MODERATE EARTHQUAKES HIT JAWA (MB 5.5) AND NORTHERN PERU (MB 5.5)

SUMMARY

Moderately strong (Mb 5.5) earthquakes were felt in Jawa and in northern
Peru today within several hours this evening (UT). These two areas
are close to antipodal to each other and both lay near the geomagnetic
equator.
After the extravagance of earthquakes of Ml>=2 in the California
(especially central/northern California) areas on April 17-18 during the
first of the recent geomagnetic storms, a dead calm has settled on the
region. In southern California (SCSN) there has not been an event of
Ml>=2 in 2.5 days and only 1 in the past 3.5 days. Things are a bit more
lively in Central/Northern CA, but not much, with 5 in the past 3.5 days.
Others have noted this lack of activity on several occasions following
strong geomagnetic storms and it may be much of the cause of the statistical
increase in activity about 4 days after geomagnetic storms - as a sudden
return to normalcy, rather than a strong increase in seismicity rate at that
time.
It is also possible that the sudden return to quiet geomagnetic conditions
brought on by the very strong proton storm (which eliminated electron
flux in the ionosphere) was partially responsible for the lull in
seismic activity today. Proton storms tend to accompany such quiet
periods and the cause may be related to the inability to form coherent
electojects in the presence of the solar protons. These in turn, would
not allow induced currents in the earth which might be triggering
agents for earthquakes.
Right now, the areas to watch will probably be volcanics. They usually
"heat up" between 2-5 days after strong geomagnetic storm. Either bubbles
are released during the storm which take 2-5 days to migrate up through
magma chambers, increasing magma chamber pressure as the rise and expand,
or some actual heating of the magma is occurring from Ohmic heating - hard
to say, but statistical evidence suggests whatever the cause, it takes
3-5 days before this effect is seen.
With the Mb 4.0 off the Coast of Oregon today and volcanic tremor north of
Mexico City the volcanic effects may be on the upswing today.
Areas which typically show some seismic increases, probably related to
underground magma chambers in California include the Mammoth Lakes,
Coso Junction and Calexico regions. Further up north the Cascade volcanics
are often unusually active after a slight delay following geomagnetic storms.
Globally, there is usually a strong eruptive episode including several
major volcanic eruptions 3-7 days after strong geomagnetic storms. Mid-Ocean
ridges also become unusually active at this time.

GLOBAL

Besides the two Mb 5.5 events at Northern Peru and Jawa, global seismicity
was otherwise near background levels today. An interesting series of
apparently volcanic-related earthquakes occurred in the EJE Volcanic zone
north of Mexico City and may be related to the recent geomagnetic storms
(this area is under seismic watch conditions). Earthquakes have also been
recorded in the eastern Caucasus (Ms 3.3 GSR) and the Celebes Sea (Ms 3.8
GSR) since last daily summary. Aftershocks of the Mw 6.3 in Mexico continued
(Ml 4.1, 3.9). Poorly located earthquakes of Ml 5.1 and 4.3 have been
reported by GSSC in Vanuatu and Northeast China as well.
A small Ml 3.4 was recorded in eastern Turkey.

U.S./CANADA

Seismicity appeared low throughout the U.S. today, although many
seismic networks were not reporting due to the weekend closure.
The only event of Ml>=3 in the U.S. or Canada (including
Alaska and Hawaii) today occurred as a Mb 4.1 off the Coast of
Oregon. This is an active area where such events are not uncommon,
and may be related to plate boundaries and volcanics.
In the California/Nevada region three earthquakes of Ml>=2 occurred -
a Ml 2.1 near Morgan Hill and a second Ml 2.1 at Mammoth Lakes and a
Ml 2.0 near San Ardo. It has now been nearly 2.5 days since the last event
of Ml>=2 in southern California.
The only other events reported in the U.S. (outside Alaska) were
two additional aftershocks to yesterdays Mb 5.1+ earthquake in the
northern Adirondacks, N.Y. Today's aftershocks registered Ml 2.3 and
2.2.

NEW ZEALAND

The IGNS on-line seismometer shows at least 3 light earthquakes
following the X1.2 solar flare this morning (UT). Only one of these
has been parameterized by IGNS - a Ml 3.7 near Porirua on the southern
coast of North Island on the Cook Strait. The others appear to be
similar sized.

The IGNS on-line Seismometer can be found at:
http://www.gns.cri.nz/news/earthquakes/latest_drum.html

GEOMAGNETIC/SOLAR FIELDS

The X1.5 solar flare that occurred this morning was reported in
yesterday's daily summary. It's parameters have been re-evaluated
by SEC and are up from the X1.2 reported in that summary currently:

Flare # START MAX END CLASS

2650 0043 0151 0238 X1.5

This makes it the largest flare since Oct 22, 2001 and the third
largest of the past year. SEC expects the CME from this flare to
deal a glancing blow to the earth with active geomagnetic conditions
likely on 23 and 24 April.
The geomagnetic field was very quiet today as the strong proton
storm inhibited electron ring currents from forming.

For general space weather conditions see:
http://sec.noaa.gov/today.html
For Solar flare data see:
http://sec.noaa.gov/ftpdir/indices/events/20020421events.txt

TIDAL EFFECTS

April 23 is the tenth 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

Alaska MB>=3.0 6 2.0 0.05
Greece MB>=4.0 8 2.0 0.05
Hawaii MB>=2.0 19 2.7 0.02
Kuriles MB>=4.0 22 1.9 0.05
Mammoth Lakes MB>=3.0 19 2.2 0.05
East Pacific Rise MB>=4.0 38 2.3 0.05
Hindu Kush MB>=4.0 20 2.9 0.01

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

No Regions

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 22 23 37 0 1898 38.600 142.000 60 8.3 Off East Coast Honshu
11 slow moving small tsunami waves were generated by this
earthquake off Sanriki.

4 22 21 56 52 1991 9.960 -83.050 8 8.1 Costa Rica
47 people were killed, 109 injured. 7430 were homeless and extensive
damage occurred in the Limon-Pandora area. Intensity X was observed
in some areas of liquifaction within the epicentral areas. Damage
included lanslides blocking roads. 28 people were killed , 454 injured
and an additional 2400 homeless and 866 buildings destroyed
in the Guabito-Almirante-Bocas del Toro area. Slight damage throughout
Central America from Colombia to El Salvador. Maximum uplift
was about 1.4 meters near Limon and sandblows and liquefaction caused
subsidence of soils in the Bocas del Toro area. Ground cracks were
also observed. A 2- meter tsunami started with a recession of the
sea of 500 m from the shoreline. During the wave recession people
went to the beach to catch trapped fish.

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 22 16 4 2 1921 44.000 -17.000 33 5.6 No. Mid-Atlantic Ridge
4 22 4 15 49 1938 49.700 -129.700 0 5.5 Vancouver Island area
4 22 9 45 48 1945 31.500 -114.000 0 5.3 Gulf of California
4 22 16 55 0 1952 46.200 -111.400 0 5.0 Yellowstone/Wyoming
Western Mointana. Maximum intensity reported near Townsend and Toston.
Plaster fell, several bricks fell from a chimney.

4 22 17 21 54 1956 53.800 -161.500 0 6.5 Unimak Islands, Aleutians
4 22 10 55 5 1959 53.800 -166.900 51 6.1 Fox Islands, Aleutians
4 22 20 29 19 1964 58.400 -150.430 33 5.1 Southern Alaska
4 22 23 27 20 1966 57.400 -152.300 26 5.9 Southern Alaska
4 22 19 40 29 1971 60.096 -152.986 110 5.1 Central Alaska
4 22 6 22 32 1977 44.230 -129.379 15 5.0 Off Coast of Oregon
4 22 19 28 19 1980 46.203 -122.182 0 5.0 Washington state, U.S.
4 22 17 21 18 1986 72.176 -130.468 10 5.0 Yukon Territory, Canada
4 22 16 6 48 1987 50.545 -172.511 33 5.0 Andreanoff Islands, Aleutians
4 22 0 51 10 1989 51.064 -178.549 33 5.0 Andreanoff Islands, Aleutians
4 22 12 45 49 1993 56.000 -157.000 0 5.3 Alaska Peninsula
4 22 22 2 13 1997 58.000 -167.000 0 5.1 Fox Islands, Aleutians

EARTHQUAKE LISTINGS

ASIA

O: 20APR2002 21:30:33 41.8N 142.1E MB=4.7 NEI HOKKAIDO, JAPAN REGION

O: 21APR2002 07:17:43 43.0N 47.1E MS=3.5 GSR EASTERN CAUCASUS

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

O: 21APR2002 19:23:38 6.4S 108.4E mb=5.5 GSR JAWA, INDONESIA

SOUTH PACIFIC ISLANDS

CARIBBEAN/CENTRAL/SOUTH AMERICA

O: 21APR2002 04:59:58 19.4N 99.0W ML=3.0 SSN EJE VOLCANICO CENTRAL, MEXICO
O: 21APR2002 04:23:16 19.5N 99.0W ML=3.1 SSN EJE VOLCANICO CENTRAL, MEXICO
O: 21APR2002 04:22:43 19.5N 98.9W ML=2.8 SSN EJE VOLCANICO ORIENTAL, MEXICO
O: 21APR2002 04:20:46 19.5N 98.9W ML=3.2 SSN EJE VOLCANICO ORIENTAL, MEXICO

O: 21APR2002 01:09:37 16.5N 100.9W ML=4.1 SSN COSTA DE GUERRERO, MEXICO
O: 21APR2002 03:00:41 16.5N 101.0W ML=3.9 SSN COSTA DE GUERRERO, MEXICO

O: 20APR2002 23:03:14 16.9N 100.1W ML=4.0 SSN COSTA DE GUERRERO, MEXICO

O: 21APR2002 22:24 5.9S 81.1W mb=5.2 IGP Piura, Peru (IV)

NEW ZEALAND/AUSTRALIA

O: 21APR2002 03:17 41.1S 174.7E ML=3.7 IGNS NW of Porirua, N.Z.
Note (IGNS) Expected to have been felt in the Porirua area
Note (ED): This earthquake occurred about an hour after a solar flare
of X1.2, the largest in half a year occurred. The solar flare hit
while this epicenter was almost exactly sub-solar. A solar/geomagnetic
trigger is therefore suspected. The area had been under seismic
watch conditions at the time of the earthquake.

OCEANIA

EUROPE/MIDDLE EAST/AFRICA

O: 20APR2002 09:23:45 39.2N 28.4E ML=3.2 KAN SINDIRGI, TURKEY

O: 21APR2002 21:00:45 40.6N 37.0E ML=3.4 KAN TOKAT, TURKEY

U.S/CANADA

CALIFORNIA/NEVADA

O: 21APR2002 03:49:09 36.1N 120.7W ML=2.0 NCSN ENE of San Ardo, CA

O: 21APR2002 01:13:45 38.6N 122.7W ML=1.3 NCSN WNW of Calistoga, CA

O: 21APR2002 02:30:46 37.9N 118.6W ML=2.1 NCSN NNE of Toms Place, CA

O: 21APR2002 05:15:15 36.5N 121.0W ML=1.9 NCSN SE of Pinnacles, CA

O: 21APR2002 10:42:50 37.4N 114.4W ML=1.8 NCSN SW of Joseco, NV

O: 21APR2002 13:50:11 37.3N 121.7W ML=2.1 NCSN N of Morgan Hill, CA

O: 21APR2002 15:38:43 39.0N 122.6W ML=1.9 NCSN NE of Clearlake, CA

PACIFIC NORTHWEST/CANADA

O: 21APR2002 16:37:39 43.6N 126.4W MB=4.1 NEI OFF COAST OF OREGON

ROCKY MOUNTAIN AREA

O: 21APR2002 04:16:19 43.6N 110.5W MD=2.0 USBR E of Kelly, WY
O: 21APR2002 09:32:36 43.6N 110.6W MD=2.8 USBR SSE of Kelly, WY

EASTERN U.S./CANADA

O: 20APR2002 11:45:29 44.5N 73.7W Mb=2.9 LDGO SW of Plattsburgh,
O: 20APR2002 11:04:42 44.5N 73.7W Mb=4.0 LDGO SW of Plattsburgh,
O: 20APR2002 10:50:48 44.5N 73.7W Mb=5.1 LDGO SW of Plattsburgh,
O: 21APR2002 12:39:11 44.5N 73.7W Mc=2.3 LDGO SW of Plattsburgh, NY
O: 21APR2002 11:47:10 44.5N 73.7W Mc=2.2 LDGO SW of Plattsburgh, NY (aftershock)
O: 20APR2002 11:08:26 44.5N 73.7W Mc=1.7 LDGO SW of Plattsburgh, NY (aftershock)

ALASKA

HAWAII