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Shaking up the earthquake scale in California

Northern and Southern California have finally gotten their acts together and decided to quantify earthquake magnitudes in the state the same way.

For the past six years, the groups of scientists that collect seismic data for northern and southern California have been using slightly different ways to calculate a parameter called ML, or local magnitude. This is a minor problem because, um, the state is supposed to be working as one under the rubric of the California Integrated Seismic Network.

ML is actually the original magnitude scale as defined by Charles Richter and Beno Gutenberg in 1935. It quantifies magnitude as how much a tremor makes the needle on a seismograph jitter; a 1-centimeter jolt measured 100 kilometers away, for instance, means the quake must be magnitude 3. ML remains useful as one among many of the magnitude scales that have sprung up over the years.

Yet researchers in both halves of California have used slightly different ways to determine ML. It all adds up to a roughly 0.15-magnitude difference when looking at 100 earthquakes – so don’t worry that some big quake will rip through San Francisco and get drastically underreported. Fixing the reporting difference is “more to unify the magnitude reporting in the state than anything else,” says Peggy Hellweg, operations manager for the ”http://seismo.berkeley.edu/">seismology laboratory at the University of California, Berkeley.

Southern California has finally gotten the new reporting system up and running in the past few weeks; Northern California is still working on implementing it.

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    Susan Hough said:

    The original Richter scale—the basis for all subsequent magnitude scales—was formulated by Charles Richter; he was the sole author of the seminal 1935 publication presenting the scale. Gutenberg contributed to further development of the scale, in particular its extension to earthquakes world-wide.

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