FAR-FIELD AFTERSHOCK FORECAST FROM TAIWAN (MJ 7.3, MS 7.1) MAR 31, 2002

A strong earthquake hit about 100 km southeast of Taipei, Taiwan
this evening. Initial magnitudes put this event at Mj 7.3 and Ms 7.1.
Far-field effects from this event are expected to be moderate since other
large events have recently occurred in nearby areas and near the
antipode in northern Chile. The maximum magnitude in subject areas
is expected to rise by about by 0.5-1.0 units above those expected
previously.

Preliminary epicentral data for this events are:

O: 31MAR2002 06:52:50 24.4N 122.2E MB=7.1 NEI TAIWAN REGION
O: 31MAR2002 06:53 24.1N 121.8E Mj=7.3 NIED TAIWAN_REGION
O: 31MAR2002 14:52:54 24.2N 122.2E ML=6.8 TAI Ilan, Taiwan

Several lines of evidence suggested a sizable event was likely in
this area at this time. These fall into four possible triggering categories:
1) Forecasts based on local strains, 2) Geomagnetic effects from today's moderate storm;and 3) Far-field effects from the Hindu Kush, Mindanao, Northern Chile and near-field effects from the Ryukyu Islands earthquakes
of March 3, 5 and 24-26.
These are summarized below:

STRAIN FORECASTS:

In the FFA forecast from the Ryukyu Islands, a forecast had been published
For the most likely events in the region at this time based on local
Strain measurements. Two forecasts were published in that document:

"F: 25MAR2002 115-22g 23.5N 121.7E 3.5-6.4 AACBA Taiwan
P: 26MAR2002 7-03/23 23.8N 122.0E 4.0-6.8 AACAA Taiwan "
That forecast had expected an event within less than 30 km of the currently
Located epicenter with Ms up to 6.8. For comparison, the event parameters
Are preliminarily:

O: 31MAR2002 06:52:50 24.4N 122.2E MB=7.1 NEI TAIWAN REGION
O: 31MAR2002 06:53 24.1N 121.8E Mj=7.3 NIED TAIWAN_REGION
O: 31MAR2002 14:52:54 24.2N 122.2E ML=6.8 TAI Ilan, Taiwan

GEOMAGNETIC EFFECTS:

In addition, the daily summary from yesterday had noted that the
geomagnetic storm which occurred yesterday morning was likely to
increase seismicity in:

" An extreme depression in the intensity of the geomagnetic
field occurred this morning at approximately 02:55 UT. Areas
where seismicity is most likely to be affected by this geomagnetic
field change would be within 20 degrees of 45W and 135E.
This depression was followed by the continuing geomagnetic
storm currently in progress."

Since this event occurred at 122E, within 20 degrees longitude of
135E, it was under seismic watch conditions at the time of occurrence.

PRECURSORY SEISMICITY:

A small Ml 2.6 occurred in the Texas Panhandle region several
hours prior to this earthquake. This was at the CM shadow-zone
boundary from this and earlier events in the Ryukyu Islands. May
have been a reaction to those earlier events or a precursor to
the event today.

FAR-FIELD TRIGGERING EFFECTS:

This earthquake occurred at 45 degrees from the Hindu
Kush earthquakes of March 24 (Mw 6.0) and March 3 (Mw 7.2) and
at 17 degrees from the Mindanao (Mw 7.5) earthquake of March 5.
It is also near the antipode of the Mw 6.5 northern Chile earthquake
of March 28 and within the near-field triggering range from the
Ryukyu Islands earthquake of March 26 (Mw 6.5).
The Far-field aftershock forecast from Hindu Kush event (March 3)
had expected an event in this region within 3 weeks and had noted
this as follows:

"The most likely events of Mw>=6 in the next 10 days appear to be:
(Number in paranthesis indicated number of times and event of M>=6
has followed a Hindu Kush mainshock within 2-3 weeks).

...
Mindanao/Mindoro Philippines (3)
Taiwan (4)"

and

"43-45 degrees: ... Taiwan"

It also occurred 17 degrees directly north of the Mindanao earthquake of
March 5 (Mw 7.5), a distance at which FFA triggering was also expected in the
Mindanao FFA forecast:

"17-19 degrees: Ryukyu Islands ..."

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.

...Taiwan (1)"

The FFA forecast from the Ryukyu Islands had also stated:

"0-5 degrees: Regional triggering- Taiwan, ...."

and

"The most likely events of Mw>=6 in the next 10 days appear to be:
(Number in paranthesis indicated number of times and event of M>=6
has followed a Ryukyu mainshock within 2-3 weeks).

...
Regional or local aftershock in Ryukyu Isl or Taiwan (4)"
and

" The most likely upcoming activity would be aftershocks in the
Ryukyu/Taiwan region and in the Hindu Kush area. Local aftershocks
in the Mw>=6 range are quite common for events in the southern
Ryukyu Islands, and should be expected in the next week (or possibly
as long as two months)."

and finally from the Northern Chile FFA forecast we find:

"176-180 degrees: ... Regional activity may occur in Taiwan"

and

"The most likely events of Mw>=6 in the next 10 days appear to be:
(Number in paranthesis indicated number of times and event of M>=6
has followed a Chile/Bolivia mainshock within 2-3 weeks).

Taiwan..."

It appears the Taiwan earthquake was an event waiting to happen.

SEISMIC HISTORY OF AREA:

Strong earthquake are common within 200 km of this event. Since
the late 18th Century 39 such events have been recorded in the
area, about one every 5 years. The last was the Chi-Chi earthquake of
September 1999 which did much damage and caused much suffering
among the people of Taiwan.
Clustering of large events in this region is quiet common. Clusters
of event so of Ms>=7 have occurred in 1909-1910; 1915-1916; 1921-1922;
1937-1938; 1951; 1972-1975 and 1999. Many of these included large
aftershocks.
Earthquakes in the region have tended to cluster in March to
April and September to October, with 22 of the 39 occurring during
these 4 months of the year as enumerated below. They are also noticably
missing during the summer months of May through August during which only
4 such events have occurred.

Month #M>=7 events
JAN 3
FEB 3
MAR 4
APR 7
MAY 1
JUN 1
JUL 1
AUG 1
SEP 7
OCT 4
NOV 3
DEC 4

Following are the events within 200 km of today's
earthquake which have been Mw>=7.0.

MO DA HR MN SC YEAR N LAT E LONG DEP MW

4 23 15 0 0 1771 24.000 124.030 0 7.4 0
3 16 22 42 40 1906 24.000 121.000 60 7.1 21
1 11 3 35 0 1908 23.700 121.400 0 7.3 0
4 14 19 54 0 1909 25.000 121.500 0 7.3 0
11 21 7 36 0 1909 25.500 122.000 10 7.0 0
4 12 0 22 13 1910 25.500 122.500 200 8.3 21
9 1 14 20 0 1910 24.000 122.000 60 7.3 21
1 5 23 26 42 1915 25.000 123.000 160 7.4 21
2 28 18 59 5 1915 23.600 123.500 60 7.7 21
3 25 23 52 17 1916 24.000 124.000 60 7.4 21
8 28 7 28 0 1916 23.900 120.500 10 7.2 0
7 4 5 36 30 1917 25.000 123.000 60 7.2 21
12 20 20 37 24 1919 22.800 121.700 0 7.0 0
6 5 4 21 28 1920 23.500 122.000 60 8.3 21
4 2 9 36 0 1921 23.000 123.000 60 7.2 0
9 1 19 16 6 1922 24.600 122.200 60 7.6 0
9 14 19 31 39 1922 24.600 122.300 0 7.2 0
4 20 22 1 54 1935 24.350 120.820 60 7.1 0
12 8 8 32 9 1937 23.000 121.500 60 7.0 21
9 7 4 3 18 1938 23.800 121.500 60 7.0 21
12 6 23 1 0 1938 22.900 121.600 0 7.0 0
9 26 16 1 57 1947 24.800 123.000 110 7.4 21
10 21 21 34 14 1951 23.800 121.500 60 7.3 21
10 22 3 29 27 1951 23.800 121.300 60 7.1 21
10 22 5 43 1 1951 24.000 121.300 60 7.1 21
11 24 18 50 20 1951 23.500 121.500 0 7.3 0
2 23 20 26 16 1957 23.950 121.600 55 7.3 0
4 26 20 40 38 1959 24.810 122.700 127 7.7 0
2 13 8 50 5 1963 24.330 122.140 67 7.3 0
3 12 16 31 21 1966 24.090 122.650 59 8.0 0
10 25 0 59 23 1967 24.500 122.200 65 7.0 0
1 25 3 41 24 1972 23.033 122.154 34 7.7 128
4 24 9 57 22 1972 23.638 121.551 33 7.3 174
3 23 7 32 37 1975 22.700 122.800 21 7.0 0
5 23 16 1 49 1975 22.700 122.600 6 7.0 0
12 23 11 23 12 1978 23.247 122.075 33 7.2 357
11 14 21 20 11 1986 23.901 121.574 34 7.8 79
9 20 17 47 18 1999 23.772 120.982 33 7.7 367
9 20 18 11 50 1999 23.811 121.136 0 7.1 19

FAR-FIELD FORECAST:

The following areas are expected to see increased seismicity
from March 31 through April 10, 2002. Maximum event size for
these regions is expected to increase by 0.5 to 1.0 magnitude units
in this period.

0-5 degrees: Regional triggering- Taiwan, Ryukyu Island, aftershocks
9-10 degrees: Southern Japan (Kyushu, Shikoku), Central Philippines (Samar).
17-19 degrees: Off Coast E. Honshu, Volcano Is. Myanmar, Celebes,
Halmahera
34-36 degrees: Northern Kurils, Papua New Guinea, Timor, Nepal,
Northern and Southern Sumatera, So. of Java
43-45 degrees: Central Solomon Is., Hindu Kush, Rat/Near Islands, Aleutians
59-61 degrees: Unimak Is., Alaska Peninsula, NO. and Central Vanuatu,
SW Australia, Northern and southern Iran to Caspian Sea
71-73 degrees: Southeast Alaska, NW Turkey/Caucasus, Samoa/Fiji Isl.
Gulf of Aden, Swedeni, Hawaii
103-107 degrees***: Gulf of California, Quebec/NY border, Oklahoma,
Texas Panhandle. New Madrid, MO. New Brunswick
142-146 degrees: Colombia, Northern Venezuela, Chile Rise, Trinidad,
northern So. Sandwich Islands
176-180 degrees: A-seismic zone in Paraguay (24S 58W). Regional
triggering is possible in the currently active area at about 24S
60-69W in northern Chile/Argentina.

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

PAST OCCURRENCES (MW>=7.5)

Following are large shocks following previous events of Mw>=7.5
within 200 km of todays' Taiwan earthquake:

4 12 0 22 13 1910 25.500 122.500 200 8.3 21
2 28 18 59 5 1915 23.600 123.500 60 7.7 21
6 5 4 21 28 1920 23.500 122.000 60 8.3 21
9 1 19 16 6 1922 24.600 122.200 60 7.6 0
4 26 20 40 38 1959 24.810 122.700 127 7.7 0
3 12 16 31 21 1966 24.090 122.650 59 8.0 0
1 25 3 41 24 1972 23.033 122.154 34 7.7 128
11 14 21 20 11 1986 23.901 121.574 34 7.8 79
9 20 17 47 18 1999 23.772 120.982 33 7.7 367

MAIN APR 12 1910 25.0N 123.0E 200 7.6

Apr 16 36N 3W Ms 5.0 Western Spain
Apr 20 20S 177W MS 7.0 Tonga Islands
Apr 24 39N 75W Ms 3.0 Delaware/ D.C.
May 1 20S 169E MS 7.1 So. Vanuatu Isl.
May 4 29N 139E Ms 6.3 SE of Honshu

MAIN FEB 28 1915 23.6N 123.5E 60 7.7

Mar 3 48N 88W Ml 3.6 Lake Superior/ So. Ontario
Mar 8 39N 141E Ms 7.0 Off East Coast Honshu
Mar 17 42N 143E Ms 7.4 Hokkaido/ So. Kuriles

MAIN JUN 5 1920 23.5N 122.0E 60 8.3

Jun 7 43N 70W Ml 3.7 New England
Jun 10 46N 151E Ms 5.7 Northern Kuriles
Jun 12 38N 21E Ms 5.2 Greece
Jun 12 38N 31E Ms 5.2 western Turkey
Jun 18 33N 118W Ms 4.5 So. of Los Angeles
Jun 20 43N 17E Ms 5.1 Bulgaria
Jun 22 33N 118W Ms 4.9 So. of Los Angeles
Some business buildings collapsed at Inglewood, Hyde PArk CA
Damage about $100,000. The Inglewood Grammar school collapsed
and walls of hotels collapsed onto streets. Intensity VIII.

MAIN SEP 1 1922 24.5N 122.2E 60 7.6

Sep 4 35N 120W Ms 4.5 South of Parkfield, CA
Sep 4 10S 69W MS 6.9 Peru
Sep 4 24N 122E Ms 6.5 Ryukyu Islands
Sep 4 45N 67W Ms 3.0 New Brunswick area
Sep 14 24N 122E Ms 7.2 Ryukyu Islands
Sep 16-18 24N 121E Ms 6.2+ Swarm in Taiwan area (six 6+ events)

MAIN APR 26 1959 24.8N 122.7E 127 7.7

Apr 27 7S 129E Ms 5.8 Flores/Banda Sea
Apr 27 32N 92E MS 6.1 Tibet
Apr 28 14N 92W Ms 6.6 Chiapas, Mexico
May 01 37N 51E Ms 5.9 No. Iran
May 04 52N 159E Ms 8.1 Kamchatka/No. Kurils (Many strong aftershocks)
May 07 3S 148E Ms 6.2 Papua New Guinea
May 12 32N 79E Ms 6.3 Pakistan
May 12 23S 64W Ms 7.0 Northern Chile/Bolivia

MAIN MAR 12 1966 24.0N 122.6E 59 8.0

Mar 13 55S 126W Ms 6.2 Pacific-Antarctic Ridge
Mar 16 21S 174W MS 5.4 Tonga Islands
Mar 16 10N 63W Ms 5.2 No. Venezuela
Mar 16 10N 122E Ms 5.4 Central Philippines
Mar 17 21S 179W MS 6.8 Tonga Islands
Mar 20 0N 30E Ms 7.2 Lake Victoria area, Tanzania
Mar 22 37N 115E Ms 7.0 NE China
Mar 23 23N 122E Ms 6.6 Taiwan/Ryukyu Islands
Mar 24 13S 166E Ms 5.8 Northern Vanuatu

MAIN JAN 25 1972 23.0N 122.1E 34 7.7

Jan 25 36N 70E Ms 5.6 Hindu Kush
Jan 25 43N 13E MS 5.0 Central Italy
Jan 26 20S 178W Ms 6.5 Fiji Islands
Jan 28 19S 169E Ms 6.7 Vanuatu Islands
Jan 29 34N 116W MS 4.5 Southern California
Feb 01 36N 90W Ms 4.1 New Madrid, MO
Feb 03 34N 80W Ms 4.4 South Carolina
Feb 08 34N 118W Ms 3.4 Southern California
Feb 12 15S 173W Ms 6.0 Samoa
Feb 13 55S 27W Ms 5.8 South Sandwich Islands
Feb 13 11S 166E Ms 6.7 Northern Vanuatu

MAIN NOV 14 1986 23.9N 121.5E 34 7.8

Nov 15 45N 111W Ms 3.4 Yellowstone N.P
Nov 15 19N 155W MS 3.9 Hawaii
Nov 21 40N 124W Ms 5.2 No. California
Nov 22 34N 139E Ms 5.8 Off E. Coast Honshu
Nov 23 3S 77W MS 6.4 Peru-Ecuador area
Nov 25 44N 16E Ms 5.5 Yugoslavia
Nov 30 38N 141W Ms 5.0 E. Coast Honshu
Dec 01 26S 177W Ms 6.1 Kermadec Islands

MAIN SEP 20 1999 23.8N 121.0E 33 7.7

Sep 21 45N 150E Ms 5.7 Kuril Islands
Sep 22 38N 122W MS 4.3 Glen Ellen, CA
Sep 28 54N 168E Ms 6.2 Komandorsky Isl.
Sep 29 31S 71W Ms 6.0 Central Chile
Sep 30 16N 97W MS 7.5 Oaxaca Mexico

Summary of far-field events following Taiwan mainshocks:

There has been little change in strain patterns since the
Ryukyu/No Chile antipodal events since this event is near
the Ryukyu event, but larger. The major change is that
events following may increase in magnitude over that which
might have been expected prior to the Taiwan earthquake.

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:
(Number in paranthesis indicated number of times and event of M>=6
has followed a Taiwan mainshock within 2-3 weeks).

Tonga - around 15S (3)
Regional or local aftershock in Ryukyu Isl or Taiwan (4)
Hindu Kush/Pakistan (3)
Northern Chile or Central Chile

The most likely events of Mw>=5 in the next 10 days appear to be:

Central Philippines
Myanmar to Nepal
Hokkaido off East Coast of Honshu, Japan
Northern Vanuatu Islands
Chiapas to Oaxaca Mexico

Other possible events of Mw>=4.5 in the next 10 days appear to be:

Northern Venezuela/Colombia
Komandorsky/Kamchatka/No. Kuriles
No/So. Iran
Unimak/Fox Islands, Aleutians
Romania/Italy/Yugoslavia area

Possible Events (Ml>=3) in the U.S. and Canada include:

Southern Ontario/Quebec/New York Border to New Brunswick
Northeast region.
New Madrid, MO.
Yellowstone
Hawaii

The observation made following the northern Chile earthquake
several days ago still holds. More events may be expected to
occur in the south-Central to northeast U.S. Previous events
have concentrated in regions from the Plains to New Madrid, MO
to the N.Y./Quebec border. The small earthquake in the Texas
Panhandle several hours before the Taiwan earthquake may have
been a precursor to some of this coming activity.

General:

The most likely upcoming activity would continue to be aftershocks in
the Ryukyu/Taiwan region and in the Hindu Kush area. Local aftershocks
in the Mw>=6 range are quite common for events in Taiwan and should
be expected in the next week (or possibly as long as two months).