2014 Articles

Spatial distribution and temporal evolution of crustal melt distribution beneath the East Pacific Rise at 9°–10°N inferred from 3-D seafloor compliance modeling

Zha, Yang; Webb, Spahr C.; Nooner, Scott L.; Crawford, Wayne C.

Determining the melt distribution in oceanic crust at mid-ocean ridges is critical to understanding how magma is transported and emplaced in the crust. Seafloor compliance—deformation under ocean wave forcing—is primarily sensitive to regions of low shear velocity in the crust, making it a useful tool to probe melt distribution. Analysis of compliance data collected at East Pacific Rise between 9° and 10°N through 3-D numerical modeling reveals strong along-axis variations in the lower crustal shear velocities, as well as temporal variation of crustal shear velocity near 9°48′N between measurements spanning 8 years. Compliance measured across the rise axis at 9°48′N and 9°33′N suggest a deep crustal low-velocity zone beneath the ridge axis, with a low Vs/Vp ratio consistent with melt in low aspect ratio cracks or sills. Changes in compliance measured at 9°48′N between years 1999 and 2007 suggest that the melt fraction in the axial crust decreased during this interval, perhaps following the 2005–2006 seafloor eruption. This temporal variability provides direct evidence for short-term variations of the magmatic system at a fast spreading ridge.