#1 Tsunami-Generating Quake Possible off Indonesia: Scientists
01-17-2010, 06:36 PM
- Join Date
- Aug 2005
– A huge wave-generating quake capable of killing as many people as in the 2004 Indian Ocean tsunami could strike off the Indonesian island of Sumatra, and the city of Padang is in the firing line, a team of seismologists said on Sunday.
The group -- led by a prominent scientist who predicted a 2005 Sumatran quake with uncanny accuracy -- issued the warning in a letter to the journal Nature Geoscience.
The peril comes from a relentless buildup of pressure over the last two centuries on a section of the Sunda Trench, one of the world's most notorious earthquake zones, which runs parallel to the western Sumatra coast, they said.
This section, named after the Mentawai islands, "is near failure," the letter warned bluntly.
"The threat of a great tsunamigenic earthquake with a magnitude of more than 8.5 on the Mentawai patch is unabated. (...) There is potential for loss of life on the scale of the 2004 Indian Ocean tsunami."
The letter gave no timeframe for this event but warned starkly of the danger for Padang, a city of 850,000 people that lies broadside to the risky segment.
"The threat from such an event is clear and the need for urgent mitigating action remains extremely high," it said.
More than 220,000 people lost their lives in the killer wave of December 26 2004 when a 9.3-magnitude earthquake, occurring farther north on the Sunda Trench, ruptured the boundary where the Australian plate of Earth's crust plunges beneath the Eurasian plate.
01-17-2010, 06:52 PM
- Join Date
- Aug 2005
Sumatra Earthquake - Prehistoric Records Found in Corals
For at least the past 700 years, clusters of large quakes have occurred about every two centuries. Last year’s 8.4 Sumatra Earthquake is the first in a series that will play out over the next few decades.
An international team of scientists has deciphered a geological record of ancient earthquakes from the coral reefs of the Mentawai islands, off the coast of West Sumatra. Their study, published today in the journal Science, shows cycles of tectonic strain accumulation and relief that have been about two centuries long and that commonly end in a spate of two or more large earthquakes.
To develop such a long history, the researchers used ancient corals that record in their annual growth bands histories of sea-level fluctuations. These changes in water level indicate that the islands subside during the long, quiet periods between earthquakes. When they pop up suddenly, during earthquakes, the corals rise above sea level and die.
Three localities, along about a 110 kilometers length of the Mentawai island chain, contain broadly similar sea level histories. At each of the three “paleoseismic” sites – on South Pagai, North Pagai and Sipora islands – sudden coral deaths occurred in the mid- to late 1300s, the late 1500s to early 1600s, and in 1797 and 1833. These broadly similar histories imply that large earthquakes occur about every two centuries.
However, the researchers found that each site’s seismic history differs significantly from its neighbours’. For example, at the South Pagai site the earliest recorded coral deaths occurred in about 1350, whereas at the other two sites, farther north, the first coral deaths occurred in about 1375. These differences show that, at least for the past 700 years, failure of the underlying active fault, the Sunda megathrust, occurs incrementally, in a series of earthquakes, rather than all at once.
This 700-year record of ancient West Sumatra earthquakes helped the scientists interpret recent seismic happenings in West Sumatra. During the September 2007 magnitude 8.4 Sumatra earthquake and its aftershocks, the South Pagai site rose about 73 cm, while the other two paleo-seismic sites remained stable. Although the details differ, this mimics what happened in about 1350.
The upshot of the 700-year-long history is that the September earthquake appears to be the beginning of the next big failure sequence for the 700-km-long section of the Sunda megathrust. The researchers refer to as the Mentawai patch. “If previous cycles are a reliable guide,” explains Professor Kerry Sieh, Director of the Earth Observatory of Singapore, Nanyang Technological University (NTU), “we can expect one or more very large West Sumatran earthquakes as the rest of the Mentawai patch fails within the next few decades.”
Prof Sieh adds, “We know that the amount of potential slip that was not relieved in September 2007 is enough to generate an Mw 8.8 earthquake, in a region with more than a million people living along the coast.”
Adds Danny H. Natawidjaja from the Research Center for Geotechnology, Indonesian Institute of Sciences; “This study shows that the next great earthquake and tsunami are very likely within the lifetimes of children and young adults currently living along the coast of Western Sumatra. We hope that our results will encourage governments and various humanitarian agencies to continue and even accelerate their preparations.”
01-17-2010, 08:31 PM
Sounds like I better lay in a good supply of their coffee...:eek:May the FORCE be with you!
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