GLOBAL SEISMICITY EXPLODES DURING STRONG GEOMAGNETIC STORM

SUMMARY

The strong geomagnetic storm which had occurred yesterday recommenced
this morning at about 00:00 UT (April 18, 2002) and lasted through about
16:00 UT this afternoon. It then declined to quiet conditions by the
end of the UT day. Yesterday's storm had occurred while California was
anti-solar and a strong increase in seismicity had been observed in
that region during that storm (see Earthquake summary from April 17, 2002).
However no large-scale global increases in seismicity were noted during
yesterday's storm. Today, however was another matter.
As the storm reached it's height about 05:00 UT this morning a Ms 6.3
earthquake occurred in Guerrero, Mexico. This event had been anticipated
on the basis of a linear clustering of earthquakes in the Central U.S.
two days ago as well as other phenomena. The Mexican quake was followed
by an active aftershock series including an event of Ml 5.9 and Ml 5.5.
Next in line was a Ms 5.8 in the South Sandwich Islands. This earthquake
occurred very near local sun-noon in the South Sandwich Islands. The
seismic alert from the flare and geomagnetic storm yesterday had noted
the possibility of strong activity at high latitudes. The South Sandwich
Islands event occurred at about 60S, in an area near the auroral
electrojet.
About two hours later a Ms 6.7 hit Central Peru. This event was near
the Ms 6.4 of March 31, but not a classical aftershock. Instead it
appeared to be a regionally triggered event with some influence from
far-field effects and solar/geomagnetic effects. This earthquake
occurred near the end of the geomagnetic storm. The region had been
suggested as a possible location for the linear string of events
in Central U.S. two days ago (see April 15, daily Earthquake summary).
As the geomagnetic storm died down towards the end of the UT day,
so did the global seismicity. The day's strong events were all found
within the time window of the geomagnetic storm. However, statistically,
it is quite common for the largest global earthquakes associated with
strong geomagnetic storms to occur 3.5-5.5 days after those storms
commence, so the seismic activity may not yet be over with April
21-23 days to watch.

GLOBAL

Besides the Ms 6.7 in Chile, the Ms 6.3 in Mexico and the Ms 5.8 in
the South Sandwich Islands today, there were other events of interest
which have been listed since the last summary. Included among these
is a Mb 4.9 in the Talaud Islands south of the Philippines. The
region southeast of Honshu also experienced several events in the
past 24 hours (Mb 4.2 nd 4.5). The Mexico mainshock was followed
by 13 listed aftershocks of Ml>=3.9 (SSN) including a Ml 5.5 and 5.9.
There were also two regional aftershocks - in the Oaxaca area (Mb 4.3)
and near El Salvador (Mb 4.4). The mainshock in Mexico was preceded
by an Mb 4.5 in the Gulf of California.
An Ml 4.5 also occurred in Central Peru this evening, perhaps
a FFA from the Central Chile earthquake earlier in the day. This event
followed a Ml 4.2 to the northwest in Peru last night.
Finally, the Fiji Islands continued to be active today. For the
third straight day events of Mb>4 were located in this area.

U.S./CANADA

The U.S. and Canada were not immune to the possible triggering effects
of the geomagnetic storm this morning. In the 3 hours between storms a
Mb 4.5 had occurred in the Gulf of California. As the second storm
began this morning, an Mb 4.0 occurred in the western Vancouver Island
region. This was followed by an Ml 4.5 in Central Alaska about 15 minutes
later and a second shock at Vancouver Island (Mb 4.2) after another
13 minutes had elapsed. These were the strongest events in the U.S./
Canada area today. It is quite unusual for 4 separate epicenters
to experience a Mb>=4 event in this region within the short span of
about 3 hours, so it appears that some regional triggering was involved
here.
The strongest earthquake in the California/Nevada region occurred
towards the end of the geomagnetic storm as a Ml 3.5 near the Geysers
in northern California. This is the strongest event in northern or
Central California since a Ml 3.6 off the Coast of Northern California
on April 1 and the strongest in California in the two weeks since
April 5 when a Ml 4.4 hit the Hector Mine aftershock zone in southern
California.
Other earthquakes today in California of Ml>=2 occurred at Mammoth
Lakes (Md 2.0); as a Geysers aftershock (Md 2.7); at Tres Pinos (Md 2.0);
and in southern California west of Fillmore (Ml 2.1) and near Mt.
San Gorgonio (Ml 2.0).
The most unusual event recorded in the U.S./Canada since the last
summary was posted was a Ml 2.0 near Quebec City, Quebec. This event
occurred towards the end of the first geomagnetic storm. This region
often shows strong effects including blackouts and downed power during
strong geomagnetic events.
A Ml 2.0 was recorded near Jackson Lake, WY this morning, but other
regions have not listed any other regionally significant events at
this time.

NEW ZEALAND

No new earthquakes were listed by IGNS today. Cultural noise was
the only evidence of earth movement on the on-line seismogram.

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 at very active levels through the first
half of the UT day (April 18) following a slightly smaller storm
yesterday. This strong geomagnetic storm was accompanied by three
moderately strong earthquakes at the height of the storm - a Ms 5.8
in the South Sandwich Islands, a Ms 6.7 in Chile and an Ms 6.3 in
west-Central Mexico.
The largest solar flare of the day occurred as C9.4 with the
following parameters:

Flare # START MAX END CLASS

1930 0636 0702 0729 C9.4

The intensity of global seismicity lessened as the storm weakened
in the last half of UT April 18, 2002. SEC expects another strong
geomagnetic storm to occur on April 19.

For general space weather conditions see:
http://sec.noaa.gov/today.html
For Solar flare data see:
http://sec.noaa.gov/ftpdir/indices/events/20020418events.txt

TIDAL EFFECTS

April 20 is the seventh day after the beginning of the 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

No Regions

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

East US MB>=1.0 -13 -2.5 0.03

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 19 2 23 0 1902 14.000 -91.000 25 7.5 Guatemala
4 19 2 23 30 1902 14.000 -91.000 60 8.3 Guatemala
2000 killed at Quetzaltenango and San Marcos, and
Amatitlan, Guatemala. Felt from Tabasco, Jalisco, Guerro, Chiapas,
Oaxaca, Hidalgo and Mexico City, Mexico. Destroyed the city of
Quetzaltenango. Extensive loss of life. Activity continued until
September 23 when an earthquake was strongly felt and an eruption of
the Volcano Santa Maria began.

4 19 0 0 0 1903 39.100 42.400 0 7.0 Turkey
1700 killed, severe damage. Intensity IX.

4 19 7 58 48 1908 42.000 134.000 480 7.3 Sea of Japan
4 19 3 9 8 1923 2.500 117.500 60 7.0 Malaysia
The shock was strongly felt at Tarakan about 140 km north of
the center and followed by a number of aftershocks. Brick buildings
collapsed, cracks developed in the ground and streams were affected.
The kitchen of a house seemed to be displace dover a distance
of about 1 meter to the west. Structures on solid ground suffered
little damage.

4 19 15 23 22 1935 31.500 15.200 33 7.1 Mediterranean/Sicily
4 19 5 7 17 1936 -7.500 156.000 40 7.4 Solomon Islands
4 19 13 3 58 1945 -21.000 169.500 40 7.0 Loyalty Islands
4 19 20 24 5 1955 -30.000 -72.000 0 7.0 Coast Central Chile
1 killed. Extensive damage from tsunami at La Serena and Tongoy.

4 19 22 19 26 1957 52.000 -166.500 0 7.3 Fox Islands, Aleutians
4 19 7 35 15 1963 36.000 97.400 0 7.0 So. China
4 19 0 19 36 1996 -23.000 -70.000 0 7.1 Coast No. Chile
Felt (VI) at Calama, V at Antofagasts, Tocopilla and Taltal.

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 19 10 50 0 1892 38.500 -122.000 0 6.8 Central California
At Vacaville, Ca. nearaly all brick structures were wrecked and many
frame buildings were damaged. Chimneys were twisted or thrown down.
In Dixon, damage was less serious, but many structures, especially
schoolhouses were seversly damaged. At Winters, damage was
similar to that in Vacaville and the loss was about the same. .
Damage at Vacaville, Dixon, and Winters was estimated
at about $225,000. Damage also ocurred in many other areas. Fisures were
found in the the bed of Putah Creek half a mile west of Winters and in
the adjoining roadway and fields. Shock was felt from Healdsburg
to Fresno and east to western Nevada.

4 19 0 30 0 1906 33.000 -115.000 0 6.0 Imperial Valley, California
A strong far-field aftershock of the great San Francisco earthquake.
Chimneys fell. Banks of New River caved in; water tanks were destroyed
at Cocopah in Baja, Cal. Nearly destroyed the Van Ness and Marlour
buildings in Brawley. Not on brick or adobe building in Brawley
was left undamaged. Slight damage was also reported at Calexico
to Imperial. Felt north to Los Angeles and to Yuma AZ.

4 19 22 47 39 1953 50.000 -179.500 33 5.5 Andreanoff Islands, Aleutians
4 19 15 44 53 1957 51.500 -168.500 0 6.7 Fox Islands, Aleutians
4 19 22 19 26 1957 52.000 -166.500 0 7.3 Fox Islands, Aleutians
4 19 6 43 29 1959 66.500 -142.500 0 5.0 Northern Alaska
4 19 15 3 26 1959 58.000 -152.500 0 6.2 Southern Alaska
4 19 19 26 16 1969 60.360 -145.980 9 5.1 Central Alaska
4 19 1 15 47 1970 59.600 -142.720 20 5.6 Southeast Alaska
4 19 0 26 1 1975 58.699 -154.193 100 5.0 Southern Alaska
4 19 1 49 2 1978 60.059 -153.487 191 5.2 Central Alaska
4 19 19 12 49 1983 63.363 -149.925 114 5.1 Central Alaska
4 19 22 4 47 1988 54.800 -160.100 0 5.7 Unimak Islands, Aleutians
4 19 22 5 4 1988 56.700 -153.900 33 5.3 Southern Alaska
4 19 15 35 17 1991 43.160 -127.650 10 5.4 Off Coast of Oregon
4 19 18 19 22 1991 59.910 -153.180 136 5.0 Southern Alaska

EARTHQUAKE LISTINGS

ASIA

O: 17APR2002 14:47:00 24.4N 122.5E MB=4.0 NEI TAIWAN REGION

O: 18APR2002 08:53:55 4.1N 126.6E Ms=4.8 GSSC TALAUD ISLANDS, INDONESIA

O: 18APR2002 03:27:41 3.4N 126.8E MB=4.9 NEI TALAUD ISLANDS, INDONESIA
O: 18APR2002 03:27:45 3.9N 127.2E Ms=4.3 GSSC TALAUD ISLANDS, INDONESIA

O: 17APR2002 20:18:00 24.7N 96.1E MB=4.1 NEI MYANMAR

O: 17APR2002 18:48:25 31.9N 142.0E MB=4.5 NEI SOUTHEAST OF HONSHU, JAPA

O: 17APR2002 18:15:32 30.9N 142.4E MB=4.4 NEI SOUTHEAST OF HONSHU, JAPA

O: 19APR2002 00:16:47 9.5N 93.6E mb=5.1 GSR NICOBAR ISLANDS, INDIA

O: 17APR2002 23:13:40 34.8N 80.3E ML=3.1 KHZ W of Songma (Xizang)

O: 17APR2002 20:29:49 33.8N 86.9E ML=3.1 KHZ Margog Caka (Xizang)

O: 18APR2002 03:10:20 34.8N 137.1E MB=4.2 NEI NEAR S. COAST OF HONSHU, JAPAN

SOUTH PACIFIC ISLANDS

O: 17APR2002 10:30:39 24.3S 180.0E MB=4.2 NEI SOUTH OF FIJI ISLANDS

O: 17APR2002 16:42:23 24.7S 176.4W MB=5.1 NEI SOUTH OF FIJI ISLANDS

O: 18APR2002 01:10:44 20.4S 178.3W MB=4.0 NEI FIJI ISLANDS REGION

CARIBBEAN/CENTRAL/SOUTH AMERICA

O: 18APR2002 16:08:36 27.4S 70.0W MW=6.7 NEI NEAR COAST OF N CHILE

O: 18APR2002 05:02:46 16.9N 100.8W MW=6.3 NEI NEAR COAST GUERRERO, MEX
O: 18APR2002 05:02:50 17.1N 102.2W MS=6.4 GSR NEAR COAST OF MICHOACAN,
O: 18APR2002 00:02:43 16.4N 101.1W ML=6.3 SSN COSTA DE GUERRERO, MEXICO

O: 18APR2002 18:47 14.4S 76.3W mb=4.6 IGP Ica, Peru

O: 18APR2002 11:19:55 11.9N 89.0W MB=4.4 NEI OFF COAST OF CEN AMERICA

O: 18APR2002 07:24:31 16.8N 100.8W MB=4.1 NEI NEAR COAST GUERRERO, MEX
O: 18APR2002 17:57:23 16.8N 101.0W MB=4.9 NEI NEAR COAST GUERRERO, MEX
O: 18APR2002 13:00:41 17.1N 101.8W ML=5.5 SSN COSTA DE GUERRERO, MEXICO
O: 18APR2002 12:57:17 16.4N 101.8W ML=5.9 SSN COSTA DE GUERRERO, MEXICO
O: 18APR2002 11:11:08 16.6N 101.3W ML=4.2 SSN COSTA DE GUERRERO, MEXICO
O: 18APR2002 06:00:40 17.0N 101.4W ML=4.9 SSN COSTA DE GUERRERO, MEXICO
O: 18APR2002 03:28:05 16.5N 100.9W ML=4.3 SSN COSTA DE GUERRERO, MEXICO
O: 18APR2002 03:01:39 16.9N 100.8W ML=4.3 SSN COSTA DE GUERRERO, MEXICO
O: 18APR2002 02:37:30 16.7N 100.7W ML=4.0 SSN COSTA DE GUERRERO, MEXICO
O: 18APR2002 02:24:30 16.8N 101.0W ML=4.6 SSN COSTA DE GUERRERO, MEXICO
O: 18APR2002 00:20:12 16.8N 101.0W ML=3.7 SSN COSTA DE GUERRERO, MEXICO
O: 18APR2002 00:15:07 17.5N 101.2W ML=4.0 SSN COSTA DE GUERRERO, MEXICO

O: 18APR2002 18:47:42 16.0N 95.2W MB=4.3 NEI OAXACA, MEXICO
O: 18APR2002 13:47:40 15.7N 95.3W ML=4.3 SSN GOLFO DE TEHUANTEPEC, MEXICO

O: 18APR2002 00:02:43 16.4N 101.1W ML=6.3 SSN COSTA DE GUERRERO, MEXICO

O: 17APR2002 22:06:55 25.8N 110.0W MB=4.5 NEI GULF OF CALIFORNIA

O: 17APR2002 21:23 11.4S 77.9W mb=4.6 IGP Huacho
O: 17APR2002 21:23:08 11.1S 78.4W MB=4.2 NEI OFF COAST OF PERU

O: 16APR2002 01:40:25 8.6N 71.1W Mc=3.7 ULA Municipio Libertador, Edo. Mér
O: 18APR2002 02:24:40 8.5N 71.2W Mc=3.2 ULA Municipio Libertador, Edo. Mér

O: 16APR2002 18:33:07 6.7N 73.2W Mc=3.8 ULA Dpto. Santander, Colombia.

O: 16APR2002 04:51:51 11.2N 86.3W MC=3.9 CASC Costa Rica, Central America

O: 18APR2002 08:49:04 10.3N 86.3W MC=4.2 CASC Costa Rica, Central America

O: 18APR2002 11:21:26 9.9N 84.5W MC=3.4 CASC Costa Rica, Central America

O: 18APR2002 12:17:08 5.2N 83.2W MC=3.9 CASC Costa Rica, Central America

NEW ZEALAND/AUSTRALIA

OCEANIA

O: 18APR2002 14:17:27 60.7S 25.7W MS=5.8 NEI SOUTH SANDWICH ISL REGION

O: 17APR2002 15:53:19 1.3N 20.6W MB=4.2 NEI CENTRAL MID-ATLANTIC RIDG

EUROPE/MIDDLE EAST/AFRICA

U.S/CANADA

CALIFORNIA/NEVADA

O: 18APR2002 11:35:40 38.8N 122.8W ML=3.5 NEI NORTHERN CALIFORNIA
O: 18APR2002 04:35:40 38.8N 122.8W ML=3.5 NCSN ESE of The Geysers, CA
O: 18APR2002 04:39:37 38.8N 122.8W ML=2.7 NCSN E of The Geysers, CA

O: 18APR2002 07:49:36 37.8N 122.0W ML=1.5 NCSN S of San Ramon, CA

O: 18APR2002 09:07:20 37.7N 118.8W ML=2.0 NCSN ENE of Mammoth Lakes, CA

O: 18APR2002 10:54:15 39.5N 119.2W ML=1.3 NCSN SSE of Fernley, NV

O: 18APR2002 12:20:53 34.4N 119.0W ML=2.1 SCSN WNW of Fillmore, CA

O: 18APR2002 13:23:49 40.4N 124.0W ML=1.7 NCSN SSE of Rio Dell, CA

O: 18APR2002 15:39:37 34.1N 116.9W ML=2.0 SCSN W of Mt. San Gorgonio, CA

O: 18APR2002 17:04:32 36.0N 120.5W ML=1.4 NCSN NNW of Parkfield, CA

PACIFIC NORTHWEST/CANADA

O: 18APR2002 00:51:44 49.6N 128.7W MB=4.0 NEI VANCOUVER ISL, CANADA REG
O: 18APR2002 00:51:41 49.5N 129.5W ML=3.7 PGC SW Pt. Hardy BC

O: 18APR2002 01:19:12 49.6N 129.1W ML=3.8 PGC SW Pt. Hardy BC
O: 18APR2002 01:19:10 49.8N 128.9W MB=4.2 NEI VANCOUVER ISL, CANADA REG

O: 14APR2002 20:49:57 52.9N 119.5W ML=1.8 PGC NEAR MT. ROBSON, B.C.

O: 14APR2002 21:01:17 53.6N 117.4W ML=2.0 PGC NEAR HINTON, ALBERTA.

O: 17APR2002 08:12:57 49.2N 125.6W ML=0.5 PGC WEST COAST VANCOUVER ISLAND, B

O: 17APR2002 12:34:24 58.8N 142.8W ML=2.7 PGC GULF OF ALASKA.

ROCKY MOUNTAIN AREA

O: 14APR2002 08:30:40 44.4N 114.1W ML=2.8 NEI WESTERN IDAHO

O: 18APR2002 14:04:32 43.6N 110.6W MD=2.1 USBR S of Kelly, WY

O: 17APR2002 09:22:37 44.6N 111.0W ML=1.8 UUSN SE of W. Yellowstone, MT

O: 17APR2002 11:13:07 39.7N 110.8W ML=2.0 UUSN NNE of Helper, UT

O: 17APR2002 12:32:36 42.1N 111.7W ML=2.2 UUSN NE of Franklin, ID

EASTERN U.S./CANADA

O: 17APR2002 20:17:01 47.0N 71.5W MN=2.0 GSC 30 KM NW FROM QUEBEC, QUE.

ALASKA

O: 18APR2002 01:06:28 62.3N 149.5W ML=4.5 AEIC Talkeetna, Alaska

HAWAII