P‐Delays from Floating Seismometers (MERMAID), Part I: Data Processing,

Description

We present methods of data analysis adapted to Mobile Earthquake Recorder in Marine Areas by Independent Divers (MERMAID) seismograms, obtained with hydrophones mounted on moving underwater floats. If the MERMAID float comes immediately to the surface after recording an earthquake signal, the seismogram location is obtained from the first Global Positioning System (GPS) position, using a correction for the surface drift of the float. In the case of earthquakes recorded without an immediate surfacing, the location is estimated using a linear interpolation between GPS positions. We performed a Bézier interpolation of the GPS positions to estimate a location error. In 67% of the cases, the distance between the two trajectories was less than 500 m. We tested the method on six months of data acquired in the Ligurian basin (Mediterranean Sea). To validate the (manually) picked onset times for P waves, we performed a preliminary tomographic inversion beneath the Ligurian basin of MERMAID data together with a much larger volume of picks from nearby land and ocean‐bottom seismometer stations. After inversion we found that 67% of MERMAID data have a misfit between ±0.17  s, but the distribution of misfits is not Gaussian and shows outliers. We conclude that floating seismometers are an excellent and accurate means for covering oceanic areas for P‐wave tomography.

Abstract

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