LARGE (MW 6.5) EARTHQUAKE HITS NORTHERN CHILE/BOLIVIA BORDER

SUMMARY

An Mw 6.5 earthquake struck the border region between Northern
Chile and Bolivia this morning. A far-field forecast was produced
and details of this event are available in that document.
There have been 36 earthquakes within 200 km of today's Chile
epicenter since 1900, an average of about one every three years.
The last, however was a Mw 6.5 on December 11, 1984 and prior to
that a Mw 6.5 on December 11, 1980. This is the first such
earthquake in this region of Ml>=6.5 in nearly 18 years. Since
the interevent time between such events over the past century has
averaged about 3 years, the 18 years since the last such event
suggests a great deal of strain has accumulated and that a much
stronger event is likely in the near future.
Possibly this is a great earthquake waiting to happen. The
earthquake history is very suggestive in this regard.
From 1905 through 1976 earthquakes of Mw>=7 occurred on average
about every five years. The earthquakes are listed below
with year of occurrence and Magnitude:

1905/1906 7.0/7.2
---> 5 years interevent time to
1910 7.3
---> 6 years interevent time to
1916 7.5
---> 6 years interevent time to
1922 7.2
---> 7 years interevent time to
1929 7.5
---> 5 years interevent time to
1934 7.0
---> 8 years interevent time to
1943 7.0
---> 6 years interevent time to
1949 7.3. 7.0
---> 4 years interevent time to
1953 7.4
---> 4 years interevent time to
1957 7.8 (aftershock in 1959 Ms 7.5)
---> 5 years interevent time to
1962 7.0
---> 7 years interevent time to
1967 7.5
---> 9 years interevent time to
1976 7.3

and then nothing !!!!
For an area where such events occur about every 5 years, 26 years
is a very long time and suggests something may be ready to give.
Today's event may be just the first salvo.

Following is a complete listing of events in the area during the
20th Century within 200 km of today's epicenter. Perhaps you will
find other patterns here.

MO DA HR MN SC YEAR S LAT W LONG DEPTH MW
4 26 21 43 0 1905 -21.000 -70.000 60 7.0
8 30 2 38 34 1906 -21.000 -70.000 60 7.2
10 4 23 0 6 1910 -22.000 -69.000 120 7.3
8 25 9 44 42 1916 -21.000 -68.000 180 7.5
8 13 2 3 0 1920 -20.000 -68.000 150 6.5
3 28 3 57 54 1922 -21.000 -68.000 90 7.2
10 3 23 55 52 1927 -21.000 -68.000 100 6.5
10 19 10 12 52 1929 -23.000 -69.000 100 7.5
7 18 5 27 5 1931 -22.500 -69.000 150 6.8
6 24 5 59 34 1934 -22.000 -68.600 100 7.0
12 23 9 52 28 1934 -21.000 -68.000 100 6.5
9 18 15 9 3 1940 -23.000 -68.000 110 6.5
12 1 10 34 46 1943 -21.000 -69.000 100 7.0
4 25 13 54 59 1949 -19.800 -69.000 110 7.3
5 8 21 24 21 1949 -21.500 -69.000 100 6.8
5 30 1 32 44 1949 -22.000 -69.000 100 7.0
11 9 22 7 54 1951 -20.800 -68.000 100 6.8
12 7 2 5 24 1953 -22.100 -68.700 128 7.4
6 21 1 48 43 1954 -23.200 -68.300 128 6.6
9 15 7 39 4 1956 -20.000 -69.000 100 6.8
10 3 8 18 47 1956 -20.090 -69.380 90 6.5
11 29 22 19 41 1957 -20.900 -67.000 170 7.8
7 11 19 10 20 1958 -21.000 -69.000 0 6.5
6 14 0 11 57 1959 -20.500 -68.000 100 7.5
7 9 16 5 18 1959 -20.500 -68.000 100 6.8
10 30 21 32 48 1960 -22.900 -68.000 60 6.8
12 6 8 56 9 1960 -21.400 -69.200 28 6.5
8 3 8 56 25 1962 -21.500 -69.000 0 7.0
6 12 18 50 11 1965 -20.470 -69.270 101 6.5
5 11 15 5 18 1967 -20.258 -68.691 79 6.8
12 21 2 25 22 1967 -21.800 -70.000 33 7.5
1 2 10 42 27 1974 -22.487 -68.264 83 6.8
11 30 0 40 58 1976 -20.520 -68.919 82 7.3
5 14 23 4 3 1979 -22.809 -69.125 85 6.5
12 11 18 15 4 1980 -21.272 -68.153 80 6.5
12 11 23 22 26 1984 -21.700 -69.000 120 6.5

GLOBAL

Seismicity was fairly light globally following the Mw 6.5 in
Chile this morning. What few events of Ml>=4 which were listed
by NEIS, however generally appeared to be FFA from the Chile
mainshock. The strongest (Mb 5.5, 5.2) of these occurred about an hour
after the Chile event in the region of the North-Mid Atlantic Ridge.
Two other events near 45 degrees from the Chile epicenter were
also listed - in Guatemala (Ml 4.6) and near the Chiapas Border
of Mexico (Ml 4.1). All these areas had been expected to see FFA
in the Forecast as stated last night:

"43-45 degrees: Guatemala, Chiapas, Mexico, ... No. mid-Atlantic
Ridge (20N 45W)"
and

" The most interesting events could occur in the Northern Mid-
Atlantic Ocean where such earthquake have usually followed Chile
mainshocks within a week."

There were two strong regional aftershocks in Argentina (Mb 4.8)
and in northern Chile (Mb 4.8). The only other event listed by
NEIS since the Chile mainshock was a Ml 3.0 near Bombay Beach,
southern California which was also at a distance where FFA
were expected in the forecast (71 degrees):

"71-73 degrees: ... Calexico, CA,"

U.S./CANADA

Seismicity in the U.S. and Canada was extraordinarily light today,
especially in the westernmost areas. The California/Nevada region has
not recorded any events of Ml>=2 since about 11:00 p.m last night
when a Ml 3.0 hit in the Bombay Beach area. There have been no
events of Ml>=2 in the region in the local solar day (28th March)
thus far. Bombay Beach is 71 degrees from the Chile mainshock and
is likely to experience FFA effects. The only other event of
Ml>=3 today in the U.S./Canada region occurred in south-central
Alaska with Ml 4.3. This earthquake lies on the CM shadow zone
boundary from the Chile earthquake, at 105 degrees a distance
and location where FFA were expected in the Forecast as follows:

"103-106 degrees***: Southern, Gulf of Alaska"

A Ml 2.4 was also recorded in northern Utah (Garland) several hours
after the Chile event. Other regions of the U.S. and Canada did
not report any events of Ml>=2 today.

NEW ZEALAND

One moderately light (Ml 4.0) earthquake was probably felt in the
South Island New Zealand area today near Marlborough. This
was the only event parameterized for the public today by IGNS.

The IGNS on-line Seismometer can be found at:
http://www.gns.cri.nz/news/earthquakes/latest_drum.html

GEOMAGNETIC/SOLAR FIELDS

The geomagnetic field remained quiet today. There were noRGE
X- of M-Class solar flares observed. The strongest flare
of the day was C7.6 with the following parameters:

Flare # START MAX END CLASS

5140 1750 1800 1816 C7.6

Two earthquakes near Idyllwild, Southern California of Ml 1.5 and
1.3 were associated with the maximum output of this flare both
occurring at 17:57 UT.

For general space weather conditions see:
http://sec.noaa.gov/today.html
For Solar flare data see:
http://sec.noaa.gov/ftpdir/indices/events/20020328events.txt

TIDAL EFFECTS

March 31 is the eighteenth 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

Pacific-Antarctic Ridge MB>=4.0 58 2.0 0.05
East Africa MB>=4.0 23 3.1 0.01
New Zealand MB>=4.0 19 2.2 0.05
Yellowstone MB>=2.0 19 2.0 0.05

Regions expected to experience reverse triggering (i.e. they are
unlikely to experience a significant event at this period of the
lunar cycle) are:

Region Magnitude range %change z-value Significance level

Utah MB>=2.0 -19 -2.0 0.05

TOMORROW IN EARTHQUAKE HISTORY

GLOBAL:

Most global earthquake of Mw>=7 have occurred at great depth
on this date limiting the loss of life and associated damage.
The exception was in Spain in 1954 when a event at 640 km caused
extensive damage at Malaga, Spain.
The following events of Mw>=7 have occurred on this date in
recorded history:

MO DA HR MN SC YEAR LATIT LONGIT DEP MW LOCATION

3 29 2 15 0 1868 19.100 -155.650 5 7.0 Hawaii
This was a foreshock to the April 3 event. At Kahuku, a
stone house was destroyed, the chimney of the Mission house
was also destroyed and the walls of the stone church
were cracked. AT Kona stone walls were thrown down, masses of
rock were thrown off the cliff at the bay, stone buildings were
damaged and the cisterns of the Kona Plantation were cracked.
At Waiohinu, walls were shaken down and the stone church was
cracked from top to bottom. Also felt at Hilo.

3 29 20 46 30 1907 3.000 122.000 500 7.2 Celebes Sea
3 29 21 12 37 1925 8.000 -78.000 60 7.1 Colombia
3 29 5 7 3 1928 31.483 138.183 380 7.1 Central/So. Honshu Japan
3 29 6 17 5 1954 37.000 -3.600 640 7.1 Morocco/Spain
There was extensive property damage at Malaga. Felt at Madrid,
Granada and Cadiz, Spain; Tangier, Spanish Morocco and Casablanca,
French Moroccs. This was a very deep focus, one of only a few
outside of recognized deep subduction zones.

3 29 19 48 17 1998 -17.577 -178.988 529 7.2 Tonga Islands

U.S./CANADA

3 29 5 7 52 1920 50.600 -129.869 0 6.4 British Colombia
No damage reported.

3 29 17 24 58 1931 51.000 -170.000 25 6.0 Fox Islands, Aleutians

3 29 5 10 28 1957 53.500 -166.900 33 6.7 Fox Islands, Aleutians
3 29 22 48 56 1957 52.608 -168.324 33 6.1 Fox Islands, Aleutians
Aftershocks continued from great Andreanoff Earthquake of March 9, 1957.

3 29 0 53 5 1964 57.440 -151.500 16 5.0 Southern Alaska
Aftershocks continued from great Alaska earthquake of March 28, 1964.

3 29 13 10 25 1965 33.600 -65.000 10 5.5 Off East Coast U.S.
3 29 12 40 40 1970 41.662 -113.839 7 5.1 Montana/Idaho
At Grouse Creek, UT a pipe on top of a chimney broke loose;
lamp overturned, objects in room teetered slightly. Rumbling noises.

3 29 21 0 43 1972 59.863 -153.103 126 5.1 Southern Alaska
3 29 21 50 35 1974 57.585 -153.922 44 5.7 Southern Alaska
3 29 1 30 58 1987 51.570 -170.300 53 5.2 Andreanoff Islands, Aleutians
3 29 1 16 26 1988 57.278 -143.051 10 5.0 Southeast Alaska
3 29 8 31 32 1988 52.630 -168.660 17 5.7 Fox Islands, Aleutians
3 29 15 33 6 1988 54.540 -163.570 33 5.4 Unimak Islands, Aleutians
3 29 6 54 32 1992 51.580 -167.060 47 5.3 Fox Islands, Aleutians