MODERATE QUAKES HIT ANDREANOFF ISL (MB 5.5) AND COLOMBIA (MB 5.9)
EXPLOSION KILLS 18 in TOULOUSE, FRANCE

SUMMARY

An earthquake of Ml 3.2 was reported south of Toulouse, France
this evening, but was artificial in origin. A Chemical plant
in the region exploded killing 18 and injuring 200. 15 are missing.
It is believed the explosion was caused by an accident and is
not related to terrorism. I worked in this area several years
ago and my sister and family live a few km from this plant. The
region of southern Toulouse is populated by a large Arab population
and there is considerable animosity between the French and this
group, so terrorism is a distinct possibility.
For news report see:
http://abcnews.go.com/wire/World/ap20010921_1838.html

Two moderate earthquakes occurred since the last report. A Mb 5.5
hit the central Andreanoff Islands late this evening (UT). This is
a region where earthquakes of this size occur about once every two
months. This was followed several hours later by an earthquake with Mb about
5.6 in the Colombia region. Reports on this event are mixed, so
the following parameters are still preliminary.

O: 21SEP2001 23:56:39 51.9N 175.4W Mb=5.5 NEIR ANDREANOF ISLANDS, AL
O: 22SEP2001 03:23:37 3.8N 75.9W Mb=5.9 NEIR COLOMBIA

The earthquake in Colombia occurred in the Armenia/Cali region
where a disastrous earthquake occurred on January 25, 1999. That
earthquake occurred at a shallow depth, however and today's was
at about 170 km depth. While the two events are located within
about 50 km of each other and affect the same area, today's is
unlikely to have caused serious damage because of it's depth.

The Colombia earthquake could trigger some activity in the active
zone south of Sumatera - at about 4S 104E, the antipode of this event.
Because that area has been active for the past year, a triggered
event from such a small mainshock as this is still a reasonable
possibility. If such an event were to occur, it would probably
happen in the next 3-4 days.
A small shock (Mb 4.3) preceded tonight's Colombia event earlier
today in northern Colombia.

GLOBAL

September 21 was actually a fairly light day for global seismicity (the
event in Colombia actually occurred on Sept. 22 and the earthquake
in the Andreanoff Isl. about 3 minutes before midnight (UT) on
Sept. 21). The only other earthquake to register Mb>=5 was a Mb 5.0
in Seram, Indonesia just west of New Guinea. Earthquakes of Mb>4
were also reported in Argentina (Mb 4.0) and Halmahera (Mb 4.6).
The most unusual earthquake in the world today was a Mb 4.6
in Poland. The region of today's earthquake was active from December
1999 through July 2000 with 6 events of Mb>=4.5, however none
have been reported within 200 km of today's event since July 18, 2000
when a Ml 4.8 occurred nearby.

U.S./CANADA

It was an interesting day for seismicity in the United States and
Canada. The largest earthquake in the 48 contiguous U.S. states
was a Ml 3.4 in the Trinidad, Colorado area. The first in this
region noted by NEIS in more than a week.
The largest earthquake was the Mb 5.5 in the Andreanoff Islands
This is the largest event in the Central Andreanoff Islands since
a Mb 6.0 west of this epicenter on Feb. 1, 2001. In the last two
years (since 9-21-99) there have been only two events within 200
km of today's earthquake of Ml>=5.5 (the other was a Mb 5.8 on Jan. 2,
2000).
But this was not the only unusual earthquake in the U.S. today.
A small earthquake of Ml 2.5 occurred WSW of Hot Springs Arkansas
this evening. Only 10 events of Ml>=2.5 have ever been located within
100 km of this event. The last occurred on Aug. 4, 2001 (Ml 3.1)
so this may be an aftershock of that earthquake.
An unusual Ml 2.8 event was also recorded near Rocky Mountain House,
AB, Canada. The is the second largest earthquake within 100 km of
it's epicenter in the past two years, the larger being a Ml 3.3
on Oct. 8, 2000.
In California/Nevada, the largest event occurred near La Jolla in
southern California. SCSN gives this Ml 3.1, NEIS - Ml 3.2.
In the past two-and-a-half years three other earthquakes of Ml>=3
have occurred within 50 km of this epicenter - on Aug. 16, 2001 (Ml 4.4);
Aug 9, 2001 (Ml 3.0); and Dec. 27, 2000 (Ml 4.1). This appears to
be a continuation of the upsurge in seismicity in the region including
Los Angeles and San Diego in the past several weeks. Other earthquakes
of Ml>=2 in California today occurred near Calexico (Ml 2.3); Dixie
Valley, NV (Ml 2.6); Mammoth Lakes (Ml 2.3); Lower Lake (the Geysers)
(Ml 2.2); Milpitas (Ml 2.3) and Daly City CA (Ml 2.0), making this
one of the more active days in California in several weeks.
Earthquakes of Ml>2 also occurred in NW and eastern Washington
state near Ellensburg (Ml 2.1) and Mount Vernon (Ml 2.4).
A minor swarm of events with Ml 2.5, 2.0 ... also occurred in
the Charlevoix Seismic zone in the St. Lawrence seaway region. This
area has seen a series of minor events in the past week.

NEW ZEALAND

A Ml 4.5 earthquake was reported by IGNS near Mt. Cook, South
Island today. This was also a relatively unusual event, being the
largest within 100 km of this epicenter this year and since Oct 21,
2000 when a Ml 4.8 occurred. Only 8 events of Ml>=4.5 have been
located in this 100 km radius region during the past 10 years.

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

GEOMAGNETIC/SOLAR FIELDS

The geomagnetic field remained at quiet conditions throughout
the day (September 21, 2001). No solar flares of X- or M- class
were observed.

For general space weather conditions see:
http://sec.noaa.gov/today.html
For Solar flare data see:
http://sec.noaa.gov/ftpdir/indices/events/20010921events.txt

TROPICAL STORMS

Tropical Depression 10 formed in the Atlantic north of Puerto
Rico today. It is expected to develop into a tropical storm by
tomorrow and into a hurricane by Monday. By the time it develops
into a class 1 Hurricane, it is projected to be south of New England.
There is a chance this storm could hit New England late next week,
although it is more likely to move into the Central Atlantic
before it reaches New England. For tracking details see:
http://www.wunderground.com/auto/HurricaneSite/tropical/tracking/at200110.html

Tropical Storm Juliette which formed from the remnants of a tropical
depression which moved over El Salvador two days ago is south of
Chiapas, Mexico at this time. It is expected to move along the
coastline of Mexico for the next three days and develop into a class 2
Hurricane. It is possible that this storm could trigger seismicity,
perhaps an event of Mb>=5.5 in the Mexican Subduction zone. For
tracking information see:
http://www.wunderground.com/auto/HurricaneSite/tropical/tracking/ep200111.html

The third possible storm to develop in the waters surrounding
North America today was tropical depression twelve-E. This depression
formed well off the west coast of Mexico and is not likely to impact
North America in any way. For tracking information see:
http://www.wunderground.com/auto/HurricaneSite/tropical/tracking/ep200112.html

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