depth to ShakeAlert Algorithms in Subduction Zones

ShakeAlert algorithms currently use a default source depth of 8 km to estimate the magnitude and location of ongoing earthquakes. The default depth is appropriate for California earthquakes that occur on shallow crustal faults, however, the most common moderate-magnitude events in the Pacific Northwest are intraslab earthquakes at depths between ~35 - 65 km. In a subduction zone setting, true depth estimates may be important for generating accurate ShakeAlert estimates of ground shaking intensity, as well as for determining which sites will receive an alert during an earthquake. Using a global dataset of M5+ interface and intraslab earthquakes and ground motion models developed for subduction zones, we compare the timeliness and accuracy of alerts computed with default and true source depths using the ShakeAlert Testing and Certification analysis procedures. We also evaluate the trade-off between the additional computation time needed to estimate true source depth and the accuracy of predicted ground motions at end-user sites. This study will inform the ShakeAlert project regarding the use of default or true depth estimates in subduction zones.