BAJA CALIFORNIA AFTERSHOCK SEQUENCE DECLINES AT EXPECTED RATE

SUMMARY

After a strong start yesterday and this morning, the aftershock sequence
of the Mw 5.7 Calexico earthquake of 2-22-02 declined to near background
levels by this evening. This report expected the aftershock sequence to
last approximately 2 days at high (M>=3) levels, so this rapid decline
was anticipated. Sequences in areas of high heat flow normally decline
rapidly after an initial burst of activity and Calexico is in such a region.
The last event before this report in the aftershock sequence of Ml>=2.8 was
recorded nearly 6 hours ago suggesting that the sequence may be nearly
over.
A new segment has been added to the daily report today. This segment
is a description of a major earthquake which occurred on this day in
history. It is located at the end of the summary section.

GLOBAL

The most active area of the world seismically today was the region
of Indonesia where an earthquake of Mb 5.5 was recorded in the Banda
Sea this evening following events of Mb 4.5 in Ceram and of Mb 5.6 in
New Britain earlier in the day. Moderate activity continued in Europe
as well with events of Mb 4.0 in Greece and Mb 3.9 reported from
Romania.
Asia saw light earthquakes in Kamchatka (Mb 4.0, 3.8); south of Sumatera
(Mb unknown) and in northern India south of Neparl. (Ml 2.8)
The only event registered thus far from the region of Latin America
was a Ml 3.8 near El Salvador this afternoon.

U.S./CANADA

Many seismic observatories are closed for the weekend in the U.S.
Automatic systems in the west (California, Nevada, Northwest and
Montana and Alaska) provide the only digital data from this region
during weekends unless a significant event should occur.
The largest event in the 48-contiguous states which was not an
aftershock in the Baja sequence was a Ml 3.6 in northern Nevada.
In the Calexico aftershock sequence there were 55 events listed
of Ml>=2 on 23 February (UT) of which 16 were of Ml>=3.0. The last
event of Ml>=3 is listed at 20:25 UT (12:25 PST) today.
One earthquake of Ml >3 was recorded in Alaska - in Central Alaska
with Ml 3.8.
The only other listed event of Ml>=2 for the U.S. occurred in
Central Idaho with Ml 2.4.

NEW ZEALAND

One red-line event of Ml probably around 3.5 was recorded on the
IGNS on-line seismometer today. This earthquake is probably near
Upper Hutt, but IGNS has made no statement relating to it's parameters.
The on-line seismometer showed light activity throughout the day.

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

GEOMAGNETIC/SOLAR FIELDS

Solar activity was quiet today. The largest flare was a C7 class event
which occurred late in the day (see below). This flare occurred several
minutes after the last event of Ml>=2.5 in the Calexico aftershock sequence
today (at about 14:37 PST). The geomagnetic field also remained at
quiet conditions today.

Flare # START MAX END CLASS

7540 + 2246 2250 2254 C7.0

For general space weather conditions see:
http://sec.noaa.gov/today.html
For Solar flare data see:
http://sec.noaa.gov/ftpdir/indices/events/20011119events.txt

TODAY IN HISTORY

The largest and most severe earthquake that has been recorded on Feb. 23
occurred in 1653 in the region of Izmir, Turkey. It has been given a Mw 7.6
magnitude. The earthquake destroyed much of Smryna, Turkey and was
responsible for up to 15,000 deaths. It did extensive damage throughout
western Anatolia. The epicenter is given as 38.2N 28.2E, near the epicenter
of the Ms 6.5 in Turkey on February 3 this year which also resulted in
considerable damage. A similar event occurred slightly to the east of
this epicenter also killing about 15,000 persons on July 10, 1688, probably
triggered by residual strain from the event on Feb. 23, 1653. These were
the most deadly events recorded in eastern Turkey until the massively
destructive earthquake at Izmit on August 17, 1999 which killed between
15,000 and 20,000. There are loads of pictures on the web on this event -
look at :

http://www.ngdc.noaa.gov/seg/hazard/slideset/earthquakes/43/43_slides.html

and

http://www.ngdc.noaa.gov/seg/hazard/slideset/earthquakes/46/46_slides.html

for example. The earthquake that followed the 2-23-1653 event in 1688
has led some to be worried that Istanbul, a heavily populated region,
may be due for the next great earthquake in this region since strain
concentrated on that area of the Anatolian fault following the Izmit
earthquake.

• Slides on the Izmit Turkey earthquake