Perlu penelitian yang mendalam agar tidak menjadikan kepanikan bagi orang awam dan yang salah menginterpretasikan. Mungkin ada yang harus rela meluangkan waktunya untuk sedikit konsentrasi pada permasalahan geotektonik di Sumatra ini beserta akibat yg akan ditimbulkannnya. Apabila memang akan menimbulkan bencana bisa disosialisasikan dengan sebaik-baiknya sehingga korban bisa diminimalisasi, tapi terhindar dari kepanikan.
Franciscus Sinartio <[EMAIL PROTECTED]> wrote: Sudah lebih dari 2500 gempa sejak 26 des 2004 yang terjadi di sekitar Sumatra terutama di NW Sumatra. Apakah kegiatan ini adalah kegiatan "cooling down" setelah pergeseran yang besar. Atau memang kondisinya (apa pun yang aktif sekarang) masih perlu "pressure release" yang besar. salah satu "sistem" yang bisa ter trigger oleh gempa 26 des 2004 tsb adalah sesar Sumatra, dan bertambah aktif nya volcanic arc. ini ada artikel ttg collapse caldera-danau Toba, yang katanya potential volumenya, sangat besar. ada artikel lainnya yang katanya ada kemungkinan meledak di June 2005. (catatan utk Pak Maryanto, artikel ini di posting juga oleh seorang pengarang buku "ulasan ttg Nostradamus" yang juga percaya akan magic number 7) fbs nb: siapa yang mau hasil download yang ada gambarnya (satelit image & kartun) bisa saya kirimkan lewat japri aja karena kebesaran. =============== Sleeping Giant Super Volcano TOBA Just NW Of Sumatra >From Harry Mason [EMAIL PROTECTED] 1-2-5 Hi Jeff, See the article below - this is the sort of beast that may be brewing under the newly-active MAJOR seismic zone NW of Sumatra. TOBA lies just inland from the 9.0 Richter tsunamis-forming earthquake epicentre - on a previously created NW trending fault harmonic - located onshore within the NW Sumatra Island Arc During an explosive mega-erruption some 75,000 years ago, TOBA is thought to have nearly taken out the entire human race. Krakatoa was a baby's baby in comparison !!! For more information on TOBA see http://www.victorynewsmagazine.com/ and http://volcano.und. For a detailed geological and geophysical analysis of TOBA see http://ees2.geo.rpi.edu/ (catatan: yang ini di karang oleh orang Indon dkk) I am indebted to anthropologist Sandra Belanger of San Francisco for the data sources re TOBA. The NW Sumatra seismic event is still in progress (Monday 3-01-05) with regular periodic 5.0-6.5 richter quakes and thousands of smaller tremblors largely focussed within the proto NNW trending Andaman-Nicobar-Sumatra Island Arc. This remains a HIGHLY-DANGEROUS situation and will remain so for many months. The lack of regular press alerts on this scenario is disturbing. The public need to know the potential dangers involved AND what to do in case of an alert. Best Regards, Harry Mason Here is a full article on TOBA from the BBC ... http://www.bbc.co.uk/ ============================ ============================ Toba, Sumatra, Indonesia Landsat image of Toba caldera. Image courtesy of the Landsat Pathfinder Project. Toba caldera produced the largest eruption in the last 2 million years. The caldera is 18 x 60 miles (30 by 100 km) and has a total relief of 5,100 feet (1700 m). The caldera probably formed in stages. Large eruptions occurred 840,000, about 700,000, and 75,000 years ago. The eruption 75,000 years ago produced the Young Toba Tuff. The Young Toba Tuff was erupted from ring fractures that surround most or all of the present-day lake. Map of the Toba caldera from Knight and others (1986). Samosir Island and the Uluan Peninsula are parts of one or two resurgent domes. Lake sediments on Samosir indicate at least 1,350 feet (450 m) of uplift. Pusukbukit, a small stratovolcano along the west margin of the caldera, formed after the eruption 75,000 years ago. There are active solfataras on the north side of the volcano. Lake Toba - view of the crater lake. Photographers A.M. & K.D.Hollitzer. Copyright 1996. Comparison of volumes produced by some of the greatest volcanic eruptions. The Young Toba Tuff has an estimated volume of 2,800 cubic kilometers (km) and was erupted about 74,000 years ago. The Huckleberry Ridge Tuff, erupted at Yellowstone 2.2 million years ago, has a volume of 2,500 cubic km. The Lava Creek Tuff, erupted at Yellowstone 600,000 years ago, has a volume of 1,000 cubic km. The May 1980 eruption of Mount St. Helens produced 1 cubic km of ash. Not shown is the Fish Canyon Tuff of the San Juan Mountains of Colorado. The Fish Canyon Tuff was erupted 27.8 million years ago and has an estimated volume of 3,000 cubic km. The volume of the youngest eruption is estimated at 2,800 cubic km, making the eruption the largest in the Quaternary. Pyroclastic flows covered an area of at least 20,000 square km. Up to 1200 feet (400 m) of Young Toba Tuff is exposed in the walls of the caldera. On Samosir Island the tuff is more than 1800 feet (600 m) thick. Ash fall from the eruption covers an area of at least 4 million square km (about half the size on the continental United States). Ash from the eruption has been recovered from deep-sea cores taken in the Bay of Bengal and in India, roughly 300 miles (500 km) inland (1,900 miles, 3100 km from Toba). Rose and Chesner suggested the ash may have reached central Asia and the Middle East. Ninkovich and others (1978) estimated of the height of the eruption column to be 30 to 50 miles (50 to 80 km) for the Young Toba Tuff. Rose and Chesner, after a study of the shapes of the ash shards, concluded this estimate was too high by a factor of 5 or more. The pumice erupted 75,000 years ago is calc-alkalic quartz-latite to rhyolite in composition (68%-76% silica). There have been no eruptions at Toba in historical time. The area is seismically active with major earthquakes in 1892, 1916, 1920-1922, and 1987. Toba is located near the Sumatra Fracture Zone (SFZ). Stratovolcanoes in Sumatra are part of the Sunda arc. Volcanism is the result of the subduction of the Indian Ocean plate under the Eurasian plate. The subduction zone is marked by the Java Trench. The geologic symbol for a subduction zone is a line with "teeth" (black triangles). The teeth are on the over-riding plate (the Eurasian plate in this case). The rate of subduction is 6.7 cm per year. From Knight and others (1986). Sources of Information: Knight, M.D., Walker, G.P.L., Ellwood, B.B., and Diehl, J.F., 1986, Stratigraphy, paleomagnetism, and magnetic fabric of the Toba Tuffs: Constraints on their sources and eruptive styles: Journal of Geophysical Research, v. 91, p. 10,355-10,382. Ninkovich, D., Sparks, R.S.J., and Ledbetter, M.T., 1978, The exceptional magnitude and intensity of the Toba eruption, Sumatra: An example of using deep-sea tephra layers as a geological tool: Bulletin of Volcanologique, v. 41, p. 286-298. Rose, W.I., and Chesner, C.A., 1987, Dispersal of ash in the great Toga eruption, 75 ka: Geology, v. 15, p. 913-917. Simkin, T., and Siebert, L., 1994, Volcanoes of the World: Geoscience Press, Tucson, Arizona, 349 p. Williams, M.A.J., and Royce, K., 1982, Quaternary geology of the Middle Son Valley, north central India: Implications for prehistoric archaeology: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 38, p. 139-162. _________________________________________________________________ Express yourself instantly with MSN Messenger! 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