MID-OCEAN RIDGE SEISMICITY REACHES HIGH LEVELS;
UNUSUAL N. GEOMAGNETIC POLE EVENT OCCURS AT END OF POLAR ABSORPTION EVENT

SUMMARY

OCEAN RIDGE EVENTS:

Long-term readers of this report will recall that we have commented
on the association of mid-ocean ridge seismicity and strong geomagnetic
storms on numerous occasions in the past three years. It is quite typical
for strong mid-ocean ridge activity to follow geomagnetic storms by about
4-6 days. It may be a delay due to required expansion or heating in the
mid-ocean ridge environment from ohmic heating or some other related cause.
Ocean ridge events have occurred in the past 3 days as follows:

South Atlantic:

O: 29Sep2001 12:19:39 43.9S 17.2W MB=4.2 NEIS S MID-ATLANTIC RIDGE

Central Atlantic:

O: 30Sep2001 18:24:00 5.8N 32.8W MB=4.3 NEIS CENTRAL MID-ATLANTIC RIDGE

East Pacific Rise:

O: 30Sep2001 06:03:32 22.6S 113.5W MS=5.2 NEIS EASTER ISLAND REGION
O: 29Sep2001 08:48:52 23.5S 111.6W MB=4.7 NEIS EASTER ISLAND REGION
O: 29Sep2001 08:08:33 23.6S 111.9W MB=4.9 NEIS EASTER ISLAND REGION
O: 29Sep2001 07:58:31 23.5S 111.7W MB=4.9 NEIS EASTER ISLAND REGION

Antarctic-Indian Ridge:

O: 02Oct2001 10:42:16 48.9S 121.4E MS=5.0 NEIS W INDIAN-ANTARCTIC RIDGE
O: 02Oct2001 10:38:29 49.1S 121.5E MB=4.4 NEIS W INDIAN-ANTARCTIC RIDGE

On average about one event is recorded on Mid-Ocean ridges during
any given 4-day period (in NEIS catalog), so this represents a
rate increase of about 8 times background.

NORTH GEOMAGNETIC POLE EARTHQUAKE

In the Arctic, in the region of the North Geomagnetic pole, which is
currently located in the Islands of northern Canada at about 79N 110W (the
geomagnetic pole actually extends over an area of several hundred
km around this point) an earthquake (Ml 4.4) occurred on 1 October. This
was the largest earthquake within 200 km of 79N 110W since Jan 1, 1999
when an event of Ml 5.3 occurred nearby. There have been 5 earthquakes
recorded in this region since 1985 of Ml>=4.4, so this event has
a recurrence time of about 4 years. The coincidence of this event
with the polar proton absorption event is interesting and had been
anticipated in this summary in the report of Sept. 23, 2001 which
stated:

"The Space Environment Center (SEC) is expecting strong solar
and geomagnetic storms over the next several days. A polar
absorption event is current taking place. When this happens,
earthquakes at high latitudes (and often near the geomagnetic poles)
are common, however activity elsewhere is often subdued until after
the proton storm has passed. This temporary quiet is followed by strong
seismic activity throughout many areas of the world."

GSC gives the parameters of this event as:

O: 01OCT2001 00:28:58 80.5N 115.8W ML=4.4 GSC QUEEN ELIZABETH SLOPE

Source:

http://www.seismo.nrcan.gc.ca/recent_canadian_eq/recent_canadian_eq_e.html

A general summary of some earth-sun interactions can be found on the web at:

http://solar-center.stanford.edu/sun-on-earth/sun-earth.html

GLOBAL

The largest event of the day was a Ms 6.2 in the Tonga Islands
which was reported on last night. Earthquakes of Mb>=5 also occurred
in the area east of Honshu, Japan (about 200 km N. of Tokyo) (MB 5.0);
and in the region south of Tokyo (Mb 4.9). This activity off the
east coast of Honshu started about a week ago, and appears to be
getting stronger.
Other activity was recorded south of Australia on the Western
Indian-Antarctic Ridge (Mb 5.0, 4.4). This was an unusual event.
In the 5.5+ years since January 1996, there have been 4 earthquakes
recorded in the area within 200 km of today's epicenter with Mb>=5.
The recurrence interval is thus about 1.5 years between such earthquakes.
Two earthquakes in eastern Indonesia also occurred in the Mb5 range -
a Mb 5.1 in the Banda Sea and a Mb 4.9 in the Savu Sea.

U.S./CANADA

The largest earthquake of the day in the lower 48 states occurred
in eastern Idaho (Ml 3.3). This is the first aftershock of Ml>=3
in the area since a Ml 5.4 earthquake struck near this epicenter
on April 21, 2001. The area has been fairly active at this level
over the years with 246 events of M>=3 since 1960. Many of these
have occurred in strong aftershock sequences in October, 1982 (22 events);
November 1992 (22 events); and in the Aftonm WY sequcence of February 1994
(68 events). The mainshock was preceded by a small foreshock.
Only one event of Ml>=3 occurred in the California/Nevada region
today - a Ml 3.1 near Mammoth Lakes. This area has shown increased
activity following the recent geomagnetic storms, a common occurrence
in the region. Another region which was active today and which
commonly becomes so during and after geomagnetic storms was the
Geysers with events of Ml 2.3, 2.1, and 2.0. Slightly north
a Ml 2.3 occurred near Willits, CA.
A Ml 3.0 event in the Hector Mine aftershock zone also occurred late
last night. During the month of September, 2001, this region had been
nearly devoid of earthquakes. Staff at SCEC had expressed some concern
that this might be a quiescence before a large aftershock.
An earthquake in the Ml 2.5-3.0? range also occurred off the
Coast of Oregon in the northwest.
Microearthquakes continued in the Los Angeles region with events of
Ml 1.6 (Pt. Dume), Ml 1.5 (Alhambra), Ml 1.6 (Valencia).
No earthquakes of Ml>3 were recorded in either Alaska or Hawaii
today. Likewise, the eastern and Central portions of North America
were also quiet today.

NEW ZEALAND

IGNS did not report any significant activity in the region today.
However, a number of small events did continue in the region and
were recorded on the on-line seismometer.

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

GEOMAGNETIC/SOLAR FIELDS

The current active geomagnetic field continued today with
a refreshened storm from 03:00 UT to 12:00 UT. This tends to
reinforce the seismic watch currently in effect. No changes
in this watch are currently needed.
A minor solar flare of M1.4 occurred today. The parameters are:

Flare # START MAX END CLASS

690 + 1012 1021 1057 M1.4

No seismic activity has been reported at the time of this flare yet.

For general space weather conditions see:
http://sec.noaa.gov/today.html
For Solar flare data see:
http://sec.noaa.gov/ftpdir/indices/events/20011002events.txt

TROPICAL STORMS

The only tropical storm currently affecting North America is
tropical Depression Juliette which is currently stalled at the
northern end of the Gulf of California. Seismicity in this region
may be slightly affected. For tracking details see:
http://www.wunderground.com/auto/HurricaneSite/tropical/tracking/ep200116.html