FAR-FIELD AFTERSHOCK FORECAST FOR SOUTHERN MARIANA ISLAND MS7.1 (PRELIMINARY)
(APRIL 26, 2002)

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 7.2 or greater (NEIS, GSSC).
The earthquake had been well forecast.

The parameters of this earthquake (NEIS) are given as:

O: 26APR2002 16:06:06 13.1N 144.5E MW=7.2 NEIS 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.
There have been 8 earthquakes of Mw>=7 recorded in the are 12-15N 140-150E
in the past century. The largest occurred last year on October 12, 2001
as a Mw 7.0. The epicenter of this earthquake was very near
the same as today's (12.8N 144.9E) 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 2001 had
a depth of 60 km, today's depth was nearly the same (50-70 km).
Other earthquakes of Mw>=7 in the region occurred on Aug 8, 1983 (Mw 8.3);
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 AFTERSHOCKS FROM KAMCHATKA AND CHILE

Two moderate foreshocks in the southern Marianas occurred over the past
two days of Mb 4.7 and 4.5. Last night a moderate Mw 5.8 earthquake
was located in the Kamchatka peninsula region. Today's Guam earthquake
falls at 43 degrees from the Kamchatka event, at 108 from the Guerrero,
Mexico earthquake and at 144 degrees from the Chile (Mw 6.7) event
of April 18. The epicenter was therefore at a triple junction of
FFA effects.
No FFA forecast from the most recent Kamchatka event had been produced,
however a previous Kamchatka FFA forecast (October 8, 2001) had stated:

"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."

The Kamchatka event appears to be the immediate trigger for this
earthquake, however effects from Chile and Mexico were likely to
have made the event larger.

The FFA forecast from Chile and Mexico (April 18, 2002) had noted:

(From Chile)

"The following areas are expected to see increased seismicity
from April 19 through April 29, 2002. Maximum event size for
these regions is expected to increase by 0.5 to 0.7 magnitude units
in this period.

...

142-146 degrees:... Central Mariana Islands, GUAM"

GEOMAGNETIC STORM AND SOLAR FLARE (X1.5)

The summary report from April 20 had placed the region under
seismic watch for the next three days. The sub-solar longitude
at the time of the X1.5 flare on April 21 had been 170E. The warning
was issued for longitudes within 30 degrees longitude of this
and especially at high latitudes and along the geomagnetic equator.
Guam lies on the geomagnetic equator, Kamchatka, another triggered
area is at high latitudes, both lie within the warning region.
The warning notice had read:

" The strongest solar flare since Oct 22, 2001 hit about an hour
ago just as the strong geomagnetic storm was returning to quiet
conditions. A strong proton storm followed this flare. Sub-solar
latitudes at the time of the flare were about 170E, anti-solar
locations at 10W. Areas within about 30 degrees longitude of either
of these longitudes will experience the greatest effects from this
flare and are under seismic watch conditions for the next two days.
High latitudes and areas along the geomagnetic equator are also likely
to see increased seismicity in the next two days. The effect of this
flare is uncertain coming at the end of a strong geomagnetic storm.
Many of the events which were ripe for geomagnetic triggering have
already had earthquakes. Nevertheless, strong earthquakes could still
accompany these storms and this X1.2 flare between April 21 and April
25. This watch includes areas of New Zealand, Kermadec, Tonga, Samoa,
the Aleutians and western Europe."

Note that in addition to the Guam earthquake, moderately strong earthquakes
have occurred in the past two days in the Kermadec Islands, Tonga, Aleutians,
and western Europe as well.

The timing of large events related to the geomagnetic storm and
Solar flare had likewise been discussed in the daily summary (April 21, 2002).
That summary had noted:

"It is also possible that the sudden return to quiet geomagnetic conditions
brought on by the very strong proton storm (which eliminated electron
flux in the ionosphere) was partially responsible for the lull in
seismic activity today. Proton storms tend to accompany such quiet
periods and the cause may be related to the inability to form coherent
electojects in the presence of the solar protons. These in turn, would
not allow induced currents in the earth which might be triggering
agents for earthquakes.
Right now, the areas to watch will probably be volcanics. They usually
"heat up" between 2-5 days after strong geomagnetic storm. Either bubbles
are released during the storm which take 2-5 days to migrate up through
magma chambers, increasing magma chamber pressure as the rise and expand,
or some actual heating of the magma is occurring from Ohmic heating - hard
to say, but statistical evidence suggests whatever the cause, it takes
3-5 days before this effect is seen.
... Globally, there is usually a strong eruptive episode including several
major volcanic eruptions 3-7 days after strong geomagnetic storms. Mid-Ocean
ridges also become unusually active at this time."

Note that this and the Kamchatka event fit this scenario quite well.

This was re-emphasized in the April 22 Daily Summary:

"... The loss of the buffering protons and the new
geomagnetic storm may bring back moderate to strong seismicity in
many areas."

and on April 24:

" Delayed effects from the recent strong geomagnetic storms were
probably important in the timing of the Balkans and the Andreanoff
Islands earthquakes today. STRONG EVENTS OFTEN FOLLOW X-CLASS SOLAR
FLARES 3-5 DAYS LATER IN SUB- AND ANTI-SOLAR REGIONS."

(Emphasis added)

FAR-FIELD FORECAST

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

0-5 degrees: Regional aftershocks in the Guam/Caroline Islands region
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
103-107 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.

Lowell Whiteside
April 26, 2002

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 event 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.