Press Release – Science Media Centre

An official tsunami warning remains in place for all of coastal New Zealand as surges of water reach parts of the country including Chatham Islands, Napier, Castlepoint, Tauranga and North Cape.Experts On Tsunami And Chilean Earthquake (Updated)
An official tsunami warning remains in place for all of coastal New Zealand as surges of water reach parts of the country including Chatham Islands, Napier, Castlepoint, Tauranga and North Cape.

Civil Defence is issuing regular updates on the tsunami warnings here.

GNS Science is also issuing updates through Geonet and has a useful backgrounder on tsunamis here.

Authoritative info about the earthquake is available from the USGS event page.

Victoria University’s Dr John Townsend has put together a graphical presentation on the Chilean earthquake which can be viewed here. John Townsend is available for comment today.Contact the SMC for details.

The tsunami reaches New Zealand just days after Civil Defence updated its tsunami risk assessment which includes an analysis of potential tsunamis originating from South America. The report can be downloaded here.

Dr Bill Fry, Seismologist at GNS Science comments:

“The magnitude 8.8 earthquake that occurred off the coast of Chile resulted from the oceanic Nazca plate being thrust under the South American plate. Since the main shock, there have been numerous large aftershocks with magnitudes greater than 6. Historical seismicity suggests that continued aftershock activity could include events with magnitudes equal to or greater than 7. The earthquake occurred in a region of known stress accumulation between the hypocentres of the great (M 9.5) earthquake of 1960 and the 1922 (M 8.5) earthquake.

“The earthquake generated a tsunami that propagated west-northwestward across the Pacific Ocean. The largest waves aren’t expected to hit New Zealand. However, numerical simulations of effects of the tsunami on New Zealand predict measurable waves with amplitudes of between 0.2 and 1 metre along much of the eastern coast. Variations in the bathymetry around New Zealand lead to amplification of the tsunami around the Chatham Islands and Bank’s Peninsula, and in these areas scientists have predicted maximum wave amplitudes of between 1 and 3 meters.

“This is based on numerical modelling and historical comparison with an analogous earthquake on the South American coast in 1877. The historical accounts suggest that the largest waves will in many areas arrive between 6 and 12 hours after the initial arrivals, and this is also supported by the numerical modelling.”

Dr John Townend EQC Fellow in Seismic Studies, School of Geography, Environment, and Earth Sciences, Victoria University of Wellington comments:

“The tectonic position of this earthquake was similar to that of the June 2009 Fiordland earthquake: on the interface between a subducting plate (“slab”) and the over-riding plate. In the Chilean case, the Nazca plate is being subducted beneath the South American plate. Subduction zones are commonly the sites of the biggest earthquakes, including the 2004 Boxing Day earthquake in Sumatra. Chile has seen many very large historic earthquakes, most notably the 1960 magnitude 9.5 one, the largest known earthquake of the last two centuries anywhere in the world.”
The comments below were gathered from scientists in Britain by our colelagues at the Science Media Centre in London. We will issue updates from New Zealand experts as soon as possible.

Dr Brian Baptie, British Geological Survey’s Head of Seismology said:

“This is thelargest earthquake to strike central Chile since a magnitude 6.7 earthquake in 2001. The epicenter lies around 200 km northeast of the magnitude 9.5 earthquake that struck Chile in 1960. This was the largest earthquake ever recorded and resulted in a destructive tsunami that killed many thousands of people around the Pacific.

“A 1.3m tsunami wave was observed at Valparaiso, 200km north of the epicentre about 20 minutes after the earthquake. Tsunami waves in the deep ocean travel about the same speed as a jet plane and would take about 15 hours to reach Hawaii and about 20 hours to reach the other side of the Pacific.”

Dr Roger Musson, British Geological Survey’s Head of Seismic Hazard said:

“This earthquake fills in an identified seismic gap – no previous large earthquake had occurred in this area since 1835, when a large earthquake was observed by Charles Darwin. Since then, an estimated 10m of potential displacement has accumulated.”

Dr David Rothery, Dept of Earth & Environmental Sciences at the Open University,
said:

“This morning’s (06:34 [UK time]) magnitude 8.8 earthquake close to the Chilean coast has caused a tsunami that is now radiating away from the epicentre and travelling at several hundred km per hour across the Pacific ocean. The first waves are expected ot Hawaii at 11:19 Hawaii Standard Time but are also travelling along the S America coast and will reach Colombia and Costa Rica after 1300 GMT (see http://www.prh.noaa.gov/ptwc/ ) Some earthquake damage is to be expected ashore in Chile near the town of Concepcion.

“A magnitude 8 quake is a rare event. On average there is only about one of these per year, globally. This one was caised by the floor of the Pacific ocean being pushed below South America. Because the epicentre was under the sea, the sudden jerking of the sea-floor displaced water and triggered a tsumani. The focus of this quake was at a depth of about 34 km – which is relatively shallow (and hence damaging) though not quite so shallow as the magnitude 9.1 quake in the Sunda Trench that caused the 26 Dec 2004 Indian Ocean Tsunami.”

ends

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