WARRING GODS, superheroes sneezing, and a more than memorable night can all make the earth’s crust shiver, but the main cause of earthquakes is really the movement of tectonic plates.
For those that have forgotten secondary school geography, there are seven major tectonic plates and nearly innumerable smaller plates across the planet. Their movement is dictated by convection currents beneath the surface of the earth where the molten innards of the planet flow and shape it.
Science has yet to find a way to predict the date, time, location or magnitude of earthquakes, and so they often strike without warning. Earthquakes may range in intensity from slight tremors that are frequently felt to rare, great shocks that last from a few seconds to as long as several minutes.
Big earthquakes are low-probability but high-impact events, and shocks (fore, main, and after) may come in series lasting several days or even months.
Most people are unaware of the fact that earthquakes can come in swarms and storms. More than just aftershocks, earthquake swarms are sequences of earthquakes striking in a specific area within a short period of time.
They are different from earthquakes followed by a series of aftershocks by the fact that no single earthquake in the sequence is obviously the main shock, therefore none have notable higher magnitudes than the other.
Sometimes a series of earthquakes occur in a sort of earthquake storm, where the earthquakes strike a fault in clusters, each triggered by the shaking or stress redistribution of the previous earthquakes. Similar to aftershocks but on adjacent segments of fault, these storms occur over the course of years, and with some of the later earthquakes as damaging as the early ones.
Though we cannot predict their occurrence, there is tireless effort being expended to monitor the globe for a potential solution. Animals tend to have some sense of natural happenings but that isn’t a reliable enough way to keep the world safe.
The Comprehensive Nuclear-Test-Ban Treaty Organisation (CTBTO) has been spying on earth for the past 18 years and is just one of the many organisations that monitor earth’s entire sphere of activities.
Using a vast network of sensors designed to detect a rogue nuclear test – like the one North Korea initiated back in 2013 – instruments have been repurposed to monitor everything from tsunamis to pollution.
Both weapons sensing and environmental monitoring are “two sides of the same coin”, said Raymond Jeanloz, an earth scientist at the University of California, Berkeley. “They are the same desire to monitor what’s going on in the environment around us,” said Jeanloz, who co-authored a paper on the topic published in the journal Science.
For instance, the international monitoring system for nuclear tests uses seismic and water-based acoustic sensors, which measure sound waves that ripple through the ground after a nuclear explosion. But those same sensors could have been used to detect the devastating 2004 Indian Ocean tsunami that killed more than 230 000 people.
The CTBTO’s International Data Centre records more than 30 000 seismic signals every day, and typically finds about 130 seismic events, or earthquakes. The number and type of signals from a certain place may indicate a small event or a larger one, such as an earthquake. Because seismic and acoustic waves travel at different speeds and along different routes, various sensors can help determine the time, location, and magnitude of each earthquake.
“Beyond nuclear monitoring, we need to understand all kinds of seismic events – which pays off in improving earthquake, fault and tectonic monitoring,” said Randy Bell, director of the CTBTO’s International Data Centre. “It also has improved our understanding of the earth itself.”
