Aftershocks and Sea Disturbances Continue

Tonga and Samoa continue to experience aftershocks of yesterday’s magnitude 8 earthquake, while sea level gauges show that the sea is still disturbed at several New Zealand locations.

Thursday 1st October 2009

Further analysis by the U.S. Geological Survey (USGS) has revised the magnitude of yesterday’s earthquake near Tonga and Samoa to magnitude 8.0 at a depth of 18 km. The undersea quake was located 185 km east-south-east of Hihifo, Tonga, 200 km south of the Samoan capital, Apia.

The USGS has reported 46 distinct aftershocks since the main earthquake, 28 of which were magnitude 5 and 18 at magnitude 4. Largest events so far have been a magnitude 5.8 quake at 7:21 a.m. New Zealand Daylight Time yesterday, 33 minutes after the main shock. A magnitude 5.9 earthquake was recorded early yesterday afternoon at 12:45.

gauge20091001.pngSea level gauges at Raoul Island, North Cape, East Cape and Chatham Island continue to show that the seas are disturbed, as the energy released by the earthquake travels around the Pacific as tsunami waves. During the past 12 hours the waves have been only a few tens of centimetres high except at Chatham Island where disturbances of nearly half a metre have been recorded.

The instruments at Raoul Island are now back online. A severe storm in the area interrupted the telemetry yesterday, but the installation saved data locally until it could be downloaded to the GeoNet datacentre overnight.

[Compiled from data provided by the U.S. Geological Survey and its contributing agencies; and the GeoNet project and its sponsors EQC, GNS Science and FRST.]

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