Event Detection and Response and Observatories working group

Chair: Chris Fox

Working Group Members:
Japan - Kyohiko Mitsuzawa

This working group was active between 1995 and 2001 to develop detection methods of transient ridge-crest seismic, volcanic and hydrothermal events, and the logistical responses to them through a strategy of international collaboration, and establish a long-term observatory in the Atlantic. This working group developed into the current working group "Monitoring and Observatories"

2001 - ED&R Working Group Update

Reprinted from InterRidge News 10.1 (Apr. 2001) by Chris Fox, Chair

Acoustic monitoring of North Atlantic seismicity continues using six hydrophones (see InterRIDGE News 8.1, March, 1999). The first year of data has been retrieved, processed and posted on NOAA/PMEL web site at http://www.pmel.noaa.gov/vents/acoustics/seismicity/seismicity.html. Results are extremely exciting and there were several presentations at the Fall 2000 AGU meeting in San Francisco. The R/V ATLANTIS will service the array in March, 2001 and the second year's results will be posted as they become available. A third year of observations was approved by the National Science Foundation and a plan to maintain the array as a long-term observation system has been proposed.
Planning for a follow-up workshop for MOMAR (MOnitoring the Mid-Atlantic Ridge) has begun with a tentative date and location of late 2001, early 2002 in the Azores. More information will be broadcast as plans are assembled.
The Working Group Chair, Chris Fox, is scheduled to rotate off the Steering Committee after the June 2001 meeting. Anyone interesting in assuming these duties should let the INTERRidge Office know of their interest.

Gorda Ridge Eruption
At about 0055 GMT on JD 094 (Tuesday April 3, 1800 PDT), volcanic seismicity was detected by the NOAA/PMEL T-phase Monitoring System, which continuously monitors northeast Pacific seismicity using the Navy SOSUS arrays. The current activity is located on the central Gorda Ridge. The initial 18 hours of activity are very similar to earlier JdF events: no large main shock, rapidly repeating earthquakes, the presence of a band of continuous tremor, and evidence of epicentre migration downrift presumably related to magma dike injection. Nearly 1,000 events were hydroacoustically detected in the first 18 hours. The event is relatively loud, being heard on multiple SOSUS arrays even without the benefit of beamforming, with several events being recorded by the Pacific Northwest seismic arrays. No clear acoustic evidence of eruption has been detected as of 4/5 0830 PDT.

The general location is at 42.17 N, 127.083W (or 42 10?N; 127 5?W). This location is on the segment just below the North Gorda segment, which was the site of the February 1996 eruption. The location is analogous to that event, being located near the summit of the "narrowgate" on the south side.

A response effort is currently under discussion by the combined event response team funded by NSF RIDGE and the NOAA Vents Program. Jim Cowen (U Hawaii) and Bob Embley (NOAA/PMEL) are coordinating the response effort. Equipment has been pre-staged in Seattle for the response.
Details of the event, response coordination, and all new developments will be broadcast at the following web site: http://www.pmel.noaa.gov/vents/acoustics/seismicity/nepac/gordaridge01.html

1998 - October - ED&R Working Group Update

Reprinted from InterRidge News 7.2 (Oct. 1998) by Chris Fox, Chair

The MOMAR (MOnitoring the Mid-Atlantic Ridge) workshop is planned for October 28-31, 1998 at the University of Lisbon, Portugal.

Volcanic activity was detected by NOAA/PMEL using the U.S. Navy SOSUS on Axial Seamount on the central Juan de Fuca Ridge in January, 1998. The activity lasted for 12 days and produced over 8,000 detectable earthquakes, the most energetic event detected to date. Seafloor and water column instruments were in place before and during the activity. A combined US RIDGE/NOAA VENTS Program cruise on the Wecoma sampled hydrothermal plumes from the site and deployed Ocean Bottom Hydrophones. Additional cruises are taking place in the summer of 1998 with seafloor ROV work planned. A special session is planned for the 1998 Fall AGU meeting.

Funded Proposals

Juan de Fuca/Gorda Ridges
- Jim Cowen (U Hawaii) and Marv Lilley (U Wash.) were funded to lead a rapid response to the Axial Seamount event using the Wecoma.
- Jim Cowen (U Hawaii) and others are funded to pre-deploy oceanographic equipment for use in a rapid response mode following NOAA/PMEL SOSUS detection. Proposal follows the model developed by RIDGE for holding back funds to be made quickly available following detection of an event by SOSUS.
- Spahr Webb and Rob Sohn (SIO) are funded to deploy a large array of OBS's over the summit of Axial Seamount for long-term monitoring of passive seismicity.
- Bill Menke and Maya Tolstoy (LDEO) are funded to shoot an active seismic experiment to the Axial Seamount OBS array to determine the internal structure of the magma system.

East Pacific Rise
Dan Fornari (WHOI) and others are funded to investigate sites of possible volcanic activity along the EPR identified by the NOAA/PMEL autonomous hydro-phone array. A cruise is scheduled for early 2000.

Mid-Atlantic Ridge
Debbie Smith (WHOI) and Maya Tolstoy (LDEO) and Chris FOX (NOAA) are funded to deploy an array of autonomous hydrophones along the MAR between 15°N and 35°N for two years. Initial deployment is scheduled aboard the Ewing for Feb./Mar. 1999 with the first data returned in Dec. 1999.

Acoustic Detection Infrastructure
Northeast Pacific

The SOSUS array in the northeast Pacific required for monitoring the Juan de Fuca and Gorda Ridges are failing, and the U. S. Navy does not have adequate funds to affect repairs. A consortium of Pacific SOSUS users, including Scripps, Univ of Washington, NOAA PMEL, and the Naval Postgraduate School was recently formed with support from the U.S. National Ocean Partnership Program. This consortium, with close cooperation from the Navy, hopes to begin participating in cable repairs using combined university, NOAA and Navy assets.

Atlantic SOSUS
The Atlantic SOSUS arrays are still being decommisioned by the U. S. Navy and no civilian users have stepped up to restore and operate them. It is hoped that a mechanism similar to that developing for the Pacific can be created in the next few years.

Autonomous Monitoring
The autonomous hydrophone arrays deployed by NOAA/PMEL continue to advance. Equatorial Pacific acoustic monitoring is in its third year. A new six component array will be deployed in the North Atlantic in Jan/Feb 1999 for a two-year pilot experiment. These instruments will be able to record for one full year. A new generation of instruments capable of continuously recording seismic frequencies for up to five years is under development. This new technology may allow long-term monitoring of remote ocean areas.

Observatory Infrastructure
RIDGE sponsored efforts continue to develop monitoring technologies for observatories at Endeavour and Cleft. Russ McDuff (U Wash) is funded for heat flow studies at Endeavour segment.

NOAA VENTS is establishing an observatory at Axial Seamount (which was proposed before the eruption) called NeMO (New Millennium Observatory) that will concentrate on rapid collection of microbes expelled from the subseafloor biosphere following seismic events detected by SOSUS. Instrumentation includes water column moorings, seafloor volcanic system monitors, acoustic extensometers, and pre-positioned autonomous underwater vehicles.

1998 - March - ED&R Working Group Update

Reprinted from InterRidge News 7.1 (March 1998)

Dear Colleagues,

In mid-1997, the InterRidge Steering Committee asked me to assist in renewing the international effort to build a detection and response capability for broad areas of the world ocean. Currently, real-time remote detection of mid-ocean ridge volcanic seismicity is restricted to a few technologies and a small portion of the global ridge system. Even if detection capabilities were more widely available, the logistics, resources, and technologies for field response would remain difficult problems. Despite these hurdles, the potential pay-offs of detection and response are great, allowing the direct study of active ridge processes. There are also valuable opportunities to study ridge processes through non-real-time detections and later field "evaluations" rather that "rapid responses".

Currently the main focus of this InterRidge Project is on organizing the upcoming InterRidge Workshop on Designing Long-term monitoring systems of the Mid-Atlantic Ridge, which will be held next Fall in Lisbon, Portugal. This workshop will be important in defining the specific directions that InterRidge should take in pursuing the goal of an Atlantic observatory.

In the following sections, I have provided my personal perspective on the current state of detection and response studies of ridge processes and some suggestions for possible strategies that are tractable in a constrained monetary environment. These ideas are not intended to be the ideal approach, but one that may be achievable through leveraging a wide range of resources. This web site is a first step toward improving communications, and I hope it will also kindle further interest for studying the North Atlantic. Please feel free to contact me via e-mail with any suggestions or ideas to accomplish these goals. I look forward to hearing from you.

Chris Fox, Chair

"Event Detection and Response" refers to a strategy for studying active ridge processes combining continuous monitoring of activity from long range, either in real-time or non-real-time, localizing that activity, and conducting a wide-range of field observations and sampling at the site as soon as possible. The strategy differs from the concept of an "observatory" in that no specific site is designated and instrumented in advance, but rather, the detection system defines the site, and the instrumentation is emplaced after (or during) the activity. The most difficult approach logistically combines real-time detection with "rapid response". A more tractable, but still challenging, approach combines non-real-time, but still long-range detection, with later event "evaluations" at the site of activity. Over much of the global ridge system, this latter approach is the only one currently feasible.

The concept of "Detection and Response" as a strategy for studying active processes on the mid-ocean ridge has been proven in recent years through the combined efforts of the U.S. RIDGE Program and the NOAA VENTS Program in the northeast Pacific Ocean. Taking advantage of civilian access to the U.S. Navy's SOund SUrveillance System (SOSUS), NOAA investigators have developed techniques to use underwater acoustics to detect volcanic seismicity at long range and localize the activity to within a few kilometers. On three separate occasions since 1991, U.S. and Canadian investigators have successfully responded to these detected events and documented the geological, chemical, and biological processes taking place on site. Even in the one case where the site could not be visited until after the activity ceased, valuable studies of the effects of mid-ocean ridge processes were conducted.

The development of real-time detection technology in other parts of the global ocean has not been as successful as the northeast Pacific effort. The SOSUS arrays were deployed in response to military needs and therefore cover only limited parts of the global ocean. Although the North Atlantic, for example, is one area with SOSUS coverage, the array geometries are not as well placed for ridge studies as the northeast Pacific. An earlier effort to implement real-time monitoring in the North Atlantic is no longer active and would be difficult to revitalize. Other potential sources of real-time detections are from land seismic networks such as those in Iceland and French Polynesia, but the sensitivity of these systems is lower than hydrophone arrays and the locations less accurate. Other seafloor technologies, such as ocean bottom seismometers or borehole seismometers, could be made real-time if undersea cables or other technologies were applied, but they would still be limited in their spatial coverage compared to hydroacoustic methods. They are probably best used as event response instruments.

Another approach to long-range ocean acoustic monitoring was developed by NOAA for use in the Eastern Tropical Pacific. Since NOAA maintains the eastern portion of the TOGA/TAO buoy array for ocean climate monitoring, access to designated sites by NOAA vessels on a semi-annual basis is assured. An Autonomous Hydrophone Array was deployed by NOAA VENTS in May, 1996, and continues to monitor the East Pacific Rise between 20°S and 20°N and the Galapagos Ridge west of 90°W. Unlike the SOSUS arrays, the data is stored within the instruments and can only be recovered when the instrument is serviced. This array provides the same sensitivity and accuracy as the SOSUS arrays, but presently provides data only at six-month intervals, although efforts are underway to make them real time. The current detection delay precludes "rapid response" in the area, but significant studies are possible through a thorough examination of the active sites with the knowledge of when the site was last active. It is doubtful that a "rapid response" effort could be mounted in the more remote areas even if real-time detection was available.

The ability to respond to an active or recent event on the mid-ocean ridge requires the coordination of ships, personnel, and equipment, as well as a new approach to scientific proposal writing and funding. The first and most critical aspect of event response is communication, between investigators performing the detections, investigators coordinating or participating in the response, ship schedulers, and program managers funding the effort. There is also general interest by the broader scientific community, the public, and the media. Experience in the northeast Pacific has shown that the combination of the World Wide Web and programs such as InterRidge have provided an excellent solution. Initial announcement of the detections are broadcast to the scientific community through the InterRidge and associated mailing lists. Further information on monitoring of the event, and on the results from any field response to the event are posted on a web sites set up specifically for the event. This model can be improved upon and utilized in the future.

The availability of ships, personnel, equipment, and funding remains the most difficult aspect of this endeavor. In an ideal world, there would be adequate resources to "set aside" some of these needed components for event response. In practice, it is not practical to maintain ships, personnel, and extensive instrumentation "standing by" on the pier to respond to an event that lies at some undetermined time in the future. Likewise, funding a field program for some undetermined time and place in the world ocean is difficult at best. A great deal of thought has gone into this area by the U.S. RIDGE community and the successes in the northeast Pacific have been due in part to this planning and in part to an ideal set of circumstances.

In the northeast Pacific case, there are many factors working to make the response effort tractable, besides the availability of SOSUS detections. First, the partnership between RIDGE investigators and the NOAA Vents Program has been mutually beneficial. In the past, NOAA has maintained a large fleet of ships in Seattle, WA that increased the possibilities that some time could be allotted to event response. In addition, several Canadian and U.S. UNOLS vessels are based in the area. Also, the NOAA Vents Program has provided a small team of investigators focused on this effort for several years, bringing expertise and basic equipment. The RIDGE community has provided complementary expertise and specialized instrumentation such as cameras, seismometers, geophysics, gas chemistry, etc. to join forces with NOAA's team. The Canadian ROV ROPOS, based in British Columbia, has been invaluable in past efforts. The proximity of the northeast Pacific ridges to shore and the number of researchers actively studying in the area have also made it an ideal area for rapid response.

Coordinating responses to more remote areas of the global ridge system with a wider international involvement is perhaps the largest challenge facing this working group. Funding must first be in place for participants. In the U.S., the NSF has created a funding model in which funds for response preparation may be released to the investigator first, and the remainder for field work is then held until needed. This approach has not yet been tested, but provides a reasonable model for international efforts as well. Ideally, government agencies such as NOAA in the U.S., can be involved in the effort to provide more stable resources. The coordinating of ships, personnel, and equipment are a most difficult proposition and must be thoroughly addressed.

The current state of detection and response for the global ridge system can best be discussed in terms of detection capability, since without detections there can be no response. The SOSUS monitoring effort in the northeast Pacific continues by NOAA's Vents Program, and it is likely that this capability will remain in place. The same is true of NOAA's eastern equatorial Pacific monitoring effort using autonomous hydrophone arrays. Icelandic and French Polynesian seismic arrays remain active. There are some acoustic monitoring efforts ongoing in New Zealand that may provide detections for activity in that region.

There are also efforts proposed but unfunded at present. These include proposals to deploy an autonomous hydrophone array in the North Atlantic and field expeditions targeted at evaluating active ridge sites defined by the existing autonomous arrays in the eastern Pacific. Many of the relevant SOSUS arrays in the North Atlantic have been decommissioned, although there are some efforts within the U.S. to reoccupy those stations for scientific use. The previous research program that was using the active military SOSUS in the Atlantic is no longer active and there are no known investigators interested in revitalizing that effort.

There is an active community of researchers beginning to exploit the use of undersea cables for scientific use (another InterRidge working group), but there are no large scale monitoring efforts planned for the near term. There are also plans for new cabled, underwater acoustic arrays for use in monitoring underwater nuclear testing, but they are several years away. Development has begun at NOAA/PMEL to allow real-time transmission of acoustic data from autonomous hydrophone arrays using buoy and satellite technology rather than more expensive cables, but this capability is also several years away.

In the near term, significant progress in event detection and response can be derived by using the current detection technologies to best advantage while developing new technologies for the future. On the detection side, many of these efforts are underway with acoustic, seismic, and undersea cable efforts. Other potential technologies may be discovered in the coming years. For the response side, many possible strategies offer themselves.

DETECTION: Although the NOAA/PMEL effort has provided proven real-time detection capabilities using hydroacoustics, there is much more to be learned using these techniques that can not be undertaken by the small NOAA research group. Questions in acoustic propagation, location accuracy, interpretation of the source parameters, and other inversions can be taken much further than at present. To address these questions does not, however, require the collection of new major data sets. The NOAA data, particularly the unclassified data from the autonomous systems, is available for study and there are several ocean bottom seismometer data sets collected within hydrophone coverage to allow direct comparison. On the technology side, there may be other monitoring strategies beyond hydroacoustics that can provide valuable understanding of the ridge systems, based on cables, satellites, tomography, etc. that have not been exploited.

RAPID RESPONSE: There are certain problems that can only be addressed with rapid response, where instruments are emplaced while the event is active. Studies in ground deformation, plume dynamics, and the subsurface biosphere all require that investigators arrive at the active site near the time of the activity (days to weeks). For these types of study, investigators are encouraged to participate in the one area of the ridge system that has an existing real-time hydroacoustic monitoring capability and some infrastructure for rapid response: the northeast Pacific spreading centers. For studies of active volcanic processes, or perhaps the subsurface biosphere, highly active targets off the ridges may be attractive, such as Loihi Seamount off Hawaii (with an operational real-time observatory) or 'Kick'em Jenny' in the Lesser Antilles. Also, the Icelandic seismic array is capable of detecting activity on the Mid-Atlantic Ridge near Iceland, and was in fact the site of one of the first response efforts. So as new areas become available in the future for real-time monitoring, the technology and expertise developed at these sites can be transferred, but for the foreseeable future, the northeast Pacific is the best available site for rapid-response ridge crest studies

EVENT EVALUATION: This is the area that has the most promise for new discoveries. Monitoring technology for hydroacoustic detection is in place in the equatorial Pacific and is currently being proposed for the North Atlantic. A better understanding of these ridge systems, which differ substantially from the Juan de Fuca system, could be a valuable focus for field research in the coming decade. These could take the form of targeted field experiments or "opportunistic" investigations using available monitoring results with scheduled cruise to the general area. Such investigations would lead directly to a better understanding of the active processes of ridge systems as well as providing important ground truth for the monitoring effort.

All of the opinions expressed here are my own, and I welcome any comments/criticisms.
Chris Fox, NOAA/PMEL