Posted by Lowell on October 02, 2001 at 15:17:22:
MID-OCEAN RIDGE SEISMICITY REACHES HIGH LEVELS; UNUSUAL N. GEOMAGNETIC POLE EVENT OCCURS AT END OF POLAR ABSORPTION EVENT SUMMARY OCEAN RIDGE EVENTS: Long-term readers of this report will recall that we have commented on the association of mid-ocean ridge seismicity and strong geomagnetic storms on numerous occasions in the past three years. It is quite typical for strong mid-ocean ridge activity to follow geomagnetic storms by about 4-6 days. It may be a delay due to required expansion or heating in the mid-ocean ridge environment from ohmic heating or some other related cause. Ocean ridge events have occurred in the past 3 days as follows: South Atlantic: O: 29Sep2001 12:19:39 43.9S 17.2W MB=4.2 NEIS S MID-ATLANTIC RIDGE Central Atlantic: O: 30Sep2001 18:24:00 5.8N 32.8W MB=4.3 NEIS CENTRAL MID-ATLANTIC RIDGE East Pacific Rise: O: 30Sep2001 06:03:32 22.6S 113.5W MS=5.2 NEIS EASTER ISLAND REGION O: 29Sep2001 08:48:52 23.5S 111.6W MB=4.7 NEIS EASTER ISLAND REGION O: 29Sep2001 08:08:33 23.6S 111.9W MB=4.9 NEIS EASTER ISLAND REGION O: 29Sep2001 07:58:31 23.5S 111.7W MB=4.9 NEIS EASTER ISLAND REGION Antarctic-Indian Ridge: O: 02Oct2001 10:42:16 48.9S 121.4E MS=5.0 NEIS W INDIAN-ANTARCTIC RIDGE O: 02Oct2001 10:38:29 49.1S 121.5E MB=4.4 NEIS W INDIAN-ANTARCTIC RIDGE On average about one event is recorded on Mid-Ocean ridges during any given 4-day period (in NEIS catalog), so this represents a rate increase of about 8 times background. NORTH GEOMAGNETIC POLE EARTHQUAKE In the Arctic, in the region of the North Geomagnetic pole, which is currently located in the Islands of northern Canada at about 79N 110W (the geomagnetic pole actually extends over an area of several hundred km around this point) an earthquake (Ml 4.4) occurred on 1 October. This was the largest earthquake within 200 km of 79N 110W since Jan 1, 1999 when an event of Ml 5.3 occurred nearby. There have been 5 earthquakes recorded in this region since 1985 of Ml>=4.4, so this event has a recurrence time of about 4 years. The coincidence of this event with the polar proton absorption event is interesting and had been anticipated in this summary in the report of Sept. 23, 2001 which stated: "The Space Environment Center (SEC) is expecting strong solar and geomagnetic storms over the next several days. A polar absorption event is current taking place. When this happens, earthquakes at high latitudes (and often near the geomagnetic poles) are common, however activity elsewhere is often subdued until after the proton storm has passed. This temporary quiet is followed by strong seismic activity throughout many areas of the world." GSC gives the parameters of this event as: O: 01OCT2001 00:28:58 80.5N 115.8W ML=4.4 GSC QUEEN ELIZABETH SLOPE Source: http://www.seismo.nrcan.gc.ca/recent_canadian_eq/recent_canadian_eq_e.html A general summary of some earth-sun interactions can be found on the web at: http://solar-center.stanford.edu/sun-on-earth/sun-earth.html GLOBAL The largest event of the day was a Ms 6.2 in the Tonga Islands which was reported on last night. Earthquakes of Mb>=5 also occurred in the area east of Honshu, Japan (about 200 km N. of Tokyo) (MB 5.0); and in the region south of Tokyo (Mb 4.9). This activity off the east coast of Honshu started about a week ago, and appears to be getting stronger. Other activity was recorded south of Australia on the Western Indian-Antarctic Ridge (Mb 5.0, 4.4). This was an unusual event. In the 5.5+ years since January 1996, there have been 4 earthquakes recorded in the area within 200 km of today's epicenter with Mb>=5. The recurrence interval is thus about 1.5 years between such earthquakes. Two earthquakes in eastern Indonesia also occurred in the Mb5 range - a Mb 5.1 in the Banda Sea and a Mb 4.9 in the Savu Sea. U.S./CANADA The largest earthquake of the day in the lower 48 states occurred in eastern Idaho (Ml 3.3). This is the first aftershock of Ml>=3 in the area since a Ml 5.4 earthquake struck near this epicenter on April 21, 2001. The area has been fairly active at this level over the years with 246 events of M>=3 since 1960. Many of these have occurred in strong aftershock sequences in October, 1982 (22 events); November 1992 (22 events); and in the Aftonm WY sequcence of February 1994 (68 events). The mainshock was preceded by a small foreshock. Only one event of Ml>=3 occurred in the California/Nevada region today - a Ml 3.1 near Mammoth Lakes. This area has shown increased activity following the recent geomagnetic storms, a common occurrence in the region. Another region which was active today and which commonly becomes so during and after geomagnetic storms was the Geysers with events of Ml 2.3, 2.1, and 2.0. Slightly north a Ml 2.3 occurred near Willits, CA. A Ml 3.0 event in the Hector Mine aftershock zone also occurred late last night. During the month of September, 2001, this region had been nearly devoid of earthquakes. Staff at SCEC had expressed some concern that this might be a quiescence before a large aftershock. An earthquake in the Ml 2.5-3.0? range also occurred off the Coast of Oregon in the northwest. Microearthquakes continued in the Los Angeles region with events of Ml 1.6 (Pt. Dume), Ml 1.5 (Alhambra), Ml 1.6 (Valencia). No earthquakes of Ml>3 were recorded in either Alaska or Hawaii today. Likewise, the eastern and Central portions of North America were also quiet today. NEW ZEALAND IGNS did not report any significant activity in the region today. However, a number of small events did continue in the region and were recorded on the on-line seismometer. The IGNS on-line Seismometer can be found at: http://www.gns.cri.nz/news/earthquakes/latest_drum.html GEOMAGNETIC/SOLAR FIELDS The current active geomagnetic field continued today with a refreshened storm from 03:00 UT to 12:00 UT. This tends to reinforce the seismic watch currently in effect. No changes in this watch are currently needed. A minor solar flare of M1.4 occurred today. The parameters are: Flare # START MAX END CLASS 690 + 1012 1021 1057 M1.4 No seismic activity has been reported at the time of this flare yet. For general space weather conditions see: http://sec.noaa.gov/today.html For Solar flare data see: http://sec.noaa.gov/ftpdir/indices/events/20011002events.txt TROPICAL STORMS The only tropical storm currently affecting North America is tropical Depression Juliette which is currently stalled at the northern end of the Gulf of California. Seismicity in this region may be slightly affected. For tracking details see: http://www.wunderground.com/auto/HurricaneSite/tropical/tracking/ep200116.html
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