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Deadly Tsunami Hits Solomon Islands
A powerful tsunami struck the western Solomon Islands on April 2, 2007 (7:40 a.m., local time), washing away hundreds of homes and taking numerous lives; the death toll was 34 at press time and is expected to rise. Triggered by an offshore earthquake of magnitude 8.1, the deadly waves were part of a so-called near-field or local tsunami. A tsunami typically begins as a single wave that, within minutes after the triggering earthquake, splits into two: a transoceanic tsunami that travels outward to the deep ocean, and a local tsunami that travels toward the nearby coast. The local-tsunami waves that crashed into the Solomon Islands reportedly reached heights of as much as 9 m (30 ft) and extended as far inland as 200 m (650 ft). According to one resident of Gizo, the largest town in the area swamped by the tsunami, the first wave came "almost instantaneously" after the earthquake shaking.
Deep-ocean Assessment and Reporting of Tsunami (DART) stations—operated by the National Oceanic and Atmospheric Administration (NOAA) and described in the article "Tsunami-Forecasting System Tested by Recent Subduction-Zone Earthquakes" (this issue)—are designed to detect transoceanic tsunamis, so that alerts can be sent to areas which would otherwise have no warning. After the earthquake in the Solomon Islands, NOAA's Pacific Tsunami Warning Center used sea-level measurements from tide gauges, DART stations, and other sources to issue a tsunami warning for numerous areas in the South Pacific (for example, see alert). This warning enabled countries at a distance from the earthquake to prepare for a possibly damaging transoceanic tsunami; Australia, for example, closed beaches along its east coast until the warning was lifted. The tsunami caused limited damage at sites across the Solomon Sea from the earthquake epicenter, but otherwise no serious effects were reported from the transoceanic tsunami.
Local tsunamis reach nearby shores too quickly for official warnings to be practical. For some local tsunamis, the only warning is the strong ground-shaking generated by the earthquake that triggers the tsunami. Commonly, the ocean recedes far from shore before the first local-tsunami wave strikes, as happened in Thailand, for example, during the 2004 Indian Ocean tsunami. Early reports are unclear as to whether this phenomenon occurred along all the affected coasts in the Solomon Islands. The earthquake that triggered the Solomon Islands tsunami originated approximately 10 km (6 mi) beneath the sea floor. Its epicenter was 345 km (215 mi) west-northwest of Honiara, the Solomon Islands' capital on the island of Guadalcanal, and just 10 km (6 mi) south-southeast of Gizo, a small fishing and diving center in the New Georgia Islands archipelago. Like most tsunami-generating earthquakes, the Solomon Islands earthquake occurred at a subduction zone, which is somewhat complex here, where the Australia, Woodlark, and Solomon Sea tectonic plates dive beneath the Pacific plate (for maps and more information, visit URL http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/us2007aqbk.php). The earthquake occurred during the day; if the quake and tsunami had struck at night, the loss of life might have been even greater. For information about tsunami safety, please read the sidebar accompanying "Indian Ocean Earthquake Triggers Deadly Tsunami" in Sound Waves, December 2004/January 2005. To learn some basic facts about how tsunamis are formed and how they change shape as they cross the ocean and run up on shore, read "Life of a Tsunami." To view preliminary computer models and animations of the Solomon Islands tsunami, visit URLs http://walrus.wr.usgs.gov/tsunami/ and http://nctr.pmel.noaa.gov/solomon20070401.html.
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in this issue:
Tsunami-Forecasting System Tested by Recent Earthquakes Sub-Sea-Floor Methane in the Bering Sea
International Workshop on High-Seas Biogeography
USGS Sirenia Project Receives Manatee Hero Award
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U. S. Department of the Interior | U.S. Geological Survey
