Migration-Based Local Event-Location Workflow for Ocean-Bottom Seismometer (OBS) Records in Subduction Zones: A Practical Approach for Addressing a Large Number of Events

ABSTRACT An efficient event-location workflow is highly desired to analyze large numbers of local earthquakes recorded by ocean-bottom seismometers (OBSs) in subduction zones. The present study proposes a migration-based event-location approach for evaluating OBS records to examine local subduction-zone earthquakes. This approach can significantly reduce the amount of manual time picks compared with conventional methods. The event-location workflow was designed to detect arrival onsets of both P and S phases. Synthetic tests have shown that the proposed migration-based event-location method is robust against different types of noise, such as environmental noise and local spike noise. This workflow was then applied to real OBS data in the off-Ibaraki region at the southern end of the Japan trench. The results show that this approach is applicable to real data from subduction-zone events: It gives reasonable agreement with manual time picks for both P and S waves and reasonable error bars, and it demonstrates a clear down-dip trend of seismicity. The results also show fair agreement with event distributions from previous studies of the off-Ibaraki region. This proposed workflow can be used to examine the seismicity of local earthquakes around the subduction zone using OBSs. This approach is especially effective when the seismicity is high and/or in cases in which long-term OBS monitoring has recorded a large number of events.