FAR-FIELD AFTERSHOCK FORECAST FROM RYUKYU ISLANDS (MJ 6.9, MS 6.8) - 03/26/02

A strong earthquake hit about 100 km northeast of the Island of Taiwan
this evening in the southernmost Ryukyu Islands of Japan. Initial
magnitudes put this event at Mj 6.9 and Ms 6.7. Far-field effects from
this event would be minimal, but quite possible.

Preliminary epicentral data for this events are:

O: 26MAR2002 03:46 23.0N 124.1E Mj=6.9 NIED NEAR_ISHIGAKIJIMA_ISLAND, Japa
O: 26MAR2002 03:45:48 23.5N 123.9E MS=6.7 NEI SW RYUKYU ISL., JAPAN
O: 26MAR2002 03:45:53 24.1N 123.8E MS=6.7 GSSC NORTHEAST OF TAIWAN

Several lines of evidence suggested a sizable event was possible in
this area at this time. These fall into three possible triggering categories:
1) Geomagnetic effects from yesterday's strong storm;
2) Far-field effects from the Hindu Kush and Mindanao earthquakes
of March 3 and 5 and from the Hindu Kush earthquake of March 25 and
3) lunar tidal effects.
These are summarized below:

GEOMAGNETIC EFFECTS:

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

" The areas most directly affected by such a sudden commencement storm are
facing the sun at the time of occurrence - that is areas where it is local
noontime, and areas which are on the opposite side of the earth - that is
areas where it is local midnight. I usually considering triggered activity
possible within 30 degrees of these longitude, although the most notable
events often occur within 5-15 degrees of this longitude. For this storm
the respective longitudes are 28W and 152E (anti- and sub-solar). A seismic
watch is automatically issued after a storm has continued for 6-8 hours
for areas within 30 degrees longitude of the sub- and anti-solar longitudes."

Since this event occurred at 124E, within 30 degrees longitude of
152E, it was under seismic watch conditions at the time of occurrence.

FAR-FIELD TRIGGERING EFFECTS:

This earthquake occurred at 47 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.

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)"

TIDAL TRIGGERING STATISTICS:

Global earthquakes of Mw>=6 occur with high significance on the
13th day of the lunar month. This was reported in the daily summary
of March 23, 2002 as follows:

"March 26 is the thirteenth day after the beginning of the new lunar month.
Regions most likely to experience tidal triggering
on this day (With associated magnitude ranges; the percent change in
seismicity rate over background seismicity rate on this
day of the lunar month; statistical z-value and
significance level) are:

Region Magnitude range %change z-value Significance level

...
Global MB>=6.0 15 2.5 0.03"

Global events of Mb>=6 occur at the highly significant (z=2.6)
rate of 15% above background on this day of they year. Apparently
there was an element of tidal triggering in tonight's earthquake
as well.

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

SEISMIC HISTORY OF AREA:

Strong earthquake are common within 200 km of this event, but
generally non-destructive as few live in the felt area. Destruction
may, however occur from tsunamis generated by events in this region.
These, however, are generally minor (less than a meter in runup
height). Fifty-nine events of Ms>=6.5 have been registered in this
area in the past 250 years, about one every 5 years. The lastest was
a Ms 7.4 about 200 km southeast of today's epicenter on May 3, 1998.
The event was felt through out the Ryukyu Islands and on eastern
Taiwan, but was non-damaging. A small 4-cm tsunami was generated.
The last event to occur in the Ryukyu Islands northeast of Taiwan
in the general region of today's event of Mw>=6.7 occurred on
January 16, 1986 and on Feb. 27, 1986 (Mw 6.9 and 6.6).
Doublet events (double mainshocks within a month or two) are
quite common in the region as occurred in 1986. Double shocks
occurred in Dec. 1990 (M 6.6 an 7.0 about 16 hours apart); August
1989 (Ms 7.1, 7.1 - 18 days separation); 1986 - see above; 1975
(Ms 7.0, 7.0, two months separation); 1966 (8.0, 6.6, 11 days
apart); 1962 (Ms 6.5, 6.6, 1.5 months separation); 1959 (1 month apart);
1951 (3 shocks 3 days and 1 month apart Ms 6.5, 6.8, 7.3); 1922(4 shocks
within 1.5 months Ms 7.6, 7.3, 6.8. 6.8); 1915 (1.5 months separation);
and 1910 (5 months separation). Of the 53 events listed below of
Mw>=6.7 in the region, 27 have occurred in groups of two or more
over a few month period. So the odds of a second strong shock
in the next two months in this area is roughly 1 in 2 (probability
about 50%).
There may also be a seasonal effect occurring. Of the 53 events,
15 (including today's have occurred in the months of March and
April), nearly 1/3 of the total, twice as many as would have
been expected in any given month. Of these, five have occurred
in the 3-day period from March 23 to March 26, including today's;
and those on 2/23/75; 3/23/66; 3/25/16 and 3/24/11. Generally seasonal
effects are most likely related to rotational or weather related
phenomena.

Following are the events within 200 km of today's
earthquake which have been Mw>=6.5.

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
9 1 9 0 0 1898 24.500 124.700 60 7.0
4 14 19 53 42 1909 24.000 123.000 80 7.3
4 12 0 22 0 1910 25.000 123.000 200 7.6
9 1 14 21 0 1910 24.100 122.400 0 6.5
3 24 3 18 0 1911 24.000 123.000 60 6.8
1 5 23 26 42 1915 25.000 123.000 160 7.4
2 28 18 59 5 1915 23.600 123.500 60 7.7
3 25 23 52 17 1916 24.000 124.000 60 7.4
7 4 5 36 30 1917 25.000 123.000 60 7.2
10 20 10 2 16 1920 24.100 122.300 0 6.5
4 2 9 36 0 1921 23.000 123.000 60 7.2
9 1 19 16 0 1922 24.500 122.200 60 7.6
9 14 19 31 39 1922 24.600 122.300 0 7.3
9 17 9 59 0 1922 23.900 122.500 0 6.8
10 14 23 47 0 1922 24.600 122.300 0 6.8
7 2 2 28 0 1923 23.500 122.500 60 6.7
8 19 2 44 0 1929 24.200 122.500 0 6.8
12 17 19 18 0 1935 23.500 125.600 20 6.8
12 19 2 57 19 1946 24.750 122.500 100 6.8
9 26 16 1 57 1947 24.800 123.000 110 7.4
1 19 15 0 0 1949 23.500 122.700 0 6.5
10 22 11 11 0 1951 24.100 122.200 40 6.5
10 25 12 19 0 1951 23.900 122.100 40 6.8
11 24 18 50 18 1951 23.000 122.500 60 7.3
1 13 4 3 40 1952 23.000 124.500 0 6.9
9 22 3 25 7 1955 23.900 122.500 33 6.8
3 11 0 26 1 1958 24.600 124.300 77 7.5
4 12 13 26 0 1958 23.000 125.000 0 7.0
4 26 20 40 38 1959 24.810 122.700 127 7.7
4 9 15 35 12 1961 24.090 122.090 53 6.5
6 25 11 10 27 1962 24.080 122.520 39 6.5
8 11 8 15 44 1962 25.200 123.300 140 6.6
2 13 8 50 5 1963 24.330 122.140 67 7.0
3 12 16 31 21 1966 24.090 122.650 59 8.0
3 23 0 4 33 1966 23.900 122.900 36 6.6
7 1 5 50 39 1966 24.800 122.400 109 6.8
10 25 0 59 23 1967 24.440 122.200 70 7.0
3 23 7 32 37 1975 22.735 122.802 21 7.0
5 23 16 1 49 1975 22.700 122.600 6 7.0
12 23 11 23 16 1978 23.067 122.683 40 6.9
6 24 9 6 46 1983 24.176 122.402 44 6.7
1 16 13 4 24 1986 23.800 123.400 0 6.9
2 27 6 23 5 1986 23.700 123.400 0 6.6
2 12 19 15 24 1988 22.600 123.800 0 6.5
8 3 11 31 15 1989 22.500 123.200 0 7.1
8 21 23 12 29 1989 22.900 123.900 0 7.1
12 13 3 1 37 1990 22.500 123.700 0 6.6
12 13 19 50 11 1990 22.600 123.300 0 7.0
5 24 4 0 42 1994 23.959 122.448 16 6.7
3 5 14 52 32 1996 24.150 122.240 42 6.5
5 3 23 30 19 1998 22.460 124.919 0 7.4

FAR-FIELD FORECAST:

The following areas are expected to see increased seismicity
from March 26 through April 01, 2002. Maximum event size for
these regions is expected to increase by 0.3 to 0.5 magnitude units
in this period.

0-5 degrees: Regional triggering- Taiwan, Ryukyu Island, northern Luzon
9-10 degrees: Southern to Central Japan, Central Philippines.
17-19 degrees: Central east coast Japan, Mindanao, NE China
34-36 degrees: Northern Kurils, Papua New Guinea, Timor, Nepal,
Northern and Southern Sumatera
43-45 degrees: New Britain, Hindu Kush, Near Islands, Aleutians
59-61 degrees: Unimak Is., Alaska Peninsula, Central Vanuatu, SE Australia,
Northern and southern Iran
71-73 degrees: South-Central Alaska, Eastern Turkey/Caucasus, Fiji Isl.
Gulf of Aden
103-107 degrees***: Gulf of California, Quebec, Oklahoma, New Madrid, MO,
Western Spain, New Brunswick
142-146 degrees: Colombia, Northern Venezuela, Chile Rise, Trinidad,
northern So. Sandwich Islands
176-180 degrees: A-seismic zone in Paraguay (23S 56W). Regional
triggering is possible in the currently active area at about 23S
66-70W in northern Chile.

***: 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' Ryukyu earthquake:

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 JUL 4 1917 25.0N 123.0E 60 7.7

Jul 4 30N 90W Ml 3.0 New Orleans, LA
Jul 9 35N 120W Ms 5.5 A series of events south of Parkfield, CA
Jul 27 19N 68W Ms 7.0 Puerto Rico

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 MAR 11 1958 24.6N 124.3E 77 7.5

Mar 11 13S 166E Ms 5.9 No. Vanuatu Islands
Mar 13 12N 122E MS 6.1 Central Philippines
Mar 15 23N 122E Ms 6.0 Taiwan
Mar 18 50N 172W Ms 6.2 Unimak/Fox Islands, Alaska (also on Mar 20, Mw 6.6)
Mar 19 46N 77W Ms 3.1 Southern Ontario/Quebec
Mar 22 23N 93E Ms 6.4 Myanmar
Mar 22 36N 68E Ms 6.2 Hindu Kush area
Mar 23 18N 120E Ms 5.9 Northern Philippines
Mar 28 36N 71E Ms 7.0 Hindu Kush area

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

Summary of far-field events following Ryukyu 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:
(Number in paranthesis indicated number of times and event of M>=6
has followed a Ryukyu mainshock within 2-3 weeks).

Tonga - around 20S (3)
Regional or local aftershock in Ryukyu Isl or Taiwan (4)
Hindu Kush/Pakistan (3)
Northern Chile (near 20-24S) especially between 60-70 W

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

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

Northern Venezuela
Kamchatka/No. Kuriles
No/So. Iran
Unimak/Fox Islands, Aleutians

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

Southern Ontario/Quebec to New Brunswick
So. of Parkfield CA.
Northeast region.

There have been several unusual events in the U.S. following
Ryukyu mainshocks, but most have been relatively small, including
the Delaware/D.C. shock of 1910, the Lake Superior shock of 1915, and
the New Orleans earthquake of 1917. Except possibly along the
St. Lawrence seaway region or in southern Alaska or the Unimak/Fox
Islands, there appears little danger of a moderate or strong FFA from
this event in the U.S. or Canada even though the core-mantle shadow
zone boundary does pass from the Gulf of California up through
the SW to Missouri and into southern Canada. These areas are
areas of generally low seismicity anyway, but small FFA are possible
here.

General:

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).