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Map of the epicenter of the March 11, 2011 earthquake in Japan. (Map credit: ©Jim McMahon/Scholastic, Inc.)

# Richter Scale Ousted by MMS

## New earthquake measurement used at USGS

While the Richter scale is still used to measure small earthquakes, a new technology is being used to measure quakes the size of the recent one in Japan.

The March 11 quake in Japan measured 9.0 on the Moment-Magnitude Scale, or MMS. It is comparable to the Richter Scare measurements, but more accurate, says an expert at the U.S. Geological Survey. The Richter scale was developed by Charles Richter in 1935. Tom Hanks and Hiroo Kanamori developed the MMS in 1979.

"The Richer scale is normally known as a local scale and is used by regional networks," said Rafael Abreu, a geologist from the U.S. Geological Survey. "For larger quakes, we are using a moment magnitude, which has the same mathematical concept behind it as Richter developed."

That concept has been refined and improved over the years to give an estimate of the total energy released in an earthquake.

"The MMS is an intensity scale, which is basically a scale that measures the level of ground shaking at a specific point," he said.

Within almost every earthquake, the earth's crust moves along a fault line, or break in the ground that represents where two "plates" meet. Along the San Andreas Fault, earthquakes are caused by the Pacific Plate sliding past the North American Plate. Sometimes, two plates catch and energy builds up. At a certain point, something has to give. In a sudden, violent jerk, the two plates grate against each other, sending shock waves through the earth. This is an earthquake.

"The size of the earthquake is directly proportional of the size of the rupture, which means it is the chunk of the earth's crust that actually moved," said Abreu.

The earthquake in Japan was so strong that the Earth tilted on its axis, shortening the length of the day. Abreu explained what that means.

"It is the equivalent to what happens when you hit a bell," he stated. "When you hit the bell, the bell is ringing and vibrating. The vibration would cause the axis in the bell to move until the energy dissipates. The shortening is a millionth of a second and the change is imperceptible to humans."

EARTHQUAKE IN JAPAN

A magnitude 9.0 earthquake struck northeast Japan on Friday, March 11, causing a destructive tsunami that reached the west coast of the United States. Scholastic News Kid Reporters are collecting information about the quake and its aftermath and talking to people who have family and friends in Japan and looking into how kids can help with relief efforts. Find their stories in the Earthquake in Japan Special Report.

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