TRIGGERED?? MB 4.9 EARTHQUAKE OCCURS IN KODIAK ISLAND AREA

SUMMARY

Shortly after the Mb 5.5 Andreanoff Islands earthquake last night
an earthquake of Mb 4.9 occurred in the Gulf of Alaska. This
earthquake occurred simultaneously with a sudden drop in electron
flux (within 5 minutes). The electron flux dropped from
2.53e+03 Electrons/cm2-s-sr at 06:45 UT to 1.20e+03 Electrons/cm2-s-sr
at 06:55 UT. This is more than a halving of electron flux in less
than 10 minutes.
SEE:
http://sec.noaa.gov/ftpdir/lists/particle/20010922_G10part_5m.txt
This sharp reduction in electron flux was accompanied by a strong
reduction in geomagnetic field strength beginning at 06:45 UT
and reducing the strength of the total field from 5.73e+1 nT at 06:44 UT
to 3.99e+1 nT at 06:58. The field strength reduced 5% from 06:44 to
06:45 UT. For data see:
http://sec.noaa.gov/ftpdir/lists/geomag/20010922_G10mag_1m.txt
The event in the Gulf of Alaska occurred three minutes later as
follows:
22Sep2001 06:48:05 55.9N 154.5W MB=4.9 NEIS SOUTH OF ALASKA

An earthquake of Mb 4.5 was also reported in Taiwan about 15 minutes
after this at:

22SEP2001 07:02:23 23.3N 120.6E ML=4.5 CWB Kaohsiung, Taiwan

It is quite possible that geomagnetic effects triggered these
earthquake given the coincidence between the events and the
geomagnetic field change. A plot of geomagnetic field over the
past three days can be viewed at:

http://sec.noaa.gov/today.html

Look at the GOES Hp panel on the Satellite Environment plot some
ways down the page to see this sudden change in geomagnetic
intensity (in blue).

Taiwan was near sub-solar at the time of the change, Alaska was
near anti-solar, both area areas where the effects would be maximized.

GLOBAL

Otherwise, conditions on the planet have been relatively quiet
since last report. Earthquakes of Mb 4.3 (Tonga Islands), Mj 4.1
(Central Honshu, Japan) and Mb 4.5 (Chile/Bolivia border) have
been listed since the last report.

U.S./CANADA

No events of Ml>=3 have been reported in the U.S. or Canada
outside Alaska since the last report. Activity has been subdued
in the California/Nevada region with events of Ml>=2 occurring
near Lovelock NV (Ml 2.4); Mammoth Lakes CA (Ml 2.0) and
Big Bear City (So. California Ml 2.1).
Most seismic networks in the U.S. and Canada do not report
events over weekends, however, examination of on-line seismographs
does not reveal any major events since the past report.
Incidentally, the earthquake reported at the USGS California
site probably did not happen (that is, it is a ghost event).
The time of this event is 06:53:35 UT. The time for the p-wave to
move from the epicenter of the Gulf of Alaska earthquake to this
location (28.72 degrees) is about 5 min. 30 sec. minutes. The Lovelock
event is recorded as follows:
22SEP2001 6:53:35 40.3N 118.0W ML=2.4 NCSN ENE of Lovelock, NV
The time is 5 min 30 seconds after the Gulf of Alaska Mb 4.9.
This is either a case of instant triggering, two events triggered
by the geomagnetic field change or a ghost event where the p-wave
from the Alaska earthquake was considered a local event by
automatic analysis programs when it really was not. The location
is the same that is usually given for ghost events as well, so
it seems likely this event will disappear into the ether shortly
joining other ghosts.

NEW ZEALAND

IGNS reported an earthquake of Ml 3.7 south of Hastings, North
Island today (22 September) which was probably felt in the area.

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

GEOMAGNETIC/SOLAR FIELDS

A minor geomagnetic storm began at about 07:00 UT this morning following
a strong change in the intensity of the geomagnetic field described above.
and lasted for around 6 hours. This short-lived storm is not
expected in affect global seismicity. No M- or X-class flares were
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/20010922events.txt

TROPICAL STORMS

Tropical Depression 10 is currently located south of Bermuda.
It is not expected to reach Hurricane class winds in the next
three days as it tracks north toward Maine and the Maritime provinces
of Canada. For tracking details see:
http://www.wunderground.com/auto/HurricaneSite/tropical/tracking/at200110.html

Tropical Storm Juliette is located south of Oaxaca, Mexico and
is expected to reach Class 1 Hurricane status within the day. Tracking
then expects this storm to move northwestward and become a Class
2 Hurricane by Sunday evening. This slow moving storm could trigger
some seismicity in the Oaxaca/Michoacan/Jalisco areas of Mexico in
the next three days. For tracking details see:
http://www.wunderground.com/auto/HurricaneSite/tropical/tracking/ep200111.html