Posted by Lowell on April 26, 2002 at 16:05:45:
FAR-FIELD AFTERSHOCK FORECAST FOR SOUTHERN MARIANA ISLAND MS7.1 (PRELIMINARY) (APRIL 26, 2002) A strong earthquake occurred today in the Southern Mariana Islands about 50 km south of Guam (Guam is at 13.5N 144.8E). Preliminary estimates place the magnitude at 7.2 or greater (NEIS, GSSC). The earthquake had been well forecast. The parameters of this earthquake (NEIS) are given as: O: 26APR2002 16:06:06 13.1N 144.5E MW=7.2 NEIS MARIANA ISLANDS
Seismicity is expected to increase in areas where seismic energy from the great shocks is concentrated due to internal reflections and refractions of waves off internal boundaries. There have been 8 earthquakes of Mw>=7 recorded in the are 12-15N 140-150E in the past century. The largest occurred last year on October 12, 2001 as a Mw 7.0. The epicenter of this earthquake was very near the same as today's (12.8N 144.9E) so this may be considered an aftershock of that event. It is likely to have occurred on the same asperity and ruptured in a different direction. The event of 2001 had a depth of 60 km, today's depth was nearly the same (50-70 km). Other earthquakes of Mw>=7 in the region occurred on Aug 8, 1983 (Mw 8.3); Nov 1, 1975 (Mw 7.1); May 25, 1950 (MB 7.3); June 14, 1942 (MW 7.0); Jan 28, 1931 (Ms 7.2); and a series of three between 1909 and 1913 (Mw 8.0 - Dec. 9, 1909; Mw 7.0 - Oct 26, 1912; and Mw 7.1 - July 18, 1913)) WARNING SIGNS FAR-FIELD AFTERSHOCKS FROM KAMCHATKA AND CHILE Two moderate foreshocks in the southern Marianas occurred over the past two days of Mb 4.7 and 4.5. Last night a moderate Mw 5.8 earthquake was located in the Kamchatka peninsula region. Today's Guam earthquake falls at 43 degrees from the Kamchatka event, at 108 from the Guerrero, Mexico earthquake and at 144 degrees from the Chile (Mw 6.7) event of April 18. The epicenter was therefore at a triple junction of FFA effects. No FFA forecast from the most recent Kamchatka event had been produced, however a previous Kamchatka FFA forecast (October 8, 2001) had stated: "Secondary location where event tend to occur but are not as large or as likely . MB>=4.8 considered likely in next 10 days. .....Central and northern Mariana Isl." The Kamchatka event appears to be the immediate trigger for this earthquake, however effects from Chile and Mexico were likely to have made the event larger. The FFA forecast from Chile and Mexico (April 18, 2002) had noted: (From Chile) "The following areas are expected to see increased seismicity from April 19 through April 29, 2002. Maximum event size for these regions is expected to increase by 0.5 to 0.7 magnitude units in this period. ... 142-146 degrees:... Central Mariana Islands, GUAM" GEOMAGNETIC STORM AND SOLAR FLARE (X1.5) The summary report from April 20 had placed the region under seismic watch for the next three days. The sub-solar longitude at the time of the X1.5 flare on April 21 had been 170E. The warning was issued for longitudes within 30 degrees longitude of this and especially at high latitudes and along the geomagnetic equator. Guam lies on the geomagnetic equator, Kamchatka, another triggered area is at high latitudes, both lie within the warning region. The warning notice had read: " The strongest solar flare since Oct 22, 2001 hit about an hour ago just as the strong geomagnetic storm was returning to quiet conditions. A strong proton storm followed this flare. Sub-solar latitudes at the time of the flare were about 170E, anti-solar locations at 10W. Areas within about 30 degrees longitude of either of these longitudes will experience the greatest effects from this flare and are under seismic watch conditions for the next two days. High latitudes and areas along the geomagnetic equator are also likely to see increased seismicity in the next two days. The effect of this flare is uncertain coming at the end of a strong geomagnetic storm. Many of the events which were ripe for geomagnetic triggering have already had earthquakes. Nevertheless, strong earthquakes could still accompany these storms and this X1.2 flare between April 21 and April 25. This watch includes areas of New Zealand, Kermadec, Tonga, Samoa, the Aleutians and western Europe." Note that in addition to the Guam earthquake, moderately strong earthquakes have occurred in the past two days in the Kermadec Islands, Tonga, Aleutians, and western Europe as well. The timing of large events related to the geomagnetic storm and Solar flare had likewise been discussed in the daily summary (April 21, 2002). That summary had noted: "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. ... 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." Note that this and the Kamchatka event fit this scenario quite well. This was re-emphasized in the April 22 Daily Summary: "... The loss of the buffering protons and the new geomagnetic storm may bring back moderate to strong seismicity in many areas." and on April 24: " Delayed effects from the recent strong geomagnetic storms were probably important in the timing of the Balkans and the Andreanoff Islands earthquakes today. STRONG EVENTS OFTEN FOLLOW X-CLASS SOLAR FLARES 3-5 DAYS LATER IN SUB- AND ANTI-SOLAR REGIONS." (Emphasis added) FAR-FIELD FORECAST
Seismicity is expected to increase the maximum magnitude event in the following regions by 0.5-1.0 magnitude units over previous estimates. 0-5 degrees: Regional aftershocks in the Guam/Caroline Islands region 9-10 degrees: Volcano Islands (21-23N) 17-19 degrees: So. of Honshu, Ryukyu Isl, Samar, Mindanao, Philippines, Halmahera, New Britain, east Papua New Guinea 34-36 degrees: Flores, Central Vanuatu Isl, Timor Sea, Sumbawa, Southern Kuril Isl. 43-45 degrees: W. Sumatera subduction zone, Myanmar, Kamchatka, Western Aleutians, Loyalty Islands 59-61 degrees: Alaska Peninsula (Unimak area), Hawaii, South Island, southern North Island, New Zealand, Nepal, Xizang, China. 71-73 degrees: Yukon/Alaska border, Pakistan, No. Carlsberg Ridge Macquarie Islands 103-107 degrees***: New Madrid, Jalisco coast Mexico, Red Sea, Aegean Seam, Romania, western Turkey, Northern Germany, Iceland 142-146 degrees: Chile/Argentina border (around 30S), northern Chile subduction zone, Peru aftershock zone, Trinidad, eastern Venezuela, Windward Islands 176-180 degrees: Off Atlantic Coast of Brazil (Aseismic area 13.0S 35.0W) ***: The strongest triggering is always expected to be along the shadow zone boundary between 103-107 degrees from the epicenter. Lowell Whiteside April 26, 2002 Historical following quakes after large events in the Guam region: MAIN: Dec 9 1909 12.5N 145.0E 100 MW=8.0 AFTEREVENTS Dec 10 45N 75W Ml 3.7 Southern Quebec, Canada Dec 13 45N 16E Ml 4.9 Austria Dec 14 33N 80W Ml 2.7 South Carolina Dec 19 46N 60W Ml 5.0 East of Nova Scotia, Canada MAIN: OCT 26 1912 14.0N 146.0E 130 MW=7.0
AFTEREVENTS Oct 31 7N 138E Mw 7.4 Caroline Islands Nov 03 24N 122E Ms 6.0 Taiwan Nov 06 39N 74W Ml 3.5 Pennsylvannia Nov 07 57N 155W Ms 7.5 Kodiak Island region MAIN: MAY 18 1913 14.5N 145.5E 60 MW=7.1 May 19 63N 21W Mb 5.5 Iceland May 20 52N 106E Mb 5.2 Lake Baykal, Russia May 20 45N 14W Mb 4.0 Austria May 21 36N 141W Mb 6.0 Off E. Coast Honshu May 29 36N 141W Mb 6.4 Off E. Coast Honshu May 30 5S 154E Ms 7.5 New Britain Jun 06 33N 80W Ml 2.4 South Carolina Jun 08 45N 74W Ml 3.7 So. Quebec, Canada Jun 14 43N 25E Ms 7.5 Romania/Bulgaria AFTEREVENTS MAIN: JAN 28 1931 11.0N 144.8E 60 MW=7.2 AFTEREVENTS Jan 30 36N 140E Mb 4.6 Off East Coast Honshu Jan 30 19N 155W Mb 4.0 Hawaii Jan 31 25N 101E Mb 5.0 Myanmar Feb 2 39S 177E Ms 7.9 North Island, N. Z. Feb 5 35N 106W Mb 5.0 New Mexico/Arizona Feb 7 13N 87W Mb 5.7 El Salvador Feb 8 39S 177E Ms 6.8 North Island, N. Z. Feb 10 5S 103E Ms 7.1 South of Sumatera Feb 13 25N 122E Ms 6.0 Ryukyu Islands/Taiwan Feb 13 39S 177E Ms 7.1 North Island, N. Z. Jan 30 36N 140E Mb 4.6 Off East Coast Honshu MAIN: JUN 14 1942 15.0N 145.0E 80 MW=7.0
AFTEREVENTS Jun 14 42N 70W Ml 3.1 New York Jun 14 33N 116W Ml 4.0 So. California Jun 15 32N 141E Mb 5.2 So. of Honshu Jun 15 31S 180W Ms 6.8 Kermadec Is. N.Z. Jun 15 18N 106W Mb 5.0 Jalisco, Mexico Jun 16 34N 26E Mb 5.6 So. of Greece Jun 16 40N 28E Mb 5.6 Istanbul, Turkey Jun 16 1N 80W Mb 6.1 Ecuador Jun 18 9N 140E Ms 7.1 Caroline Islands Jun 19 42N 146E Mb 5.8 Southern Kuril Isl. Jun 20 19N 101W Ms 6.8 Guerrero, Mexico Jun 21 36N 27W Ms 6.5 Aegean Sea/Turkey Jun 22 34N 118W Ml 3.0 Los Angeles, CA Jun 22 36N 118W Ml 4.0 Coso Juntion swarm (many quakes in Ml 4+ range) Jun 24 41S 176E Ms 7.2 North Island, New Zealand (Many aftershocks of Ml 4-6) Jun 27 37S 177E Ms 6.4 North Island, New Zealand Jun 29 33S 71W Ms 6.9 Central Chile coast MAIN: MAY 25 1950 12.6N 143.7E 90 MW=7.3 AFTEREVENTS May 25 41S 172E Mb 4.5 South Island, New Zealand May 26 32N 169E Mb 7.2 Loyalty Islands May 27 41N 142E Mb 4.9 Hokkaido May 27 18S 178W MS 6.8 Tonga Islands May 28 34N 118W ML 3.0 Los Angeles, CA May 26 32N 169E Mb 5.6 So. of Honshu, Japan May 29 41S 123W Mb 3.9 Northern California May 30 19N 156W Mb 6.3 Hawaii May 30 37S 178E Mb 5.5 North Island, N.Z. May 30 20S 179W Ms 6.4 Tonga Islands May 31 30S 132E Ms 6.1 So of Honshu, Japan Jun 01 41N 123W Ml 4.2 Northern California Jun 02 36N 121W Ml 3.6 Pinnacles, California Jun 03 36N 118W Mb 3.2 Coso Junction, CA Jun 04 36S 178E Mb 6.6 North Island, New Zealand Jun 06 4S 77W Mb 6.8 Ecuador Jun 08 47S 15W Mb 7.1 So. Atlantic Ocean Jun 11 57S 148E Mb 6.4 Macquarie Ridge MAIN: NOV 1 1975 13.8N 144.7E 113 MW=7.1
Nov 1 12N 125E Mb 5.5 Samar, Philippines Nov 1 17S 172W Mb 5.4 Tonga Islands Nov 2 68N 19W Mb 4.5 Iceland Nov 3 44N 74W Ml 4.0 New York Nov 6 19N 155W Mb 4.5 Hawaii Nov 11 41N 144E Mb 5.4 Hokkaido Nov 15 18N 102W Mb 5.9 Michoacan, Mexico Nov 15 12N 126E Mb 6.0 Samar, Philippines AFTEREVENTS MAIN: AUG 8 1993 12.9N 144.8E 59 MW=8.2 AFTEREVENTS Aug 9 36N 71E Mw 6.4 Hindu Kush (Followed by a Mw 7.0) Aug 10 45S 167E Mw 7.1 South Island, N.Z. Aug 10 38S 177E Mw 6.4 North Island, N.Z. Aug 11 37S 118W Mw 4.5 Mammoth Lakes, CA. Aug 11 37N 122W Ml 4.9 Central California Aug 12 20N 156W Ml 3.7 Hawaii Aug 13 36S 178E Mw 6.3 Off E. Coasat of N.Z. Aug 19 7N 126E Mw 5.5 Mindanao, Philippines Aug 20 6S 142E Mw 6.2 Papua New Guinea Aug 21 34N 116W Ml 5.0 Southern California Aug 21 21S 178W Mw 6.1 Fiji Islands Summary of far-field events following Guam mainshocks:
In general, the events of Mb>=5 tend to fall in the areas described by the listing of far-field events expected above from distance considerations. The most likely events of Mw>=6 in the next 10 days appear to be: New Zealand - North Island 37S 177E Earthquakes of Mw>=6.5 have occurred within 2 weeks in New Zealand after each earthquake in Guam since 1930 (with the one exception of 1975). The probability of such an earthquake in the next week to 10 days is considered very high. Local personnel should be on watch, especially on North Island. 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: Off East Coast of Honshu Mindanao to Samar, Philippines Taiwan Hokkaido Western Mexico South of Honshu Secondary location where event tend to occur but are not as large or as likely . MB>=4.8 considered likely in next 10 days. Fiji/Tonga Islands Ecuador Loyalty Islands New Britain Greece/Aegean Sea/Romania/Austria Areas of U.S. and Canada where triggering may occur (Ml>=4.5) Hawaii - Earthquakes of Ml>=4 have occurred on 4 occasions considered very likely. Areas of U.S. and Canada where triggering may occur (Ml>=3) New York/Pennsylvannia/So. Quebec, Canada Los Angeles region, CA Coso Junction region, CA Northern and Central California (scattered) Unusual events may occur in Iceland New Mexico/Arizona South Carolina On two occasions, a large M>=7 regional shock in the Caroline Islands has followed Guam events within a week. This should also be considered a possibility in this case.
Follow Ups:
● Re: FFA Map Marianas 7.1Mw - Jenny frm NZ 00:56:40 - 4/27/2002 (15259) (1)
● Re: FFA Map Marianas 7.1Mw - Lowell 06:49:32 - 4/27/2002 (15261) (0)
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