The 7.7 magnitude earthquake that hit Panama on Friday (9) was followed by more than 80 aftershocks, according to data released this Saturday (10). Among the new tremors, there was one with a magnitude greater than 6.0, strong enough to cause new damage in areas already affected by the first tremor.
The main earthquake left at least 27 people injured, caused landslides and damaged roads and buildings. The greatest damage was recorded in the center of the country, but tremors were also felt in the capital, around 200 kilometers from the epicenter.
The aftershock is common after large-magnitude earthquakes and can continue for weeks, months or even years. This happens because the movement of rocks underground does not necessarily end with the first tremor.
But why does the earth keep shaking? Can aftershocks be as strong as the initial earthquake? And is it possible to know when there will be another shock?
Why do aftershocks happen?
Earthquakes occur when tension built up in rocks in the Earth's crust is suddenly released, usually along fault lines.
The planet's surface is made up of large blocks called tectonic plates, which move slowly, a few centimeters per year. In certain regions, these plates collide, move apart or slide relative to each other.
Although the movement is continuous, rocks can become stuck due to friction. The pressure increases until part of them breaks or slides suddenly, releasing energy in the form of seismic waves that make the ground shake.
The main earthquake, however, changes the distribution of stresses in the rocks around the fault. As a result, other parts of the region may suffer new displacements, producing so-called aftershocks, or aftershocks.
According to the United States Geological Survey (USGS), these tremors are part of the rock readjustment process after the initial rupture.
Can aftershocks be stronger than the first earthquake?
In general, aftershocks are lower in magnitude than the main earthquake, but this does not mean they are harmless.
Even a less intense tremor can collapse structures that were compromised by the first shock, trigger new landslides and increase damage in a region.
It is also possible for an earthquake to be followed by an even stronger one, although this is less common.
When this happens in the same seismic sequence, the first tremor is classified as a precursor shock, and the event of greater magnitude becomes a main earthquake.
Therefore, the occurrence of several aftershocks does not allow us to conclude, in itself, that a new earthquake of great magnitude is about to happen.
How long can replicas last?
There is no fixed deadline for aftershocks to end.
According to the USGS, aftershocks are typically most frequent in the first few hours and days after the main earthquake. Over time, the number of new concussions tends to decrease.
This does not mean, however, that each replica will be weaker than the previous one. The reduction pattern refers primarily to the frequency of earthquakes, not necessarily the magnitude of each one.
In very strong earthquakes, aftershocks can continue for months or even years, although they become progressively less frequent.
The number and duration of aftershocks depend on factors such as the magnitude of the first earthquake, the characteristics of the geological faults and the conditions of the affected region.
Is it possible to predict when another earthquake will occur?
Despite advances in seismic monitoring, science still cannot accurately predict when, where and with what magnitude an earthquake will occur.
What experts can do is identify the most vulnerable regions and calculate the probability of new earthquakes based on seismic records and the geological characteristics of each area.
After a large earthquake, it is also possible to estimate the expected frequency of aftershocks and the probability of tremors of different magnitudes. These estimates are updated as new shocks are recorded.
But that's different from predicting exactly when the earth will shake again.
Some countries have warning systems that identify an earthquake soon after it begins and can warn the population seconds before the most intense seismic waves reach certain locations. These systems, however, do not anticipate the occurrence of the earthquake.
How to protect yourself during aftershocks?
The main risk from aftershocks lies with structures that were already damaged by the initial earthquake.
Buildings with cracks, damaged parts or at risk of collapsing may not be able to withstand new ground movements.
Therefore, civil protection authorities recommend avoiding access to damaged properties until they have been assessed by qualified professionals.
During a new tremor, the advice is to get down, protect your head and neck and, if possible, take shelter under a sturdy table until the movement ends.
In coastal areas, strong or prolonged tremors also require attention to tsunami risk and guidance from local authorities.
As earthquakes cannot be predicted with precision, the main way to reduce their consequences continues to be the preparation of cities, especially through earthquake-resistant construction, inspection of structures and emergency plans.
