CALIFORNIA EXTREME QUIET BROKEN BY GEYSERS (Ml 3.4) AND BRAWLEY SWARMS

SUMMARY

Twenty-three hours of extreme seismic quiet in the California/Nevada today
was broken by a Ml 3.4 at the end of the 23-hour period in the Geysers
region. This was followed by a minor swarm at the Geysers as well as
a minor swarm including a Ml 2.7 near Brawley in southern California.

GLOBAL

Seismicity continued to reflect FFA activity, although this now
appears to be diminishing. A number of mid-oceanic ridges were moderately
active today, possible due to several M-class solar flares in recent
days. None of this activity was of Mb>5 however.
For the most part, while seismicity has been relatively subdued
over the past two days, a number of moderate earthquakes have occurred.
The strongest of these occurred as a Mb 5.0 in the Mariana Islands
north of Guam followed later in the day by a Mb 5.6 south of Guam.
Other quakes of Mb>=4.5 occurred in the Fiji Islands (Mb 4.1),
the northern Mid-Atlantic Ridge (Mb 4.7), Colombia and Costa Rica
(Mb 4.4 and 4.3); Taiwan (Mb 4.0, 4.7. 4.6); Peru (Mb 4.7, 4.8); Sumatera
(Mb 4.7); and the South Sandwich Islands (Mb 4.7).
Most of these had been expected as Far-field aftershocks.

U.S./CANADA

During the first 22 hours of the UT day (April 15) only 3 earthquakes
were recorded in the California/Nevada region. Such extreme quiet
in the region is often precursory to a moderate or strong earthquake.
In today's case a Ml 3.4 earthquake in the Geysers (and aftershocks)
broke the quiet period at 22:57 UT. This was apparently followed by
a more active seismic pattern beginning on April 16 with a minor
swarm near Brawley, CA (Ml 2.7, 2.0, 2.2). The Geysers earthquake was
the first within California (Not including 2 in the Calexico swarm)
of Ml>=3 in more than a week.
A minor swarm also occurred in California last night with a Ml 2.8
and several micro-aftershocks. The only other events breaking the Ml 2
barrier in the past two days occurred at Mammoth Lakes yesterday (Ml 2.7);
at Ridgecrest (Ml 2.0) and near Calexico (Ml 2.1).

The real activity in the past past two days was occurring in the
Eastern and Central U.S. on the 40th parallel (i.e. 40N). The most unusual
event was a Ml 2.9 in Kansas near Norcater Kansas. This was the second
earthquake within 100 km of this epicenter since November 13, 2001 when a
Ml 3.3 occurred nearby. These were the first event so Ml>=2.8 in that region
since June 1986, and two of only 6 events which have ever been recorded in
that area.

Another unusual event occurred in Central Colorado about 100 miles
west of Boulder. This earthquake of Ml 3.3 was the largest within
50 km of this epicenter since March 31, 1974 and the fifth largest ever
recorded in that region (the others were in 1966 (Ml 4.0); 1967 (Ml 3.8);
1971 (Ml 4.4) and 1974 (Ml 3.5).

A third unusual event also occurred near the 40th parallel yesterday
in the region of Nevada. This was a Ml 2.9 near the Nevada/Utah Border.
This is the largest earthquake within 50 km of this epicenter since
August, 1988, although four events of Ml 2.8 have occurred in the intervening
14 years (in 12-90; 4-92; 9-92 and 12-98).

Finally, an earthquake was also listed in the New Madrid, MO region
of Ml 2.0 yesterday.

When unusual events occur in short succession across the Central U.S.
they occasionally precede a major event elsewhere. A small circle
from the Saturday events centers in the region about 21.3N 105.8W
on the coast of Jalisco, Mexico. This might be an area to watch
in the next week for a moderate or strong earthquake. It is equally
possible that this line of events is the result of strong recent
earthquakes (including a Mb 5.9 the day before this string appeared)
in the Afghanistan/Hindu Kush area. All of these are at the CM shadow
zone boundary from the lastest Hindu Kush earthquake, an area which
where earthquakes were expected as FFA from Hindu Kush. A further
possibility is effects from the Chile mainshocks. That FFA forecast
had stated:

"Plains States - Oklahoma, Kansas, So. Dakota
Each of these states has experienced one of it's strongest
felt earthquakes three days after a strong earthquake near the
Chile/Bolivia border. Although this event was smaller, a high
probability exists of a felt earthquake in the Central Plains
of the U.S. within 2 days of March 31, 2002."
No events of Ml>=3 were reported in Alaska or Hawaii today.

NEW ZEALAND

IGNS did not report on any new earthquakes today. The on-line
seismogram continued to show much cultural noise.

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 quiet today. An M3.7 solar
flare was observed early this morning and a second (M1.2) was observed
late this evening (UT). Following are the parameters for these
events:

Flare # START MAX END CLASS

770 2334 0014 0025 M3.7 April 14, 2002
1130 2305 2324 2341 M1.2 April 15, 2002

For general space weather conditions see:
http://sec.noaa.gov/today.html
For Solar flare data see:
http://sec.noaa.gov/ftpdir/indices/events/20020415events.txt

TIDAL EFFECTS

April 17 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:

No strongly damaging earthquakes have been recorded on April 16.

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 16 13 40 0 1899 40.500 -125.500 0 7.0 Off Coast of No. California
4 16 19 52 35 1925 22.000 121.000 60 7.1 Taiwan
4 16 3 1 37 1937 -21.500 -177.000 400 8.1 Tonga Islands
4 16 6 7 43 1940 52.000 173.500 25 7.1 Rat Islands
4 16 6 43 7 1940 52.000 173.500 25 7.2 Rat Islands
4 16 19 52 56 1951 31.000 137.000 500 7.0 Central/So. Honshu Japan
4 16 4 4 0 1957 -4.600 107.100 546 7.5 So. of Java
4 16 1 29 16 1963 -0.900 128.200 6 7.0 Ceram area
4 16 0 30 55 1996 -24.061 -177.036 111 7.1 Tonga Islands

U.S./CANADA

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

MO DA HR MN SC YEAR LATIT LONGIT DEP MW LOCATION

4 16 8 2 0 1895 48.000 -123.000 0 5.0 Washington state, U.S.
Many persons were frightened at Ft. Townsend, Washington.

4 16 13 40 0 1899 40.500 -125.500 0 7.0 Off Coast of No. California
4 16 14 30 40 1930 49.730 -129.330 0 5.5 Vancouver Island area
4 16 5 2 39 1961 39.340 -111.660 0 5.0 Utah area
Felt in Central Utah in central Sanpete County. Several towns
reported plaster cracked and damaged chimneys.

4 16 3 19 35 1964 57.200 -151.400 10 5.0 Southern Alaska
4 16 13 43 9 1964 52.090 -169.470 34 5.1 Fox Islands, Aleutians
4 16 19 26 57 1964 56.410 -152.900 25 6.6 Southern Alaska
4 16 20 12 37 1964 56.600 -152.800 33 5.0 Southern Alaska
4 16 21 25 46 1964 58.900 -148.800 33 5.2 Southern Alaska
4 16 8 1 46 1965 66.700 -135.600 33 5.0 Northern Alaska
4 16 23 22 19 1965 64.700 -160.100 5 5.9 Northern Alaska
4 16 1 27 15 1966 57.000 -153.600 33 5.7 Southern Alaska
4 16 5 33 18 1970 59.840 -142.430 7 6.8 Southeast Alaska
4 16 14 48 3 1973 51.123 -178.829 54 5.5 Andreanoff Islands, Aleutians
4 16 4 9 25 1993 56.670 -155.300 44 6.1 Alaska Peninsula
4 16 8 37 32 1994 52.400 -176.900 138 5.1 Andreanoff Islands, Aleutians

EARTHQUAKE LISTINGS

ASIA

O: 15APR2002 23:43:19 3.9N 126.6E MS=4.2 GSR TALAUD ISLANDS, INDONESIA

O: 15APR2002 03:52:06 13.1N 143.8E MB=5.6 NEI SOUTH OF MARIANA ISLANDS

O: 14APR2002 05:58:30 14.1N 144.6E MB=5.0 GSSC MARIANA ISLANDS
Note: This event was expected as an FFA from Northern and Central Chile.

The Central Chile FFA forecast had read:

"The most likely events of Mw>=5 in the next 10 days appear to be:

Guam/Central Mariana Islands"

and

"142-146 degrees: ...Central Mariana Islands, Guam"

O: 16APR2002 02:46:06 24.9N 122.0E ML=4.5 TAI Ilan, Taiwan
O: 15APR2002 00:08:05 24.4N 122.0E ML=4.7 TAI Ilan, Taiwan
O: 15APR2002 01:44:09 24.5N 121.9E ML=4.7 TAI Ilan, Taiwan

O: 14APR2002 16:08:24 24.8N 121.9E MB=4.0 NEI TAIWAN

O: 12APR2002 05:04:52 22.5N 102.8E MB=4.5 NEI YUNNAN, CHINA

O: 13APR2002 18:18:25 28.5N 139.6E MB=3.9 NEI BONIN ISL, JAPAN REGION

O: 13APR2002 13:27:13 18.2N 120.7E MB=5.0 NEI LUZON, PHILIPPINES

O: 13APR2002 06:58:23 29.0N 51.1E MB=4.6 NEI SOUTHERN IRAN

O: 13APR2002 06:06:14 6.6S 130.0E MB=4.9 NEI BANDA SEA

O: 13APR2002 06:18:17 53.1N 159.6E MB=4.7 NEI NEAR E COAST OF KAMCHATKA
O: 13APR2002 02:44:15 51.6N 159.2E MB=4.1 NEI OFF E COAST OF KAMCHATKA

O: 15APR2002 00:13:06 5.4S 104.2E MB=4.7 NEI S SUMATERA, INDONESIA

O: 15APR2002 06:10:50 41.6N 141.8E MB=3.9 NEI HOKKAIDO, JAPAN REGION

O: 13APR2002 12:43 43.8N 147.4E Mj=3.7 NIED E_OFF_HOKKAIDO, Japan

O: 13APR2002 07:54 37.1N 138.8E Mj=3.9 NIED MID_NIIGATA_PREF, Japan

O: 11APR2002 14:16 34.9N 137.1E Mj=4.3 NIED MIKAWA_BAY_REGION, Japan

SOUTH PACIFIC ISLANDS

O: 14APR2002 06:24:41 21.8S 179.6W MB=4.1 NEI FIJI ISLANDS REGION

O: 14APR2002 09:48:10 16.4S 173.5W MB=4.3 NEI TONGA ISLANDS

O: 11APR2002 08:03:48 6.2S 151.0E MB=4.6 NEI NEW BRITAIN REGION, P.N.G

O: 13APR2002 22:45:01 13.2S 167.2E MB=4.8 NEI VANUATU ISLANDS

CARIBBEAN/CENTRAL/SOUTH AMERICA

O: 15APR2002 08:57:49 16.9N 100.1W ML=3.9 SSN COSTA DE GUERRERO, MEXICO
O: 14APR2002 18:57:23 16.9N 100.1W ML=3.8 SSN COSTA DE GUERRERO, MEXICO
O: 14APR2002 04:18:56 16.9N 100.1W ML=3.3 SSN COSTA DE GUERRERO, MEXICO

O: 15APR2002 12:15:05 34.9S 70.3W MB=4.1 DGF Talca, Chile

O: 15APR2002 01:27:41 34.9S 71.9W MB=4.2 DGF Licantén, Chile
O: 15APR2002 12:48:54 35.2S 71.7W MB=4.1 DGF Talca, Chile

O: 14APR2002 04:18:56 16.9N 100.1W ML=3.3 SSN COSTA DE GUERRERO, MEXICO

O: 13APR2002 23:21:40 16.2N 96.0W ML=3.9 SSN OAXACA, MEXICO

O: 14APR2002 04:01:52 17.3N 100.3W ML=3.4 SSN GUERRERO, MEXICO

O: 13APR2002 19:22:02 13.8N 92.5W ML=4.9 SSN COSTA, MEXICO

O: 13APR2002 19:05:59 16.2N 95.2W ML=4.7 SSN OAXACA, MEXICO

O: 15APR2002 10:14:32 10.9N 86.4W MB=4.4 NEI OFF COAST OF COSTA RICA

O: 14APR2002 20:27:27 16.3S 72.5W MB=4.7 NEI NEAR COAST OF PERU

O: 15APR2002 05:08:57 9.5S 79.0W MB=4.8 NEI OFF COAST OF NORTHERN PER

O: 15APR2002 23:08:27 20.5S 68.3W MS=4.6 GSR CHILE-BOLIVIA BORDER REGI

O: 15APR2002 09:18:32 10.9N 87.7W MC=3.7 SIS Nicaragua, Central America

O: 15APR2002 10:14:24 9.9N 86.3W ML=3.8 SIS Nicaragua, Central America

NEW ZEALAND

OCEANIA

O: 14APR2002 06:36:02 16.7N 44.8W Ms=3.8 GSSC NORTHERN MID-ATLANTIC RIDGE
Note: This event was not forecast, however it was expected as a
FFA from both the northern Chile and the mainshock south of Australia.
It lies at the IOC boundary from Australia (145 degrees) and at 45 degrees
from Northern Chile. The FFA forecasts had said:

From the South of Australia event:

" The most prominent locations appear to be ...
North mid-Atlantic regional events .."

And from Chile we read:

"The most likely events of Mw>=6 in the next 10 days appear to be:
(Number in paranthesis indicated number of times and event of M>=6
has followed a Chile/Bolivia mainshock within 2-3 weeks).

...Northern Atlantic - especially ridge events"

and

"43-45 degrees: ... No mid-Atlantic Ridge (20N 45W)"

O: 15APR2002 07:11:26 59.9S 26.6W MB=4.7 NEI SOUTH SANDWICH ISL REGION

O: 14APR2002 22:38:13 14.7S 66.3E MB=4.6 NEI MID-INDIAN RIDGE
O: 14APR2002 19:21:35 7.9S 67.9E MB=4.5 NEI MID-INDIAN RIDGE
O: 14APR2002 02:46:19 20.0S 67.2E MB=4.5 NEI MID-INDIAN RIDGE

O: 14APR2002 11:17:02 12.0N 44.0W MB=5.0 NEI N MID-ATLANTIC RIDGE
O: 14APR2002 06:35:41 15.0N 44.9W MB=4.7 NEI N MID-ATLANTIC RIDGE

EUROPE/MIDDLE EAST/AFRICA

O: 14APR2002 22:23:39 40.6N 50.0E MB=3.9 NEI EASTERN CAUCASUS

O: 15APR2002 08:10:06 34.8N 24.5E MB=4.9 NEI CRETE, GREECE

O: 15APR2002 03:14:49 38.5N 27.0E ML=3.4 KAN MENEMEN, TURKEY

U.S/CANADA

CALIFORNIA/NEVADA

O: 14APR2002 23:01:40 38.8N 122.8W MD=2.8 NEI NORTHERN CALIFORNIA

O: 14APR2002 23:24:17 35.6N 117.9W ML=2.0 SCSN W of Ridgecrest, CA

O: 15APR2002 22:57:00 38.8N 122.8W ML=3.4 NCSN N of The Geysers, CA
O: 14APR2002 23:03:00 38.8N 122.8W ML=2.0 NCSN ENE of The Geysers, CA
O: 16APR2002 01:07:59 38.8N 122.7W ML=2.0 NCSN ESE of The Geysers, CA
O: 14APR2002 16:01:40 38.8N 122.8W ML=2.8 NCSN ENE of The Geysers, CA

O: 16APR2002 03:34:03 32.9N 115.5W ML=2.2 SCSN SSE of Brawley, CA
O: 16APR2002 03:49:20 32.9N 115.5W ML=2.7 SCSN S of Brawley, CA

O: 15APR2002 13:17:37 39.1N 114.2W ML=2.9 NEI NEVADA
O: 15APR2002 13:17:37 39.1N 114.2W ML=2.9 UUSN SE of McGill, NV

PACIFIC NORTHWEST/CANADA

O: 13APR2002 01:26:23 47.7N 120.1W ML=1.7 PNSN SSW of Chelan, WA

O: 14APR2002 13:20:13 46.5N 121.3W ML=1.8 PNSN ESE of Goat Rocks

O: 14APR2002 15:50:31 47.7N 122.0W ML=1.2 PNSN SSW of Duvall, WA

O: 14APR2002 22:23:09 47.6N 122.5W ML=1.5 PNSN NE of Bremerton, WA

ROCKY MOUNTAIN AREA

O: 12APR2002 01:26:53 39.1N 111.9W ML=2.9 NEI UTAH

O: 14APR2002 18:16:34 40.4N 106.9W ML=3.3 NEI COLORADO

O: 14APR2002 00:36:02 44.8N 111.0W ML=2.5 UUSN NNW of Madison Junc., WY

O: 14APR2002 20:16:09 44.4N 109.9W ML=2.2 UUSN ESE of Fishing Bridge, WY

EASTERN U.S./CANADA

O: 12APR2002 07:01:17 46.7N 74.1W MN=1.6 GSC N FROM STE-AGATHE-DES-MO

O: 14APR2002 03:35:02 39.9N 100.3W LG=2.8 NEI KANSAS
O: 13APR2002 22:35:02 39.9N 100.3W ML=2.8 CERI NW of Norcatur, KS

O: 14APR2002 13:14:16 36.0N 89.5W ML=2.0 CERI W of Dyersburg, TN
P: 25APR2002 8-04/22 36.7N 89.5W 2.0-3.2 DAAAA New Madrid

ALASKA

HAWAII