Historical data from the US Geological Survey shows that on average, only one earthquake of magnitude 8 or above on the Richter scale, known to scientists as a ‘Great Earthquake’, takes place in a year anywhere in the world.
Fewer than one a year, in fact — considering that only 95 such events have happened since 1900. But there have been aberrations. 2007, for example, witnessed as many as four 8-plus earthquakes — in the Kuril Islands in North Pacific, Solomon Islands near Australia, central Peru, and in Sumatra in Indonesia. And each of the years 1920, 1923, 1946, 1960 and 1995 saw three of these big events.
On the other hand, in recent memory, the years 2002, 2008 and 2013 did not have any 8-plus earthquake. And yet, as many as 20 ‘Great Earthquakes’ have taken place in the 15 years since 2000.
The frequency of smaller earthquakes increases exponentially as we look at smaller magnitudes. Earthquakes of magnitude between 7 and 7.9 on the Richter scale happen 15 times on average every year; and those between 6 and 6.9 on the Richter scale, 134 times on average.
An eight-plus magnitude quake is yet to happen this year, while seven earthquakes of magnitude between 7 and 7.9 have already happened, including two in Nepal.
The April 25 earthquake was measured 7.8 on the Richter scale while Tuesday’s earthquake was of magnitude 7.3. Papua New Guinea has had three earthquakes of magnitude more than 7, including two this month. Indonesia had an earthquake of magnitude 7 in February.
Experts have been warning that a catastrophic ‘Great Earthquake’ is due in the Himalayas any time.
The 2,500-km stretch from the Hindukush mountains to the northeastern part of India, which is the meeting point of the Indian and Eurasian tectonic plates, has not had an 8-plus earthquake since 1950. Scientists say the accumulated energy along the faultline is enough to produce a massive earthquake of more than 8.5 on the Richter scale.
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