Seafloor Geodesy using Wave Gliders

The Sumatra subduction zone.  Our SuGAr GPS stations are marked with white triangles. Because they are restricted to the land we cannot measure near the toe of the fault, or between the islands and the mainland.

The Sumatra subduction zone.  Our SuGAr GPS stations are marked with white triangles. Because they are restricted to the land we cannot measure near the toe of the fault, or between the islands and the mainland.

Our understanding of tectonic processes along subduction megathrusts is hindered by the fact that we are mostly relying on land-based networks, while much of the fault lies under the deep ocean -- see the figure above.  This is especially the case for the shallow megathrust; scientists have often marked this area as creeping (not storing up the large amounts of stress needed to generate earthquakes), but this inference may be in part due to a lack of resolution from the monitoring networks being so far away. We saw in the case of the 2010 Mw 7.8 Mentawai earthquake that the shallow fault is actually capable of rupturing dramatically (Hill et al., 2012), generating a particularly large tsunami and teaching us that it is critical we better understand this dangerous part of the fault.

To address this, Sylvain Barbot, Sharadha Sathiakumar and I are working on integrating acoustic GPS technology into Wave Gliders, with the eventual goal of using them to monitor seafloor deformation offshore Sumatra.  Wave Gliders are wave-powered marine robots that can carry a collection of scientific instruments (powered by solar panels) and be navigated remotely through satellite connections.  Acoustic GPS has been used successfully to monitor seafloor deformation from research vessels, but these are expensive; our hope is to have a less expensive platform to carry out regular surveys.

The position of the Wave Gliders is measured using GPS (which is based on the travel time of electromagnetic waves from the satellites to the receivers).  The position of the seafloor instruments is measured using the travel time of acoustic waves from a source on the bottom of the Wave Gliders.

The position of the Wave Gliders is measured using GPS (which is based on the travel time of electromagnetic waves from the satellites to the receivers).  The position of the seafloor instruments is measured using the travel time of acoustic waves from a source on the bottom of the Wave Gliders.

We now have two Wave Gliders, Fajar and Merantau.  Fajar means "sunrise" in Indonesian.  Merantau means, also in Indonesian, "to go out into the world with the goal of gathering knowledge and bettering oneself, eventually to bring that knowledge home."  Soon we will have finished integrating the instruments, and we can start testing them in the water.  You can see photos of our adventures so far in the gallery below...