The main cause of earthquakes is the movement of the Earth’s lithospheric plates due to processes occurring in its more viscous interior. There are three main types of movements between large lithospheric plates:
- spreading, where oceanic plates form reefs and large mid-ocean ridges;
- subduction in plate overlap zones, where one plate subducts beneath another (Pacific Belt in Chile, Alaska, Japan). Similar processes occur during collisions between two continental plates (Himalayan, Alpine);
- lateral displacements that occur at transform faults (the San Andreas Fault in California, the North Anatolian Fault in Turkey).
The Earth’s surface is slowly deformed by the relative movement of tectonic plates. This movement is accompanied by friction in the rock contact zone and the accumulation of deformational stress. Rocks resist this stress and, like a spring, are compressed, deformed, accumulating elastic energy.
When a threshold value is reached, the energy is released in a few seconds, spreading seismic waves around like a spring and causing earthquakes. After this, the contact zone is blocked again, and a new cycle of energy accumulation begins.
Which regions are most prone to earthquakes?
Although it is impossible to predict when strong earthquakes will occur, some regions of the world are much more vulnerable to such natural disasters than others. The largest earthquakes occur in subduction zones, where two lithospheric plates collide and one dives beneath the other. The greatest tensions accumulate here, causing the most destructive disasters. The greatest stress accumulates here, causing the most destructive disasters. Regions located on or near active plate boundaries are more at risk of earthquakes.
Destructive energy also accumulates in areas where plates move sideways instead of one diving beneath the other. Here earthquakes occur practically on the surface and can be very powerful. At the same time, other areas of the Earth’s crust, located far from plate boundaries, are relatively calm, such as Siberia, Canada or Central Africa.
Regions of the highest seismic risk
If tectonic activity takes priority in determining seismic hazard in a region, then disaster risk assessment is primarily related to the population’s vulnerability to earthquakes. In this case, the population density of the region, construction standards, disaster warning system are taken into account.
Japan and Indonesia
These regions have the highest seismic risks in the world due to their proximity to three subducting lithospheric plates. The east coast of Japan is most prone to earthquakes and tsunamis. Thus, during the powerful 9.1 magnitude earthquake in 2011, Japan experienced a technological catastrophe despite implementing the highest seismic construction standards. It was aggravated by a tsunami wave coming from the ocean.
Thanks to directed efforts, Japan is able to significantly limit the number of victims in destructive disasters. Much earlier, in 2004 Indonesia also suffered from a powerful earthquake with a magnitude of over 9.0 and the tsunami it triggered. The cataclysm occurred in the ocean (seaquake), which led to large casualties on the coast.
The Mediterranean region and the Antilles
Despite their distance, Haiti and the Mediterranean regions of Turkey experience similar problems – high earthquake risks and significant casualties among the population due to the lack of seismic construction standards. In 2010, more than 220, 000 people died in Haiti due to building collapses. The events of February 2023 in the densely populated part of Turkey, situated in the zone of several strike-slip faults, led to numerous casualties and the collapse of buildings unable to withstand strong tremors. Tectonics makes the Mediterranean region an area of high seismic risk, including the threat of tsunamis. In addition to Turkey, the population of Greece and Southern Italy is particularly at risk.
California
The two largest cities in California, San Francisco and Los Angeles, located on the large San Andres Fault, are preparing for a powerful earthquake. The previous event occurred in 1908, and for more than a century, stress has been building at the junction of tectonic plates. Scientists cannot predict exactly when the next strong earthquake will occur.
Andes and Himalayas
Despite efforts to bring buildings into compliance with seismic standards, Chile and Peru remain countries prone to significant seismic risk due to the movement of the Pacific Plate beneath the South America Plate. In 1960, the most powerful earthquake in modern history was recorded in Chile with a magnitude of 9.5. In the year 800, a similar earthquake caused a devastating mega-tsunami on the coast of Chile. The local surviving population took refuge far from the coast, preserving the memory of this catastrophe for over 1000 years.
The capital of Nepal, Kathmandu, located near the Himalayan range, is at significant seismic risk due to the drift of continents and the split of the Indian Plate. Research confirms concerns about the potentially devastating magnitude 9.0 earthquake in this densely populated region with low seismic building standards.