Geologists know that the most devastating earthquakes happen along subduction zones — those areas where tectonic plates slide beneath another. Less known, however, is where exactly along these danger zones an earthquake is likely to occur. But as new research from the University of Sydney suggests, scarred regions along the ocean floor — what are called fracture zones — are remarkably strong indicators of where great earthquakes are likely to happen. Based on this insight, the researchers have created a comprehensive map of our planet's most threatening danger zones.
According to geologists Thomas Landgrebe and Dietmar Müller, about 87% of the 15 largest earthquakes (8.6 magnitude or higher) and 50% of the 50 largest earthquakes (8.4 magnitude or higher) from the past 100 years can be linked to intersections between oceanic fracture zones and subduction zones. At the same time, smaller earthquakes don't tend to share this connection.
Not surprisingly, the catastrophic 2011 Tohoku-Oki and 2004 Sumatra quakes are located directly at these geological hotspots.
Other danger zones include the western coast of South America (especially Peru and southern Chile), western Central America, the west coast of North America, the southern Caribbean, and the continental ridges of the north Pacific.
In order to get the data required to make their map, Landgrebe and Müller analyzed 1,500 earthquakes that occurred since 1900. In addition, they studied the pre-existing geophysical evidence showing the Earth's fracture zones and subduction zones.
The information was then parsed through a data mining software program — one that was originally developed to analyze online user data. But instead of surveying items that are most likely to appeal to an Internet user, they used it to find tectonic environments most suitable for generating huge earthquakes.
But while the data mining technique helped to produce a map, it did not explain why great earthquakes are more prominent at these intersections.
The geologists theorize that it's on account of the physical properties of fracture zones — which result in strong, persistent coupling in the subduction boundaries. Essentially, the subduction areas become locked and capable of accumulating huge stresses over long periods of time. So when a critical threshold is reached, all the stored energy is released in a single cataclysmic event.
You can read the entire study at Solid Earth.
Image via Müller and Landgrebe.