Last year’s deadly 9.0 earthquake in Japan, an 8.8 quake in Chile and the 2004 Sumatra-And­aman earthquake that registered 9.0 on the moment magnitude scale (which was followed by the great Indian Ocean tsunami) have raised alarm in some science and media circles. That apart, earthquakes have been a matter of popular faith: It is a popular belief among some Christians that earthquake activity has been on the increase in recent times. They believe that such an increase was predicted in the Bible by Jesus during the “Olivet Discourse.” Well, in the aftermath of the recent magnitude-5.8 earthquake in Virginia that actually cracked the Washington Monument for an indefinite period of repairs, people the world over are asking the same question: Is the number of earthquakes increasing?

Before we get to that question, one needs to know a little about earthquake science. According to US Geological Survey (USGS), the largest database of recorded earthquakes to date, earthquake occurs when two blocks of the earth suddenly slip past one another. It represents the abrupt release of seismic strain that has built up over the years as plates of the earth's crust slowly grind and catch against each other. The surface where they slip is called the fault or “fault plane”. The location below the earth’s surface where the earthquake starts is called the “hypocentre” and the location directly above it on the surface of the earth is called the “epicentre”. Sometimes an earthquake has foreshocks. These are smaller earthquakes that happen in the same place as the larger earthquake that follows. Scientists can’t tell if an earthquake is a foreshock until the larger earthquake happens. The larg-est, earthquake is called the mainshock. Mainshocks are always followed by aftershocks. The biggest earthquake ever recorded was the 1960’s magnitude-9.5 Chilean earthquake. It accounted for about a quarter of the total seismic strain released worldwide since 1900. According to geophysicist Richard Aster at the New Mexico Institute of Mining and Technology in Socorro, in just three minutes, the recent quake in Japan unleashed 1/20th of global total.

Are earthquakes really on the increase? Although it may seem that we are having more earthquakes recently, earthquakes of magnitude 7.0 or greater have remained fairly constant, according to USGS. A partial explanation about the increase in earthquakes may lie in the fact that in the past 20 years, because of the tremendous increase in the number of seismograph stations in the world and the many improvements in global communications, we are able to record earthquakes more consistently, including small earthquakes, which were undetected earlier. Just to give you an estimate, in 1931, there were about 350 stations operating in the world; today, there are more than 8,000 stations. The National Earthquake Information Center (NEIC) now locates about 20,000 earthquakes per year or approximately 50 per day. World-wide, strong earthquakes happen more than once per month. Smaller earthquakes, such as magnitude 2 earthquakes, occur several hundred times a day. To create a mountain system like the Himalayas it might take several million medium sized earthquakes over tens of millions of years.

In reality, our perception that earthquakes are increasing could have been skewed by the ubiquity of the media and its usage of modern communications. Never before were we able to learn of events that transpire half a world away in so quick a time. Our awareness of events has increased — even when the events themselves have not.

This line of reasoning is supported by recent research at the University of California, where researchers went back over the world's earthquake records dating back to 1900 and found that statistically there were no significant rise in the number of big quakes — 7.0 and higher — over time. “One has to be careful, because humans have a tendency to see patterns in random sequences,” said lead author, Peter Shearer, of the UC Berkeley Department of Statistics. “So what we wanted to do here was apply statistical tests to see whether you could say it wasn't just a random sequence of events,” said Shearer, whose study appeared in the Proceedings of the National Academy of Sciences earlier this year. “Those tests showed that you can't say that it is not random; that is, there is not a statistically significant degree of the clustering of events,” he said. Even though there is “a disproportionate number of very large 8.5 earthquakes between 1950 and 1965”, there were uncommonly fewer of these during a much longer period afterward from 1965 to 2004. And although there has been a more frequent rate of 8.0 and larger quakes since 2004, in the past five years in particular, “there have been rates nearly as high in the past”, said the study. The findings are in line with another study in Nature Geo­science earlier this year that found the regional hazard of larger earthquakes has increased after a main shock, but the global hazard has not.

Bottom line: Earth isn’t becoming more active, dangerous, or even “out of control”. Despite what esteemed mainstream media networks would have you believe, the simple reality is that statistics do not support these fears.

(The writer is a faculty member of Carnegie Mellon University, Pittsburgh, US, and knowledge editor of Financial Chronicle)