They may be but it doesn't make predicting them any easier

Is there any seismic significance to the fact that already this year there have been massive earthquakes in Haiti, Chile, Taiwan and Turkey?

According to Mary Lou Zoback, vice president of earthquake risk at RMS, there is not, the only remarkable thing to note is that this year huge earthquakes have occurred in densely populated regions and have therefore hit the headlines.

In January Haiti was devastated by a magnitude 7 quake, which leveled parts of the capital Port au Prince. At the end of February a huge magnitude 8 quake struck offshore of Chile and ranked in the ten most powerful quakes in history. A strong magnitude 6 earthquake struck Taiwan in March followed by another magnitude 6 quake in Turkey.

This level of earthquake activity is not unusual, says Zoback. “This level of activity is consistent with long-term average earthquake activity. On average, 17 magnitude 7 or larger earthquakes occur globally each year. There is generally one magnitude 8 or larger earthquake each year. Many of these earthquakes occur either very deep or in remote oceanic regions, so they are rarely felt.”

There is, however, evidence that some of the quakes may be linked. A large earthquake changes the stress field in its immediate vicinity, generally this is an area with dimensions equal to the fault rupture length, in the case of the recent Chile quake, this would be about 350 km.

Mehrdad Mahdyiar, director of earthquake hazard at AIR Worldwide, added that some level of earthquake clustering is possible, considering the interconnectivity of fault lines. “We know that large earthquakes change the state of the stress on their nearby faults and thus advance or delay their ruptures. Also, it has been shown that the long period seismic waves created by large magnitude earthquakes can influence the state of stress on distant faults and under favorable conditions, could initiate earthquake activity on faults that are close to their rupture state.”

He added: “However, there is a lot that we do not know about the dynamics of how earthquakes are triggered and the issue of clustering is an interesting topic of research.”

But this doesn’t mean that one earthquake immediately tirggers another, Zoback said, the February 2010 earthquake in Chile could have been set off by the 1960 magnitude 9.5 earthquake on the same fault line, so the triggered quake occurred 50 years later.

The time lag makes it very hard to predict when an earthquake is going to occur. “Even when we can model a potential increase in stress, and there may be a link, a 50 year time lag is pretty large,” said Zoback.

“The real significance of the recent events is in their reminder of the on-going peril—earthquakes are occurring all the time and generally they strike without warning. We do not have days of dramatic satellite images alerting us,” she added.

“I think the most important message from these recent earthquakes is that the scale of disasters we have seen, particularly in Haiti, are not isolated events. Many of the world’s largest cities are subject to significant earthquake hazards, they are also hotspots of extreme poverty, where millions of people live in informal and substandard housing. As development proceeds, we should be speaking up to be sure that risk reduction be included as part of poverty reduction goals.”