NU Online News Service, Oct. 17, 2:30 p.m. EDT

Scientists believe there is evidence that great earthquakes occur in clusters over a period of years and that a significant event is on the horizon, according to a report from catastrophe modeler Eqecat.

The report, “Spatial and Temporal Earthquake Clustering: Part 1, Global Earthquake Clustering,” lays out evidence that giant earthquakes of magnitude 8 or higher may occur in clusters over a decade or more.

The authors of the report, Paul C. Thenhaus, Kenneth W. Campbell and Mahmoud M. Khater, say the occurrences of great and giant earthquakes “on a global scale cannot be attributed to chance.”

They say the giant Andaman-Nicobar (Sumatra, Indonesia) earthquake of 2004 of magnitude 9.1 began “a new cycle of global great earthquake activity.”

If this cycle follows the cycle of earthquakes in the 1950-1965 timeframe, “we may be only about halfway through the cycle, and the largest earthquake in the current cluster may not have yet occurred.

During that period starting 1950, there were three earthquakes of magnitude 9 or higher:

Kamchatka, magnitude 9 that struck in 1952.
Prince William Sound, Alaska, magnitude 9.2 that struck in 1964.
Chile, magnitude 9.5 that struck in 1960.

Why this is happening is unknown, they say, but it may have something to do with “post-seismic relaxations and strain transfer mechanisms in the deep ductile layers of the Earth.”

If earthquakes follow the pattern of the 1900s then a third major earthquake is a very real possibility.

So far this century, there has been the Indonesia 9.1 earthquake that struck in 2004 and then the Tohoku-oki earthquake and tsunami in 2011 which was a magnitude 9 earthquake.

Regarding how destructive an earthquake is, whether it is devastating or not has less to do with magnitude than other factors such as proximity of “occurrence to population centers, construction vulnerability to shaking, soil stability, and local soil, basin and topographic amplification.

“This distinction between earthquake consequences and magnitude is important,” the report notes. '“Devastating earthquakes' as a class have only an obscure relationship to magnitude.”

The report is the first in a series of three reports Eqecat plans to produce on this subject of global clusters of damaging earthquakes.

Special Reports /

Scientists See Evidence of Great Earthquake Clusters

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