FAR-FIELD AFTERSHOCK FORECAST FOR SOUTHERN MARIANA ISLAND MS7.0 (PRELIMINARY)
(OCTOBER 12, 2001)

A strong earthquake occurred today in the Southern Mariana Islands
about 50 km south of Guam (Guam is at 13.5N 144.8E). Preliminary
estimates place the magnitude at 7.0 or greater (NEIS, GSSC).
Current parameters are:

12Oct2001 15:02:19.4 13.0N 145.0E 50 MS=7.0 M*GSR MARIANA ISLANDS
12Oct2001 15:02:21.0 12.6N 144.9E 70 M =7.0 M*NEI SOUTH OF MARIANA ISLANDS

Seismicity is expected to increase in areas where seismic energy
from the great shocks is concentrated due to internal reflections
and refractions of waves off internal boundaries. Following are the
locations and distances where this is expected to occur.
There have been 7 earthquakes recorded in the are 12-15N 140-150E
in the past century. The largest occurred 8 years ago as a Mw 8.2
on August 8, 1993. The epicenter of this earthquake was very near
the same as today's (12.9N 144.8E) so this may be considered an
aftershock of that event. It is likely to have occurred on the same
asperity and ruptured in a different direction. The event of 1993 had
a depth of 59 km, today's depth was nearly the same (50-70 km).
Other earthquakes of Mw>=7 in the region occurred on Nov 1, 1975 (Mw 7.1);
May 25, 1950 (MB 7.3); June 14, 1942 (MW 7.0); Jan 28, 1931 (Ms 7.2);
and a series of three between 1909 and 1913 (Mw 8.0 - Dec. 9, 1909;
Mw 7.0 - Oct 26, 1912; and Mw 7.1 - July 18, 1913))

WARNING SIGNS

FAR-FIELD FROM KAMCHATKA

Two moderate foreshocks in the southern Marianas occurred yesterday
(October 11) of Mb 5.2 and Mb 4.8. These were noted in yesterday's
report as probably being far-field aftershocks from Kamchatka as they
occurred at 43 degrees from the Kamchatka quakes of 8 October, 2001,
a distance at which far-field aftershocks were expected as stated:

"Seismicity is expected to increase in the following areas. Maximum
likely magnitude for these areas is increased 0.75-1.0 unit over previous
estimates.

34-36 degrees: .... Central Marianas
43-45 degrees"

and

"Secondary location where event tend to occur but are not
as large or as likely . MB>=4.8 considered likely in next
10 days.

.....Central and northern Mariana Isl."

These foreshocks were emphasized on three different occasions in
the October 11 report (in summary and twice in the Global section)
because the geomagnetic storm appeared to be concentrating energy
in that vicinity and a strong earthquake appeared possible.

GEOMAGNETIC STORM

The summary report from October 11 had placed the region under
seismic watch for the next three days. The anti-solar longitude
at the time of the geomagnetic storm commencement at 15:00 UT
was 135E. Watch areas are within 20 degrees longitude of this,
a region which includes Guam (144E). Regions along the geomagnetic
equator and under the auroral electrojets are also automatically
placed in watch status when a strong storm occurs. Guam is almost
exactly on the geomagnetic equator. The final report (e-mail version)
from yesterday had stated:

"A strong geomagnetic storm began about 15:00 UT today (October 11).
This was apparently related to a CME which was forecast by SEC
to arrive in the earth's space environment today. Areas where
seismicity is most likely to be affected are sub- and anti-solar
and at high latitudes. The storm re-invigorated about 23:00 UT
and became strong about 04:00 UT on 12 October. Because of the
length and intensity of these storms seismicity in most of the
world will be affected, however as usual areas where seismicity
is most likely to be affected are sub- and anti-solar
and at high latitudes.
Maximum event magnitudes may rise 1.0 units above previous
estimates over the next three days."

The preliminary report (posted by not mailed) had added:

" Many areas, including most of the NORTHWESTERN PACIFIC SUBDUCTION ZONE
(emphasis added) and the western South America subduction zone are included
in this area where maximum event magnitudes may rise 0.5 units over the next
two days"

The two (posted and e-mail versions) differed because the geomagnetic
storm re-invigorated after the initial (posted version) was posted
and before the e-mail version was sent.

Seismicity is expected to increase the maximum magnitude event in the
following regions by 0.5-1.0 magnitude units over previous estimates.

9-10 degrees: Volcano Islands (21-23N)
17-19 degrees: So. of Honshu, Ryukyu Isl, Samar, Mindanao, Philippines,
Halmahera, New Britain, east Papua New Guinea
34-36 degrees: Flores, Central Vanuatu Isl, Timor Sea, Sumbawa,
Southern Kuril Isl.
43-45 degrees: W. Sumatera subduction zone, Myanmar, Kamchatka,
Western Aleutians, Loyalty Islands
59-61 degrees: Alaska Peninsula (Unimak area), Hawaii, South Island,
southern North Island, New Zealand, Nepal, Xizang, China.
71-73 degrees: Yukon/Alaska border, Pakistan, No. Carlsberg Ridge
Macquarie Islands
103-106 degrees***: New Madrid, Jalisco coast Mexico, Red Sea, Aegean
Seam, Romania, western Turkey, Northern Germany, Iceland
142-146 degrees: Chile/Argentina border (around 30S), northern
Chile subduction zone, Peru aftershock zone, Trinidad, eastern
Venezuela, Windward Islands
176-180 degrees: Off Atlantic Coast of Brazil (Aseismic area 13.0S 35.0W)

***: The strongest triggering is always expected to be along the
shadow zone boundary between 103-107 degrees from the epicenter.

Historical following quakes after large events in the Guam region:

MAIN: Dec 9 1909 12.5N 145.0E 100 MW=8.0

AFTEREVENTS
Dec 10 45N 75W Ml 3.7 Southern Quebec, Canada
Dec 13 45N 16E Ml 4.9 Austria
Dec 14 33N 80W Ml 2.7 South Carolina
Dec 19 46N 60W Ml 5.0 East of Nova Scotia, Canada

MAIN: OCT 26 1912 14.0N 146.0E 130 MW=7.0

AFTEREVENTS

Oct 31 7N 138E Mw 7.4 Caroline Islands
Nov 03 24N 122E Ms 6.0 Taiwan
Nov 06 39N 74W Ml 3.5 Pennsylvannia
Nov 07 57N 155W Ms 7.5 Kodiak Island region

MAIN: MAY 18 1913 14.5N 145.5E 60 MW=7.1

May 19 63N 21W Mb 5.5 Iceland
May 20 52N 106E Mb 5.2 Lake Baykal, Russia
May 20 45N 14W Mb 4.0 Austria
May 21 36N 141W Mb 6.0 Off E. Coast Honshu
May 29 36N 141W Mb 6.4 Off E. Coast Honshu
May 30 5S 154E Ms 7.5 New Britain
Jun 06 33N 80W Ml 2.4 South Carolina
Jun 08 45N 74W Ml 3.7 So. Quebec, Canada
Jun 14 43N 25E Ms 7.5 Romania/Bulgaria

AFTEREVENTS

MAIN: JAN 28 1931 11.0N 144.8E 60 MW=7.2

AFTEREVENTS

Jan 30 36N 140E Mb 4.6 Off East Coast Honshu
Jan 30 19N 155W Mb 4.0 Hawaii
Jan 31 25N 101E Mb 5.0 Myanmar
Feb 2 39S 177E Ms 7.9 North Island, N. Z.
Feb 5 35N 106W Mb 5.0 New Mexico/Arizona
Feb 7 13N 87W Mb 5.7 El Salvador
Feb 8 39S 177E Ms 6.8 North Island, N. Z.
Feb 10 5S 103E Ms 7.1 South of Sumatera
Feb 13 25N 122E Ms 6.0 Ryukyu Islands/Taiwan
Feb 13 39S 177E Ms 7.1 North Island, N. Z.
Jan 30 36N 140E Mb 4.6 Off East Coast Honshu

MAIN: JUN 14 1942 15.0N 145.0E 80 MW=7.0

AFTEREVENTS

Jun 14 42N 70W Ml 3.1 New York
Jun 14 33N 116W Ml 4.0 So. California
Jun 15 32N 141E Mb 5.2 So. of Honshu
Jun 15 31S 180W Ms 6.8 Kermadec Is. N.Z.
Jun 15 18N 106W Mb 5.0 Jalisco, Mexico
Jun 16 34N 26E Mb 5.6 So. of Greece
Jun 16 40N 28E Mb 5.6 Istanbul, Turkey
Jun 16 1N 80W Mb 6.1 Ecuador
Jun 18 9N 140E Ms 7.1 Caroline Islands
Jun 19 42N 146E Mb 5.8 Southern Kuril Isl.
Jun 20 19N 101W Ms 6.8 Guerrero, Mexico
Jun 21 36N 27W Ms 6.5 Aegean Sea/Turkey
Jun 22 34N 118W Ml 3.0 Los Angeles, CA
Jun 22 36N 118W Ml 4.0 Coso Juntion swarm (many quakes in Ml 4+ range)
Jun 24 41S 176E Ms 7.2 North Island, New Zealand (Many aftershocks of Ml 4-6)
Jun 27 37S 177E Ms 6.4 North Island, New Zealand
Jun 29 33S 71W Ms 6.9 Central Chile coast

MAIN: MAY 25 1950 12.6N 143.7E 90 MW=7.3

AFTEREVENTS

May 25 41S 172E Mb 4.5 South Island, New Zealand
May 26 32N 169E Mb 7.2 Loyalty Islands
May 27 41N 142E Mb 4.9 Hokkaido
May 27 18S 178W MS 6.8 Tonga Islands
May 28 34N 118W ML 3.0 Los Angeles, CA
May 26 32N 169E Mb 5.6 So. of Honshu, Japan
May 29 41S 123W Mb 3.9 Northern California
May 30 19N 156W Mb 6.3 Hawaii
May 30 37S 178E Mb 5.5 North Island, N.Z.
May 30 20S 179W Ms 6.4 Tonga Islands
May 31 30S 132E Ms 6.1 So of Honshu, Japan
Jun 01 41N 123W Ml 4.2 Northern California
Jun 02 36N 121W Ml 3.6 Pinnacles, California
Jun 03 36N 118W Mb 3.2 Coso Junction, CA
Jun 04 36S 178E Mb 6.6 North Island, New Zealand
Jun 06 4S 77W Mb 6.8 Ecuador
Jun 08 47S 15W Mb 7.1 So. Atlantic Ocean
Jun 11 57S 148E Mb 6.4 Macquarie Ridge

MAIN: NOV 1 1975 13.8N 144.7E 113 MW=7.1

Nov 1 12N 125E Mb 5.5 Samar, Philippines
Nov 1 17S 172W Mb 5.4 Tonga Islands
Nov 2 68N 19W Mb 4.5 Iceland
Nov 3 44N 74W Ml 4.0 New York
Nov 6 19N 155W Mb 4.5 Hawaii
Nov 11 41N 144E Mb 5.4 Hokkaido
Nov 15 18N 102W Mb 5.9 Michoacan, Mexico
Nov 15 12N 126E Mb 6.0 Samar, Philippines

AFTEREVENTS

MAIN: AUG 8 1993 12.9N 144.8E 59 MW=8.2

AFTEREVENTS

Aug 9 36N 71E Mw 6.4 Hindu Kush (Followed by a Mw 7.0)
Aug 10 45S 167E Mw 7.1 South Island, N.Z.
Aug 10 38S 177E Mw 6.4 North Island, N.Z.
Aug 11 37S 118W Mw 4.5 Mammoth Lakes, CA.
Aug 11 37N 122W Ml 4.9 Central California
Aug 12 20N 156W Ml 3.7 Hawaii
Aug 13 36S 178E Mw 6.3 Off E. Coasat of N.Z.
Aug 19 7N 126E Mw 5.5 Mindanao, Philippines
Aug 20 6S 142E Mw 6.2 Papua New Guinea
Aug 21 34N 116W Ml 5.0 Southern California
Aug 21 21S 178W Mw 6.1 Fiji Islands

Summary of far-field events following Guam mainshocks:

In general, the events of Mb>=5 tend to fall in the areas
described by the listing of far-field events expected above
from distance considerations.

The most likely events of Mw>=6 in the next 10 days appear to be:

New Zealand - North Island 37S 177E
Earthquakes of Mw>=6.5 have occurred within 2 weeks in New
Zealand after each earthquake in Guam since 1930 (with the
one exception of 1975). The probability of such an earthquake
in the next week to 10 days is considered very high. Local
personnel should be on watch, especially on North Island.

The most likely events of M>=5 in the next 10 days on the
basis of history and far-field triggering theory appear to be:

Off East Coast of Honshu
Mindanao to Samar, Philippines
Taiwan
Hokkaido
Western Mexico
South of Honshu

Secondary location where events tend to occur but are not
as large or as likely . MB>=4.8 considered likely in next
10 days.

Fiji/Tonga Islands
Ecuador
Loyalty Islands
New Britain
Greece/Aegean Sea/Romania/Austria

Areas of U.S. and Canada where triggering may occur (Ml>=4.5)

Hawaii - Earthquakes of Ml>=4 have occurred on 4 occasions
considered very likely.

Areas of U.S. and Canada where triggering may occuR (Ml>=3)

New York/Pennsylvannia/So. Quebec, Canada
Los Angeles region, CA
Coso Junction region, CA
Northern and Central California (scattered)

Unusual events may occur in

Iceland
New Mexico/Arizona
South Carolina

On two occasions, a large M>=7 regional shock in the Caroline
Islands has followed Guam events within a week. This should
also be considered a possibility in this case.