MERMAIDs in the South Pacific Ocean: Observations, Measurements, Modeling, Data Availability, and First Hints at Mantle Structure

MERMAIDs (Mobile Earthquake Recording in Marine Areas by Independent Divers) are seismic instruments which record local, regional and teleseismic earthquakes, and other signals, in the oceans. In the Southern Pacific Ocean, some fifty MERMAIDs are collecting acoustic pressure time series as part of the South Pacific Plume Imaging and Modeling (SPPIM) project. Deployed in 2018 and 2019 by members of the EarthScope-Oceans consortium, these instruments record continuous time series data on a one-year buffer and autonomously report a wealth of waveforms, selectively triggered mostly by teleseismic events, suitable for mantle tomography. 

Listening for signals while roughly 1.5 km below the ocean surface, MERMAIDs' primary mission is to detect and deliver records of P-waves generated by distant earthquakes, and collectively they have returned many thousands of seismograms corresponding to such signals. We present highlights from our earthquake catalog and discuss the changing character and causes of the background noise. Whilst the South Pacific fleet is programmed to only send short seismic records, corresponding to confident identifications of teleseismic first arrivals, some records contain later-arriving phases. In addition to P-waves, we present a miscellany of observations of other signals, including core phases, converted S- and surface waves, and T-phases. Furthermore, we illustrate that we are able to obtain other recorded data segments through buffer requests via satellite. 

Data from the MERMAIDs owned by Geoazur and Princeton University that we report on here are being archived by IRIS—those from three instruments is available without embargo. We highlight MERMAID waveform availability and its utility to the scientific community via examples of their modeling and preliminary interpretations that can be made regarding wavespeed heterogeneity in the dynamic mantle below the Pacific Ocean.