GLOBAL SEISMICITY RETURNS TO BACKGROUND RATES

SUMMARY

After a day of very high rates of seismicity yesterday around the
world, seismicity returned to relatively quiet conditions again today.
Following are the number of events per day registered by NEIS
over the past 10 days:
Date # events (Mb>=4.0)
MAR 06 22
MAR 07 20
MAR 08 10
MAR 09 19
MAR 10 24
MAR 11 20
MAR 12 22
MAR 13 17
MAR 14 30
MAR 15 10
The rate on March 14 was about 1.6 times that of the other
9 days which average about 18 events +/-3 events per day. Speculation
regarding the cause of this increased activity could range from
far-field effects of the Andreanoff Islands Mw 5.9 to solar effects
of the M5.6 flare that began the day to natural variations in seismic
activity.

GLOBAL

The largest event recorded today occurred as a Mb 5.3 in the Banda
Sea area of Indonesia. No other events of Mb>=5 were listed by
NEIC today, and global seismograms were quiet throughout most of
the day.
Earthquakes of Mb>=4.5 occurred in the northern Kuril Islands (Mb 4.8);
in Mindanao (Mb 4.5) and as aftershocks of the Andreanoff Islands
earthquake yesterday (Mb 4.5, 4.6). Lighter earthquakes were observed
in the Mid-Atlantic Ridge (Mb 4.2); Northern Colombia (Mb 4.1);
New Guinea (Mb 4.4) and the Fiji Islands in the past 24 hours.

U.S./CANADA

The largest earthquakes in the U.S./Canada today were continuing
aftershocks in the eastern Andreanoff Islands region (Mb 4.5, 4.6, 4.1).
A Ml 3.0 was also registerd in Central Alaska.
In California, nine earthquakes have been recorded of Ml>=2.
The largest of these wer Ml 3.1 and 3.4 in the Hector Mine aftershock
zone. These follow a Ml 3.3 in the same general area but northwest
of today's earthquakes last night. Ml 2.9 events were also observed
in the Bishop, CA area (which also experienced a Ml 2.2) and in the
Calexico/Baja swarm. One of the strongest events in west-Central
California in recent weeks occurred as a Ml 2.6 near Milpitas, CA
this morning. Other regional events of Ml>=2 were recorded near
Big Bear City (Ml 2.0) and the Geysers (Ml 2.0).
In the Pacific northwest and western Canada the strongest earthquake
of the day was a Ml 2.7 near Ft. Simpson, Northwest Territories,
Nunavit, Canada. A Ml 2.0 also occurred this evening near Mt. Rainier.
No events of Ml>=2 were recorded in the Rocky Mountain section, but
the eastern and Central U.S. and Canada did see several events.
In Oklahoma the fourth earthquake in the past three days occurred
with Ml 2.5, the largest in this series. A Ml 2.8 was also registered
near the New York State/Quebec border near Buckingham, QUE this
morning.

NEW ZEALAND

The IGNS on-line seismometer remained at quiet conditions today.
It is Saturday in New Zealand, and IGNS offices are closed for the
weekend, so no earthquake parameters were reported.

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 throughout the
day. Towards the end of the UT day a strong solar flare of class
M2.2 occurred and lasted into the beginning of UT March 16. This
flare was slightly smaller than that of March 14 (M 5.6) but lasted
for a longer period so effects on the earth systems could be similar.
The general sub-solar areas at the time of tonight's flare are
within about 30 deg. longitude of 152 W (sub-solar) and 28E (anti-solar).
This includes the current Andreanoff aftershock zone. Areas within
these longitudinal boundaries, especially those above 50N and below
50S may experience a slight seismicity increase or larger events than normal
during the next day. A ml 2.9 occurred the maximum of this flare
near Bishop, CA.

The flare parameters were:

Flare # START MAX END CLASS

1730 2209 2310 0042 M2.2

For general space weather conditions see:
http://sec.noaa.gov/today.html
For Solar flare data see:
http://sec.noaa.gov/ftpdir/indices/events/20020315events.txt

TIDAL EFFECTS

March 18 is the fourth 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

Caribbean MB>=4.0 20 2.3 0.05
Caucasus MB>=4.0 25 3.1 0.01
East Pacific Rise MB>=4.0 35 2.1 0.05
Japan MB>=4.0 23 3.3 0.01
JMA MB>=4.0 21 2.9 0.01
Kanto MB>=4.0 61 3.9 0.01
So.California MB>=0.0 11 3.1 0.01
Indian Ocean MB>=4.0 16 1.9 0.05
Kamchatka MB>=4.0 33 2.4 0.04
Washington MB>=2.0 33 3.1 0.01
West Pacific MB>=4.0 23 2.3 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

China MB>=4.0 -17 -2.1 0.05
Italy MB>=4.0 -30 -2.0 0.05

TOMORROW IN EARTHQUAKE HISTORY

GLOBAL

The two worst earthquake disasters on this day in history (March 16)
both occurred in China. The first of these happened in Taiwan in
1906. This earthquake was the second severely damaging earthquake
of the year 1906 which was probably the most seismic year in modern
times. It was felt throughout the region of Taiwan and killed about
1300 causing severe damage throughout. An interesting study was
found on the relationship between this and other earthquakes in 1906
in the British Association for the Advancement of Science - Report on
the Committee for Seismic Investigations, 1907. The report on
seismic activity during 1906 stated:

" The number of entries in the Shide register for 1906 [the yearly
earthquake catalog at the time] is 207. Out of this number ninety-two
may be regarded as megaseismic in character. This number is distinctly
above the average. ... The Formosan earthquak occurred which ruined
5,556 homes. On April 18 San Francisco was destroyed...
On August 17 Valparaiso and the towns in its neighbourhood were
reduced to ruin. In Greenwich mean time the Valparaiso earthquake
occurred at 0 hr. 41 m 2 s. Thirty-three minutes before this or at
0h 8 m or 0hr 11 m G.M.T., a very large earthquake took place
beneath the North Pacific to the north of the Sandwich Islands
[Hawaii - this earthquake actually was a Mw 8.3 in the Central
Aleutian Islands]. The time taken for the second phase of this
shock to travel from its origin to Valparaiso, as distance of
122 degrees would be about 31 minutes. This time interval suggests
at least three possibilities: a) the earth-waves from the North
Pacific may have released a state of seismic strain in Chili; or
b) the earthquakes in this latter country may represent an effort
to establish a dynamical counterbalance consequent on a molar
displacement in the North Pacific; or c) the two disturbances
were due to some common influence.
The fact that large earthquakes so frequently occur in pairs
or groups precludes the idea that these short intervals between
megaseismic effects are merely matters of chance."

Note: The idea of earthquake triggering is clearly not new. This
article published in 1906 has many of the same ideas we consider
today. The earthquake in the North Pacific was eventually well
located at 51N 179E and the travel time to Chile would have
been 33 minutes for the waves - they would have arrived at
the exact moment the Mw 8.5 occurred in Chile.

Incidentally, the next article in the same publication
was entitled:

"V. On the Apparently Luminous Effects from Certain Rocks"
and dealt with earthquake lights observed during the Valparaiso
earthquake of 1906. It stated in this regard:

"..Accounts of luminosity in the heaves or on hills at the
time of large earthquakes area common. One of the last occasions
upon which phenomena of this nature were observed was at the
time of the Valparaiso earthquake, August 17, 1906. Mr. W.G.Davis,
Director of the Meteorlogical Survey of Argentina, tells me that
as seen by Captain Taylor from the deck of the R.M.S. 'Orissa' lying
fifty meters from the wharf at Valparaiso, there appeared upon the
hills at a height of about 500 metres waves of light. These waves,
which were compared to chain lightning, extended as far as the
eye could reach, and lasted during the first shock or nearly
two minutes."

The other earthquake in China on March 16 occurred in 1925.
The USCGS Seismological report for that year states:

March 16 - "A report from the American Consulate, Yunnanfu, China
indicated that about 5,000 lives were lost when an earthquake
practically destroyed the city of Tali, Yunnan, Province. Fengyu and
Mitu suffered heavily. Some property damage and loss of life
occurred in Tengehuan, Erhyuan, Pinchuan , Menghus and Hsiangyun."
Later investigations showed that up to 6000 had been lost in
this earthquake (MW 7.1) throughout the province of Yunnan, China.

U.S./CANADA

No damaging mainshocks were located in the U.S. or Canada on
this day in history. The largest events occurred in the Gulf
of California (Ms 6.3) on March 16, 1990 and off the Coast of
Northern California 10 years later in 2000 (Ms 5.9). An unusual
earthquake of Ml 5.7 occurred in Northern Quebec in 1989, but
did no damage in this largely unpopulated region. The first
in a series of shocks near Helena, Montana occurred in 1930. This
Ml 5.0 caused plaster to crack and objects to fall. This series
of events lasted off and on for the next 5-6 years.

Aftershocks continued with Ms 7 in the Aleutians in 1957 and
in 1978 an in the Coso California swarm of 1946.