Earthquakes are among the most powerful natural events on Earth. They can happen with little warning, last only seconds, and still leave lasting changes to landscapes, buildings, infrastructure and communities. Although scientists now understand far more about earthquakes than people did centuries ago, seismic activity still produces surprising effects that go well beyond the ground simply shaking.
Most earthquakes occur when stress that has built up along a fault is suddenly released. That movement sends seismic waves through the Earth, producing the shaking people feel at the surface. The severity of the effects depends on several factors, including the size and depth of the earthquake, local geology, distance from the fault and the way nearby buildings have been designed and constructed.
Earthquakes Can Affect Buildings in More Than One Way
Strong ground shaking is one of the most obvious earthquake hazards, but buildings can be affected in several different ways. Foundations may shift, walls can crack, structural connections can weaken and retaining systems may move. Older properties can be especially vulnerable when they were constructed before modern seismic standards or have already suffered deterioration.
This is one reason structural assessment and retrofitting play such an important role in earthquake-prone regions. Improving a building’s ability to withstand movement can reduce the likelihood of severe structural failure and help property owners identify weaknesses before another seismic event exposes them.
In areas with significant seismic activity, specialist assessment may be appropriate when there are signs of settlement, foundation movement or structural damage. Property owners in Southern California, for example, may use professional Los Angeles foundation repair services when investigating problems affecting foundations and other structural elements. The appropriate solution depends on the building, soil conditions and the nature of the damage rather than on earthquake risk alone.
The Ground Can Temporarily Behave Like a Liquid
One of the stranger effects associated with earthquakes is liquefaction. This can occur when strong shaking affects loose, water-saturated soil. The shaking increases pressure in the water between soil particles, temporarily reducing the soil’s strength and causing it to behave more like a fluid than a stable solid.
For buildings and infrastructure, the consequences can be serious. Foundations may settle unevenly, structures can tilt and sections of ground may move laterally. Liquefaction does not occur everywhere an earthquake happens; local soil composition and groundwater conditions play an important role in determining where the risk exists.
This explains why two buildings exposed to similar levels of shaking can experience very different outcomes. The condition of the ground beneath a structure may be just as important as the strength of the shaking itself.
Earthquakes Can Trigger Fires and Other Secondary Hazards
Not all earthquake damage comes directly from seismic movement. Major earthquakes can also trigger secondary hazards such as landslides, liquefaction, tsunamis and fires. Damage to utilities, electrical equipment and building systems can create additional problems after the initial shaking has stopped.
For property owners and those responsible for buildings, this illustrates why resilience involves more than protecting the structure against movement. Fire safety measures have a different purpose from seismic strengthening, but both can form part of wider planning for how a building performs when something goes wrong. Passive fire protection is designed to restrict the spread of fire and smoke through features built into the property, including compartmentation, fire stopping and fire doors.
For UK property owners and building managers reviewing these measures, information about fire doors, fire stopping and wider passive fire protection services is available from www.preventr.co/. These measures do not prevent earthquakes or structural damage; they address the separate problem of limiting the movement of fire and smoke within a building.
Aftershocks Can Continue Long After the Main Earthquake
An earthquake sequence does not necessarily end when the strongest shaking stops. After a significant earthquake, smaller earthquakes known as aftershocks can continue in the surrounding area. Their frequency generally decreases over time, although the sequence can continue for an extended period.
The terminology can be slightly confusing because scientists identify a mainshock partly by comparing events within the same sequence. If a later earthquake turns out to be larger than the first, the larger event becomes the mainshock and the earlier earthquake may instead be classified as a foreshock.
This is one reason earthquake sequences can only be fully understood after scientists have had time to examine how the events developed. What initially appears to be the principal earthquake is not always the largest event in the sequence.
Mars Has Earthquakes Too — They Are Called Marsquakes
Earth is not the only planet where seismic activity has been detected. NASA’s InSight mission placed a seismometer on Mars and recorded seismic events known as marsquakes. Studying these events helped scientists investigate the structure of the Martian crust, mantle and core.
Mars does not have the same system of moving tectonic plates that drives many earthquakes on Earth. Instead, seismic activity can result from stresses within the planet as it cools and contracts, while impacts from meteoroids can also generate detectable seismic waves.
InSight detected more than a thousand seismic events during its mission, including a magnitude 5 marsquake in 2022. These measurements gave researchers a new way to study a planet that cannot be explored internally through drilling or direct observation.
Icequakes Are Real, but They Are Not Ordinary Earthquakes
The word “earthquake” is sometimes used loosely for other types of sudden ground movement. One unusual example is a cryoseism, commonly called an icequake or frost quake. These events can occur when rapid freezing causes water in saturated ground or rock to expand, creating stress that is released suddenly.
An icequake can produce a loud noise and noticeable vibration, which may make it feel similar to a small earthquake. However, the underlying process is different from the movement along geological faults responsible for tectonic earthquakes.
The distinction matters because similar sensations at the surface do not necessarily have the same cause. Seismologists examine wave patterns, locations and other evidence to determine what produced a particular event.
Earthquake Magnitude and Intensity Are Not the Same Thing
When an earthquake is reported, its magnitude often receives the most attention. Magnitude measures the size of the earthquake at its source and is represented by a single value for the event. Intensity describes the effects of the shaking at a particular location.
That means one earthquake can produce very different levels of intensity across different places. A community close to the fault may experience severe shaking while another much farther away notices only gentle movement. Soil type, building construction and local geography can also affect what people experience.
This difference helps explain why magnitude alone cannot describe the full impact of an earthquake. Two events of similar magnitude may cause very different levels of damage depending on where and how they occur.
People Once Explained Earthquakes Through Myths and Legends
Before plate tectonics and modern seismology provided scientific explanations for earthquakes, cultures around the world developed stories to explain why the ground suddenly moved.
One famous Japanese legend involves a giant catfish called Namazu. According to the traditional story, the creature lives beneath Japan and is normally restrained so that it cannot move. When that restraint fails, the catfish thrashes around and the ground shakes.
The story is folklore rather than a scientific explanation, but it provides an interesting example of how societies tried to make sense of natural hazards before their physical causes could be measured. Similar earthquake legends involving animals, gods and supernatural forces can be found in cultures around the world.
Earthquakes Cannot Yet Be Predicted Precisely
Scientists can identify faults, monitor seismic activity and estimate the probability of earthquakes occurring in particular regions over time. What they cannot currently do is reliably predict the exact date, location and magnitude of a future major earthquake.
Monitoring still provides valuable information. Seismic networks allow earthquakes to be detected and measured rapidly, while geological research helps communities understand where hazards such as strong shaking, liquefaction and landslides are more likely to occur.
The science of earthquakes has advanced enormously, but uncertainty remains part of the subject. That is what makes earthquakes both challenging and fascinating: researchers understand the physical processes far better than previous generations did, yet the Earth can still produce events whose timing and consequences cannot be known precisely in advance.