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Gorda
Ridge Seismic Event 2001: Event Details |
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 DETAILS:
INTRODUCTION
Volcanic
seismicity was detected by the NOAA/PMEL T-phase Monitoring
System beginning at about 0050GMT on JD 094, 2001 (Tuesday
April 3, 1750 PST). The system makes use of signals collected
by the U.S. Navy's SOund
SUrveillance System (SOSUS) in the northeast Pacific.
The activity is located on the central Gorda Ridge near 42.15'N;
127.05W (or 42 9'N; 127 3'W). This location is on the Jackson
segment just below the North Gorda segment, which was the
site of the February
1996 eruption. The activity is closely analogous to that
earlier event, being located near the summit of the "narrowgate"
on the south side.
(click
image for full-size)
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SEISMIC
CHARACTER
The nature of the activity is consistent with other examples
of volcanic seismicity detected hydroacoustically and documented
by field observations. These events are characterized by low-magnitude
earthquakes emergent from background ocean ambient noise without
a large "mainshock" to initiate the sequence. This
is then followed by days to weeks of rapidly repeating (up to
100 events/ hour) small earthquakes and a nearly continuous
band of volcanic tremor in the range of 2-30 Hz. The event is
relatively loud, being heard on multiple SOSUS arrays even without
the benefit of beamforming. |
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Click for explanation
Spectrogram of the onset of activity |
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Click
for larger image
Histogram
of seismic activity. Each bar represents the number of events
detected in one hour
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 EARTHQUAKE
LOCATIONS
Earthquake
epicenters inferred from hydroacoustic analysis show the
volcanic seismicity emanating from the central Gorda Ridge
near 42.15'N; 127.05W (or 42 9'N; 127 3'W). Comparison with
multibeam bathymetry from the area indicates the site to
be within the central axial valley of the second segment
from the north (Jackson segment). The activity began just
below the segment high ("narrow gate") and appears
to be migrating to the south, while activity continues in
the narrow gate area. This is very similar to the behavior
of the North Gorda eruption in 1996.
Events
vs. latitude
Earthquake
locations derived from hydroacoustic monitoring
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go
to ->LAND SEISMIC ARRAY REPORT
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Address
inquiries to:
Robert Dziak
- Seismologist - robert.p.dziak@noaa.gov
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