HIGHER LATITUDES BEGIN TO SHOW EFFECT OF CONTINUING GEOMAGNETIC STORMS

SUMMARY

The moderate to strong geomagnetic storms of the past week continued
unabated today. Seismicity in regions within 35 degrees of the North
Geomagnetic pole was very high over the past 2 days. This may be an
effect of this continuing geomagnetic activity.
The strongest earthquake of the day was a Ms 6.0 (GSSC) (M 5.9 NEIS)
in the Kuril Islands (47N). Although the Kurils are normally considered
an area of high seismicity, this event occurred in a region of that
Island chain which is relatively aseismic. The event today is the
largest within 100 km of it's epicenter since June 13, 1987. The last
event of Ms >=5.8 was on Feb 5, 1999 (Ms 5.8) and March 27, 1992 (Ms 5.9).
Only 5 earthquakes of Ms>=5.8 have occurred in this region in the
past 15 years.
In the United States and Canada a series of regionally significant
earthquakes has been occurring in the northern portions of the U.S
and in southern Canada. The most unusual of these was an event on the
New Hampshire/Vermont border last night (44N). This event has been given
magnitudes ranging from Ml 2.2 (LDG) to LG 2.4 (NEIS) to ML 2.9 (GSC).
This is the largest recorded event on the NH/VT border since August
21, 1996 when a Ml 3.8 occurred. A Ml 2.9 was also recorded in the
Charlevoix Fault zone (47N) along the St. Lawrence Seaway today. This was
the largest event within 50 km of it's epicenter since May 22, 2001.
There have been 8 days since 1-1-1998 on which an event of Ml>=2.8
occurred in this region.
Several unusual events have also occurred in the Rocky Mountains
in the past two days. These have included an event at 43N in Eastern
Idaho yesterday of Ml 3.3; a series of events near Summit, UT of Ml
2.5, 2.6, 2.1, and 1.9 and an Md 2.8 in Montana this afternoon at 46N.
Only 2 events of ML>=2.5 have occurred within 50 km of the Montana
earthquake - those being on Nov. 8, 1997 (Ml 3.8) and Setp. 27, 1995 (Ml 3.8).
The largest events in the U.S. today appear to have occurred
off the Coast of Oregon about 44N 128-129W with two events of Ml 3-4.5.
Reporting of locations and magnitudes for this region by PNSN is
very poor and any event with a given magnitude of 2.5-3.0 in this
area is likely to have true magnitude in the 3.5-4.5 range.
In the Yukon Territory, Canada, a swarm of unusual event is also
occurring. These are at Haines Junction (60N) (Ml 3.3, 3.0, 2.1, 2.4, 2.4);
and northwest of Ft. St. John, B.C. (Ml 3.2). This area appears to
be very sensitive to strong geomagnetic storms. On April 14 a strong
earthquake occurred nearby with Ml 5.4. A strong geomagnetic storm
had begun on Apr. 11 and lasted through Apr. 14. The strongest
aftershocks occurred on April 25 (Ml 3.0) which followed a strong
geomagnetic storm which began on Apr 22 and lasted through Apr. 25; on
June 12, 2001 (Ml 3.9) which also followed a strong geomagnetic storm
which had begun on June 9 and lasted through June 11.
To provide an idea of how the current geomagnetic storms rank
with others this year, the strongest geomagnetic storms thus far this year
have occurred as follows with highest high latitude A-Index given:

January 21-24 A-index: 44
March 19-20 A-index: 105
March 28-31 A-index: 93
April 11-14 A-index: 100
April 22-25 A-index: 52
May 12-15 A-index: 36
June 9-10 A-index: 31
June 18-21 A-index: 46
August 5- 6 A-index: 37
August 17-18 A-index: 60
September 23 A-index: 51
Sep 29-OCT 03 A-index: 82

In terms of strength and duration, the current storm is the
strongest of the year, having now lasted 5 days at active levels.

Data Sources:
http://sec.noaa.gov/ftpdir/indices/old_indices/2001Q4_DGD.txt
http://sec.noaa.gov/ftpdir/indices/old_indices/2001Q3_DGD.txt
http://sec.noaa.gov/ftpdir/indices/old_indices/2001Q2_DGD.txt
http://sec.noaa.gov/ftpdir/indices/old_indices/2001Q1_DGD.txt

GLOBAL

Seismic activity remained moderately high today throughout the
world. The strongest events were the Ms5.9/6.0 in the Kuril
Islands, but a Mb 5.4 also occurred in West Irian, New Guinea.
Events of Mb>=4.3 since the last report have occurred in New Britain
(Mb 4.8,4.9); the Fiji Islands (Mb 4.4, 4.3); the Solomon Islands (Mb 4.6);
New Britain (Mb 4.9); Argentina (Mb 4.9), Samoa (Mb 4.7); the Kermadec Isl.
N.Z. (Mb 4.8); the Ryukyu Islands south of Japan (Mb 4.7) and the Molucca
Sea south of the Philippines (Mb 4.7). Most of these lie very near the
geomagnetic equator.

U.S./CANADA

Seismic activity in the U.S. south of 40N was relatively quiet
today. Only 4 earthquaakes of Ml>=2 have occurred in the California/
Nevada region since last report. The most active areas were
Sylvannia, NV (Ml 2.5...); Coso Junction CA (Ml 2.4 and 2.6)
and Yountville, CA (Ml 2.2...). Minor activity continued in the
greater Los Angeles area.
With the exception of the Summit Utah swarm, other areas of the
U.S. south of 40N remained quiet with no events of Ml>=2 reported.

NEW ZEALAND

NEIS reported a Mb 4.6 earthquake in the Kermadec Islands, New
Zealand today. The on-line seismometer showed several strong
regional events, but local activity was down from previous days.

The IGNS on-line Seismometer can be found at:
http://www.gns.cri.nz/news/earthquakes/latest_drum.html

GEOMAGNETIC/SOLAR FIELDS

The current disturbance in the geomagnetic field continued today
with a strong storm which commenced at about 05:30 UT and lasted
12 hours through 18:00 UT. This storm is expected to affect seismicity
in areas within 20 degrees longitude of 90W and 90E. Seismic
watch is in effect for these areas through October 5, 2001.
The most unusual event associated with this geomagnetic storm
commencement was a Ml 2.9 in the Charlevoix Fault Zone, Quebec, Canada
which occurred at 05:29 UT as the storm was starting.
There were no M- or X- class flares observed on the sun today.

For general space weather conditions see:
http://sec.noaa.gov/today.html
For Solar flare data see:
http://sec.noaa.gov/ftpdir/indices/events/20011003events.txt

TROPICAL STORMS

A new tropical storm - Tropical Storm Lorena formed off the coast
of southwestern Mexico today. Lorena is not expected be be long-lasating
or powerful and forecasters expect it to hit the coast of Jalisco,
Mexico tomorrow. Seismicity along the Mexican subduction zone, especially
in Michoacan and Jalisco may be affected as the winds push Mexico
north reducing normal stress on the subduction zone and the tidal
surge adds about 1 million tons per sq. mile to the subduction zone off
the coast, pushing it down. These two effects tend to decouple the
subduction zone from the North American plate. Larger earthquakes
can occur under these circumstances (Mb 5-6). The force of Lorena
is relatively minor, so this effect should not increase the maximum
magnitude in the region by more than 0.5-0.75 units over previous
estimates. This watch is in effect until 6 October, 2001.