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| July 14 X1.2 Flare & Two Hawaiian Quakes |
Hi All, Due to our trip last weekend I didn't have the time to put together a proper post about the two 5.2 earthquakes which occurred in Hawaii as listed below: 2005/07/15 15:48:53 20.436N 155.140W 7.8 5.2 49 km (30 mi) NNE of `O`okala From time to time we have brief discussions about the effects of solar flares; and usually it seems we reach a point of no conclusion. Thus I thought this time with some proper preparation this might clarify how these two specific events were directly influenced by the X1.2 event on July 14, 2005 between began 10:13-10:16UT according to the Space Environment Center (SEC). The last X-class flare occurred as an X7.1 on January 20, 2005 about half a year earlier. And lastly, not only was the timing of the events significant in relationship to the flare and the earthquakes, but these earthquakes were unusual as well. To gain an understanding of where to find associated earthquakes to solar flares, we must first understand what part of the earth would be affected and why. At the time of this flare on 7/14 between 10:13-10:16 UT, the sun was directly overhead at 22-23 degrees East Longitude and antipodal to 157-158 degrees West longitude at 10:15 UT. Maximum effects of solar flares to the ionosphere occur at the longitudes where the sun is directly overhead or at the antipodal longitude (180 degrees around the earth from this). In other words at local noon and local midnight. In addition, the sun was directly overhead (because of the tilt of the earth) at 24 degrees north latitude on June 22 - first day of summer and at the equator on Sept. 22 - first day of fall. In the intervening time it will be between these two latitudes. In this case July 14 is 21 days into summer so it will be 21/93 = 0.22 of the ways from 24 North latitude to the equator or 5 degrees south of 24 degrees north latitude - that is the sun will be directly overhead at about 19 degrees north latitude (24-5) around July 14. This gives us two specific locations to look at for the major effects of the X-class flare - at 19N 23E - in northern Africa or opposite this at 19N 157W. These are located in the Sahara desert - an area where seismicity is very rare and the Island of Hawaii where effects might well be seen. Choosing the Island of Hawaii as the location where effects of this flare would most likely be seen we can then go to the catalogs and see if anything unusual occurred in Hawaii in the several days following the flare. Going to the catalog, we find the first event in Hawaii to occur following the flare occurs about one hour later at: 2005/07/14 11:32:38 20.191N 156.129W 27.6 2.2 31 km (19 mi) W of Hawaii The catalog says 01:32 but this is 10 hours earlier than UT so the UT time is 11:32. Checking this we find this is something of a rare earthquake - one of only three in the region (20-21N 156-157W) recorded by the Hawaii Volcano Observatory during the year 2005 (others occurred on April 19 and July 2, 2005). This is also the deepest (27 km depth) event in the region in more than a year - since an M 3.2 on May 25, 2004. This suggests that the flare may have affected either a deep-seated fault or a deep magma chamber north of Hawaii. This we could have noticed immediately as the data is available within minutes of these events. The next day (about 1 day 4 hours later) the following earthquake of M 5.2 is recorded: 2005/07/15 15:48:53 20.436N 155.140W 7.8 5.2 49 km (30 mi) NNE of `O`okala This earthquake of M 5.2 was located off the north coast of the big Island of Hawaii on July 14. It was reported felt with maximum intensity V (possible minor damage) at Honokaa, Honomu, Ookala, Papaikou, Pepeekeo and with lesser intensities in many other communities of Hawaii according to data on the NEIC website. Associated Press also indicated that the earthquake off the north coast of Hawaii today was reported as far as the west coast of Hawaii at Kailua-Kona but that no reports of damage were immediately available. According to the Honolulu Star Bulletin the quake was felt as far away as Maui and Oahu. Two earthquakes of M 3.4 have occurred near Kilauea Volcano and were felt in the region in the previous week. The main shock was followed by a series of aftershocks. The epicenter lies in an area where slumping is known and may be related to depression of the ocean floor due to the weight of the Island of Hawaii. This is the most widely felt and strongest earthquake located in Hawaii by NEIC in the past six years. A similar M 5.2 was located south of Hawaii in the Lo'ihi Seamount area on Sept. 13, 2001, but the last event of larger size occurred on April 17, 1999 with M 5.8. The aftershock sequence was still going strong when two days later the following earthquake was recorded by Hawaiian Volcano Observatory (HVO): 2005/07/17 19:15:03 18.810N 155.446W 28.4 5.2 24 km (15 mi) WSW of Lo`ihi Seamount Activity on July 17, 2005 hit in a series from south of the Island near Loi'hi Seamount on the south into the Island and to the north of Hawaii. The strongest event was M 5.0-5.1 in the Lo'ihi Seamount area which was felt with maximum magnitude IV at Pahala, Naalehu, Mountain View and Kealakekua and with lesser intensity in most of southern Hawaii according to data on the NEIC website. It may have been followed a few seconds later by a second event of similar size, or this may be the same event. At least one aftershock of M 3.9 was felt with intensity III at Hilo, Honokaa and Pahala and with intensity II at Keaau and Naalehu. Three other aftershocks of M 3.4, 3.4 and 3.2 also occurred and may have been lightly felt. Local News sources and Associated Press indicated that some of these tremors were felt as far as Oahu. While the quakes were widely felt no damage or casualties were reported. Today's Loi'hi quake was the strongest located in the region (17-19N 154-157W) since earthquakes of similar size occurred on May 13, 2005 and Sept. 13, 2001. This was the second earthquake of M>=5 in the region of Hawaii in two days - an M 5.2-5.3 hit the north coast of Hawaii on July 15. Seismicity in Hawaii quickly returned to normal following these two moderate earthquakes and today is back to background levels. On the basis of this study of the recent history of seismicity in Hawaii, it should be plain that two events of M>5 in the area in the course of two days - at different epicenters and apparently unrelated to the main volcanism of the Island is quite unusual. It is also clear that the X-class solar flare was rare and even rarer since such an event will very seldom occur just when the sun is positioned directly at noon or midnight and directly overhead in Hawaii. Petra
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