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September 12, 2007 | Sumatra, Indonesia
At 7:10 AM Charleston, South Carolina time an Mw (moment magnitude) 8.2 earthquake rocked the west coast of the Indonesian island of Sumatra and generated a small tsunami in the Indian Ocean. The earthquake has been recorded by seismometers worldwide (including those in South Carolina, see: http://www.cofc.edu/~scearthquakes/educators/SCEQSeismo.html) and the tsunami has been recorded by a DART (Deep-ocean Assessment and Recording of Tsunamis) buoy in the Indian Ocean (see: http://www.ndbc.noaa.gov/station_page.php?station=23401&type=2&seriestime=20070912112000). As of the time of this bulletin (12 PM EDT) three people have been reported killed and a 2 foot tsunami reported at the Indonesian coastal city of Padang.
Today’s earthquake occurred approximately 1000 kilometers (600 miles) southeast of the devastating Mw 9.1 earthquake and tsunami of December 26, 2004. Its source is likely the same as that earthquake, the shallow fault interface where Indian Ocean crust is being subducted beneath the island of Sumatra. Faults of this type produce both the largest magnitude earthquakes and are also capable of producing massive tsunamis. See http://earthquake.usgs.gov/... for more details on this earthquake and its geologic environment.
Earthquakes of this type and their associated tsunamis are most common in the Pacific Ocean and more rare in the Atlantic and Indian Oceans. This is because the Pacific Ocean is nearly completely surrounded by subduction zones, whereas there are only a few such faults in the Atlantic. Thus coastal South Carolina experiences far fewer tsunamis than states like Oregon that border the Pacific Ocean. However, the Charleston Harbor tide gauge has recorded small tsunamis from subduction earthquakes along the northern border of the Caribbean Sea (1918 and 1946). It is also likely that a tsunami washed ashore in South Carolina following the Mw 8.5-9.0 November 1, 1755 offshore Lisbon, Portugal earthquake, which killed approximately 100,000 people in Europe, North Africa and the Caribbean from the combined effects of the earthquake and tsunami.
Curator: hallcr@cofc.edu
