SAN JUAN BAUTISTA, CA EARTHQUAKE (MW 3.7) LARGEST IN 5 MONTHS

SUMMARY

An earthquakes of Mw 3.7 hit near San Juan Bautista (SJB), CA this morning.
It was the largest within 35 km of this epicenter since November 26, 2001.
Both the November and today's earthquakes followed X-class solar flares
by 1-2 days, there have been no other X-class flares in the intervening time.
The immediate trigger for the SJB earthquake, however, appeared to be
geomagnetic.
After a day of quiet conditions, the geomagnetic field became active
about 07:00 UT (midnight at San Juan Bautista). The maximum influence
of this storm therefore was near longitude 120W and 60E. After two
hours of fluctuating magnetic field at satellite levels, the total field
began to decline in intensity and reached it's low value at approximately
11:59 UT. The San Juan Bautista earthquake occurred at 11:59 at the lowest
point in the geomagnetic field fluctuation. For detail see:

http://sec.noaa.gov/ftpdir/lists/geomag/20020423_G10mag_1m.txt

GLOBAL

The largest earthquake of the day was a Ms 5.6 in the northern
Vanuatu/Santa Cruz Islands regions. This is the third event of Ml>=4.5
in the region in the past two days.

NEIS is listing the earthquake at M 5.6 at about 13S 167E.
This was an expected far-field aftershock and the last of the
events for which epicentral data had been provided in lat/lon pairs
in the FFA forecast for Chile/Mexico/So. Sandwich Islands.
That FFA forecast had stated:

" From the combination effects of these events several areas seem
likely to see events of Ms>=5.5 in the next 10 days. These include

... northern Vanuatu Is. 14S 167E"

Foreshocks of Mb 4.3 (Apr. 22) and Mb 4.5 (Apr. 20) had occurred.

A moderately light earthquake also occurred at 5S 153E on 21 April.
This event also had been well located in the FFA forecast which had
stated:

"New Britain/New Ireland 5S 153E"
Other nearby events of Mb 5.2 and 5.1 have also occurred in the past
two days.

Additional seismicity today and yesterday was widespread at the Ml>=4 level.
Mid-ocean ridge events occurred south of Australia along the Macquarie/
Indian-Antarctic ridge system (Mb 4.4 and 4.0). Another active region
was the southern Philippines (Talaud, Celebes, Mindanao) where
earthquakes of Mb 4.3, 4.6, and 5.2 have occurred in the past 48 hours.
The most active area in the western hemisphere has been Peru. Two
groups of epicenters have been active in this nation - two (Mb 5.2, 4.5)
in the north near the Peru/Ecuador border, ant two (Mb 4.7 and 4.4)
in the Central coast of Peru. Panama has experienced a Mb 4.5 and 4.2
event in the same time, and Venezuela a Mb 4.0. An unusual earthquake
was also reported without a magnitude by NEIS in southern Chile
In Asia, besides the events south of the Philippines earthquakes have
identified in Taiwan (Ml 4.6) and Japan (Mj 4.7, Mb 4.0). Other events
occurred in Banda ( MB 4.4) and the Caroline Sea (Mb 4.7).
Also active over the past two days has been the Fiji-Tonga Island
chain. Here events of Mb 4.4, 4.3, and 4.6 have occurred in the past
two days. This region has been under seismic watch conditions.
The Kuril Islands saw an earthquake of Mb 4.5. Also in that region,
after a long quiet period, two earthquake occurred in the Komandorsky
Islands east of Kamchatka perhaps beginning a new cycle in that region
(Mb 3.9, 4.1).

U.S./CANADA

Most areas of the U.S. and Canada reported moderately high regional
rates of seismicity today. The largest event was a Ml 4.5 in Alaska
south of Anchorage this evening. Hawaii did not report any events
of Ml>3 today.
The region of the Central Rockies in Utah and surrounding states
has been much more active than the California area over the past
48 hours. There have been 8 earthquakes of Ml>=2 in this region and
3 of Ml 1.9 in this time. The five have concentrated in the Jackson
Lake (WY) are (three events Ml 2.8, 2.2, 2.0); in the Old Faithful
region of Yellowstone National Park (Ml 2.1, 2.0, 1.9) and in the
Sevier Utah area of western Utah (Mb 2.4, 2.2, 2.1).
The Vancouver Island/Pacific northwest region was also active
at levels of Ml>=2.5 today. Six earthquakes of Ml>=2.5 have hit this
area in the past 24 hours. These occurred in Nunavit (72N 129W) with
Ml 2.8; in western Vancouver Island region (Ml 2.8, 2.8 and 2.5);
in the area south of Vancouver Island (Ml 3.3); and near Dawson,
Yukon Territory (Ml 2.5).
In California/Nevada the main event was the Mw 3.7 near San Juan
Bautista this morning (see summary section above). The only other
event in central or northern California was a Ml 2.4 at the Geysers
which occurred near midnight this morning. Southern California saw
more events of Ml>=2 than Central California did over the past 30 hours -
all have occurred in the Calexico/Ocotillo region near the Mexico
border (Ml 2.7, 2.1, 2.1, 2.0). This breaks the 3-day drought of seismicity
in the region.
Other areas of the U.S. and Canada did not list any important
regional activity today.

NEW ZEALAND

Cultural noise was visible on the IGNS on-line seismometer. Two
earthquakes of Mb 4.0 and 4.3 have occurred along the Indian-Antarctic
ridge near the Macquarie ridge in the past two days. IGNS did not
report any new earthquake parameters 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 was quiet except for a strong geomagnetic storm
which began about 06:00 - 07:00 UT this morning. Areas most likely to
be affected for then next 24 hours lie within 30 degress longitude of
120W and 60E, however effects are expected to be minimal.
There were no X- or M-class solar flares observed today.

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/20020423events.txt

TIDAL EFFECTS

April 25 is the twelvth 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

Australia MB>=4.0 38 3.0 0.01
So Indonesia MB>=4.0 49 3.7 0.01
Global MB>=5.0 5 1.9 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

Tonga MB>=4.0 -28 -2.0 0.05
Turkey MB>=4.0 -10 -2.0 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 24 0 0 0 1771 24.000 124.300 0 7.4 Taiwan
Quake was felt throughout the Ryukyu Islands. The tsunami arrived
about 1 hour after the quake. The first of three was the largest
killing 11,941, destroying 3137 houses. The heights of the tsunami
ranged from 12-115 meters. Seven villages were totally washed away.

4 24 15 0 0 1843 42.000 146.000 0 7.5 Hokkaido, Japan
Great damage by the tsunami after the quake. Many houses were
completely washed away and 45 were killed at Shinryu village.

4 24 23 16 0 1900 35.000 136.000 60 7.0 No. Honshu, Japan
Slight Damage, cracks on walls and ground

4 24 4 26 42 1916 18.500 -68.000 80 7.2 Puerto Rico
At Santo Domingo, Dominican Republic. Damaging at Santo Domingo.
Felt on Puerto Rico.

4 24 8 2 8 1916 11.000 -85.000 60 7.6 Honduras
4 24 19 35 14 1947 8.500 -39.000 50 7.0 Central Mid-Atlantic Ridge
4 24 12 14 40 1960 27.500 55.000 0 7.1 So. Iran/Persian Gulf
420 killed. Damage about $20 million. 3,000 injured. Greatest damage
at Kourdeh and Lar. Damage also at Latifi, Khur, Beraq and Gerash.

4 24 9 57 21 1972 23.600 121.550 29 7.7 Taiwan
Five killed 17 injured and moderate damage in Hualien area.
50 houses destroyed, 90 partially destroyed. Felt throughout Taiwan.

4 24 21 50 6 1981 -13.426 166.421 33 7.3 Vanuatu Islands

U.S./CANADA

The following events of Mw>=5 have occurred on this date in
recorded history:

MO DA HR MN SC YEAR LATIT LONGIT DEP MW LOCATION

4 24 20 22 0 1867 39.200 -96.300 0 5.3 Lawrence, Kansas
Shocks with rumbling. Doors and windows were shaken, objects
thrown from shelves, and plaster cracked. Several were injured,
though not seriously. At Marysville, Marshall County, doors and
shutters swung back and forth. A two-story building was strongly
shaken in the upper story and there was a loud rumbling noise.
Also felt strongly at Manhattan where a wave 2 feet high was
observed on the Kansas River; stones loosened on buildings and
walls cracked. At different places there appeared to be one
or two waves. Plaster fell and many fled outside at Dubuque, Iowa.
The shock was alos felt in Illinois, Indiana, Missouri, Nebraska,
Arkansas, Kentucky and Ohio.

4 24 11 36 0 1890 36.900 -121.600 0 5.8 Central California
Monterey Bay region. At Watsonville, chimneys were thrown down.
The area of the highest intensity included Watsonville, Hollister
and Gilroy, and centered near Chittenden with fissuring in the
San Andreas Fault zone near that locality. The railroad was damaged
through settling of ground and displacement of a bridge.
Aftershocks occurred for many days.

4 24 8 34 0 1914 39.500 -119.800 0 6.4 California/Nevada area
Near Reno, NEV. At Reno, brick chimneys fell including some at the
University of Nevada.

4 24 22 44 42 1923 59.000 -135.500 0 5.0 Southeast Alaska
4 24 0 10 46 1943 47.300 -120.600 0 5.0 Washington state, U.S.
AT Entiat, Washington. Knickknacks were knocked off shelves at
Leavenworth. A rockslide occurred near Republic.

4 24 1 20 55 1964 31.300 -93.800 10 5.0 Southeast U.S.
First in a series of earthquakes near Pineland Texas. Intensity
about V to VI. Residents were apprehensive during shocks, but the
only damage was at Hemphill where wall paper and plaster cracked.
A roof was cracked in the county seat. Knickknacks fell from shelves
furniture moved, buildings creaked, object rattled. No noise
accompanied the earthquake.

4 24 3 51 4 1964 59.490 -144.450 19 5.1 Southeast Alaska
4 24 2 18 44 1969 52.770 -172.510 131 5.2 Andreanoff Islands, Aleutians
4 24 19 17 54 1970 49.800 -114.800 0 5.0 Montana/Idaho
4 24 0 39 18 1971 60.530 -139.050 18 5.1 Central Alaska
4 24 4 28 48 1978 51.642 -176.097 58 5.2 Andreanoff Islands, Aleutians
4 24 21 15 19 1984 37.309 -121.678 8 6.2 Central California
The Morgan Hill earthquake. This event injured 27 people and caused
damage estimated at $8 million. Most of the loss was in Santa Clara
County where 522 houses and 43 other buildings were severely damaged.
VIII effects occurred east of Morgan Hill on two streets. Some
mobile homes were shaken off supports and some fell. Three school
sustained damage. Several underground water lines were broken.
A Chemical plant near Coyote suffered severe damage when
braces separaed from the roof. In other buildings ceiling
panels and fixtures fell.
Small landslides, broken chimneys and flow of water were
disrupted. Felt over a large area of California and western Nevada.

4 24 22 6 46 1985 54.900 -159.100 0 5.1 Alaska Peninsula
4 24 15 59 1 1988 51.000 -179.700 0 5.4 Andreanoff Islands, Aleutians
4 24 10 4 15 2000 51.312 -178.005 33 5.0 Andreanoff Islands, Aleutians

EARTHQUAKE LISTINGS

ASIA

O: 21APR2002 00:10 38.3N 141.6E Mj=4.5 NIED KINKAZAN_REGION, Japan

O: 21APR2002 09:23:21 47.5N 153.9E MB=4.5 NEI KURIL ISLANDS

O: 19APR2002 19:58 42.2N 144.8E Mj=4.4 NIED SE_OFF_TOKACHI, Japan

O: 20APR2002 10:00:13 33.8N 136.4E MB=3.5 NEI NEAR S. COAST OF W HONSHU

O: 20APR2002 22:39:45 5.3N 124.4E MS=5.3 NEI MINDANAO, PHILIPPINES

O: 22APR2002 13:05:03 6.1S 130.4E MB=4.4 NEI BANDA SEA

O: 22APR2002 10:58:21 5.8N 125.7E MB=4.6 NEI MINDANAO, PHILIPPINES

O: 21APR2002 06:00:23 53.8N 169.7E MB=3.9 NEI KOMANDORSKIYE OSTROVA REG

O: 23APR2002 10:01:06 54.8N 165.7E MB=4.1 NEI KOMANDORSKIYE OSTROVA REG

O: 23APR2002 07:03:05 34.7N 139.2E MB=4.0 NEI NR S. COAST HONSHU, JAPAN

O: 23APR2002 18:11:00 1.2N 126.2E MB=5.2 NEI NORTHERN MOLUCCA SEA

O: 23APR2002 18:11:20 2.4N 125.8E MB=5.0 GSSC TALAUD ISLANDS, INDONESIA

SOUTH PACIFIC ISLANDS

O: 23APR2002 15:05:32 12.5S 166.9E MB=5.6 NEI SANTA CRUZ ISLANDS

O: 22APR2002 08:52:03 12.5S 167.3E MB=4.3 NEI SANTA CRUZ ISLANDS

O: 20APR2002 09:42:19 15.5S 167.6E MB=4.5 NEI VANUATU ISLANDS

O: 21APR2002 00:42:31 4.6S 153.5E MB=4.0 NEI NEW IRELAND REGION, P.N.G

O: 21APR2002 09:08:12 15.5S 178.8W MB=4.4 NEI FIJI ISLANDS REGION

O: 22APR2002 21:41:17 18.7S 174.2W MB=4.6 NEI TONGA ISLANDS

CARIBBEAN/CENTRAL/SOUTH AMERICA

O: 22APR2002 04:57 12.5S 76.8W mb=4.7 IGP Chilca
O: 21APR2002 05:43 12.4S 76.8W mb=3.8 IGP Chilca

O: 22APR2002 04:56:52 13.0S 75.9W MB=4.4 NEI CENTRAL PERU

O: 23APR2002 01:00:35 18.5N 104.4W ML=4.1 SSN COSTA COLIMA, MEXICO

O: 22APR2002 09:41:16 16.2N 99.7W ML=4.1 SSN COSTA DE GUERRERO, MEXICO

O: 23APR2002 05:18:02 6.9N 82.5W MC=4.3 CASC Panama, Central America

O: 23APR2002 07:51:08 10.5N 84.8W MC=2.8 CASC Costa Rica, Central America

O: 23APR2002 13:46:47 10.1N 84.3W MC=3.3 CASC Costa Rica, Central America

O: 23APR2002 11:08:50 27.7S 70.4W MB=4.7 DGF Copiapo, Chile

O: 23APR2002 07:49:51 6.4N 73.6W Mc=3.8 ULA Dpto. Santander, Colombia.

O: 21APR2002 21:10:05 22.7S 74.9W MB=4.4 NEI OFF COAST OF N CHILE

O: 23APR2002 05:18:03 7.5N 81.5W MB=4.5 NEI PANAMA

NEW ZEALAND/AUSTRALIA

O: 21APR2002 05:29:54 53.3S 140.8E MB=4.4 NEI WEST OF MACQUARIE ISLAND

O: 23APR2002 04:37:44 51.3S 140.5E MB=4.0 NEI W INDIAN-ANTARCTIC RIDGE

OCEANIA

O: 23APR2002 04:37:44 51.3S 140.5E MB=4.0 NEI W INDIAN-ANTARCTIC RIDGE

O: 21APR2002 05:29:54 53.3S 140.8E MB=4.4 NEI WEST OF MACQUARIE ISLAND

O: 20APR2002 18:50:44 57.6S 25.1W MB=4.6 NEI SOUTH SANDWICH ISL REGION

EUROPE/MIDDLE EAST/AFRICA

O: 23APR2002 07:08:52 40.7N 30.6E ML=3.4 KAN AKYAZI (ADAPAZARI), TURKEY

O: 21APR2002 17:57:16 45.7N 7.7E MD=3.4 IGG Northern Italy

O: 22APR2002 16:57:13 44.7N 6.7E MD=2.5 IGG Northern Italy

O: 23APR2002 18:02:14 36.2N 22.7E Ml=3.8 INGV SOUTHERN GREECE

U.S/CANADA

CALIFORNIA/NEVADA

O: 23APR2002 11:59:20 36.9N 121.6W ML=3.6 NEI CENTRAL CALIFORNIA
O: 23APR2002 11:59:20 36.9N 121.6W Mw=3.7 NCSN WNW of San Juan Bautista, CA
O: 23APR2002 04:59:20 36.9N 121.6W ML=3.6 NCSN WNW of San Juan Bautista, CA

O: 23APR2002 06:06:06 33.1N 115.6W ML=2.0 SCSN SSE of Obsidian Butte, CA
O: 23APR2002 10:41:34 32.4N 115.4W ML=2.1 SCSN SSE of Calexico, CA

O: 23APR2002 07:07:05 38.8N 122.8W Md=2.4 NCSN N of The Geysers

PACIFIC NORTHWEST/CANADA

O: 22APR2002 15:46:57 46.5N 121.3W ML=1.1 PNSN E of Goat Rocks
O: 22APR2002 17:07:37 46.9N 121.9W ML=1.5 PNSN WNW of Mount Rainier

O: 23APR2002 02:40:56 48.9N 129.1W ML=3.3 PGC SSW Pt. Hardy BC

O: 22APR2002 00:19:35 49.1N 128.0W ML=2.1 PGC W Tofino BC
O: 22APR2002 00:19:35 49.1N 128.0W ML=2.1 PGC WEST OF VANCOUVER ISLAND, B.C.

O: 22APR2002 11:20:13 52.6N 132.5W ML=1.9 PGC WEST COAST MORESBY ISLAND, B.C
O: 22APR2002 11:20:13 52.6N 132.5W ML=1.9 PGC SSW Sandspit BC

O: 23APR2002 14:42:47 52.7N 132.1W ML=2.8 PGC SSW Sandspit BC
O: 23APR2002 08:02:12 53.9N 132.5W ML=2.5 PGC SW Massett BC
O: 23APR2002 01:43:59 53.2N 132.9W ML=2.8 PGC W Sandspit BC

ROCKY MOUNTAIN AREA

O: 21APR2002 03:39:52 44.8N 111.0W ML=2.1 UUSN NNE of W. Yellowstone, MT
O: 21APR2002 23:43:13 44.8N 111.0W ML=2.0 UUSN NNE of W. Yellowstone, MT
O: 22APR2002 05:51:25 44.5N 110.9W ML=1.9 UUSN W of Old Faithful, WY
O: 22APR2002 06:29:31 44.5N 111.0W ML=1.9 UUSN W of Old Faithful, WY

O: 21APR2002 06:04:35 38.6N 112.3W ML=2.6 UUSN SSW of Sevier, UT
O: 21APR2002 06:30:05 38.6N 112.3W ML=2.4 UUSN S of Sevier, UT
O: 21APR2002 07:13:00 38.6N 112.3W ML=2.1 UUSN S of Sevier, UT

O: 21APR2002 11:42:44 37.4N 113.9W ML=2.2 UUSN SW of Enterprise, UT

EASTERN U.S./CANADA

O: 21APR2002 19:06:26 76.8N 107.0W MN=3.1 GSC E FROM MOULD BAY, N.W.T.

ALASKA

O: 23APR2002 23:15:55 55.1N 155.6W ML=4.5 AEIC Anchorage, Alaska
P: 30APR2002 7-04/27 54.9N 159.1W 3.5-4.5 CACAA Alaska Peninsula

HAWAII