Research > Keck Seafloor Seismic Network - Microearthquakes and Hydrothermal Systems
The W.M. Keck Foundation supported a five-year prototype NEPTUNE experiment to conduct prototype seafloor observatory experiments to monitor the relationships between episodic deformation, fluid venting and microbial productivity on the Endeavour segment of the Juan de Fuca Ridge and at the intersection of the Nootka fault and the Cascadia subduction zone. At the Endeavour, the experiment was sited on the central portion of the segment in a region where the spreading axis is characterized by a 100-m-deep, 500-m-wide axial valley that hosts five high-temperature hydrothermal vent fields spaced 2-3 km apart. The objectives of the experiment were to develop experiments to monitor local and regional seismicity around the vent fields in conjunction with the deployment of sensors and samplers to monitor temporal variations in the physical, chemical and ultimately microbial characteristics of the hydrothermal fluids.
|Configuration of the Endeavour Seismic Network (Full Sized Version)|
The seismic portion of this project is a collaborative project involving my group at the the University of Washington, the University of Oregon (Doug Toomey and Emilie Hooft), and Monterey Bay Aquarium Research Institute (MBARI) (Paul McGill and Debra Stakes). We installed the Endeavour seismic network in the summer of 2003 - it was the first seismic network on a mid-ocean ridge in which the sensors are deployed with an ROV beneath the seafloor in order to ensure good coupling and minimize the effects of current-generated noise. The comprised seven MBARI GEOSense three-component short-period corehole seismometers and one buried MBARI Guralp CMG-1T broadband seismometer. In August 2004, we serviced the network, recovered the first year of data, and deployed additional seismometers on the Nootka Fault and Explorer Plate. As part of the VISIONS’05 cruise in September 2005, we recovered the Nootka and Explorer plate instruments and redeployed the Endeavour network for a third year. The Endeavour network was recovered in August 2007 during a student research cruise to the Juan de Fuca Ridge. Five of the seismometers will be deployed on the NEPTUNE Canada seafloor cabled observatory in the Summer of 2010 to form the first permanent cabled seafloor seismic network on a mid-ocean ridge.
|Epicenters for 2003-2004 from the first pass analysis (Full Sized Version)|
The first pass analysis of the 2003-2004 earthquake data was completed during a research apprenticeship class at the University of Washington’s Friday Harbor Laboratories. The apprentices located over 12,000 earthquakes along the ridge-axis of the Endeavour, of which ~3,000 proximal event occur within or near the network and appear to be associated with the hydrothermal systems.
|Epicenters for 2003-2004 from the second pass analysis (Full Sized Version)|
A second pass analysis of the proximal earthquakes was completed by two of the apprentices - Calla Schmidt and Hemali Patel - with additional analysis by two IRIS undergraduate interns Danny Bowman from Macalester College working at the University of Washington and Jonathan Parker from the Colorado School of Mines working at the University of Oregon. William Wilcock has worked to apply cross-correlation and relative relocation techiques to obtain improved locations for earthquakes beneath the vent fields and has also obtained focal mechanisms for 170 earthquakes from P-wave first motions and S/P amplitude ratios.
The majority of earthquakes occur within a narrow depth range centered at 2-2.5 km depth and in an intense zone of seismicity within the reaction zone overlying the axial magma chamber. The levels of seismicity are strongly correlated with the intensity of venting. There are particularly high rates of seismicity beneath the Main Endeavour and High Rise Fields and substantially lower rates to the north beneath the relatively inactive Salty Dawg and Sasquatch fields. The focal mechanisms below the High Rise and Main Endeavour Fields suggest that pressurized magma was being steadily into the axial magma chamber during 2003-4 and led us to postulate that ongoing magma injection may may be necessary to support the most vigorous hydrothermal sites . These results were recently published in Nature Geosciences (link the PDF file on their web site)
|Cross-section across the ridge axis showing earthquakes overlying the axial magma chamber imaged by Van Ark et al. (2007) (Full Sized Version)|
Emilie Hooft at the University of Oregon have been analyzing the seismicity associated with a large swarm in February/March 2005. The swarm was detected by the US Navy's SOSUS hydrophone arrays and a response cruise searched unsuccessfully for a volcanic eruption. The epicenters determined with the Keck network show that the swarm was extremely complex with the center of activity migrated southwards over about a week, jumping betwen four regions of seismicity. A paper describing these results is in preparation
Robert Weekly, a graduate student at the University of Washington has developed an automatic location algorithm to locate earthquakes for the 2nd and 3rd years of the delpoyment and is preparing a paper describing the full 3 years of seismicity. You can download a poster (9 MBytes) showing some of his latest results.
Go to the Downloads page to get the earthquake catalog for 2003-2004. The full 3-year catalog will be available early in 2010.