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Will This Earthquake Cause Damage? – Part 1

Understanding Big Earthquakes

Maiclaire Bolton    |    Natural Hazard Risk

Earthquakes have the potential to cause major destruction and disruption to society. Damage caused by earthquakes can be catastrophic and can have both a humanitarian and financial impact.  So when an earthquake occurs, having a prompt understanding of potential catastrophic consequences is critical for risk managers, who rely on this information to make informed decisions about how to manage the impact of disastrous events. With services like theUSGS Earthquake Notification Service (ENS) providing readily available, automated earthquake notifications, obtaining information about earthquake activity around the world is now easier than ever.

Several million earthquakes occur each year worldwide, but many of these are actually insignificant (i.e. too small or in remote locations), and should not cause any great concern. Despite the large number of events, the USGS locates approximately 50 earthquakes each day, or about 20,000 a year. Fortunately, only a small number of these annual events will cause any significant damage. So when you receive a notification that there has been an earthquake, how do you know if you need to be concerned? Here’s my advice: Think like a seismologist!

Recent Large Earthquakes around the Globe

Before we dive in to the specifics of thinking like a seismologist, let’s review the most recent large earthquakes that have occurred around the world. In 2011, an M9.0 earthquake struck off the coast of Japan causing a massive tsunami which lead to more than $200 billion in economic damages and more than 19,000 lives lost. Also in 2011, a series of strong earthquakes struck the Canterbury region of New Zealand – cumulatively leading to more than $15 billion in economic losses1. So far in 2015, eleven earthquakes have been recorded in the M7 to M8 range2. This includes the devastating earthquakes to strike Nepal in April and May, but most of the others occurred in remote locations far from any exposure.

Since the time of the Great Tohoku earthquake in Japan, one of the largest earthquakes to occur globally has been a M8.3 earthquake off Russia’s Kamchatka Peninsula, in the Sea of Okhotsk in May 2013. This event is a great example of a very large magnitude event that should not cause concern, as although a M8.3 earthquake is very large, it not only occurred in a low-exposure area - more importantly, it was approximately 600km deep, and earthquakes of this depth are actually too deep to cause damage. More recently, an M8.3 earthquake occurred off the coast of Chile on September 16, 2015. Compared to the earthquake of the same magnitude in the Sea of Okhotsk, the Chile earthquake was shallow and produced strong ground motions on land. Fortunately, the event was still quite a distance from larger cities and concentration of exposure in Chile and the losses were relatively low given the very large magnitude.

Understanding Big Earthquakes

As unpredictable as earthquakes can be, there is one thing that is very intuitive: the larger the magnitude, the greater the potential of damage. Or more simply –big earthquakes cause more damage than small earthquakes. However, it’s not just magnitude that needs to be considered, as sometimes a smaller magnitude earthquake can cause more damage than one of larger magnitude.

When you hear of the potential of an earthquake occurring, what you really want to know is – Will it result in significant damage? Another blog will be posted where I will be sharing specific tips on how to think like a seismologist.

[1] http://media.swissre.com/documents/sigma2_2012_en.pdf
[2] http://earthquake.usgs.gov/earthquakes/search/

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