Tempat-tempat dengan amplitudo pasang surut yang tinggi + jalur-jalur sesar aktif lebih dari 6 meter apa terbukti memicu gempa? Selama ini kan amplitudo pasang surut dipengaruhi oleh jenis morfologi garis pantai, morfologi shoreface, posisi bulan - bumi - matahari, dll? Kompleks sesar --> mempengaruhi morfologi --> mempengaruhi pasang surut (ini yang mungkin?). Sedimentasi yang cepat karena dinamika pasang surut yang tinggi akan memberikan pembebanan pula dan mungkin pembebanan akan me-reaktifasi sesar-sesar di base tempat sedimentasi (cekungan sedimentasi).... ??? Salam, Ery
Salahuddin Husein <[EMAIL PROTECTED]> wrote: Quote: ... the overall effect of the tides is smaller, he said, because the faults studied are many miles inland from the coast and the tides are not particularly large Di sepanjang Java trench, tidal range tampaknya cukup kecil, di barat Sumatera < 1 m, dan semakin membesar ke arah timur. Di selatan Jawa sekitar 1 m, dan di selatan Nusa Tenggara > 2 m (tampaknya geomteris benua Australia sangat mempengaruhi ketinggian pasang-surut di kawasan ini). Meskipun kisaran pasang-surut tersebut kecil hingga menengah, namun ditakdirkan sebagai negara kepulauan, apa boleh buat bisa jadi akhirnya memang punya pengaruh besar terhadap kegempaan. Saya bayangkan, mestinya bisa dilakukan pengukuran/eksperimen untuk menghitung efek pasang-surut tersebut terhadap dinamika sesar. Karena pasang-surut adalah sesuatu yang reguler, di Indonesia terjadi 2 kali sehari, jadi mungkin bisa dihitung respon blok sesar terhadapnya dan berapa lama akumulasi gaya tersebut disimpan sebelum mencapai titik rupture-nya. Nanti tinggal ditambahkan saja gaya kompresi akibat subduksi lempeng.. Mudah-mudahan bisa dilakukan prediksi kegempaan dari situ. udin,- Rovicky Dwi Putrohari wrote: > Tulisan ini malah hanya beberap bulan sebelum gempa-tsunami besar Aceh > > ===== > Strong Earth tides can trigger earthquakes, UCLA scientists report > > October 22, 2004 - Earthquakes can be triggered by the Earth's tides, > UCLA scientists confirmed Oct. 21 in Science Express, the online > journal of Science. Earth tides are produced by the gravitational pull > of the moon and the sun on the Earth, causing the ocean's waters to > slosh, which in turn raise and lower stress on faults roughly twice a > day. Scientists have wondered about the effects of Earth tides for > more than 100 years. (The research will be published in the print > version of Science in November.) > > "Large tides have a significant effect in triggering earthquakes," > said Elizabeth Cochran, a UCLA graduate student in Earth and space > sciences and lead author of the Science paper. "The earthquakes would > have happened anyway, but they can be pushed sooner or later by the > stress fluctuations of the tides." > > "Scientists have long suspected the tides played a role, but no one > has been able to prove that for earthquakes worldwide until now," said > John Vidale, UCLA professor of Earth and space sciences, interim > director of UCLA's Institute of Geophysics and Planetary Physics, and > co-author of the paper. "Earthquakes have shown such clear > correlations in only a few special settings, such as just below the > sea-floor or near volcanoes." > > "There are many mysteries about how earthquakes occur, and this clears > up one of them," Vidale said. "We find that it takes about the force > arising from changing the sea level by a couple of meters of water to > noticeably affect the rate of earthquakes. This is a concrete step in > understanding what it takes to set off an earthquake." > > Cochran, Vidale and co-author Sachiko Tanaka are the first researchers > to factor in both the phase of the tides and the size of the tides, > and are using calculations of the effects of the tides more accurate > than were available just three years ago. Tanaka is a seismologist > with Japan's National Research Institute for Earth Science and > Disaster Prevention. > > Cochran and Vidale analyzed more than 2,000 earthquakes worldwide, > magnitude 5.5 and higher, which struck from 1977 to 2000. They studied > earthquakes in "subduction zones" where one tectonic plate dives under > another, such as near the coasts of Alaska, Japan, New Zealand and > western South America. "These earthquakes show a correlation with > tides because along continent edges ocean tides are strong," Vidale > said, "and the orientation of the fault plane is better known than for > faults elsewhere." > > Cochran conducted a statistical analysis of the earthquakes and tidal > stress data, using state-of-the-science tide calculations from Tanaka > and the best global earthquake data, which came from Harvard > seismologists. This research follows up on a 2002 study by Tanaka. The > current research was funded by the National Science Foundation and the > Laurence Livermore National Laboratory. > > Cochran and Vidale found a strong correlation between when earthquakes > strike and when tidal stress on fault planes is high, and the > likelihood of these results occurring by chance is less than one in > 10,000, Cochran said. They found that strong tides impose enough > stress on shallow faults to trigger earthquakes. If the tides are very > large, more than two meters, three?quarters of the earthquakes occur > when tidal stress acts to encourage triggering, she found. Fewer > earthquakes are triggered when the tides are smaller. > > In California, and in fact in most places in the world, the > correlation between earthquakes and tides is considerably smaller, > Vidale said. In California, tides may vary the rate of earthquakes at > most one or two percent; the overall effect of the tides is smaller, > he said, because the faults studied are many miles inland from the > coast and the tides are not particularly large. > > University of California - Los Angeles --------------------------------------------------------------------- ----- PIT IAGI ke 35 di Pekanbaru ----- Call For Papers until 26 May 2006 ----- Submit to: [EMAIL PROTECTED] --------------------------------------------------------------------- To unsubscribe, send email to: iagi-net-unsubscribe[at]iagi.or.id To subscribe, send email to: iagi-net-subscribe[at]iagi.or.id Visit IAGI Website: http://iagi.or.id Pembayaran iuran anggota ditujukan ke: Bank Mandiri Cab. Wisma Alia Jakarta No. Rek: 123 0085005314 Atas nama: Ikatan Ahli Geologi Indonesia (IAGI) Bank BCA KCP. 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