A broadband seismometer and hydrophone are rigged for installion at the summit of Axial Seamount during VISIONS'14. Image Credit: Skip Denny, University of Washington, V14.
The ROV ROPOS vacuums out the sediment in a caisson at the summit of Southern Hydrate Ridge. In 2014, a broadband seismometer will be placed in the caisson and covered in silica beads to optimize aquisition of acoustic signals by lowering ocean "noise" (e.g. currents). Photo credit: NSF-OOI/UW/CSSF.
Broadband seismometers provide characterization of seismicity/earthquake activity along tectonic plate boundaries where two key phenomena can occur: large-magnitude subduction zone earthquakes and seismicity associated with migration of melt (magma) beneath the seafloor at underwater volcanoes. Historically, these instruments have been deployed by free-fall from the ship, which has often resulted in poor coupling to the seafloor, and, therefore, poor data quality.
A small array of broadband seismometers will be deployed on the RSN cabled system in 2014 to detect earthquakes along the subducation zone of the Oregon margin and at Axial Volcano. In sedimented areas, the seismometers will be buried beneath the seafloor to obtain the highest quality resolution of seismic waves. On Axial Volcano, where there is little sediment, they will be deployed in small depressions. Because the seismometers will be cabled, they will provide detection of earthquakes in real-time. Much larger arrays of cabled seismometers and pressure sensors are being utilized offshore in Japan to provide early warning dectection of seismic events such as the 9.0 magnitude megathrust Tohoku event and tsunamis (Dense OceanFloor Network System for Earthquakes and Tsunamis - DONET).