image for full size)
March 9 Update: Five earthquakes occurred
overnight on the ridge between the southern west valley
and the northern Endeavour segment at ~48-18'N, 129-02W.
Overall, however, earthquake remain at background levels.
Three magnitude 5.2, 5.1 and 4.3 earthquakes occurred
on the northern Gorda Ridge
segment over a 7.5 hr period beginning at 02:34Z on
links covering this event:
(Associated Press, RIDGE 2000, etc.)
there was another swarm of earthquakes in this same
area in October 2004.
on images below for full-size versions of the plots
Sunday morning 27 February at 0031Z, there has been
an ongoing, intense earthquake swarm on the Endeavour
segment of the northern Juan de Fuca Ridge. SOSUS has
detected 3,742 earthquakes over a 5.5 day period. Event
counts were as high as 50-70 per hour which is very
similar in scale to past seafloor spreading events at
Middle Valley in 2001 and Endeavour in 1999. We are
currently working through the data, but have a preliminary
location of 48-14.5'N 128-57.6'W which is ~36 km north-northeast
of the Main Endeavour vent field and a few kms east
of the intersection of the Heck Seamounts with the JdF
Ridge axis. We have not located enough events yet to
evaluate whether or not the earthquakes have migrated,
or are currently migrating along the ridge axis. The
sequence has also produced three large earthquakes (mb=4.5,
4.8, 4.9) which have been detected by NEIC, UW, PNSN.
lists the location of the largest event a little east
of the SOSUS location at 48-18.6'N 128-49.2'W. The Canadian
Geological Survey/Pacific Geoscience Center has computed
mechanisms for the largest earthquakes.
the event response cruise on the R/V Thompson:
Response cruise summary map:
white stars = CTD casts
white lines & stars = CTD tows
blue lines & dots = camera tow
red dots = earthquake epicenters
Bathymetry is NOAA multibeam.
9: It appears unlikely that this February/March
2005 earthquake swarm induced corresponding expression
at the seafloor (e.g., eruptive flow) or in the water
column (e.g., hydrothermal chronic or event plume).
The in situ and ship-board physical and chemical data
from the 3 long tow-yo casts and 7 vertical casts revealed
no water column signal that can be clearly associated
with the recent earthquake swarm, whether magmatic or