A MERMAID Miscellany: Seismoacoustic Signals beyond the P Wave

Mobile Earthquake Recorder in Marine Areas by Independent Divers (MERMAID) is a passively drifting oceanic diving float that transmits acoustic pressure records from global earthquakes within hours or days of their rupture. The onboard algorithm used for the detection and identification of signals from the hydrophone prioritizes the recovery of ∼1 Hz teleseismic P waves, which are useful for seismic imaging of Earth’s mantle. Two years into a mission that launched 50 MERMAIDs to map 3D mantle wavespeed anomalies with high resolution under the Pacific in French Polynesia, it is clear that the data returned contain much information beyond the first‐arriving seismic P phases. These include acoustic conversions from S waves, surface waves, T waves, and inner‐ and outer‐core phases, generated by earthquakes heard across the globe—and sounds from otherwise unidentified events occurring in remote and uninstrumented parts of the world’s oceans. Our growing database of automatically accumulating ∼240 s long‐triggered segments contains a treasure trove for geophysicists interested in seismology beyond P‐wave tomography. Furthermore, equipped with two‐way communication capabilities, MERMAID can entertain requests to deliver data from its 1 yr buffer. In this article, we highlight the data classes and categories in MERMAID’s “extended‐utility” catalog.