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Is Southern California's San Andreas Fault the Hole in Mogi's Donut?

In 1969 the famous Japanese seismologist Kiyoo Mogi (1929-) wrote a paper entitled:  "Some Features of Recent Seismic Activity in and near Japan.  Activity before and after Great Earthquakes."  Published in the Bulletin of the Earthquake Research Institute, Japan [1], it described patterns of smaller earthquakes that precede great earthquakes. 

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A New Type of Forecast

The recent April 4, 2010 M7.2 Mexicali earthquake has been the subject of considerable analysis and speculation.  It occurred at a location of high probability in the California border region with Mexico, as shown by the Open Hazards viewer (available under the Tools tab).  And while the baseline forecast on this web site does an excellent job of forecasting locations of major events, we are continually seeking to improve our forecast technology, particularly to better capture times of heightened probability.

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Today's Magnitude 6.9 Earthquake, Yushu, China

An earthquake measuring 6.9 on the Moment-magnitude scale has struck southern Qinghai,
China, near the city of Yushu in the Tibet Autonomous Region.  Using the Hazard Viewer tool
on this web site, together with the Recent Earthquakes display, it can be determined that the ground
shaking resulting from the earthquake in Yushu was between 8% g and 12% g, equivalent
to Modified Mercalli Intensity V to VI.  Shaking of this intensity is enough to collapse some buildings
constructed of unreinforced masonry, as might be common in the region.

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Earthquake Insurance and You

In an article published today on the web site InsuranceRate.com, Lucas Eichman discusses earthquake insurance in California.  He quotes Glenn Pomeroy, CEO of the California Earthquake Authority:   "Lets say the 7.2 (Baja earthquake) that happened on Sunday happened under Los Angeles.  We would see massive destruction.  Homes destroyed.  Infrastructure badly damaged."

 

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Aftershocks

Aftershocks are earthquakes that are triggered by a previous, larger earthquake mainshock.  Today we know that aftershocks are a result of the transfer of stress from the region of the mainshock to surrounding, smaller faults.   About 5%-10% of mainshocks have foreshocks, which can be regarded as instances when the aftershock is larger than the mainshock.

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Earthquake Correlations - II

In the year 1657, the Dutch scientist Christian Huygens observed that if two pendulum clocks were mounted adjacent to each other on the same support, the subtle and almost imperceptible vibrations of the swinging pendulums would cause those pendulums to become synchronized, swinging in opposite directions.  He referred to this phenomenon as "odd sympathy".

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Earthquake Correlations

Haiti, January 12, 2010, magnitude 7.0.  Chile, February 27, 2010, magnitude 8.8.  Baja, April 4, 2010, magnitude 7.0.  Sumatra, April 6, 2010, magnitude 7.7.   Are they related?  Although it is rather unlikely, the simple answer is that no one knows for sure, because it is a very difficult proposition to unequivocally prove. 

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Today's Magnitude 7.7 Sumatra Earthquake

 

Yet another earthquake occurred today in Sumatra, Indonesia.  Preliminary estimates place the magnitude at 7.7, a very large earthquake.  The depth was about 30 km.  Earthquakes of this size can cause damage, injuries and deaths as was seen in Haiti. A tsunami watch was issued.

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Yesterday's Magnitude 7.2 Mexicali Earthquake

About 40 years ago a Japanese seismologist by the name of Kiyoo Mogi proposed the idea that before a large earthquake occurs, there are a series of earthquakes of increasing magnitude that occur as a "run-up" to the main event.  These events surround the eventual fault that breaks in the main earthquake in a kind of "donut" pattern, with the main earthquake then occurring in the "hole" of the "donut".  Since that time, seismologists call this type of precursory pattern a "Mogi Donut". 

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When Charleston was Destroyed

On January 9, 1861, the first shots of the American Civil War were fired in Charleston, South Carolina.  Cadets from the military school "The Citadel" opened fire on the Union ship Star of the West as it was entering Charleston harbor.  Twenty-six years later, the city of Charleston was destroyed by the largest earthquake to strike the eastern United States in recorded history.

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