Posted by Lowell on September 25, 2001 at 23:06:06:
THE WINDS THEY ARE A'BLOWIN' SUMMARY A strong solar storm hit the earth this evening at 20:25 UT. Seismicity is expected to be affected in the western U.S. among other regions. Maximum Kp for this storm is thus far 6-7 making it a very strong storm. SEC is expecting periods of severe geomagnetic storms for the next two days. Hurricane Juliette is still tracking along the west coast of Mexico. This hurricane has now reach Class 5, the highest hurricane classification. For the moment, it appears it will continue to move offshore and not to make landfall. GLOBAL It was an active day in global seismicity. The largest event of the day occurred in the Bay of Bengal, India (Mb 5.5). This is the largest earthquake located in the Bay of Bengal (9-14N 77-83E) since a M 5.7 on July 3, 1867 (yes that is not a typo - 1867). and the second largest ever recorded in that region. The last event of Mb>=5 was an Mb 5.0 on July 29, 1972. The Bay of Bengal is situated on the geomagnetic equator where geomagnetic effects are greatly enhanced. The earthquake occurred while the area was under a seismic watch (within 20 degrees of 90E) from the geomagnetic storms of 23 September - the Bay of Bengal was sub-solar at the time of the commencement of that storm. The earthquake in the Bay of Bengal on July 29, 1972 was also associated with a strong geomagmetic storm on July 25-26, 1972. This storm preceded one of the most active periods every recorded on the sun beginning on July 30-31, 1972 and culminating with a massive geomagnetic storm on Aug. 4, 1972. The geomagnetic storms and solar flares of late July - early August 1972 were accompanied by an earthquake of Ms 7.6 on July 30 in southeastern Alaska, a Ms 6.2 (Aug 3) in the Andreanoff Islands; a swarm of large earthquakes in the Solomon Isl. (6.1, 6.1, 6.1, 6.2, 6.5; the Vanuatu Isl. (6.2); Samoa (6.1) Iceland, the Congo and the Arabian Sea among others. This is typical of seismic activity associated with extreme geomagnetic events. The storm of August 4, 1972 was the second largest geomagnetic storm since 1960, the largest (and the largest ever recorded) occurred on March 13, 1989. A strong earthquake (Mb 5.4) also occurred in the Leeward Islands, Caribbean this evening. This area has been quiet at this magnitude level since October, 2000 when a Mb 5.8 occurred near today's epicenter. This event lies slightly outside the seismic watch area which was 70-110 E and W. An earthquake (Ml 4.3) in Guatemala (along with two late on 23 Sept., however did lie within this watch area. Moderate earthquakes also occurred in southwestern Turkey (Ml 4.6) and the Aegean Sea (Ml 4.6) which were sub-solar at the time of the X-flare yesterday and the Kermadec Islands (Mb 5.0/5.6) which was anti-solar to that flare, all of which were under seismic watch today. U.S./CANADA Seismicity was up in the California/Nevada region today as expected following the recent geomagnetic and solar disturbances. Two events of Ml>=3 occurred in California in the Coso Junction /Olancha area. This is an area where seismicity commonly increases following geomagnetic storms, as previously noted. SCSN has reported 14 events of Ml>=2 in the two days since the end of the last geomagnetic storm. Compare this was the 5 earthquakes of Ml>=2 in the two days prior to that storm to get an idea of the effect. For SCSN listing see: http://www.scecdc.scec.org/scecusers/.plan Other earthquakes in California/Nevada today which exceeeded Ml 2.0 occurred south of San Luis Obispo (Ml 2.2, 2.6); at Bodie CA (Ml 2.6); at Ludlow (Ml 2.2) and Arvin (Ml 2.1). The swarm continued in the area near L.A. with events of Mlk 1.8, 1.8, 1.4, 1.4 and 1.2 today. The swarm of events under Mt. St. Helens WA is also continuing. Seismograms show that in addition to the Ml 1.4 and 1.2 listed events, a stronger event occurred there this evening. The swarm also continued offshore south of Vancouver Island. The largest earthquake in Alaska was a Ml 4.3 off the western coast in the Bristol Bay region. Earthquakes of this size are quite uncommon in the Bristol Bay area. This is the first earthquake of M>=4 recorded within 100 km of this epicenter since a Ml 4.7 on Sept. 2, 1988. There have been only 5 earthquakes recorded of M>=4 in this region in the past 100 years. The region was under seismic watch at the time of the earthquake from a X-class flare that had occurred while the region was sub-solar earlier on Sept. 25 (high latitude and within 35 degrees of 150W). The largest earthquake in the U.S./Canada on 24 September occurred in Ontario north of Lake Erie. A Ml 3.1 event hit SE of Elliot Lake ONT. This area was also under seismic watch from the geomagnetic storm of Sept. 23 (within 20 deg of 90W). This is the largest earthquake within 100 km of this epicenter since a Ml 3.5 on Dec. 18, 1984. Only 4 earthquakes have been recorded within 100 km of this event of Ml>=3. NEW ZEALAND Seismicity was also high in the New Zealand region, which was under seismic watch also from the X2.3 solar flare yesterday. A Ml 4.0 earthquake occurred south of Wanganui, North Island, and a Mb 5.0 was recorded by NEIS (5.6 GSSC) in the Kermadec Islands region. The on-line seismometer also shows a number of non-reported events in the region today. The IGNS on-line Seismometer can be found at: http://www.gns.cri.nz/news/earthquakes/latest_drum.html GEOMAGNETIC/SOLAR FIELDS A very strong sudden commencement geomagnetic storm began today at 20:25 UT. This storm has now lasted for 9 hours, so a seismic watch is being called for the region within 20 degrees longitude of the sub- and anti-solar locations at the time of the storm commencement. These areas are 126W and 54E. The areas covered include high latitudes and regions of western U.S. and Canada east to the plains and west to southern Alaska - these regions were sub-solar at the time of the sudden commencement. Anti- solar regions include areas of Turkey, Iran east to Afghanistan and along the East African Rift zone. Magnitudes of maximum expected events in these regions should be increased by up to 1.0 magnitude units over the next 4 days. The alert will cease 4 days after the end of the geomagnetic storm which is continuing at this time. In the California/Nevada region earthquakes occurred in the Ludlow (Ml 2.2), Gilroy (Ml 1.6) and the Geysers (Ml 0.9) regions within minutes of the onset of this storm. One strong M-class solar flare was identified on the sun today. The parameters are: Flare # START MAX END CLASS 8100 0424 0440 0452 M7.6 In California/Nevada earthquakes in Hawthorne, CA (Ml 1.8) (21:35 PST/04:35 UT) and Midway NV (Ml 1.1) occurred during this flare and may have been affected by it. For general space weather conditions see: http://sec.noaa.gov/today.html For Solar flare data see: http://sec.noaa.gov/ftpdir/indices/events/20010925events.txt For geomagnetic field details see: http://sec.noaa.gov/ftpdir/lists/particle/20010925_G10part_5m.txt TROPICAL STORMS Hurricane Humberto is currently at 40N 60W about 1500 km east of New York City. Tracking expects this storm to move into the Atlantic and to have no effect on the coastline. No seismicity is expected to be associated with this storm on the No. American continent. For tracking details see: http://www.wunderground.com/auto/HurricaneSite/tropical/tracking/at200110.html Hurricane Juliette is now a class 5 Hurricane with maximum sustained winds of 145 mph, gusts to 180 mph. It continues to track along the west coast of Mexico. By Thursday it should begin to weaken. Seismicity along the region of Jalisco and into the Gulf of California could be enhanced by the presence of this hurricane. For tracking details see: http://www.wunderground.com/auto/HurricaneSite/tropical/tracking/ep200111.html
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