Earthquake Summary for October 21, 2001

Earthquake Summary for October 21, 2001

Posted by Lowell on October 21, 2001 at 13:44:18:

GROUND MOTION OBSERVED WITH STRONG GEOMAGNETIC STORM TODAY

It is not generally known that ground motion is associated with
the onset of strong geomagnetic storms. The geomagnetic storm which
started at 16:48 UT is being well recorded on many high-latitude
seismometers. To see the associated ground motion look at the following
seismographic records on the USGS on-line seismograms at:
URL:
http://aslwww.cr.usgs.gov/Seismic_Data/heli2.htm

GT/VNDA - undulatory motion beginning at 16:48 (Antarctica)
COLA - strong undulatory motion beginning at 16:49 (College Alaska)
IU/KBS - strong undulatory motion beginning at 16:50 (Spitzbergen Norway)
KONO - strong undulatory motion beginning at about 18:00 (Norway)
There is an unexplained delay in this motion
SNZO - strong Undulatory motion beginning at 16:48 (New Zealand)
SPA - undulatory motion beginning at 16:48 (South Pole)
TIXI - very strong undulatory motion beginning at 16:48 (Siberia)
ULN - strong undulatory motion beginning at 16:46 or 16:47 (Mongolia)
YAK - strong undulatory motion beginning at 16:49 (Siberia)

Also see the PGC broad-band seismometer at:
http://www.pgc.nrcan.gc.ca/seismo/seismos/24hr-PGC.LHZ.shtml

So those looking for a physical mechanism by which sudden commencement
geomagnetic storms may trigger earthquakes need look no further than
these seismograms for related ground motion which could trigger
additional seismic activity.

STRONG EARTHQUAKE (MW 6.8) HITS OFF EAST COAST NORTH ISLAND, NEW ZEALAND
FAR-FIELD AFTERSHOCK FROM NEW ZEALAND/GUAM/BANDA SEA PROMINENT

SUMMARY

A strong (Mw 6.8) earthquake struck off the east coast of North
Island, New Zealand yesterday. Details of triggering and expected
far-field aftershocks from this event were presented in the
far-field aftershock forecast and will not be restated here.
Many factors favorable for a large quake in this area at this
time were in effect at the time of this event. These included
far-field triggering. geomagnetic, tidal triggers.

The preliminary NEIS parameters are given as:

O: 21Oct2001 00:29:23 37.0S 179.0E MS=6.8 NEIS OFF E. COAST N. ISL, N.Z.
Note (IGNS): Reported felt at Whakatane. Also likely to have been felt
widely on the Raukumara Peninsula.
A number of moderate aftershocks have already been recorded
with this shock.

This is the second largest event in this general region since a Mw 7.5
on 5 Feb. 1995 and the third largest event ever recorded within
200 km of this epicenter. A Ms 7.0 occurred about 100 km to the
east on August 21, 2001. This may be a regional aftershock of that
event. Other events of Mw>6.7 have occurred on:
Oct 6, 1914 (Mw 6.5), Sep. 22, 1930 (Mw 6.5); Sept 21, 1931 (Mw 6.8);
Feb 13, 1938 (Mw 6.5); Apr 23, 1951 (Mw 6.7); Feb 5, 1995 (Mw 7.5);
and Feb 10, 1995 (Mw 6.5).

Far-field aftershocks have occurred in the Molucca Sea (Mb 5.7);
Halmahera (Mb 5.0) (both at 60-62 degrees); the Alaska Peninsula (Mb 4.2)
and the Fox Islands (Mb 4.6).

GLOBAL

A Mb 5.0 was also recorded in Kamchatka yesterday as an aftershock
of the Mw 6.5, 6.4 earthquakes of October 8. Two moderate aftershocks
of the Banda Sea earthquake were also recorded (SR 5.5 and 5.9).
An earthquake of Mb 4.9 was also recorded in the Minahassa Peninsula
this afternoon.

U.S./CANADA

The strongest activity in the U.S./Canada region since the
last report occurred in the Alaska Peninsula/Fox Islands region
with a Mb 4.2 in the Unimak Is. area followed about 2.5 hours later
by a Mb 4.6 in the Fox Islands, Aleutians. These events were probably
far-field aftershock from recent large global earthquakes.
The California/Nevada area has remained very quiet. Three events
of Ml>=2 have occurred since last report - a Ml 2.7 north of the
Geysers and SW of Ukiah, northern California and two events (Ml 2.2, 2.4)
in the Coso Junction, CA area.
About 3 minutes after the New Zealand earthquake a Mb 2.4 was recorded
in the Challis, Idaho area. This was not an FFA as information from
the New Zealand quake could not have arrived at Idaho in the intervening
3 minutes (the p-wave would arrive about 9 minutes later).
Most other networks in the U.S. and Canada are not reporting events today
as it is a weekend and personnel are not available.

NEW ZEALAND

IGNS is reporting the major shock off the northeast Coast as
an aftershock of the event on August 21, 2001 in approximately
the same epicentral zone as that event. This is contrasted with
locations from both Obninsk, Russia (GSSR) and Golden, Colorado (NEIS)
giving the location about 150 km to the west of the IGNS epicenter.
A number of aftershocks in the Ml>=4 range have been recorded
on the IGNS on-line seismometer, but no regional triggering is
yet known.

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

GEOMAGNETIC/SOLAR FIELDS

A strong sudden commencement storm arrived at about 16:48 UT
today (October 21, 2001). This is the first expected arrival of the
CME from the X-flares of two days ago. Areas which were sub-solar
at the time of the commencement are at 72 +/- 20 degrees W longitude
or anti-solar areas are at 108 +/- 20 degrees E longitude. These
regions are expected to see increased seismic activity for the next
4 days with strong events possible on Oct. 25-27. Areas at high
latitudes (45+ degrees) and along the geomagnetic equator may
also show increased seismicity if the storm continues for at least
9 hours. For details see:
http://sec.noaa.gov/ftpdir/lists/geomag/20011021_G8mag_1m.txt
Two M-class flares were observed on the sun today with the
following parameters:

Flare # START MAX END CLASS

5120 + 0509 0518 0527 M1.3
5180 + 1112 1136 1148 M2.5

A microearthquake (Ml 0.8) was recorded near Palomar Observatory,CA
during evnet #5180. No seismicity has been reported associated
with the beginning of the geomagnetic storm nor with Flare # 5120
at this time.

For general space weather conditions see:
http://sec.noaa.gov/today.html
For Solar flare data see:
http://sec.noaa.gov/ftpdir/indices/events/20011021events.txt

Also see the PGC broad-band seismometer at:
http://www.pgc.nrcan.gc.ca/seismo/seismos/24hr-PGC.LHZ.shtml

TROPICAL STORMS

Tropical Storm Narda continues moving towards Hawaii where
it may arrive on Thursday. Increased seismic activity in Hawaii
may occur around October 23-26. Hawaii is also at far-field
triggering locations from several recent large events, so a
moderate-sized event may occur there in the next week.
For tracking details of Narda see:
http://www.wunderground.com/auto/HurricaneSite/tropical/tracking/ep200121.html

In the western Pacific, Podul has reached Typhoon status and is
about miles east of Guam and tracking to the northwest. No seismically
active areas lie in the immediate path, however if Podul continues
on it's current course, it may encounter the Volcano Islands and
eventually Honshu.
For a public advisory on Typhoon Podul see:
http://www.wunderground.com/auto/HurricaneSite/tropical/wp200101.public.html

TIDAL TRIGGERING (LUNAR)

Statistics have been done on many regions of the world in terms of
relationship of significant regional earthquakes with respect to lunar cycle.
Each report will summarize the most likely areas for tidal triggering
for the next day based on these statistics. It is expected
that tidal triggering will add an additional 0.5 - 1.0 units of
magnitude to events which are about to occur or will move these
events forward in time by up to seven days in the regions where
there is a statistical correlation between lunar phase and
earthquakes.

October 22 is six days after the beginning 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

Indian Ocean MB>=4.0 17 2.1 0.05
Kamchatka MB>=4.0 35 2.6 0.03

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

Global MB>=6.0 -17 -2.8 0.02
West Pacific MB>=4.0 -20 -1.9 0.05
Yellowstone MB>=0.0 -19 -2.0 0.05
Puerto Rico MB>=4.0 -17 -1.9 0.05

EARTHQUAKE LISTINGS

GLOBAL

NEW ZEALAND

O: 21Oct2001 00:29:23 37.0S 179.0E MS=6.8 NEIS OFF E. COAST N. ISL, N.Z.

ASIA

O: 21OCT2001 19:03:27 1.6N 123.1E Ms=4.9 GSSC MINAHASSA PENINSULA,
Note: This event is located at 60 degrees from Kamchata, and is
probably an FFA of that event.

O: 21Oct2001 03:40:18 1.9N 126.5E MB=5.7 NEIS NORTHERN MOLUCCA SEA
O: 21OCT2001 03:40:17 1.9N 126.3E Ms=5.1 GSSA NORTHERN MOLUCCA SEA
Note: This is probably and FFA from New Zealand and perhaps Kamchatka.
The epicenter lies at 62 degrees from New Zealand and at 58 degrees
from Kamchatka.

O: 21OCT2001 12:36:49 3.7N 128.5E Ms=4.5 GSSC NORTH OF HALMAHERA, I
Note: This is probably an FFA from New Zealand and Banda and Guam.
It lies at at 62 degrees from New Zealand, 9 degrees from the Banda Sea quake
and 18 degrees from Guam. All are distances where FFAs are expeceted.
In particular the New Zealand forecast had said:

"In general, areas which appear to consistently have moderate to

strong earthquakes in the 10 days following Ms 7+ earthquakes in
this area of New Zealand are:

Halmahera/Molucca 2-5N 126-129E"

and from Guam:

"17-19 degrees: .... Halmahera"

and from the Banda Sea:

"0-5 degrees: Regional triggering- ...Moluccas, Halmahera"

O: 20OCT2001 23:09:23 52.7N 160.5E Ms=4.3 GSSC OFF E. CST KAMCHATKA

O: 21OCT2001 05:27:16 4.0S 140.1E Ms=4.5 GSSC IRIAN JAYA, INDONESIA
Note: This may be a far-field aftershock from both Kamchatka, Guam and
the Banda Sea. It lies at 17 degrees from Kamchatka and the Banda Sea
and at 59 degrees from Kamchatka, all distances where FFAs are expected.
The Banda Sea forecast had said:

"17-19 degrees: ... Papua New Guinea (140-141E)"

and

"Secondary location where event tend to occur but are not
as large or as likely . MB>=4.8 considered likely in next
10 days.

...West Irian/Papua New Guinea"

From the Kamchatka forecast:

"59-61 degrees: ...New Britain/Papua, West Irian New Guinea"

and

"The most likely events of M>=5 in the next 10 days on the
basis of history and far-field triggering theory appear to be:

...Papua, West Irian New Guinea"

and from Guam:

"17-19 degrees: ...east Papua New Guinea"

O: 20OCT2001 20:47:20 4.1S 124.0E SR=5.5 AEIC1 NE RAHA , INDONESIA
O: 20OCT2001 19:17:50 4.0S 124.0E SR=5.9 AEIC1 NE RAHA , INDONESIA

EUROPE

O: 20OCT2001 23:10:58 35.5N 26.6E ML=3.9 NOA GREECE

U.S/CANADA

CALIFORNIA/NEVADA

O: 21OCT2001 7:32:59 36.0N 117.8W ML=2.2 NCSN ESE of Coso Junction, CA
O: 21OCT2001 7:32:52 36.0N 117.8W ML=2.4 NCSN ESE of Coso Junction, CA

O: 21OCT2001 3:44:15 39.0N 123.4W ML=2.7 NCSN SW of Ukiah, CA

ROCKY MOUNTAIN AREA

O: 21Oct2001 00:33:23 44.3N 114.3W ML=2.4 NEIS WESTERN IDAHO

O: 21OCT2001 03:13:50 45.7N 112.1W MD=1.4 MBMG MONTANA

O: 21OCT2001 13:50:23 46.9N 112.3W MD=0.9 MBMG MONTANA

ALASKA

O: 21Oct2001 12:16:59 55.6N 162.4W MB=4.1 NEIS ALASKA PENINSULA
O: 21OCT2001 12:17:05 55.3N 162.0W ML=4.2 AEIC NNE of King Cove, Alaska
Note: This is probably a FFA from Guam as it lies at 59 degrees from
that mainshock.
The Guam forecast had noted:
"59-61 degrees: Alaska Peninsula (Unimak area)"
This event was followed less than three hours later by a second Ms 4.5
(see next event) to the west in the Fox Islands.

O: 21Oct2001 14:40:10 52.7N 166.9W MB=4.6 NEIS FOX ISL, ALEUTIAN ISLANDS
O: 21OCT2001 14:40:16 53.4N 167.3W Ms=4.5 GSSC FOX ISLANDS, ALEUTIAN
Note: Activity following the New Zealand earthquake was expected in
the Central Aleutians because of the orientation of the subuction zone
there wrt incoming seismic waves from New Zealand. The far-field
New Zealand forecast had stated:

" Alaska Peninsula/Southern Alaska

While the distance is 90 degrees, wave fronts hit the Central
San Andreas parallel to the fault. This can cause larger events
to occur in the Central California region following strong events
in this area of New Zealand. A similar effect may be observed
along the Central Andreanoff Islands where strong triggering potential
from the Banda Sea also exists."

This epicenter also lies 19 degrees from the Kamchatka earthquakes
and may be an FFA from those events. That forecast had said:

"17-19 degrees: Fox Islands"

and

"Areas of U.S. and Canada where triggering may occuR (Ml>=4.5)

Fox Islands/Unimak Islands"

P.S. The summary today is a bit early so I could get this out before/if
activity increases considerably (and I can take the rest of the day off)