FAR-FIELD AFTERSHOCK FORECAST EVALUATION FOR PACIFIC-ANTARCTIC RIDGE
EARTHQUAKE OF 6 AUGUST, 2001

This is a preliminary evaluation of the moderate to strong seismicity
of the world in the 10 days following the Pacific-Antarctic Ridge
earthquake (PAR) of 6 August, 2001. The parameters of that event were:

O: 06Aug2001 03:52:59 55.7S 123.2W MW=6.6 NEIS SOUTHERN EAST PACIFIC RISE

The far-field forecast posted on August 6 suggested the following
distances and locations would see increased activity during the
7 or 10 days following that event. Evaluation here is for the normal
10-day period usually given as the period of triggering after
large events. (In the introduction a 7-day period was prescibed,
in the conclusion this was given as a 10-day period).

GENERAL PREDICTION:

FORECAST FOR U.S. and CANADA

Two regions in the U.S. were specifically noted as areas where
far-field effects might be prevalent in the United States. These
were Colorado and New York/New England. The general region of the
northern U.S. and Canada was expected to see far-field triggering to some
extent.

During this time 6 events of Ml>=2 were located by GSC along the
New York/Quebec/Ontario border area. The largest was a Ml 2.5 at
Hawksbury Ont. on 10 August. The largest event in the Connecticut
region in the past 14 years also occurred on August 15 (Ml 1.9).

In Colorado, the largest event in the Central Rockies in 30 years
occurred near Glenwood Springs (Ml 4.0). It was followed the next
day by a Ml 2.2 aftershock. Similar earthquakes in Colorado had
followed PAR events in Sept, 1944, May 1957, and April 1963.

Canada experienced 3 unusual events of Mb 4.8, 4.9 and Ml 5.8
during this period. The Ml 4.8 and 4.9 occurred in the Yukon and
Northwest Territories, the Ml 5.8 was the Queen Elizabeth Island
earthquake, the largest ever recorded at latitudes higher than
76 degrees N in the western hemisphere. The forecast had pointed
out that a Mb 6.4 at 72N 68W which followed a PAR event on
May 2, 1957 had previously held this record for northern
Canada (and still does).

The only area of California noted in the forecast where
far-field triggering had previously occurred was 39N 122W where
a series of events Ml 4.0-5.0 had occurred on Nov 14-15 after a
Ms 6.5 PAR event on Nov. 13. This was not far from the Ml 5.5
event which occurred on 10 August, 2001 near Portola, CA.

SUBDUCTION ZONE ACTIVITY

The general prediction at the end of the forecast gave
specific subduction zones where seismicity was expected to be
high in the succeeding 10 days. 15 (50%) of the 30 events of MB>=5
in the NEIS listing for these 10 days occur in these 9 listed areas
as tabulated at the end of this report:

DISTANCE EFFECTS:

Tests with global seismicity show that approximately 14% of
global seismicity falls in the prescribed distances at the Mb>=4.7
(a range which is reasonably complete in teleseismic (NEIS) catalogs).
We would therefore expect that approximately 14% of events of Mb>=4.7
during the period 6-16 August would fall in the prescribed distance
ranges provided no triggering were occurring. In the evaluation
aftershocks of the great Peru event were removed from consideration.
During this 10-day interval NEIS lists 60 non-Peru aftershocks
with Mb>=4.7. Of these, 32 (53%) fall within the forecast distance
ranges. The expected number would have been 8 such events (14%).
This suggests that at least 24 events were larger because of the
effects from the PAR event.

THE FORECAST AS POSTED

The forecast stated that seismicity was likely to increase
at the following distances and locations:

9-10 degrees: Pacific-Antarctic Ridge events and aftershocks
17-19 degrees: East Pacific Rise near 37S
34-36 degrees: East Pacific Rise near 20S
43-45 degrees: Central Chile (about 30 S), southern So. Sandwich Islands,
Alpine fault zone, New Zealand (strikes this area with
wave front parallel to the fault, this is a situation where
a moderate event can be triggered if strain conditions in this
region are otherwise favorable).
59-61 degrees: Loyalty Isl., Fiji, Samoa Ecuador, Galapagos
71-73 degrees: SE Solomon Islands, Santa Cruz Isl. Central
American subduction zone. The wave front is parallel to
the Mexican Subduction zone, a moderate to large event
is possible in this region especially given the effect
of landfall of Hurricane Barry tonight. This event could
be Ms>6 in the next 3 days along the Mexican Subduction zone.
103-106 degrees***: South of Sumatera (100-106E), Molucca Sea, Sulawesi,
Central Marianas, Vancouver B.C, Seattle, Spokane, WA, Central
Mid-Atlantic Ocean, Indian Ocean near Mauritius (triple junction)
142-146 degrees: Nepal, No. of Iceland, Greenland area,
France, Sicily, Arctic Ocean
176-180 degrees: Aseismic area 56N 58E east of Moscow, Russia

Most likely areas to be affected are 103-106 degrees distance and
at 142-146 degrees away from the epicenter.

SUMMARY OF EXPECTED FAR-FIELD EVENTS

Areas where the wave-front is parallel to the local
faulting have experienced large events following earthquakes
in this region of the Pacific-Antarctic Ridge. These
areas include the Central American/Mexican subduction
zone, the subduction zone near the Fox Islands and
the Alpine fault in New Zealand. These areas should be
on seismic watch for the next 10 days. Earthquakes
of Ms>6.0 are possible in these areas. The area south
of the Kermadec Islands is also subject to strong
far-field triggering.
Regions at distances where seismicity is expected
to increase often do show moderate to large earthquakes
following events in this area of the Pacific-Antarctic
Ridge. Some of these which have a record of strong far-field
seismicity include the subduction zone south of Java and
Sumatera; the area south of the Loyalty Islands, the Moluccas
Tonga/Fiji and the Galapagos Islands.
In the United States seismic events in Colorado often
follow earthquake in this area of the Pacific. The largest
event ever in New York State followed by one day the largest
event ever recorded in this area of the south Pacific in
1944. One of the largest earthquakes in eastern Canada
was also associated with a strong event in the South
Pacific. The zone across the northern U.S. should be carefully
monitored for the next 10 days for far-field activity.

THE SPECIFIC EVENTS EVALUATION
Distance effects:

Following are the events and distances of all non-Chile
aftershocks to the PAR event.

Format is:
MO-DA-YEAR LAT LONG MB DISTANCE to PAR Earthquake Location
(N+/S-)(E+/W-) Degrees

Immediate (Classical Aftershocks Distance < 2 degrees)

08-06-2001 -55.7 -123.3 5.6 0.12 Degrees Pacific-Antarctic Ridge
08-06-2001 -55.8 -122.6 4.7 0.39 Degrees Pacific-Antarctic Ridge

9-10 degrees: Pacific-Antarctic Ridge events and aftershocks

08-06-2001 -56.8 -140.3 5.0 9.61 Degrees Pacific-Antarctic Ridge

17-19 degrees: East Pacific Rise near 37S
34-36 degrees: East Pacific Rise near 20S

No NEIS events of Mb 10-43 degrees from PAR occurred during this 10-day period
43-45 degrees: Central Chile (about 30 S), southern So. Sandwich Islands,
Alpine fault zone, New Zealand (strikes this area with
wave front parallel to the fault, this is a situation where
a moderate event can be triggered if strain conditions in this
region are otherwise favorable).

08-10-2001 -13.6 -111.7 4.9 43 Degrees East Pacific Rise
08-16-2001 -49.4 163.9 5.0 43 Degrees Alpine Fault Zone, New Zealand
08-10-2001 -31.9 -71.2 4.7 43 Degrees Central Chile
08-16-2001 -31.7 -69.5 4.8 44 Degrees Central Chile
08-06-2001 -59.4 -29.4 4.7 45 Degrees So. South Sandwich Islands
08-06-2001 -59.4 -29.4 4.7 45 Degrees So. South Sandwich Islands
08-14-2001 -34.7 -179.5 4.9 43 Degrees Kermadec Islands, New Zealand
08-10-2001 -30.3 -177.7 5.2 45 Degrees Kermadec Islands, New Zealand
08-09-2001 -30.5 -178.0 5.3 45 Degrees Kermadec Islands, New Zealand

08-08-2001 -56.0 -27.7 4.9 49 Degrees So. Sandwich Islands
08-11-2001 -23.5 -175.9 4.8 50 Degrees Tonga
08-11-2001 -22.1 -174.9 5.2 50 Degrees Tonga

59-61 degrees: Loyalty Isl., Fiji, Samoa Ecuador, Galapagos

08-10-2001 -22.3 170.6 5.3 59 Degrees Loyalty Islands
08-06-2001 -8.5 -74.8 5.5 60 Degrees Central Peru

08-10-2001 -14.7 167.1 5.2 66 Degrees Vanuatu Islands
08-13-2001 -13.9 167.9 5.3 66 Degrees Vanuatu Islands
08-13-2001 -13.6 166.2 5.3 66 Degrees Vanuatu Islands

71-73 degrees: SE Solomon Islands, Santa Cruz Isl. Central
American subduction zone. The wave front is parallel to
the Mexican Subduction zone, a moderate to large event
is possible in this region especially given the effect
of landfall of Hurricane Barry tonight. This event could
be Ms>6 in the next 3 days along the Mexican Subduction zone.

08-16-2001 -10.7 166.0 4.7 71 Degrees Santa Cruz Islands
08-08-2001 -10.9 165.4 5.4 71 Degrees Santa Cruz Islands
08-13-2001 -10.9 165.2 4.9 71 Degrees Santa Cruz Islands
08-09-2001 -10.1 161.2 4.9 73 Degrees SE Solomon Islands
08-12-2001 11.5 -86.7 5.1 73 Degrees Nicaragua
08-10-2001 14.0 -91.9 5.1 73 Degrees Guatemala
08-11-2001 14.0 -91.8 5.1 73 Degrees Guatemala
08-06-2001 17.5 -93.7 4.7 76 Degrees Gulf of Tehuantepec, Mexico
08-13-2001 25.5 -109.6 4.7 81 Degrees Gulf of California
08-09-2001 -5.6 149.7 5.3 83 Degrees Papua New Guinea
08-11-2001 12.1 -60.0 4.8 85 Degrees Trinidad
08-13-2001 -5.7 142.4 5.2 87 Degrees Papua New Guinea
08-10-2001 39.8 -120.6 5.5 95 Degrees Northern California
08-12-2001 -6.9 125.4 4.9 96 Degrees Banda Sea
08-09-2001 -7.3 120.7 5.2 98 Degrees Flores

103-106 degrees***: South of Sumatera (100-106E), Molucca Sea, Sulawesi,
Central Marianas, Vancouver B.C, Seattle, Spokane, WA, Central
Mid-Atlantic Ocean, Indian Ocean near Mauritius (triple junction)

08-15-2001 0.7 -25.5 4.9 102 Degrees Central Mid-Atlantic Ocean
08-07-2001 -8.6 113.8 5.6 102 Degrees So. of Sumatera
08-07-2001 -8.6 113.8 5.7 102 Degrees So. of Sumatera
08-11-2001 13.3 145.8 4.8 102 Degrees Central Marianas
08-11-2001 13.4 145.9 4.8 102 Degrees Central Marianas
08-06-2001 2.1 128.5 5.1 102 Degrees Molucca Sea
08-16-2001 2.0 128.3 5.2 102 Degrees Molucca Sea
08-09-2001 1.3 126.3 4.8 102 Degrees Molucca Sea
08-12-2001 2.7 127.0 5.0 103 Degrees Molucca Sea
08-15-2001 4.3 127.9 5.2 104 Degrees Molucca Sea
08-10-2001 19.2 146.8 4.7 105 Degrees Northern Marianas
08-13-2001 19.3 146.9 4.7 105 Degrees Northern Marianas

08-10-2001 22.7 143.9 5.0 110 Degrees Volcano Islands
08-08-2001 26.9 143.3 4.8 113 Degrees Volcano Islands
08-13-2001 51.7 -172.8 4.7 114 Degrees Fox Islands
08-09-2001 51.4 -178.1 5.2 115 Degrees Andreanoff Islands
08-10-2001 64.3 -131.0 4.8 119 Degrees Yukon Territory Canada
08-12-2001 6.5 94.7 5.3 122 Degrees Andaman Islands
08-13-2001 46.3 152.3 4.8 123 Degrees Kuril Islands
08-12-2001 31.4 130.5 4.7 124 Degrees Kyushu
08-13-2001 41.1 142.2 6.4 124 Degrees Hokkaido
08-06-2001 47.2 142.8 5.0 128 Degrees Sakhalin
08-08-2001 47.4 142.6 4.8 129 Degrees Sakhalin
08-12-2001 24.4 94.9 4.8 138 Degrees Myanmar

142-146 degrees: Nepal, No. of Iceland, Greenland area,
France, Sicily, Arctic Ocean

08-06-2001 71.0 -12.0 4.9 147 Degrees Norwegian Sea

08-14-2001 30.0 65.1 5.0 153 Degrees Pakistan
08-13-2001 42.6 26.5 4.8 156 Degrees Black Sea

176-180 degrees: Aseismic area 56N 58E east of Moscow, Russia

No events were observed further away than 156 from PAR in NEIS catalog.

GENERAL PREDICTION:

The general prediction at the end of the forecast gave
specific subduction zones where seismicity was expected to be
high in the succeeding 10 days. 15 (50%) of the 30 events of MB>=5
occurred in these 9 listed areas as follows:

The Central American/Mexican subduction

08-12-2001 11.5 -86.7 5.1 73 Degrees Nicaragua
08-10-2001 14.0 -91.9 5.1 73 Degrees Guatemala
08-11-2001 14.0 -91.8 5.1 73 Degrees Guatemala
08-06-2001 17.5 -93.7 4.7 76 Degrees Gulf of Tehuantepec, Mexico
08-13-2001 25.5 -109.6 4.7 81 Degrees Gulf of California

The subduction zone near the Fox Islands

08-13-2001 51.7 -172.8 4.7 114 Degrees Fox Islands
08-09-2001 51.4 -178.1 5.2 115 Degrees Andreanoff Islands

The Alpine fault in New Zealand.

08-16-2001 -49.4 163.9 5.0 43 Degrees Alpine Fault Zone, New Zealand

The area south of the Kermadec Islands

08-14-2001 -34.7 -179.5 4.9 43 Degrees Kermadec Islands, New Zealand
08-10-2001 -30.3 -177.7 5.2 45 Degrees Kermadec Islands, New Zealand
08-09-2001 -30.5 -178.0 5.3 45 Degrees Kermadec Islands, New Zealand

The subduction zone south of Java and Sumatera

08-07-2001 -8.6 113.8 5.6 102 Degrees So. of Sumatera
08-07-2001 -8.6 113.8 5.7 102 Degrees So. of Sumatera

The area south of the Loyalty Islands

08-10-2001 -22.3 170.6 5.3 59 Degrees Loyalty Islands

The Moluccas

08-06-2001 2.1 128.5 5.1 102 Degrees Molucca Sea
08-16-2001 2.0 128.3 5.2 102 Degrees Molucca Sea
08-09-2001 1.3 126.3 4.8 102 Degrees Molucca Sea
08-12-2001 2.7 127.0 5.0 103 Degrees Molucca Sea
08-15-2001 4.3 127.9 5.2 104 Degrees Molucca Sea

Tonga/Fiji

08-11-2001 -23.5 -175.9 4.8 50 Degrees Tonga
08-11-2001 -22.1 -174.9 5.2 50 Degrees Tonga

The Galapagos Islands

None