
Our planet has numerous regions with high seismic hazard levels. However, some of these regions have experienced the most powerful earthquakes, causing total devastation, altering landscapes, triggering tsunamis, and even impacting the course of history.
The deadliest earthquakes are usually atypical and occur under specific scenarios. The scale of casualties and destruction often depends on:
- Hypocenter depth β surface earthquakes are typically more intense and exert greater seismic stress;
- Population density, with potential victims of seismic tremors;
- The ability of buildings and structures to withstand strong shocks and vibrations before collapsing;
- The presence of secondary hazards β powerful aftershocks, landslides, and the arrival of tsunami waves.
Events like the 2004 Indonesia earthquake and the 2011 Sendai (Japan) earthquake triggered tsunamis that claimed over 250,000 lives. Conversely, the two most powerful earthquakes ever recorded β Chilean earthquakes in 1960 and 2010 β had relatively fewer casualties. Can we assess the likelihood of a powerful earthquake occurring in a seismically hazardous region and how deadly it will be?
Subduction Zones β Why Are They Dangerous?
In subduction zones, two tectonic plates converge, with one being forced under the other. These conditions present significant geological hazards. The largest earthquakes on Earth occur at the contact of two such tectonic plates, and if the event happens in the ocean, seabed movement generates large tsunamis. Chains of active volcanoes form along subduction zones, many of which are capable of explosive eruptions.
Such seismically and volcanically active conditions create dynamic landscapes, lead to ecosystem changes, and even affect the planet’s climate. Large cities around the world are situated along subduction zones, placing their populations at the greatest risk. Traditionally, it is believed that megathrust earthquakes in subduction zones occur with a certain periodicity, depending on the type of plate sliding, their sizes, and geology. However, other factors can also influence the behavior of the sliding and the recurrence of earthquakes in open subduction zones, such as:
- Soil or seabed erosion, increasing stress in the upper plate faults;
- Climate changes characterized by intensified storms;
- Changes in the composition of seawater and the transportation of large amounts of impurities into the oceanic fault;
- Volcanic and magmatic processes;
- Changes in the temperature of the Earth’s crust, which can redistribute deformation across subduction zone systems;
- Extraction of natural resources and the formation of cavities in the Earth’s crust.
The list of factors affecting seismic activity in subduction faults is constantly growing. This is the main reason why traditional science has not yet learned to make accurate and timely short-term earthquake forecasts.
Earth’s belts with the highest seismic hazard
The most dangerous region, where sudden and severe earthquakes with significant consequences occur, is considered to be the Pacific Ring of Fire. Seismic activity in this area (81% of all earthquakes on the planet) is due to the presence of powerful subduction processes. Besides it, there are several other zones with high earthquake risks:
- The Alpide belt, extending from Java through Sumatra, the Himalayas, the Mediterranean, and into the Atlantic. This belt accounts for about 17% of the world’s largest earthquakes, including some of the most destructive, such as the magnitude 7.6 quake in Pakistan in 2005, which resulted in over 80,000 deaths. Another example of activity in the Alpide belt is the magnitude 9.1 earthquake in Indonesia in 2004, which triggered a tsunami that killed more than 230,000 people;
- The Mid-Atlantic belt with diverging plates and the formation of an oceanic ridge on the seabed. Most of the Mid-Atlantic Ridge is located deep underwater, and its seismic activity does not impact humans. However, Iceland, which sits directly above the Mid-Atlantic Ridge, has experienced earthquakes with magnitudes of 7.0. Other seismically hazardous zones are scattered across different regions of the world. Notable examples in the United States include New Madrid, Missouri (1811-1812), and Charleston, South Carolina (1886). However, such events usually occur many years apart.
New Tools for Deeper Seismic Risk Assessment
New knowledge and technologies allow geophysicists and seismologists to study processes in and around subduction zones more comprehensively. Scientists are utilizing new methods and tools that were previously unattainable:
- High-resolution remote sensors aboard satellites, drones, and submarines enable thorough mapping of the Earth’s surface to identify the causes and consequences of seismic events.
- Various types of sensors, including multispectral imagers, interferometric synthetic aperture radars (InSAR), and lidars, allow capturing landscapes of both land and marine areas.
- System cameras mounted on suborbital platforms are used to create ultra-high-resolution topography, facilitating quick and effective analysis of damage and changes caused by seismic activity.
- Simple networked sensors can monitor climatic conditions before and during earthquakes.
These innovative tools provide insights into how lithospheric formations deform over time, and how geological and atmospheric processes, working together, can create potential seismic hazards.