LOBAL SEISMICITY AT MODERATE LEVELS

SUMMARY

Nine earthquakes of Mb>4.5 have occurred in the past 24 hours.
It is useful to have a term to describe the relative seismicity
of the earth on any given day. Table 1 below shows the number
of days on which specific numbers of earthquakes of Mb>=4.5 were
recorded in the NEIS (PDE) catalog from 1990-2000. For example,
four earthquakes of Mb>=4.5 were recorded in this catalog on
160 separate days, five earthquakes at this magnitude level were
recorded on 238 days. A total of 3924 days occur in this period.
A reasonable way to describe these is in terms of statistical distribution.
The top and bottom category contain appoximately the 10 most and
least seismic days. The next categories - the next 30-35 next
most and least seismic days; the next - about 250 days each, the
next about 600 days each and the middle (moderate seismicity) catalog
will contain about half the days in the catalog.
If 8 descriptive categories are chosen, then Table 1 shows
the number of earthquakes/day in each category based on the
above numbers. The first column is the number of observed
days on which the number of earthquakes in the second column
occurred in the NEIS catalog from Jan 1990 - Sept 2000. This
is followed by a descriptive phrase describing the relative seismicity
of the globe given the number of observed events of M>=4.5 on that day.

Table 1: Proposed definition of Global seismicity levels based
f
on global seismicity patterns 1990 - 2001.

#Day #events Description

1 0 Extremely low global Seismicity
9 1 Extremely low global Seismicity
33 2 Very low global Seismicity
91 3 low global Seismicity
160 4 low global Seismicity
238 5 Moderately low global Seismicity
369 6 Moderately low Global Seismicity
392 7 Moderate Global Seismicity
427 8 Moderate Global Seismicity
383 9 Moderate Global Seismicity
349 10 Moderate Global Seismicity
316 11 Moderate Global Seismicity
263 12 Moderate Global Seismicity
202 13 Moderate Global Seismicity
185 14 Moderately High global Seismicity or aftershock sequence
115 15 Moderately High global Seismicity or aftershock sequence
99 16 Moderately High global Seismicity or aftershock sequence
57 17 Moderately High global Seismicity or aftershock sequence
42 18 Moderately High Global Seismicity or aftershock sequence
35 19 Moderately High Global Seismicity or aftershock sequence
29 20 High Global Seismicity or aftershock sequence
22 21 High Global Seismicity or aftershock sequence
16 22 High Global Seismicity or aftershock sequence
7 23 High global seismicity or aftershock sequence
13 24 High global seismicity or aftershock sequence
3 25 High global seismicity or aftershock sequence
5 26 High global seismicity or aftershock sequence
4 27 High global seismicity or aftershock sequence
3 28 High global seismicity or aftershock sequence
3 29 High global seismicity or aftershock sequence
9 30 High global seismicity or aftershock sequence
3 31 High global seismicity or aftershock sequence
4 32 Very High global seismicity or aftershock sequence
5 33 Very High global seismicity or aftershock sequence
3 34 Very High global seismicity or aftershock sequence
4 35 Very High global seismicity or aftershock sequence
3 36 Very High global seismicity or aftershock sequence
1 37 Very High global seismicity or aftershock sequence
1 38 Very High global seismicity or aftershock sequence
1 39 Very High global seismicity or aftershock sequence
1 41 Very High global seismicity or aftershock sequence
1 43 Very High global seismicity or aftershock sequence
3 44 Very High global seismicity or aftershock sequence
2 46 Very High global seismicity or aftershock sequence
2 47 Very High global seismicity or aftershock sequence
3 48 Very high global seismicity or aftershock sequence
1 49 Extremely high global seismicity or aftershock sequence
1 55 Extremely high global seismicity or aftershock sequence
1 66 Extremely high global seismicity or aftershock sequence
1 68 Extremely high global seismicity or aftershock sequence
1 72 Extremely high global seismicity or aftershock sequence
1 84 Extremely high global seismicity or aftershock sequence
1 102 Extremely high global seismicity or aftershock sequence
1 103 Extremely high global seismicity or aftershock sequencey

GLOBAL

Global seismicity was at moderate levels today. Earthquakes
of Mb>=5 were reported in the Kermadec/Fiji (Mb 5.3); in the
Tonga Islands (Mb 5.2); in the New Ireland region (Mb 5.4); in the
Dodecanese Islands, Greece (Mb 5.1); and in the Leeward Islands,
Caribbean (Mb 5.4) since last report.
Other moderate earthquakes (4.5<=MB<=4.9) occurred in the Azores (Mb 4.8);
in Argentina (Mb 4.8); near El Salvador (MB 4.6) and in Norhern
Peru (Mb 4.7) since the last report. No strong or great earthquakes
have yet occurred since the X-class flare and strong geomagnetic
events of the past two days, however these are still expected to
occur in about 2 days.

U.S./CANADA

The largest earthquake of the day in the California/Nevada region
was a Ml 3.1 near Coalinga, CA. This is the largest earthquake within 30 km
of this epicenter since April 16, 2000 when a Ml 3.2 occurred in the region.
A Ml 3.8 also occurred on March 16, 2001 near this epicenter.
The parameters of this event are given as:

26SEP2001 17:52:11 36.2N 120.3W ML=3.1 NCSN NE of Coalinga, CA
26Sep2001 17:52:11 36.2N 120.3W ML=3.1 NEIS CENTRAL CALIFORNIA

An earthquake of Ml 3.0 occurred near this location on Feb. 6, 2001.
There he been 7 events of Ml>=3 in this region in the past 3 years
(since 8-13-1998).
A swarm of earthquakes in the Ml>2 range began about local noon
in the Obsidian Butte/Niland California region in the Imperial
Valley area of So. California. It is quiet common for earthquakes
in this area to occur following strong geomagnetic storms. Similar
swarms have occurred this year on Jan 22, Feb 1, Apr 18, June 7, and
July 15. The last activity occurred on September 14, 2001 (Ml 2.3, 2.4).
Microearthquakes continued in the L.A. area with events today
near Sunland (Ml 1.4), Century City (Ml 1.6), Culver City (Ml 1.7)
and Moorpark (Ml 1.4). An earthquake of Ml 2.3 was observed near
Mammoth Lakes (Bishop, CA).
An earthquake of Ml 2.9 also occurred in the Cedar City/Hurricane
region of southern Utah. This event had been forecast in both
weekly and yearly listings for the area. No earthquakes occurred
within 50 km of this epicenter in 1999, two in 2000, but a series
of eight such events have occurred at Ml 2.8-2.9 during 2001. The
largest event in this area this year was a Ml 3.4 on May 20, 2001.
The latest of this series occurred on Aug 28 (Ml 2.9).
No earthquake of Ml>=3 have been reported in in the eastern U.S.
or Canada or in Alaska or Hawaii since last report.

NEW ZEALAND

Late in the day a strong earthquake was reported from the
Kermadec/Fiji Islands region. A report will be made on this
event in tomorrow's summary. The on-line seismometer shows
a number of small events in the region today. The area was
under seismic watch from the X-class flare on 24 September
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

The geomagnetic storm which began last yesterday about 12:30 UT
continued on through about 12:00 UT today (Sept. 26). The seismic
watch should continue for three days in areas identified in the
previous report. There was one solar flare of M- or X- class today
The parameters of this flare are:

Flare # START MAX END CLASS

8500 + 0252 0258 0303 M1.8

No earthquakes have been reported during the duration of this
flare.

For general space weather conditions see:
http://sec.noaa.gov/today.html
For Solar flare data see:
http://sec.noaa.gov/ftpdir/indices/events/20010926events.txt

TROPICAL STORMS

Hurricane Humberto is headed east in the North Atlantic where
it is expected to arrive at the Azores in about 2 days. The
Azores experienced a moderate earthquake today. This is probably
a delayed reaction to the passage of Erin through the Azores
a week ago. This report had said on September 15th:

"Tracking information suggests a strike in the Azores tomorrow
(September 16). Some associated seismicity may be observed along the north
mid-Atlantic ridge and in the Azores in the next 3-4 days."
This event occurred about 5 days later than expected.

For tracking details of Hurricane Humberto see:

http://www.wunderground.com/auto/HurricaneSite/tropical/tracking/at200110.html

Hurricane Juliette is off the Coast of Jalisco, Mexico today,
but appears to be losing intensity and is expected to be a Category
1 hurricane within 3 days. Forecasters have also changed the
expected path and now expect Juliette to miss the mainland altogether,
taking a sharp turn to the west away from Baja California in about
two days. This will reduce any likely seismic impact from this
hurricane.
For tracking details see:
http://www.wunderground.com/auto/HurricaneSite/tropical/tracking/ep200111.html

News of Hurricane Juliette off Baja California can be found at:
http://home.netscape.com/ex/shak/news/stories/0901/20010925hurricane.html
This hurricane has killed at least one fisherman. Acapulco and
other ports have been closed because of high seas.