SOUTH SANDWICH ISLANDS (FFA) EARTHQUAKE MW 5.6 LARGEST OF THE DAY

SUMMARY

The largest earthquake of the day was recorded in the South
Sandwich Islands off of southern South America this afternoon.
This event of Ms 5.6 had been expected as a far-field aftershock
of the Mindanao mainshock. The FFA forecast had put it this way:

"Secondary location where event tend to occur but are not
as large or as likely . MB>=4.8 considered likely in next
10 days.

South Sandwich Islands (1)"

GLOBAL

Only two other events were listed today by global teleseismic
networks. This is often the case on Saturdays while these organizations
are relaxed for the weekend holiday. The other two events occurred
in the Alaska Peninsula (Mb 4.5) east of the Fox Islands and
in the Fiji Islands (Mb 4.6). Both of these earthquakes occurred
at deep focus and were probably not felt at the surface.

Local network data did not add any events of Ml>=4 to today's
listing.

U.S./CANADA

Seismicity also seemed exceptionally quiet in the U.S./Canada
today, again partially due to the weekend shut down of network
operations.
The largest earthquake was at a focus of 147 km depth in the
Alaska Peninsula region (Mb 4.5). This area often shows activity at this
time of year (see recent History sections). A Ml 3.6 was also
recorded by AEIC south of Anchorage, Alaska.
In the Pacific northwest, one event of Ml>=2 was recorded in the
region of Victoria, B.C. this afternoon (Ml 2.0). While events
in the region area common, earthquakes within 20 km of the beautiful city
of Victoria are relatively rare. Since 1960 only 31 such earthquakes
have been recorded, less than one per year. This is the first since
Oct 15, 2001.
Seismicity in California and Nevada today was extremely light.
Only 3 earthquakes of Ml>=2 were recorded outside of the Calexico
swarm. Four earthquakes of Ml>=2 were reported in the Calexico swarm. The
other regional events occurred as a Ml 2.9 near Punta Gorda, off the coast
of No. California, a Ml 2.2 south of Long Beach in So. California
and a Ml 2.0 east of Parkfield at Avenal. This is the fourth earthquake
in the Parkfield area in the past two days, two of which were
in the mid-2 (Ml2.5 and 2.6) range. Tomorrow (March 10) is the
80th anniversary of the 1922 Mag 6.3-6.5 earthquake at Parkfield.
The history section today contains a summary of some of the previous
larger earthquake in the Parkfield area and a bit of explanation of
the USGS "Parkfield Experiment".
Other areas of the U.S. and Canada were not reporting today, however
no significant earthquake appear to have occurred based on visual
observation of on-line seismograms from these networks.

NEW ZEALAND

The on-line seismogram from IGSN was very quiet today. No events
are expected to be reported from New Zealand for today.

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 very quiet levels throughout
the day. There were two M-Class solar flares this evening (UT)
whose parameters are listed below:

Flare # START MAX END CLASS

530 1831 1856 1939 M2.6
540 2144 2210 2243 M1.3

An micro-earthquake occurred at Mammoth Lakes near the maximum
of flare 530 (Ml 0.7); and a Ml 2.2 was recorded near Long Beach,
CA toward the end of flare 540. Neither of these flares are
considered powerful enough to strongly affect seismicity. SEC
is expecting a geomagnetic storm to develop as wind from flare
530 arrives in the earth vicinity about 12 or 13 March.

For general space weather conditions see:
http://sec.noaa.gov/today.html
For Solar flare data see:
http://sec.noaa.gov/ftpdir/indices/events/20020310events.txt

TIDAL EFFECTS

March 10 is the twenty-fifth 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

Antarctica MB>=4.0 343 2.8 0.02
India MB>=4.0 48 2.0 0.05
Yellowstone MB>=2.0 20 2.1 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

Arctic MB>=4.0 -36 -2.3 0.05

TOMORROW IN EARTHQUAKE HISTORY

GLOBAL

No destructive earthquakes have been recorded on March 10.
The largest events which were likely to have done local damage which
has not been recorded was a Mw 7.3 in southern Peru in 1681 and
a Mw 7.3 in 1763 in Hokkaido, Japan. A mw 7.4 also occurred
in the Kuril Islands on this date in 1951.

U.S./CANADA

Aftershocks of the Aleutian Island earthquake of 1957 were the
strongest events recorded in the U.S. or Canada on this date.
However, one of the most noteworthy earthquake in the U.S. on
March 10 occurred as a Mw 6.5 in the Parkfield, California
region. Houses were damaged severely along the San Andreas fault
zone in Monerey and San Luis Obispo Counties. Chimneys fell at
Parkfield and in southern Cholame Valley. One house was jolted
from foundations and another was twisted into two parts. A water
tank was knowed down on a ranch and oil pipelines broke
betwenn Shandon and Antelope, CA. There were 3 breaks in the
Producers Transportation Line, one close to a 1934 bread in a
nearby oil pipelin. A ground crack 15-30 cm
wide and about 800 m long was observed in Cholame Valley but
smaller cracks formed throughout the San Andreas fault zone.
This was the earliest Parkfield shock for which seismograms
exits. A comparison of the Berkeley recordings implied that the
1922 epicenter was located 6 km NW of the 1934 epicenter. Later
studies suggested that the magnitude of this quake was identical
to that of June 8, 1934.
The USGS started the Parkfield earthquake prediction program
largely on the basis of relatively stable periodic events
of about the same magnitude in the region approximately every
21 to 22 years. Previous events had been recorded in 1857, 1881,
1901, 1922, 1934, and 1966. This had suggested a strong Parkfield
earthquake was likely in 1988 - 1989. To study the possible
precursory activity in the area in preparation for the 1988
Parkfield earthquake and to make a short-term prediction for that
event. In the USGS terminology a short-term prediction means that
the likelihood of an earthquake occurring within a specified
period has increased, not that an earthquake is certain to happen.
The instruments that were installed included a Strong Motion and
a dense strong motion array, a differential strong motion array,
a liquefaction array, a pipeline experiment, seismometers, creepmeters,
strainmeters, tiltmeters, water well monitors, magnetic field
monitors, instruments for measuring electrical resistivity and
radio-frequency transmissions, a permanent and portable laser geodimeter
network, a geodolite network, a leveling network and monitoring
of geochemical changes such as might be seen in the Radon or Hydrogen
gas near deep water wells. Initially, $1 million Federal and a matching
$1 million state dollars were appropriated to support this project.
The earthquake had been expected to occur within several years after
the project begun and then the state expected to reap the rewards
of the new scientific knowledge for future hazard mitigation.

The Coalinga 1983 earthquake

What no one had expected was the effect of the 1983 Coalinga (Ms 6.8)
earthquake just over the hill from Parkfield (40 km to the NE). Recent
studies have shown that this event relieved stress on the Parkfield
segment of the San Andreas, delaying the timing of the next event. Until
the Coalinga quake, the Parkfield segment had been relatively free
of stress changes due to nearby shocks and the 22-year cycle held.
With the stress change from Coalinga in Parkfield it was a whole new
ballgame. Up until then the only event that had occurred out of
sequence had been the 1934 earthquake which had occurred 11+ years
after the 1922 event, otherwise the 22-year cycle held pretty much
unaltered. It is interesting to note that each event, including
the 1934 earthquake has occurred as the solar activity begins to increase
in the 22-year solar/geomagnetic cycle. The absence of an event in
the Parkfield are in 1988-1989 and in 1999-2000 both, suggests that
the next earthquake in the area could be considerably larger than
previous "characteristic" quakes of around Ms 6.0-6.5.

Following are some notes on each earthquake in this sequence:

1857:

This was the gret Fort Tejon earthquak of Jan. 9, 1857. There was
a sudden right-lateral slip on the San Andreas that lasted about
3 minutes and was felt over 350,000 sq km. Maximum fault movement
was about 9 meters centered SE of Parkfield. The potential for
3 to 7 meters slip may have accumulated in the Parkfield/Cholame
segment since that time, so a Mw 6 at Parkfield or south could
trigger a larger earthquake in this region. The 1857 earthquake
apparently was preceded by several moderate earthquakes in Central
California earlier that day. Two foreshocks were widely felt. These
events were of Ms 5-6 along the Parkfield segment, suggesting
that the Ft. Tejon quake actually initiated in the Parkfield region
(Kerry Sieh, CALTECH).

1881:

Reports are consistent with other Parkfield earthquakes - chimneys
toppled, cracks in the ground. Sulphur Springs were formed in the
area and the road appeared to be boiling up. Cracks were noted
along the San Andreas.

1901:

The shaking from this event appears to have been twice that
of the 1966 earthquake, suggesting a larger magnitude. A Homer
Hamblin, resident reported seeing cracks, landsliding, and slumping.
He described extensive cracking northwest of Middle Mountain.
According to resident C.W. Wilson "nearly all the goods in the store
were on the floor...Daylight revealed a scend of destruction. All
the chimneys in town were shaken down and the ground is seamed for
miles they tell me. Half the people around seem half scared to
death....it seemed queer to feel that what you had under you could
not keep still"

1922:
See above for some description. Resident Buck Kester was plowing with
a ten horse team on the San Andreas fault. Buck recalls the
shake arrived at around 3 a.m. He could hear dead limgs falling
off the trees, and the children screaming from fright. He relates
that a tramp had come the night before and asked to sleep in the
barn. The next morning the horses had stampeded from the bard and were
gone - and so was the tramp. He recalls making the remark:
"I needed spurs to ride the bed". Kester was in Parkfield at the
time of the 1901, 1922, 1934 and 1966 earthquakes and believes
the 1966 event was the strongest.

1934:

The 1934 earthquake was preceded by a number of foreshocks including
two magnitude 5 earthquakes and about 13 felt or located Ml 3-4
events in the 67 hours before tha mainshock. One of the Ml 5 events
occurred less than 20 minutes before the mainshock. This event appears
to have ruptured to the south leading to widely differing magnitude
estimates from stations north (which registered it as Ml 5) to those
in the south which registered it as Ml 6+.
The earthquake struck during an end-of the year play at the old
Parkfield Community Hall. The first Ml 5 foreshock struck and brought
the play to a halt for a few minutes until someone in the audience
said "the big one always comes first" and the program went on.
Donalee Thomason, one of the students in the program recalled:
"I remember being thrown back and forth against the walls of teh
narrow runway behind the stage. It seemed the hall was turning upside
down there in the darkness for a few seconds. I could hear people
screaming and trying to run to the exit, falling down, of course.
The program came to a halt for the second time that evening. People
stuood around this time discussion what they should do. It was
decided that the show must on!
Little aftershock kept arriving. By now we were all out on the
stage and kept in a panic by these little unwelcome shocks. I've
often wondered how we completed the program, and I've also wondered
if that earthquake happened jost to celebrate my mother's lsat day to
teach in Parkfield."

1966:

As in 1934, a magnitude 5 foreshock occurred 17 minutes before the
mainshock on June 28, 1966. In all respects the 17-minute foreshocks
in 1934 and 1966 were virtually identical. In 1966 there had been
reports of anomalous surface deformations in the days before the
earthquake, including a broken irrigation pipeline and fresh cracks
that were observed about 12 days before. As in 1934, rupture began
at Midddlemountain and propagated southward. Resident Donalee Thomasen
was still living in Parkfield now a mother on her own. She reported:

" Between 8:00 and 9:00 p.m. on a hot Monday evening in June the
heavy foreshock arrived, and there was no rumble. The very first
thing my ears recorded was similar to a great drawing in of a
breath, or a suction sound may be a better description. Then a
blast of hot air hit my back as the shock wave rushed through."

...

"One family said later that during the day before the big earthquake
teir dog hung under their feet all day; he made such a pest of
himself they had to tie him up to keep from tripping over him."

The following probabilities (in percentage) of a shock within
72 hours are defined for the Alert status in Parkfield:

Alert level Probab. of shock within 72 hours
E (Normal conditions) 0.03 to 0.07
D 0.7 to 2.8
C 2.8 to 11
B 11 to 37
A >37

Most of the material in this report can be found in greater
detail in"

Earthquakes and Volcaons, Vol . 20, No. 2, 1988, U.S. Dept. of
Interior, USGS, 1989.