Have you ever wondered why are some earthquakes stronger than others? You are not alone.
The destruction caused by earthquakes can range from mild to devastating. But first things first, several factors affect the severity of their impact and strength.
Some earthquakes are stronger than others because they have a higher energy release, higher shaking intensity, and greater magnitude. Even though earthquake strengths are not limited to the three measurements, the three are often confused with one another.
What Causes an Earthquake?
An earthquake is caused when two earth blocks suddenly slip past one another. This happens in the space between them, called a fault or fault plane.
When the energy stored in the earth’s crust is suddenly released, seismic waves are produced.
Seismologists have discovered that earthquakes often occur along geologic faults. These are narrow zones where rock masses move in relation to one another.
Earth’s major fault lines run between or along the edges of the huge tectonic plates that make up the planet’s outer layer.
Why Are Some Earthquakes Stronger Than Others
Now that we have understood what earthquakes are and what causes them let’s delve into why an earthquake could be stronger.
Some earthquakes are relatively stronger than others because one or more of the major continental plates that cover parts of the earth’s surface has moved against another.
Here are other factors affecting earthquake strengths:
When wondering what makes some earthquakes stronger than others, the first thing that must come to mind is earthquake magnitude, which differs from one quake to another.
Large quakes tend to produce more shaking, are stronger, and affect a larger area than small quakes.
After an earthquake occurs, seismologists can collect data from seismometers to estimate the quake’s time, location, and magnitude. Both ordinal numbers and fractions are used to describe the magnitude of earthquakes.
How to Measure Magnitude
The Richter Scale is used to measure earthquake magnitude. For example, a 5.3 magnitude earthquake is considered a moderate quake, while a 6.3 magnitude earthquake is stronger.
For every number increase in the magnitude of an earthquake, the amplitude increases tenfold on a seismogram.
Fact: Sensitive instruments can detect tiny movements of the earth, which are amplified greatly to reveal earthquakes occurring anywhere in the world.
The amplitude of the vibration produced by an earthquake decreases as the distance from the earthquake’s epicenter increases.
The shaking at the earth’s surface is much stronger if the earthquake has occurred 20 kilometers (12.4 miles) below the surface than if it had occurred 500 kilometers (300 miles) deeper than that.
Therefore, if you’re located far from the epicenter, you may feel the earthquake is weaker than someone closer to the epicenter.
This explains why the Italian earthquake was significantly weaker than the one in Myanmar, resulting in greater damage because its epicenter hit a shallower region.
Seismic Waves and Depth
Seismic waves produced by earthquakes with epicenters deeper than about 150 kilometers (90 miles) must travel farther to the Earth’s surface.
Hence they lose more energy than do waves produced by shallower quakes.
Note: While shallow quakes usually cause less damage, they can be felt over a much wider area.
The intensity of an earthquake depends on the amount of shaking that occurs at each point.
The shaking is greater in places close to the fault rupture than in places that are farther away.
The earthquake will certainly be stronger in areas with too much shaking and weaker in areas with relatively weaker shaking.
Intensity vs. Magnitude
Because the magnitude of an earthquake is only one of many values that describe its size and strength, intensity values—distributed across the geographic area around the epicenter—are also important to consider when determining why are some earthquakes stronger than others.
Earthquakes generally appear weaker at the epicenter than at locations farther from ground zero.
The depth of the tremor, the orientation of the rupture, and the type of surface geology in the region can affect how strong an earthquake you feel in your own home.
Fact: earthquake intensity is measured by the Modified Mercalli Intensity Scale and is expressed in Roman numerals like V, VI, X, etc.
Distance from the Epicenter
The epicenter is the point on the surface directly above and closest to the origin of an earthquake.
It is usually somewhere within the circle of greatest intensity and can be located by triangulation.
If you’re right above the epicenter, you should expect to feel the full strength and impact of the earthquake compared to those far from the epicenter.
Seismologists have identified earthquake-prone areas in countries such as Japan, Indonesia, and Myanmar.
Note: It's important to always be as far from the epicenter as possible when an earthquake occurs.
Because energy is a measure of the strength of an earthquake, scientists can also compute how much energy was released by an earthquake.
Therefore, earthquakes that release more energy tend to be stronger and even cause more destruction to both natural and artificial structures.
Earthquakes emit energy at many frequencies. When you add up all of the shakings over the entire duration of an earthquake, you get the most accurate measurement of its energy.
Understanding Energy Magnitude
Apart from the Richter Scale magnitude new type of magnitude, the Energy Magnitude can be derived to measure the total amount of energy released during the earthquake event.
For quakes with stronger and higher energy magnitudes, you’re likely to have buildings destroyed, trees uprooted, cars damaged, and more wreckage.
Note: Each whole-number increase in magnitude represents a tenfold increase in the measured amplitude but a 32-time-greater release of energy.
When an earthquake occurs, the type of building structure you are on greatly determines how you feel and experience the quake.
When designing buildings to withstand earthquakes, engineers must account for the transfer of seismic forces through the structure.
Reinforcement and Building Height
The reinforcement of buildings depends on how you design components like cross braces, shear walls, moment-resisting frames, and diaphragms.
The natural period, or the frequency at which its parts vibrate, is an integral characteristic of any given building.
Taller buildings are typically more flexible and tend to sway, while shorter buildings are typically more rigid and tend to “pulse” or “quiver.”
Therefore, you’ll feel like an earthquake is stronger when you’re in a taller building.
Fact: In addition to its height, another factor that affects a building's natural period is the type of material made of—steel, concrete, or wood.
Local Geological Conditions
Earthquakes begin in an area called the epicenter, which is a region of sudden subsurface rupture or discontinuity.
When seismic waves–resonating through the ground from an earthquake–hit the soil, the vibrations are felt at ground level differ.
Type of Soil and Earthquake Strength
When a surface experiences an earthquake, one factor that significantly affects the intensity of the shaking is the type of soil beneath it.
Soils can be categorized as rigid, flexible, or somewhere in between.
Variations in the composition of soils and the shapes of structures create a wide range of strength differences in earthquakes.
Soils that are more prone to the effects of earthquakes, such as soft soils, tend to experience stronger shaking intensity than rocky sites.
Note: The effect is the same regardless of whether the location is near or far from the fault.
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There are numerous explanations as to why are some earthquakes stronger than others.
Apart from the described reasons above, another reason is the size of the geographic region over which an earthquake’s impact is felt.
Moreover, this measure has been particularly helpful in reconstructing the severity of prehistoric earthquakes that did not register on seismographs and occurred in sparsely populated areas.
It’s, however, imperative that necessary precautions are adhered to during an earthquake to avoid damages and loss of life.