Dr. Spahr Webb
Earth Institute Contact: Dr. Spahr Webb
Locations: Pacific Ocean
Seafloor compliance will be measured at more than 50 sites on the rise axis and flanks of the East Pacific Rise between 9°20’N and 10°20’N, to map the melt distribution in the lower crust and uppermost mantle. This region includes the RIDGE2000 integrated study site at 9°50’N and the Clipperton fracture zone. The results should elucidate the mechanisms of melt transport and storage involved with the construction of the oceanic crust under seafloor spreading. The primary scientific questions are: 1) how and why do morphologically “melt starved” segments differ from “robust” segments? 2) does melt pool at the crust mantle boundary before percolating through the lower crust? If so, where?, 3) how does lower crustal melt decrease toward segment ends? 4) are ridge transform highs partially supported by low density crust and mantle? 5) are there usually lower crustal partial melt regions several km off axis? and 6) is melt to near axis seamounts supplied independently from the rise axis? Answering these questions would provide strong constraints on the magma plumbing of fast spreading ridges, and would indicate the forces behind this plumbing system. All of these questions have previously been addressed using other techniques, but the compliance method should provide new constraints on these problems through its unique capability to detect small partial melt regions within the lower crust and at the base of the crust.
The broader impacts of this work include providing a new understanding of the formation and thermal structure of the lower crust within the EPR RIDGE2000 study site, training a postdoctoral student, furthering the development of technology for broad band ocean floor seismology and furthering cooperation between French and US scientists. The finished work will be presented at major scientific conferences and published in a scientific journal. Like previous compliance work, the results from this project should enhance our understanding of oceanographic effects on seafloor seismic measurements. Previous work has lead to techniques for removing from seismic data tilt noise induced by ocean currents, and signals induced by the displacement of the seafloor under ocean infragravity waves. These two techniques offer a very important 20-40dB of improvement in long period signal to noise in deep water and even greater improvements in shallow water allowing the full suite of seismic data to be acquired from the seafloor.
National Science Foundation