STRONG MW 5.7 EARTHQUAKE AND AFTERSHOCKS HIT BAJA CALIFORNIA REGION

SUMMARY

The big news of the day was the Mw 5.7 earthquake in the Baja California region. Kate Hutton noted of this earthquake :

"Not exactly in Southern California, but felt by quite a few here - mostly in Imperial and San Diego Counties - a M5.7
earthquake occurred in Baja California at 11:32 am today. Locally referenced it was located 29 miles south-southeast of
Calexico, California. The focal mechanism for the event shows strike-slip movement along the fault. Also interesting to mention,this is the largest sized earthquake "we've" had in that area since 1987 when there was a M5.4. Regarding today's earthquake we've had, so far, one M4.1 aftershock (at 12:33 pm) and about a dozen greater or equal to M3.0. As of yet, I have received no reports of the M4.1 being felt."

Source:
http://www.trinet.org/eqreports/comments/February2002.html

Since this event was in the Calexico region, solar triggering is suspected. There does appear to have been a "burp" in X-ray flux which may have triggered the Calexico earthquake this afternoon. This event was not large but occurred at 19:32 UT (11:32 PST) while Calexico was very nearly at exactly solar noon (11:40 PST is solar noon at Calexico). The combination of the suddenness of the burp and the location of Calexico directly beneath the sun was probably enough to trigger this event.
This is very similar to the conditions at midnight on October 31, when a Mb 5.1 quake occurred during a strong solar flare in Anza, CA. The coincidence was commented on in these daily summaries at the time of that event as well.

Dozens of aftershocks have occurred since that time in the Ml>=2 range with 15 having been recorded
Of Ml>=3.0 since the mainshock of 11:32 PST.

GLOBAL

Global seismicity was relatively quiet today. With the exception of the Mw 5.7 in Baja California, no other events of Mb>=5 were listed by any of the major teleseismic agencies. Earthquakes of Mb 4.8 and 4.7 did, however, occur in Indonesia in the Sunda Strait and in Hokkaido, Japan (Mb 4.2). Light activity also continued throughout most of Europe after two days of unusually large events on that continent. See:

http://www.emsc-csem.org/cgi-bin/ALERT_all_messages.sh?1

U.S./CANADA

Fourteen earthquakes of Mb>=5.5 have occurred in historic times within 50 km of today's Calexico earthquake. Table 1 lists the parameters of these events.

Table 1: Earthquakes within 50 km of event of 2-22-2002 (Mw>=5.5)

MO DA HR MN SC YEAR N LAT W LONG DEP MW

11 29 20 0 0 1852 32.500 -115.000 0 6.6 No Geomagnetic data
4 19 0 30 0 1906 32.500 -115.500 0 6.0 Mild G-storm 4-19 Probably
triggered by SF earthquake
11 21 0 13 42 1915 32.000 -115.000 0 7.1 Strong G-storms 11-17 to 11-21
11 7 23 57 0 1923 32.500 -115.500 0 5.5 Light geomag-storm end of 11-7
1 1 8 16 45 1927 32.500 -115.500 0 5.8 Strong geomag-storm 1-1-1927
1 1 9 13 30 1927 32.500 -115.500 0 5.5 Strong geomag-storm 1-1-1927
12 30 13 52 14 1934 32.250 -115.500 16 6.5 Strong Geomag-storm 12-29 to 12-30
2 24 1 45 10 1935 31.983 -115.200 16 6.0 Geomagnetic storm 2-24
5 19 4 36 0 1940 32.700 -115.500 16 6.7 Geomagnetic storm 5-18 to 5-19
2 1 4 32 2 1954 32.300 -115.300 16 5.6 Geomagnetic storm in progress 2-1
12 1 3 21 18 1958 32.250 -115.750 16 5.8 Flares occurred but were not
12 1 6 2 0 1958 32.250 -115.750 16 5.5 classified. A strong geomagnetic
storm occurred from 11-29 to 11-30
5 5 21 3 16 1978 32.216 -115.316 5 5.5 5 M-class flares
10 15 23 16 53 1979 32.614 -115.318 12 6.8 3 M-class flares
10 16 23 16 38 1979 32.650 -115.340 22 5.5 4 M-class flares
6 9 3 28 19 1980 32.220 -114.985 5 6.4 6 M-class flares
2 7 3 45 15 1987 32.390 -115.310 6 5.5 0 moderate geomagnetic storminess

Note: The Mw 6.5 on June 9, 1980 was also preceded by several days of M-class solar flares (M2, M3, M8, M1, M3, M4).

Table 1 gives the parameters of each of the large events in the region of
Today's earthquake. Specific flare data is not available prior to 1960, however geomagnetic indices are. All but two large events in this region were either preceded by a number of M-class solar flares in the previous two days (numbers in last column represent number of M- or X-class flares in the two days prior to the Baja event after 1960 or were associated with moderate or strong geomagnetic storms on the day of the quake or during the previous two days.
The two exceptions were the event of Mw 6.0 following the great San Francisco earthquake on April 18, 1906 and the last event on Feb. 7, 1987.

Seismicity was at moderate levels throughout most of the rest of the western U.S. and Canada today. Four earthquakes of Ml>=2.5, but not associated with the Calexico swarm occurred in Viola (northern California) (M 2.7); Parkfield (Ml 2.2); Awakening, Nevada (Ml 2.4); and the Hector Mine aftershock zone (Ml 2.9) today in the California-Nevada region.
Also occurring near local noontime was an unusual Ml 2.6 event near Diamondville, WY about an hour before the Calexico earthquake. Near Snohomish, WA a Ml 2.2 was recorded this afternoon. An unusual Ml 4.3 earthquake was
Also recorded this afternoon in northern Alaska.
As is often the case with moderately large earthquakes in the California region, several unusual earthquakes occurred in eastern Canada several hours before the Calexico earthquake - these were a Ml 3.5 in the Baffin Bay region and a Ml 2.5 in New Brunswick, Canada. Both occurred during late morning local time.

NEW ZEALAND

A series of light to moderate earthquakes were recorded on the on-line IGNS seismogram, but IGNS did not report any earthquake parameters today.

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

GEOMAGNETIC/SOLAR FIELDS

SEC still expects a geomagnetic active period to begin tonight or tomorrow from the solar wind associated with the recent flares, however the geomagnetic field was at quiet conditions throughout the day. The only M-class flare
Today was a M4.4 which occurred shortly after midnight this morning.

Flare # START MAX END CLASS
7180 + 2349 0010 0027 M4.4

For general space weather conditions see:
http://sec.noaa.gov/today.html
For Solar flare data see:
http://sec.noaa.gov/ftpdir/indices/events/20020222events.txt