MODERATELY STRONG EARTHQUAKE HITS BOLIVIA (MB 5.9 GSSC)

SUMMARY

A moderately strong earthquake occurred at intermediate depths
this evening in southern Bolivia. This earthquake which initially
measured Mb 5.9 (GSSC) was located 320 km below the surface, and
thus did little damage on the surface. Earthquakes in southern
Bolivia fall into two categories - strong events which have little
effect on the surface and moderate earthquakes near the surface.
The most widely felt earthquake on record occurred in this region
on June 9, 1994 with Mw 8.2. This Bolivian earthquake was felt as
far away as Quebec, Canada and in many areas of the U.S. and
throughout South America. The deep focus of the earthquake and it
great size allowed shaking effects to be noted for nearly 6000 km
in all directions.

GLOBAL

While it was Saturday today, and most teleseismic reporting
agencies were taking a break, there still did not appear to be
much in the way of global seismicity today other than the Bolivia
earthquake.
Two mild events were reported in Ecuador (Mb 4.6, and 4.4), and
an Mj 4.3 was recorded in southern Honshu, Japan. Small earthquakes
continued in the Balkans and Italy. A Ml 4.2 was also recorded in
Iceland. Such events are commonly associated with increased volanism
on the island.

U,S./CANADA

The earthquake listed for the U.S. and Canada today
occurred in the New Madrid, MO region in northern Arkansas (Ml 2.7).
This is the third event of Ml>=2.5 in the area in the past week.
The region had been expected to be active with FFA from Chile and
Mexico, so this level of activity is not totally unexpected at this
time, although it is the highest level of seismicity in the region
in more than a year.
The largest earthquake in the U.S./Canada was a Ml 3.4 NNE of
Willits, northern California this morning. This is the fourth
event of Ml>=3.4 in the NCSN area in the past 8 days (see yesterday's
summary for more details. Two other earthquakes of Ml 2.6 occurred
in the Ukiah and Weaverville areas of northern California along the
Pacific coast today along with a Ml 2.4 at the Geysers. The
dry spell in southern California continued with only one event of Ml>=2
recorded in the region in the past 24 hours - a Ml 2.1 near Westmorland
this morning. An earthquake with preliminary Ml 2.9 was listed tonight
in the eastern Nevada area near Hoya. This may be a teleseismic arrival
however, and thus a ghost event.
Two earthquakes of Ml 3.3 and 3.1 occurred in the Gulf of Alaska
area south of Anchorage, and a Ml 3.3 was listed in northern Hawaii
today.

NEW ZEALAND

IGNS did not list any new earthquake parameters today. No moderate
or large events could be located on the on-line seismometer.

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 X- or M- class solar flares observed. SEC is expecting
some disturbance from a geo-effective CME in the next day, however.

Flare # START MAX END CLASS

For general space weather conditions see:
http://sec.noaa.gov/today.html
For Solar flare data see:
http://sec.noaa.gov/ftpdir/indices/events/20020427events.txt

TIDAL EFFECTS

April 29 is the sixteenth 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

Kermadec MB>=4.0 14 2.0 0.05
Nevada MB>=2.0 22 3.3 0.01
Spain MB>=4.0 35 2.5 0.03
Puerto Rico MB>=4.0 18 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

So.California MB>=0.0 -8 -2.1 0.05

TOMORROW IN EARTHQUAKE HISTORY

GLOBAL:

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

4 28 23 39 0 1903 39.100 42.600 0 7.0 Turkey
Aftershock of April 19. 3400 killed, severe damage. Intensity IX.

4 28 9 52 54 1911 0.000 -71.000 600 7.1 Colombia
4 28 11 13 50 1926 -24.000 -69.000 180 7.0 Coast No. Chile

U.S./CANADA

Following are events of Mb>=5 which have occurred in this region on

MO DA HR MN SC YEAR LATIT LONGIT DEP MW LOCATION

4 28 19 4 59 1955 51.000 -178.500 0 6.5 Andreanoff Islands, Aleutians
4 28 14 48 50 1957 52.500 -168.500 0 5.8 Fox Islands, Aleutians
4 28 1 25 42 1965 52.000 -176.100 47 5.0 Andreanoff Islands, Aleutians
4 28 22 30 5 1966 44.000 -127.800 18 5.0 Off Coast of Oregon
4 28 23 20 43 1969 33.300 -116.300 20 6.1 So. California
Borrego Springs Earthquake. The heaviest damage occurred in the
Borrego Springs area where large pieces of a ceiling fell, brick
walls cracked, and light fixtures were damaged. The ceiling of the
First National Bank buckled. A two lane highway about 3 miles
west of town was blocked by large boulders. Giant boulders were observed
bounding down the Santa Rosa mountains. Minor damage occurred at
several towns in the vicinity.

4 28 10 5 47 1984 51.000 -168.000 33 5.3 Fox Islands, Aleutians
4 28 8 18 32 1996 51.000 -168.000 0 5.4 Fox Islands, Aleutians
4 28 22 10 6 1999 53.582 -163.503 33 5.3 Unimak Islands, Aleutians

EARTHQUAKE LISTINGS

ASIA

SOUTH PACIFIC ISLANDS

CARIBBEAN/CENTRAL/SOUTH AMERICA

O: 27APR2002 02:50:05 15.3N 96.5W ML=4.3 SSN COSTA DE OAXACA, MEXICO
O: 27APR2002 00:53:32 15.4N 96.6W ML=4.4 SSN COSTA DE OAXACA, MEXICO

O: 27APR2002 02:50:05 15.3N 96.5W ML=4.3 SSN COSTA DE OAXACA, MEXICO
O: 27APR2002 00:53:32 15.4N 96.6W ML=4.4 SSN COSTA DE OAXACA, MEXICO

O: 26APR2002 00:32:15 16.7N 101.0W ML=3.9 SSN COSTA DE GUERRERO, MEXICO

O: 27APR2002 03:45:27 1.2N 79.4W MB=4.4 NEI NEAR COAST OF ECUADOR
O: 27APR2002 03:41:35 1.1N 79.5W MB=4.6 NEI NEAR COAST OF ECUADOR
Note: These events occurred at 17 degrees from Mexico and 37 degrees
from Northern Chile (Mw 6.7). They are probably FFA as they lie in
a region where FFAs were expected as noted in the Forecast.

O: 27APR2002 23:54:48 19.1S 65.2W mb=5.9 GSR SOUTHERN BOLIVIA
Note: This earthquake lies at 9 degrees from the northern Chile earthquake
of April 18. It is probably an FFA as it lies at a distance and in an
area where FFA were expected in the forecast:

"9-10 degrees: Southern Peru (About 17-18S)..."

NEW ZEALAND/AUSTRALIA

OCEANIA

O: 27APR2002 07:21:45 63.7N 19.1W Ml=4.1 IMO ICELAND
Note: Iceland is 102 degrees from the Guam mainshock (Mw 7.2) and
71 degrees from Mexico. This event is probably a FFA from both
these mainshocks as it lies at a distance and location where FFA
were expected in the forecasts:

From Guam:

"103-107 degrees***: ... Iceland"

From Chile:

"103-106 degrees***: ... Iceland"

EUROPE/MIDDLE EAST/AFRICA

U.S/CANADA

CALIFORNIA/NEVADA

O: 26APR2002 16:43:14 40.3N 119.5W ML=2.5 NCSN SE of Smoke Creek, NV

O: 26APR2002 20:05:56 39.5N 123.3W ML=3.4 NCSN NNE of Willits, CA
O: 26APR2002 20:31:31 39.5N 123.3W ML=2.0 NCSN NNE of Willits, CA

O: 26APR2002 21:23:03 37.0N 121.6W ML=1.9 NCSN WSW of Gilroy, CA

O: 26APR2002 22:28:54 35.7N 118.1W ML=2.1 SCSN ENE of town of Lake Isabella,

O: 27APR2002 06:48:18 38.8N 122.8W ML=2.4 NCSN E of The Geysers, CA

O: 28APR2002 00:58:27 39.4N 122.9W Md=2.6 NCSN NE of Ukiah, CA

O: 28APR2002 01:43:13 37.2N 121.5W ML=1.2 NCSN NE of San Martin, CA

O: 27APR2002 17:58:27 39.3N 122.9W ML=2.6 NCSN SSE of Lake Pillsbury, CA

O: 27APR2002 18:23:55 36.9N 114.6W ML=2.9 NCSN SE of Hoya, NV

O: 27APR2002 19:47:35 40.7N 123.4W ML=2.6 NCSN NW of Hayfork, CA

PACIFIC NORTHWEST/CANADA

O: 26APR2002 22:31:23 46.9N 121.9W ML=1.0 PNSN WNW of Mount Rainier
O: 27APR2002 03:35:43 46.9N 122.0W ML=1.2 PNSN W of Mount Rainier

O: 27APR2002 10:32:06 47.7N 120.1W ML=1.1 PNSN ENE of Entiat, WA

O: 27APR2002 13:11:29 47.6N 122.4W ML=2.0 PNSN WSW of Bellevue, WA

ROCKY MOUNTAIN AREA

EASTERN U.S./CANADA

O: 27APR2002 02:33:43 36.0N 90.0W MB=2.7 NEI ARKANSAS
O: 27APR2002 02:33:43 36.0N 90.0W ML=2.7 CERI ENE of Gosnell, AR

ALASKA

O: 27APR2002 10:49:23 55.7N 156.5W ML=3.4 AEIC Anchorage, Alaska

HAWAII

O: 27APR2002 03:26:25 20.0N 155.4W ML=3.3 HVO SW of Pa`auilo, Hawaii