Last updated 6 months ago by Michael Darmanin
Where do really big earthquakes take place? This is one of the biggest questions for earth scientists, but also for the nearly 4 billion people who live close to zones that are prone to major earthquakes.
Earth scientist Dr. Ylona van Dinther of the Utrecht University and her colleagues from renowned Italian and Swiss universities have taken the initiative in answering this question with new models they have developed. These predict how different characteristics of the earth’s crust influence the magnitude of earthquakes and the amount of damage they cause.
Scientists have already suggested that the effects caused by giant earthquakes with a magnitude of more than 8.5 Mw on the Richter scale are partly determined by sediment thickness. This sediment which lies on the heaviest oceanic plate shifts on a massive scale during an earthquake when these plates push their way into the mantle as a result of the quake. They made this suggestion based on observations from the past 50 to 100 years.
Sedimentary layers and their effect during earthquakes
With their new models, which simulate both long and short timescales, Van Dinther and her colleagues were able to examine this idea. The results show that the strongest earthquakes do indeed occur in places where the sediment layer is thick.
This could be the difference between an earthquake which only causes minor damage compared to the one that caused a city-wide catastrophe such as the Great Sendai Earthquake which took place off the coast of Tōhoku on the 11th of March 2011. That same quake caused a tsunami which swept over the entire region leading to nuclear meltdown at the Fukushima power plant with widespread damages totaling over US$ 360 billion.
The Model of Van Dinther
Van Dinther and her colleagues concluded that this difference in quake magnitude is due to the weight of the accumulating sediments which force their way up the subducing plate, flattening the sliding surface between the two plates and increasing the surface area in turn allowing the earthquakes to amplify in size (see diagram below).
Large tsunamis with a thick sediment layer
Van Dinther’s model also predicts that larger earthquakes with more devastating effects occur as a result of sedimentary shifts on the upper continental crust (see figure above). These types of earthquakes are more capable of triggering large tsunamis due to the abundance of sedimentary deposits that lie at crust level.
Matter of time for certain regions
There are a number of regions worldwide where the sedimentary deposits are known to be high such as the region of Calabria, the Aegean Sea and the region of Makran, a mountainous zone with a coastal line that spans an area over Iran and Pakistan. Although only minor earthquakes have been experienced at these locations in recent years, researchers believe that it is simply a question of time before one occurs below sea level where sedimentary movements will play a key role in the quake’s devastating effect.
Source: Utrecht University