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No damage reported

By Teri Hunkin PAGO PAGO, American Samoa (Samoa News, Dec. 27, 2011) - Did you feel the quake on Christmas Day in American Samoa? According to several residents of the territory, there was a strong jolt on Sunday afternoon—Christmas Day— which was described as "sharp, but very brief" by a woman in Utulei who was staying at Sadie’s by the Sea. There has been no damage reported, and an official at American Samoa Department of Homeland Security (ASDHS) verified that the territory had, indeed, experienced a short, but strong earthquake on Sunday afternoon. However, noted the official, the quake was not long enough or strong enough to generate a tsunami or sound the sirens.

According to the United States Geological Survey (USGS), the magnitude of the quake registered a 6.0 on the Richter Scale, which calculates the magnitude of most earthquakes measured on the earth. The Richter Scale magnitude is calculated from the amplitude of the largest seismic wave recorded for the earthquake, no matter what type of wave was the strongest.

The Christmas day quake occurred late in the afternoon at 5:48 pm local time, and was located at a depth of 48.9 miles, according to ASDHS. According to the USGS website, the epicenter was located 173 miles north of Neiafu, Tonga—which means the quake was fairly close to home. The recorded time of the quake in Tonga was 6:48 pm on Monday, December 26. (Because Tonga is over the International Dateline, the quake is recorded on the books as occurring on Monday, December 26, which was December 25 here in American Samoa.)

This information was monitored by ASDHS- Emergency Operations Center (EOC) 24/7 watch personnel, who have constant access to USGS, which monitors earthquakes world-wide, as well as other tracking and warning sites.

One Tula resident who felt the quake said she immediately went next door to see if anyone else had felt it. According to the Tula woman, her relatives said they never felt a thing. However, the USGS site records comments and information submitted from around the world, and they noted that residents from Faga’alu, Iliili and Nuuuli had recorded on the USGS website that they felt the quake. DPS said they received just one phone call asking about the earthquake, but there was no damage reported.

According to the website, www.geo.mtu.edu, "How are Earthquake Magnitudes Measured?" the Richter magnitudes are base on a longtime scale (base 10). This means that for each whole number you go up the Richter Scale, the amplitude of the ground motion recorded by a seismograph goes up ten times. Using this scale, a magnitude 5 earthquake would result in ten times the level of ground shaking as a magnitude 4 earthquake (and 32 times as much energy would be released).

To give you an idea how these numbers can add up, think of it in terms of the energy released by explosives: a magnitude 1 seismic wave releases as much energy as blowing up 6 ounces of TNT. A magnitude 8 earthquake releases as much energy as detonating 6 million tons of TNT. Fortunately, most of the earthquakes that occur each year, are magnitude 2.5 or less, according to the website.

It was an 8.0 quake which generated the 2009 tsunami— and the earthquake which preceded the tsunami was extremely strong, and "seemed to go on forever" — in reality, several minutes — according to early reports following that quake.

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