Giant Earthquakes are not as Random as Thought

Why are Eartquakes happening like never before?

Giant Earthquakes have rattled various parts of the world from time to time. From Asian regions like Bangladesh and India to Chile and Los Angeles in American territories. The long-term perception about them was that they are natural disasters which have no scientific explanation. But, like many other theories, this idea has changed. According to the latest study conducted by scientists at Chilean lakes, these earthquakes reoccur at relatively regular intervals.

Sediment cores of the lakes were used for analyzing procedure and the results were concluded. The scientists also said that if we take smaller earthquakes into account, the irregularity in this pattern increases. This happens to an extent where earthquakes happen irregularly in time.

Jasper Moernaut, who is an assistant professor at the University of Innsbruck in Austria, described the Chilean Earthquake:

“In 1960, South-Central Chile was hit by the largest known quake on Earth with a magnitude of 9.5. Its tsunami was so massive that – in addition to inundating the Chilean coastline – it traveled across the Pacific Ocean and even killed about 200 persons in Japan. Understanding when and where such devastating giant earthquakes may occur in the future is a crucial task for the geoscientific community.” He further added that “These Chilean lakes form a fantastic opportunity to study earthquake recurrence. Glacial erosion during the last Ice Age resulted in a chain of large and deep lakes above the subduction zone, where the most powerful earthquakes are getting generated.”

A common concept among scientists is that the energy released during a giant earthquake is so much that stress accumulation of centuries is needed in order to produce such a tragic incident again. This is the major hurdle that science faces today to determine the pattern of such events. The data available is not sufficient enough to gauge the trend. The study of Chilean lake shows that each strong earthquake is accompanied by an underwater landslide. That part of the land is settled in the sedimentary layers of the water body.

Scientists sampled these layers into an 8-meter long core to retrieve the complete history of earthquakes over the last 5000 years. This record included 35 instances where the magnitude was more than 7.7. These happenings take place after 292 years on average. Similarly, smaller earthquakes can take place after 139 years. Having said that, scientists also warned us that there is 29.5% chance of such an event in next 50 years.

In light of this study and the other research that is being done in this field, we need to break the traditional mindset about these events and rethink the causes of giant earthquakes. The major arguments about giant earthquakes before December 2004 were that:

•  It was thought that only the subduction of young, buoyant crust could produce giant earthquakes but the 2004 earthquake in Sumatra region had an old and dense crust.
•  Secondly, it was thought that the convergence rate had to be fast. The movement speed of plate was slow at the location of the 2004 earthquake.
•  Lastly, it was a popular belief that a large earthquake could only occur in a region with no back-arc spreading. Contrary to that Sumatra region has a lot of islands.

After this horrific incident, humans needed to perform a new assessment in order to calculate the risk of earthquakes. The mechanism used by scientists was to identify the areas of locked fault zones. The locations and sizes of such regions were mapped. Surface deformation measurements were used as the mapped regions were somewhere deep in the Earth’s crust. One way to measure this entity was the use of Global Positioning System (GPS) stations. These stations can measure the movement of a surface to a fraction of a millimeter. The useful information extracted from this method was:

The regions which experienced no large earthquakes had a relatively narrow locked fault zone with an average width of 10 kilometers while the regions which experienced large earthquakes had a 10 times larger locked fault zone ranging to a width of 175 kilometers.

All this data can be used to calculate the intensity of an earthquake, in a region where stress is building and the chances of a calamity are high. Under these circumstances, we can easily conclude that Giant Earthquakes are certainly not that RANDOM.