(freshrant.com) Is there historical precedent for very large earthquakes to strike in the same region within relatively short intervals?
When there is a major earthquake measuring around 8.0 or more on the Richter scale, there is often another quake of equal or greater force within months of the first temblor. Keep in mind the March 11th quake off the coast of Japan was measured at 8.9/9.0, the largest quake in the history of Japan.
The following series of sequential quakes within relatively short intervals were often followed by years, even decades, of far lesser seismic activity. Note nearly all of the examples of the past two hundred years were recorded in Japan.
The 1811-1812 New Madrid Earthquakes
The largest earthquakes ever recorded in the continental United States had their epicenters in Northeast Arkansas and the state of Missouri. The quakes changed the course of the Mississippi River and caused church bells to ring as far away as Boston. From December 16, 1811 until February 7, 1812 four shocks occurred measuring between 7.8 and 8.1.
The Tokai-Edo Earthquakes of 1854-1855
Conservative estimates suggest nearly 20,000 people were killed in three successive earthquakes, two of which measured at 8.4.
The Meiji Era Earthquakes of 1891-1896
This series of three earthquakes began in the fall of 1891 and ended in the summer of 1896, two of which were 8.0 and 8.5, claiming more than 34,000 lives and causing tsunamis as far away as Hawaii and California.
The Nankaidō-Fukui Quakes of 1946-1948
Eighteen months separated these 8.1 & 7.1 quakes that killed more than 5000.
The Great Chilean Earthquake of 1960
At 9.5, the largest earthquake ever measured, occurred following another earthquake in Arauco Province that had already knocked out communication and power causing Chile’s president to cancel celebrations for a public holiday to oversee emergency aid efforts.
The Nankaidō-Aomori Quakes of 1968
While these two quakes (7.5 and 8.2), occurred only 6 weeks apart in the spring of 1968, they did not cause a large number of casualties. But the second quake was followed by a tsunami that did cause significant damage to buildings in northern regions of Japan.
Has Japan, if not the entire ring of fire, entered new hyperactive era of increased seismic activity? Beginning with the Chūetsu earthquake in Niigata prefecture in October 2004, there have been no fewer than 15 earthquakes measuring 6.5 or greater.
Of particular note are The Kirul Island Earthquakes in the north of Japan, the only two Japanese temblors of this decade measuring greater than 8.0. Significantly, they occurred two months apart. An 8.3 quake struck on November 15, 2006, followed by a 8.1 quake on January 13, 2007.
I lived on the west coast of Honshu and felt the shaking when The Great Kobe Earthquake of 1995 struck. It is significant to note that while the quake measured in at “only” 6.8, it claimed more than 6,400 lives because its epicenter was located near a large metropolitan area. The Kobe quake should be a sober warning to the occupants of other urban areas in Japan.
The increase in frequency and the severity of quakes in Japan and its accompanying history of multiple and significant seismic events should give pause, but not too long, in planning strategies for future earthquake preparedness. To repeat a tired truism, for the Japanese and for many of the rest of us living in earthquake zones, it is not if, but when the next major destructive earthquake will occur.
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