Great Quake, Chile

A shallow, great quake of 8th magnitude struck Chile last night, causing serious damage and generating a tsunami in the Pacific Ocean.

Sunday 28th February 2010

An earthquake of magnitude 8.8 struck just off the coast of Chile at 7:34 p.m. New Zealand time last night. The quake was located 325 km south-west of the Chilean capital Santiago (105 km west-south-west of Talca Chile, 115 km north-north-east of Concepcion Chile) at a depth of 35 km.

Initial reports from both the U.S. Geological Survey and the Pacific Tsunami Warning Centre put the quake at magnitude 8.3 and 8.5 respectively. As the evening progressed, the strength of the earthquake was revised upward by both agencies to magnitude 8.8 at a depth of 35 to 55 km.

Geoscience Australia also reports the event at magnitude 8.8 but deeper at 50 km. It estimates the quake would have caused damge within 600 km of the epicentre and would have been felt up to 7,500 km away.

Geofon, Potsdam, the Global Seismic Monitor, reports the quake as magnitude 8.3 at a depth of 30 km. Geofon has placed the epicentre just onshore but, like the USGS, to the west of Talca and Chillan, Chile, and north of Concepcion.

At 8:33 p.m. New Zealand’s Ministry of Civil Defence and Emergency Management (MCDEM) issued an update on its website advising that, “There is no reported tsunami threat for New Zealand.”

As the evening progressed and the size of the quake was revised upward, tsunami experts revised their projections as to whether a tsunami had been generated. The first measurements of a tsunami were announced by the Pacific Tsunami Warning Centre at 8:45 p.m. NZDT when it announced that a wave of 1.29 metres had been measured at Valparaiso, Chile, at 8:08 p.m. New Zealand time and a wave of 1.15 metres at Talcahuano, Chile at 7:52 p.m. NZDT. At that stage a tsunami warning was in effect for Chile and Peru, and a less urgent watch in place for Ecuador, Colombia, Antarctica, Panama, and Costa Rica.

The situation abruptly changed at 10:47 p.m. NZDT when the Pacific Tsunami Warning Centre issued a bulletin reporting a 2.3 metre wave at Talcahuano, Chile and extended the area covered by its tsunami watch.

In a bulletin issued at 11:45 p.m. NZDT and containing more sea level measurements, the PTWC issued a warning for New Zealand and many other Pacific countries. At that time their evaluation stated, “Sea level readings confirm that a tsunami has been generated which could cause widespread damage.”

The MCDEM issued a National Warning: Threat to New Zealand on its website at 12 minutes after midnight. At that time it was thought that sea level changes of up to a metre might be expected along eastern coasts of the North and South Islands and Chatham Island, with the first arrival time at the Chathams at 7:05 this morning.

The latest detailed bulletin issued by the PTWC, at 1:49 this morning, announces that “a widespread tsunami warning is in effect.” The list of measurements of wave activity is slowly growing, but the peak measurements of 2.3 metres at Talcahuano Chile at 7:52 p.m. NZDT and 1.3 metres at Coquimbo Chile at 9:52 p.m. have not been exceeded at other stations.

Nevertheless, the PTWC regards the situation as “severe.” Forecast arrival times for first arrivals in New Zealand territory in the 1:49 a.m. bulletin are:
East Cape 8:18 a.m.
Dunedin 8:52 a.m.
Wellington 8:55 a.m.
Lyttelton 9:40 a.m.

New Zealand’s Ministry of Civil Defence and Emergency Management maintains its national warning of a tsunami threat to New Zealand. It advises that Chatham Island will experience the first contact at about 7:05 a.m. The first wave may not be the largest, with expected wave heights between 1 and 3 metres above normal sea levels. It states, “Based on historical events it is expected that the greatest wave heights will occur between 6 and 12 hours after the initial arrivals.”

The PTWC predicts that the first wave will reach Raoul Island at 8:12 a.m. In a supplement issued at 2:46 a.m. the tsunami warning for New Zealand and many other Pacific Islands was still in effect.

The GeoNet website has tide gauges at both the Chatham Islands and Raoul Island. The gauges can be viewed here.

The Ministry of Civil Defence and Emergency Management website can be found here.

Since the main earthquake, Chile has experienced five earthquakes of magnitude 6 and sixteen of magnitude 5.

For up-to-date information on the tsunami threat to New Zealand on Sunday morning, tune to Radio New Zealand National. Your local radio station may also be broadcasting updates.

[Compiled from data supplied by the U.S. Geological Survey and its contributing agencies; the U.S. National Oceanic & Atmospheric Administration’s Pacific Tsunami Warning Centre; Geoscience Australia, Geofon, Potsdam, and New Zealand’s Ministry of Civil Defence and Emergency Management.]

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