dear all....
mungkin bagi sebagian org blm paham bahwa...negara kita ini terbentuk akibat
timbulan dr dua buah lempeng benua raksasa yg saling bertemu..yaitu lempeng
euroasia dan lempeng australia. karena masa jenis yg lebih berat maka lempeng
australia menghunjam ke bawah dan sebaliknya krn masa jenis yg lbh ringan,
lempeng euroasia terangkat ke atas..nah kejadian ini memunculkan kepulauan
indonesia.
jadi dengan kata lain hampir semua wilayah di indonesia tdk terbebas dr gempa
dan tsunami, juga aktivitas gunung berapi yg sangat tinggi...coba perhatikan
tingkah laku merapi...hampir setiap ada gempa di belahan lain..apalagi yg deket
dengan dia..maka merapi akan bergolak.
dg pergeseran yg aktif dr tumbukan ini...klo ga salah benua lempeng australia
akan menggeser lempeng euroasia, setiap tahunnya adalah sekitar 10 cm....memang
klo dr segi ukuran adalah jarak yg ga seberapa..tp lihatlah dr wujud benda yg
begitu besarnya dan setiap benda memiliki tingkat elastis yg berbeda2 dan batas
kelastisannya..bila ambang itu terlewati maka dia akan patah..nah ini yg
disebut gempa..bila itu terjadi di lautan..dimana ada blok dasar samudra yg
amblas..dan secara fisika air laut akan mengisi blok yg kosong tsbt...suatu
saat dia akan penuh...dan menimbulkan arus balik....yg disebut tsunami (dr
bahasa jepun). makannya tanda2 tsunami adalah sesaat terjadi gempa maka air
laut di pantai akan surut drastis.....sesaat setelah itu akan balik gelombang
yg maha dahsyat..kadangkala masyarakat ga faham kejadian ini justru malah
ramai2 pergi ke pantai utk ngambil ikan yg terperangkap dsb.
bahkan di utara maluku dan papua...merupakan daerah triple junction..yaitu
daerah pertemuan tiga buah lempeng...betapa dahsyatnya bukan.
memang sampai saat ini blm ada pendekatan yg cocok utk menentukan kapan
terjadinya gempa.
mungkin metoda yg paling mumpuni adalah metoda statistik atau bahkan metoda
fraktal (cabang ilmu matematika yg mungkin paling bontot).
jadi data2 tentang gempa dan tsunami dijadikan inputnya.
dari data2 terdahulu juga bisa kita liat...mungkin dr citra seismik..yaitu
metoda dlm ilmu geofisika yg memberikan pulsa kepada bawah permukaan bumi
kemudian dicatat dan di proses..dr sini ketahuan pola2nya termasuk pola erosi
akibat tsunami..yg mungkin bs dijadikan masukan juga utk data statistik atau
fraktal tsbt.
salam
FF
Ambon <[EMAIL PROTECTED]> wrote:
http://www.nytimes.com/2006/12/05/science/05tsunami.html?n=Top%2fReference%2fTimes%20Topics%2fPeople%2fR%2fRevkin%2c%20Andrew%20C%2e
Indonesian Cities Lie in Shadow of Cyclical Tsunami, Scientists Say
By ANDREW C. REVKIN
Published: December 5, 2006
Two Indonesian cities that escaped the devastating tsunamis of December
2004 are at risk of inundation over the next few decades from undersea
earthquakes predicted along the coast of Sumatra, researchers say.
Skip to next paragraph The New York Times
Related Tsunami Simulations (December 5, 2006)
The researchers, using computer models, produced simulations showing that a
major earthquake could send a series of waves 15 to 20 feet high sweeping
ashore around Padang or Bengkulu, coastal cities of 800,000 and 350,000 just
south of the Equator on Sumatras Indian Ocean coast. Many seismologists say
such quakes are inevitable off the coast near those cities.
The analysis was published Monday on the Web by The Proceedings of the
National Academy of Sciences.
The Sundra Fault, a seam in the earths ever shifting crust beneath the
seafloor and just beyond a chain of islands parallel to the coast, generates
clusters of great earthquakes roughly every 230 years, according to old records
and studies of coral reefs in the region. The reefs lift or sink abruptly after
such jolts, with the skewed orientation of successive layers of coral providing
a chronology of these seismic shifts.
A tsunami in 1797 carried a 200-ton British ship half a mile inland in
Padang, and another deadly set of waves struck the coast not long afterward, in
1833, focused more around Bengkulu.
Then, however, coastal populations were counted in the thousands, said Kerry
Sieh, an author of the study and a seismologist at the California Institute of
Technology who has spent decades studying the quake patterns in the area. The
other authors are from Caltech and the University of Southern California.
Now there are hundreds of times as many people in harms way, Dr. Sieh said.
We hope that these initial results will help focus educational efforts,
emergency preparedness activities, and changes in the basic infrastructure of
cities and towns along the Sumatran coast, Dr. Sieh said in a printed
statement.
Costas E. Synolakis, the director of the Tsunami Research Center of the
University of Southern California and an author of the study, said it was a
rough initial projection. The hazard is there, he said. It is a loaded
missile pointing at one million people.
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