Modern mermaids: New floats image the deep Earth

Abstract

Scientists get a window into deep Earth structures by using a method called seismic tomography. Similar to computed tomography (CT) scans of the brain, seismic tomography uses delays in the arrival times of seismic P waves to make scans and three‐dimensional images of the variations in seismic wave speed in the Earth's interior. Patterns in the delays indicate thermal or compositional anomalies in the Earth's mantle and core, such as those caused by sinking cold oceanic lithosphere or rising hot thermal plumes. A large number of observations of such delays are available for continental regions; the number of observations for the United States is especially high due to a dense deployment of stations currently being installed temporarily and moved across a large area as part of the USArray project, a branch of the U.S. National Science Foundation's EarthScope program. In contrast, no comparable sensor density has been available in the oceans

Automatic recognition of T and teleseismic P waves by statistical analysis of their spectra: An application to continuous records of moored hydrophones

“…Matsumoto et al [] have proposed a simple algorithm to perform an automatic detection of T waves by autonomous underwater robots. Recently, Sukhovich et al [] have developed a probabilistic method for use on similar floats dedicated to record acoustic signals generated by teleseismic P waves [ Simons et al , ; Hello et al , ]. While showing promising results, these methods are not quite universal as they require separate tailoring of their parameters for the detection of signals of a given type.…”

How Students Can Experience Science and Become Researchers: Tracking MERMAID Floats in the Oceans

“…The oceans cover about 71% of Earth's surface and have been so far virtually inaccessible for seismic recording. By creating MER-MAID, this team of researchers and engineers has created a marine laboratory (Simons et al, 2006(Simons et al, , 2009Hello et al, 2011) comprising 17 free-floating seismometers continuously monitoring and transmitting detected seismograms in quasireal time (Fig. 1).…”

“…Here, we introduce an educational activity combining a research program (Mobile Earthquakes Recording in Marine Areas by Independent Divers [MERMAID project]; Hello et al, 2011) and students' research skills using specific numerical tools to analyze seismic data.…”

“…Figure 1. Picture of a Mobile Earthquakes Recording in Marine Areas by Independent Divers (MERMAID) float(Hello et al, 2011). The color version of this figure is available only in the electronic edition.▴Figure 2.…”

Hydrophone Calibration at Very Low Frequencies

“…Recently, hydrophones mounted on oceanographic Mobile Earthquake Recorder in Marine Areas by Independent Divers (MERMAID) floats, cruising at depths down to 2000 m in the Mediterranean Sea and Indian Ocean, have begun to record P waves from teleseismic and local earthquakes. The MERMAID float was developed to record teleseismic arrival times from strong earthquakes and to improve the knowledge of the dynamics of the mantle, more specifically by imaging the hotspot-rich mantle in the southern hemisphere, where the lack of land-based seismic stations results in poorly resolved global tomographic models (Simons et al, 2006(Simons et al, , 2009Hello et al, 2011). MERMAIDs have also demonstrated the ability to record weak local and regional events.…”