QUIET CONDITIONS CONTINUE IN GLOBAL SEISMICITY

SUMMARY

Global and regional seismicity remained at relatively low
levels again today. The largest earthquake in the past three
days was a Mb 5.3 in northern Chile. Only two other events of
Mb>=5 have been registered by NEIC in the past 3.5 days -
a Mb 5.2 in Peru and an Mb 5.0 in the Santa Cruz Islands, an
average of less than one such event per day. In the 40 years
since 1962, there have been 14,610 events of M>=5 registered
in seismicity catalogs. This is an average of about 10 per day,
so compared to this, the seismicity has been very calm over the
past several days.

GLOBAL

The largest earthquake in the world today occurred in northern
Chile (Mb 5.3). This continues a trend over the past several days
in which South and Central America has dominated global seismicity
in the Mb>=4 range. During the past 3 days 7 of 20 events of Mb>=4
(NEIC) have occurred in Latin America. Over the past 40 years
of the 146,081 events of Ml>=5 which has been cataloged in the world,
only 18.172 have occurred in Latin America (about 13%). In the past
three days this area has been producing about one-third of the
earthquakes in the world at this magnitude level, considerably
higher seismicity compared to the rest of the globe than normal.
It is even high for Latin America which averages about 1.2 such
events per day - the rate over the past three days is about 2.5
time that. Earthquakes today in Latin America occurred in Mexico
(Mb 4.7); and three in different locations in northern Chile
(Mb 5.3, 4.1 and 4.4).
Events of Mb>=4 were also recorded in Tonga (Mb 4.9), Honshu (Mb 4.3),
and Pakistan (Mb 4.6) today.

U.S./CANADA

The aftershock sequence in the Calexico, CA area produced only
three events today, but these included the largest earthquake registed
in the U.S/Canada region today - a Ml 3.3 this evening. Other areas
of California with tremors of Ml>=2 included Gustine (Ml 2.3) in central
California; Bishop (Ml 2.2) SE of Mammoth Lakes; and southern Nevada
(Ml 2.1). Several events of Ml>2 also continued in the Borrego Springs/
Ocotillo area north of Calexico.
Other areas of the U.S. and Canada were also relatively quiet.
A Ml 2.3 was recorded in SW Utah near Sevier, UT. Several quakes
occurred near Vancouver Island in the Ml 2 range.
The most unusual earthquake in the past two days in the U.S.
occurred yesterday morning near Bangor, Maine (Ml 2.2). Maine
normally experiences a handful of such earthquakes each year.
No earthquakes of Ml>=3 have occurred in Alaska or Hawaii today. The
largest earthquake in the U.S. possessions was a Ml 4.0 in the Virgin
Islands yesterday morning.

NEW ZEALAND

The IGNS on-line seismometer showed noisy conditions again today,
however, IGNS did not issue any event parameters for today.
The current moderate activity near White Volcano appears to
be continuing off North Island.

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 at quiet conditions today. There
were no solar flares of M- of X- class recorded. The largest flare
of the day occurred between 10:25 and 10:29 UT. Now seismicity was
known to have been associated with this flare.

Flare # START MAX END CLASS

8390 1025 1027 1029 C9.6

For general space weather conditions see:
http://sec.noaa.gov/today.html
For Solar flare data see:
http://sec.noaa.gov/ftpdir/indices/events/20020226events.txt

TOMORROW IN EARTHQUAKE HISTORY

WORLD

The largest earthquake recorded on February 27 was a Mw 8.0 in the
northern Kermadec Islands, N.Z. in 1955. This earthquake is part of
a long and possibly instructive pattern of repeating earthquakes.
Starting in 1932 the largest shallow earthquakes in the northern Kermadec
Islands have generally occurred at approximately 11-year intervals
(+/- about 5 months) with the exception of the period between
Feb 27, 1955 and Jan 14, 1976. The largest earthquakes near 28-29S
175-178W have occurred as follows with the interevent times between
event indicated:

Event Date Magnitude Interevent Period

May 26, 1932 Ms 7.8
11 years 4 months
Sept 14, 1943 Ms 7.6
11 years 5 months
Feb 27, 1955 Ms 8.0
20 years 11 months
Jan 14, 1976 Ms 8.1
10 years 9 months
Oct 20, 1986 Ms 8.9
10 years 11 months
Sept 20, 1997 Ms 7.3

The exception that proves the rule was an event on Sept. 14, 1959
of Ms 7.8 which occurred only 4.6 years after the previous large
earthquake in the region
It is interesting that the average interval between events which
differ by approximately 11 years is exactly 11.1 years, the same
as the length of the solar cycle. Even the period between Feb. 1955
and Jan 1976 is approximately double the solar period. Of course,
this may be just coincidence. But it is something to think about.

U.S./CANADA

The largest event to occur in the U.S./Canada region on Feb. 27 was
a Ms 6.8 earthquake in the Fox Islands region of the Aleutians, Alaska
in 1987. This earthquake produced minor damage at Dutch Harbor and Unalaska.
A similar but smaller event had occurred at the same epicenter with
Ms 6.1 twenty-six years earlier on Feb. 27, 1961. The only other earthquakes
of Mb>=6 to occur in the U.S./Canada region struck the western Andreanoff
Islands (Aleutians) at nearly the same epicenter in 1960 (Ms 6.0) and again
exactly 10 years to the day later on Feb 27, 1970 (Ms 6.0). These two
earthquakes were not exactly 10 years apart, however, as the first occurred
at 08:10UT and the second an hour earlier at 07:07UT.
The only events of Mb>=5.0 in California on Feb. 27 occurred in Baja
in 1937 (Mb 5.0) and in 1965 (Mb 5.7) and off the Coast of Northern
California on Feb. 27, 1971 (Mb 5.4).