Animal trials were truly a strange part of Europe’s medieval history
Many earthquakes occur as a group of small earthquakes in a cluster, with no identifiable mainshock. These are sometimes called swarms.
Temporary increases and decreases in seismic activity are a normal part of the fluctuation rate of earthquakes. But are there more earthquakes occurring now, compared to in the past?
The movement of the plates worldwide is the main source of strain that leads to earthquakes. Those with a magnitude of seven or greater tend to occur around 15 times per year.
Earthquakes often occur along plate boundaries, when sudden movements of the "stuck" plates release elastic strain energy, sending out seismic waves that result in the ground shaking.
The actual shaking due to an earthquake usually isn't what causes injury. Collapsing walls, roofs, and glass from buildings, however, tend to fly or fall. Indoors, seek shelter under a sturdy desk or table until shaking stops. Outside, avoid trees, buildings, power lines, streetlights, and drop until the shaking stops.
Sources: (USA Today) (BGS Earthquake Seismology) (Phys.org) (U.S. Geological Survey) (World Economic Forum) (Atmos) (Worldcrunch)
See also: How earthquakes reshape our planet
If earthquakes are becoming more frequent due to rising sea levels associated with climate change, it's good to be prepared just in case.
There are about 20,000 earthquakes around the world each year, or approximately 55 earthquakes occurring each and every day.
Well, there are certainly a lot more seismic instruments available for measuring seismic activity, which means we're able to record more earthquakes.
Major earthquakes are often followed by foreshocks, aftershocks, and smaller earthquakes, which might still be quite large.
The dramatic improvement in the quality and quantity of equipment that records seismic activity means that smaller earthquakes, in the most remote locations (including the seafloor), can now be detected.
The risk from earthquakes, however, is rising as a result of greater human and economic exposure because assets are being built in high earthquake hazard areas.
For instance, although Alaska is seismically the most active state in the US, the risk and impact of an earthquake is bigger in California because the potential losses are higher.
The crust of the Earth is like the shell of an egg. It's thin compared to the planet, and similar to an egg when cracked, the crust is made up of large pieces, called plates, that move around.
The North American plate moves to the west-southwest about an inch per year, whereas the Pacific plate moves northwest three to four inches per year.
At the University of Utah, a group of researchers have been examining the quakes that happen there. They're mainly small, imperceptible surges, clustered in time and space.
These are called "seismic groups" and they strike a region over a short period of time. In central Utah, dozens of these occur over a few hours before there is a pause. This happens repeatedly.
It's now impossible to ignore that the impacts of climate change are becoming more evident, with unusual weather becoming the norm and not the exception.
According to NASA, when there are significant changes in atmospheric pressure that occur in congruence with hurricanes, it causes a release of energy stored in the Earth’s crust.
Seismic scientists have focused on attempting to predict the location, timing, and magnitude of earthquakes in recent years. However, the planet's mighty movements still remain a bit of a mystery.
More rarely, earthquakes occur within plates (intraplate) in zones of weakness, such as the reactivation of old faults or rifts.
New research published in 2023 explored the possibility that earthquakes are being triggered by the activity of Earth's glacial cycles.
In the study, which took place in South Korea, researchers investigated the possible link to interglacial periods occurring over 100,000 year cycles.
Analyzing more than 450 Electron Spin Resonance (ESR) age dates of earthquakes in fault zones in the Korean Peninsula, they found the setting coincided with five key interglacial time periods.
The scientists postulated that massive changes in sea levels during these intervals played a significant role in triggering seismic events.
However, the melting ice sheets may be too far from the Korean Peninsula to cause this response. Instead, the researchers believe it suggests that compressive stress on the underlying lithosphere from glacial meltwater loading (which is causing rising sea levels across the Pacific Ocean) may be the answer.
One theory is that this may result from stress release due to glacial unloading, as the weight of ice over the landmass reduces with melting.
The research has implications for seismic activity, as climate change affects the melting of the ice glaciers. As sea levels rise, if correct, it implies the pressure on the lithosphere could trigger further earthquakes.
Separately, scientists have also found that monsoon season increases the weight of water on the Earth's crust on the Indian subcontinent to such a degree that seismic activity in the Himalayan mountains changes.
As glaciers melt, this also shifts subsurface magma, causing changes beneath the Earth's crust.
This leads to increased volcanic activity, which is directly related to earthquake development, referred to as glacial earthquakes.
Are earthquakes more frequent now?
Is there a reason why we have seen so many take place recently?
LIFESTYLE Seismic activity
The prospect of an earthquake is a terrifying one for many of us, and it seems like there have been a lot of earthquakes in recent years. But is the frequency increasing? Or are we now just a lot more aware of what's taking place in the wider world, thanks to increased communications and reporting? And if they have become more frequent, is climate change a contributing factor? Click on the following gallery for these answers and more.