Earthquake Risk High In Sumatra, Indonesia

[ferd54]

The violent thrust of the seabed near Sumatra, Indonesia, that touched off catastrophic tsunamis in December created significant new risks of earthquakes and tsunamis there, seismologists are reporting today.

The researchers say that the place at greatest risk from a new earthquake is the devastated city of Banda Aceh and that the tsunami risk lies along Sumatra's heavily populated southern coasts. But they added that any fresh tremors or waves would be unlikely to have anywhere near the destructive power of the December earthquake, the world's second most powerful seismic shock in 100 years.

Advertisement

Still, the researchers, from the University of Ulster in Northern Ireland, said the new threat added urgency to efforts to extend the world's only existing tsunami-warning network, in the Pacific, to include the Indian Ocean.

They said they could not predict when the next shocks might occur, but noted that in similar geological settings, in Turkey and Japan, big quakes had set off tremors in adjacent faults in a few months or years.

The findings are described in the journal Nature.

Ross S. Stein, a seismologist with the United States Geological Survey in Menlo Park, Calif., who was not involved in the new study but developed a method the authors used to calculate risks, called the analysis "important and sobering."

"What we need now are networks of seismometers in Sumatra and its offshore islands," he said. "If the rate of small shocks climbs, I would become very worried about the prospects of a successive shock."

The Ulster researchers pinpointed the risks by mapping patterns of aftershocks and using a computer simulation to determine where the quake had intensified or relaxed stresses on nearby seams in earth's crust.

Beneath Banda Aceh, the tectonic shifts in December appear to have loosened two vast rock faces pressing together along 180 miles of the Sumatra Fault, which bisects the island. The change makes it more likely that one side could slip abruptly past the other and cause a destructive horizontal jolt, said Prof. John McCloskey, the lead author of the study.

Elsewhere the Sumatra Fault has produced major earthquakes, but the northern section, where the pressures have changed, has not seen a big earthquake in more than 100 years, he said. That means it is probably experiencing pent-up stress.

The other quake-prone fault lies in the Sunda Trench, a deep scar in the sea bottom running southeast from the epicenter of the December earthquake, the team said. An earthquake there could generate deadly waves, as previous quakes did at least twice before, in 1833 and 1861.

Recent computer simulations recreating the 19th-century upheavals and waves suggest that tsunamis from the Sunda Trench would pose a grave risk to Sumatra's southern shores but would not sweep other South Asian coasts.

The most imminent risk, Dr. McCloskey said, is probably in the fault beneath Banda Aceh.

[astral]

The other quake-prone fault lies in the Sunda Trench, a deep scar in the sea bottom running southeast from the epicenter of the December earthquake, the team said. An earthquake there could generate deadly waves, as previous quakes did at least twice before, in 1833 and 1861.

<{POST_SNAPBACK}>

Three times in 200 years is HIGH RISK??