Time critical studies [TCS]

Latest news

(April 29, 2008) A large earthquake swarm began April 22, 2008 on the northern segment of the Gorda Ridge. This event continued April 23, 2008 but was tapering off quite a bit. The response cruise aboard R/V Wecoma obtained 2 CTD casts at Gorda on the way into port. Shipboard analyses did not suggest a plume but onshore analyses are required before such occurrence can be ruled out. Updates will be available.

An intense Juan de Fuca plate earthquake swarm (3/30/08 – 4/9/08) subsequently decreased and later earthquakes shifted from the intraplate area to Blanco fracture zone (mainly cascade depression and Blanco Ridge). A short response cruise (4/20/08 – 4/24/08) obtained a series of CTD casts to assess potential water column expressions associated with the earthquakes.

For more information on the response cruise, please visit the PMEL event response page
(April 21, 2008) The intense Juan de Fuca plate earthquake swarm (3/30/08–4/9/08) has now decreased and recent earthquakes have locations that are shifted from the intraplate area to Blanco fracture zone (mainly cascade depression and Blanco Ridge) ( view seismicity map). A short response cruise from April 20 – 23, 2008 is investigating potential water column expressions associated with the earthquake swarm.
(30 March 2008) On Sunday March 30, 2008, a large earthquake swarm began within the central Juan de Fuca plate, located ~150 nautical miles west of the Oregon coast and ~ 70 km north of the Blanco Transform Fault (enclosed map). This earthquake swarm (with red, yellow, brown, purple dots representing different days) is located on a basin between two faulted basement highs that rise above the surrounding, deep abyssal sediments. The swarm, located using the SOSUS hydrophone arrays, has produced more than 600 earthquakes in the past 10 days. This earthquake swarm is unique since it is the first time in 17 years of SOSUS recordings that a set of earthquakes this focused and intense has occurred within the middle of the Juan de Fuca plate away from the major, regional tectonic boundaries. The abyssal hill nearest the swarm location appears to be on a curved structure that trends northwestward from the Cascadia Depression in the BTFZ toward the Juan de Fuca Ridge. However, seismicity decay rates indicate this is not a standard mainshock-aftershock sequence and some process is sustaining a high stress rate in the crust (Figure 2).

Given the midplate location of the swarm, a volcanic event response effort does not seem warranted. However, this situation represents a rare opportunity to learn more about this very unusual event. Accordingly, we are exploring options for ships-of-opportunity that might be able to take some key samples and measurements with a CTD over the earthquake swarm site with a minimum of time and effort.
- Figure 1. View map of the earthquake locations
- Figure 2. See plots of rates of seismicity
(22 November 2007) Using SOSUS, we detected a small swarm of 5 earthquakes centered on a seamount along the west flank of the Cobb segment of the Juan de Fuca Ridge (View map, general earthquake locations shown with star). The swarm began at 1400Z on 22 November 2007 and lasted for 1 hour. Given the small number of earthquakes, a response cruise is certainly not warranted, however it is interesting from the standpoint that this part of the Cobb segment continues to exhibit a steady, low-level amount of seismicity.
View map, general earthquake locations shown with star
(1 August 2007) There has been a progression of earthquakes beginning at the Northern Gorda, moving to the eastern then western Blanco Transform, and ending at the Cleft-Vance intersection at the southern Juan de Fuca Ridge. This past week of earthquake activity recorded by SOSUS contrasts with low levels of activity that characterized the prior three months. The recent plate boundary sequence began on July 18 at 2014Z with a large earthquake that occurred in the central valley of the northern Gorda Ridge which was followed by 20 aftershocks.
(24 July 2006) Review sequence of findings and response cruise efforts for East Pacific Rise 9°50'N 2005-2006 eruption
Swarm Fan email list to distribute information about the real-time detection of moderate-sized earthquake swarms and tectonic events on the Juan de Fuca Ridge or other evidence of spreading center activity that R2K is following.
See the TCS news archive for previous TCS news and updates.

Resources

Event response contacts.
PMEL VENTS program website and ocean seismicity pages.
A list of relevant references, up to the present day, is available online for each integrated study site.
Request samples for analysis.

TCS overview

Introduction to TCS
Insight from TCS
New proposals sought
This TCS overview is also available as a 1MB, 11-page pdf download (includes all figures)

Introduction to TCS

The Time-Critical Studies (TCS) Theme of Ridge 2000 focuses on observations of the immediate geochemical and geobiological consequences of magmatic and tectonic events along the global mid-ocean ridge system.

To date funding has centered on the Juan de Fuca and Gorda Ridges (Figure 1) which are within the range of the U.S. Navy’s Northeast Pacific Sound Surveillance System (SOSUS). NOAA’s T-Phase Monitoring Program has accessed SOSUS in real-time since 1993, providing the TCS community with detection of seismicity associated with eruptive or tectonic activity along these two ridges (Figure 2). This remote detection of earthquake swarms along the N.E. Pacific mid-ocean ridge coupled to NSF funding for pre-event staging of equipment and supplies has allowed directed and increasingly well-organized field responses to the event site. Major rapid and follow-up response cruises have been successfully mounted to 1993 CoAxial, 1996 and 2001 Gorda Ridge, the 1998 Axial Volcano, and 2001 Middle Valley magmatic episodes. The logistical approach required to study these events has been greatly facilitated by the RIDGE/Ridge 2000 programs and collaboration between university, NOAA and Canadian investigators. Not only have our studies of these events significantly impacted our ideas on the nature of crustal accretion, but they also have led to the discovery and preliminary documentation of a previously unrecognized biomass reservoir that lives below the seafloor and is swept out during these cataclysmic events, and to increased appreciation of the formation and thermal, chemical and biogeochemical implications of the “Event Plumes” commonly associated with seafloor magmatic events.

Insight from TCS

Some examples of new insights into the causes and implications of MOR magmatic (and tectonic) events that have been derived from TCS efforts include:

SOSUS system is an effective means of remotely detecting MOR seismic events (Figure 2);
SOSUS detected seismic events can be associated with episodes of significant magmatic activity within the crust and seafloor eruptions;
Events occur along the MOR with high frequency (>0.5 year within Northeast Pacific SOSUS system in 1993–2003);
Event plumes are commonly associated with seismic events; multiple event plumes can be released during a seismic event (Figure 3 and Figure 4). (At least 7 event plumes have been encountered in the Northeast Pacific MOR);
Thermochemical fluxes of event plumes have a distinct signature, differing qualitatively from those of chronic plumes;
Total thermochemical fluxes associated with events change rapidly with time following the event (Figure 5);
Subseafloor populations of extremophiles are released in association with events (Figure 6);
Lagrangian drifter floats (e.g., RAFOS) are an effective means of tracking event plumes for time series observations of physical and biogeochemical processes that ultimately link event thermochemical fluxes to the global ocean (Figure 4).
210Po-210Pb and 210Pb-226Ra dating of young-appearing lavas allow determination of high-resolution eruption ages, eruption durations, and age offset with antecedent topography. They can also provide event “verification” in cases where no seismic data is available at suspected eruption locales (Figure 10 and Ridge 2000 Events 3, Spring 2005, 28-30).

New proposals sought

The Ridge 2000 Program is seeking proposals for innovative ways of augmenting and extending existing Time Critical Studies. Proposals are encouraged for all aspects of TCS, including event detection, rapid response efforts and instrument development. Even the most rapid shore-to-event site response will not be fast enough to record the earliest subsurface and water column expressions of magmatic events. The development of alternate ultra-rapid response methods are needed to extend the ship response efforts. These might range from air-droppable monitoring devices (e.g., vertical profilers, moorings, AUVs) to in situ sensors. The latter include continuous recording instruments, as well as more sophisticated autonomous instruments/vehicles that are pre-programmed to respond to signals detected by an array of physical, chemical and biological sensors. In this regard, Time Critical Studies should get a helping hand from the increasing instrument deployments at R2K’s Integrated Studies Sites. If a future event occurs at an established Integrated Studies Site, it is likely that the earliest perturbations will be captured by in situ monitoring instruments, providing data that could be acquired in no other way.

Presently, NSF will fund primarily Time Critical Studies supported by real-time detection capabilities through the Ridge 2000 program. Nevertheless, the usefulness of autonomous monitoring systems is clearly recognized. While unable to provide from the Ridge 2000 program, Ridge 2000 may assist such efforts with communication and other logistical support. Non-real-time detection uses autonomous hydrophone arrays (e.g. see PMEL VENTS Program seismicity page) to monitor activity along large sections of the mid-ocean ridge system that are not accessible to real-time monitoring (e.g. equatorial East Pacific Rise; Galapagos Spreading Center; northern Mid-Atlantic Ridge). The principal scientific purpose of such monitoring is to determine the size, distribution and frequency of events in different, complementary parts of the global mid-ocean ridge system. Such events, although interesting in their own right, may be important triggers, precursors or complements to activity recorded in more detail at the Integrated Studies Site. For instance, the recovery of data from the EPR autonomous hydrophone arrays indicated a significant seismic event near 8° 37' N EPR, that led to a “ship-of-opportunity” delayed response to this site (Bohnenstiehl et al. 2003). Similarly a delayed response was mounted to investigate possible magmatic effects from a significant earthquake swarm at the hydrothermally active Lucky Strike segment in 2001 that was identified from recovered MAR autonomous hydrophone arrays.