Earthquake Resistant Buildings Explained
Earthquakes are a powerful, destructive and unpredictable force that can demolish buildings, devastated communities and put the work of construction companies to the test. There are certain locations around the world that are much more prone to earthquakes than others and these cities, towns, communities and urban centers need to protect themselves and their residents from these natural disasters. Building earthquake resistant buildings is one way to do this.
But what are earthquakes? Why do they happen? What areas are more prone to earthquakes? What makes a building earthquake resistant? And can buildings be earthquake proof?
Here is everything you need to know about earthquakes and buildings.
What are Earthquakes?
Earthquakes are as natural to the planet as rain, snow, hurricanes and tornadoes. Unfortunately that doesn’t make them any less destructive. Earthquakes are just that - quakes of the earth. Ground shaking and road rumbling can lead to collapsed buildings, skink holes, shifting earth and - if they happen in the ocean - even giant tsunamis.
The Earliest Recorded Earthquake in History
The earliest earthquake in recorded history took place in 1177 B.C. in China. European earthquakes are noted as far back at 580 B.C. A Mexican earthquake in the late 1300s and another in Peru in 1471 are the first noted earthquakes in the western hemisphere.
According to a record kept on Volcano Discover, “During 2020, there were 8 quakes of magnitude 7.0 or above, 115 quakes between 6.0 and 7.0, 1,689 quakes between 5.0 and 6.0, 12,720 quakes between 4.0 and 5.0, 38,963 quakes between 3.0 and 4.0, and 85,247 quakes between 2.0 and 3.0. There were also 208,207 quakes below magnitude 2.0 which people don't normally feel.” So earthquakes really are not uncommon.
What Causes Earthquakes?
There are a few different causes of earthquakes.
The movement of tectonic plates is the biggest source. Volcanic eruptions and the flowing of magma under the earth's crust is another natural source of earthly tremors. Man made sources such as bombing or mining could shake the earth or cause underground shifting. Lastly, more minor earthquakes can be caused by other natural forces such as landslides, avalanches, etc.
Tectonic Plates and Earthquakes
The earth is made up of plates - tectonic plates - that float on the earth’s mantle and fit together like a jigsaw puzzle to make up our planet. The earth’s mantle is a thick layer of hot rock and magma. The mantle flows much like the currents in our ocean, constantly shifting and moving the plates. Tectonic plates can shift up to 4 inches in a year, but many move much slower than that.
There are three major ways that these plates move around each other: constructive, destructive and conservative movements.
Constructive moving plates are ones that move away from each other. This pulling causes minor quakes. They’re also called divergent plates.
Destructive plates move towards each other and collide. These collisions cause incredibly destructive quakes - just as the name suggests.
Finally, conservative plates rub against each other, resulting in quakes of different sizes.
One of the most destructive zones of tectonic plates is the Pacific and North American plates. These plates cover half of California and are the reason that Californian earthquakes have been so damaging. Just this past July a 6.0 magnitude earthquake was felt in California. These plates are also part of the Ring of Fire.
The Ring of Fire
The Ring of Fire - also called the Circum-Pacific Belt - is one of the most seismically active areas in the world. It forms a horseshoe-type “ring” from the tip of Chile, up along the pacific coast of the United States and Canada across to Japan, down the side of China to the Philippines and Indonesia through to New Zealand. Many of the most active areas for earthquakes can be found along this ring.
The History of the Richter Scale
Charles F. Richter was a man working at the California Institute of Technology when in 1935 he developed a mathematical device to compare the sizes of earthquakes. Now known as the Richter scale, earthquakes are measured by his mathematical equation that breaks down the intensity of amplitude “waves” created by earthquakes. These waves are created by the energy released during a quake and measured by a machine called a seismograph. This scale is now used as the universal truth to measure the size and force of quakes.
What Are the Different Scale Levels of Earthquakes?
Richter scale levels range from 0 - 9+. The damage inflicted by an earthquake can be estimated depending on its measurement.
Here are the different levels and zones on the Richter scale.
| Richter Scale Levels | Description | Estimated Per Year |
| < 2.5 | Usually not felt and only detected on seismographs | 1 million |
| 2.5 - 5.4 | Often felt with minor damage | 500,000 |
| 5.5 - 6 | Slight damage to building and structures | 350 |
| 6.1 - 6.9 | May cause a lot of damage to populated areas with many buildings | 100 |
| 7.0 - 7.9 | Considered a major earthquake with major damage expected | 10 - 15 |
| 8.0 + | Considered a great earthquake and can completely destroy communities close to the center of it | 1 - 2 |
The largest earthquake ever recorded happened in Chile on May 22, 1960. That earthquake was measured at a magnitude of 9.5 and lasted for 10 minutes. The tremors not only devastated communities within Chile but also caused major tsunamis in other pacific countries. It was a true example of the power and force of these natural forces.
How do Earthquakes Impact Buildings?
When earthquakes happen, the energy created by the force shakes the ground, moving through it in waves. It spreads out in different directions from the source, kind of like a ripple when you throw a stone into a pond. The biggest, strongest force is closest to the center.
Buildings are traditionally made to withstand winds, rain, gravity and general weight in a vertical sense but not underground forces or horizontal waves of force. When the ground shakes, it causes vibrations of floors, support beams, foundations and walls. As the top shakes and moves at different speeds and forces than the bottom, the integrity of the building weakens. Supporting frames can collapse, foundations can crack and buildings can fall.
What Areas Are More Prone to Earthquakes?
The areas that are most vulnerable to earthquakes depend entirely on their geographical location.
Countries
The countries with the most earthquakes include Japan, Nepal, India, Ecuador, the Philippines, Pakistan, El Salvador, Mexico, Turkey and Indonesia.
Cities
The cities most susceptible to earthquakes and ones that experience the most include Tokyo and Osaka in Japan, Istanbul in Turkey, both San Francisco and Los Angeles in California, as well as Quite, Ecuador, Jakarta in Indonesia, Manila in the Philippines, and Lima in Peru.
Can Buildings be Earthquake Proof?
Earthquake-proof buildings do not exist. To date, we are still unable to build something stronger than the planet. That being said, scientifically-backed design processes that capitalize on what we do know about earthquakes have allowed us to build buildings that are earthquake resistant.
What Makes a Building Earthquake Resistant?
The ability of a building to withstand an earthquake depends both on the structure, the design, the materials and the building processes that go behind that building. Over the years, there has been much research done by engineers, architects and scientists to discover the best designs and materials for building in areas that are prone to earthquakes.
Buildings that are designed to withstand the forces of an earthquake usually have different foundational makeups, can be built with special beams and materials to absorb shockwaves and usually make use of triangle shapes to maximize strength.
Triangles
Triangles are incredibly strong shapes. When a force is applied to one of the corners of a triangle, it is distributed down each side. The two sides of the triangle are squeezed and lean on each other. When a building sways, twists or shifts, the force is managed by these shapes to hold the structural integrity of the building together. Triangles can be used internally in the structure or externally as support factors for a building. Many eathquake resistant buildings incorprorate the shape in their design.
Foundations of an Earthquake Resistant Building
Concrete is perhaps one of the worst foundational materials for building something you want to be earthquake resistant. Concrete absorbs little energy making it vulnerable to cracks during an earthquake. Gone unnoticed, a building with a cracked foundation could fall days, weeks, months or years later depending on the damage. That being said, some innovations such as self-healing concrete could make a different name for concrete in the future.
Concrete can however be used alongside more quake-friendly foundations such as concrete foundations reinforced with steel. If a building was to shake during an earthquake, the steel helps to keep it steady. But if a neighboring building were to collapse and put pressure on the ground around a building, then the concrete helps to keep the building standing firm. The two complement each other.
Other types of flexible foundations include building buildings on literal pads that keep the building separate from the ground, creating a barrier between any waves that come from an earthquake and the building itself. Japan builds on literal blocks of rubber to help protect buidlings because the country experiences so many earthquakes. Pillars that shift and self-correct to keep a building level have also been used to battle unpredictable earthquakes.
A Strong & Reinforced Structure
The structural makeup of a building makes all the difference when it comes to earthquake resistance. The building needs to be able to withstand and disperse any energy that could move through it.
Triangles are the go-to shape for earthquake-resistant buildings. Their shape provides more resistance to twisting motions, reducing the swaying of a building during a quake. There are also more crafty materials such as columns and beams built with shock absorbers to reduce the movement any earthquake waves have on a building. By removing some of the pressure put on the building itself, the less likely it is that that building will crack or break down.
As a whole, our ability to construct buildings that can withstand earthquakes is much better than it used to be.
Modern Building Codes
Building codes and earthquake engineering are far more advanced today than they once were. One of the more challenging parts of building something that can withstand earthquakes is getting older buildings up to code for current standards. Soft-story buildings are common in warmer climates and California specifically.
Soft-story buildings refer to buildings more than one story tall with one or more floors that have large open spaces, doors, few walls, etc. Apartments with underground parking or open-air ground level parking all fall under the umbrella of soft-story buildings.
In areas like California soft-story buildings or buildings that generally do not meet modern building codes are slowly being retrofitted or updated to ensure that they are as safe as can be when the next earthquake inevitably happens. .
Designing Earthquake Resistant Buildings
The challenging part of building for earthquakes is that no one can know when one is coming or how big it will be. Modern technology for measuring and detecting can help us be more prepared for them. Advancement in building-resistant materials also makes the construction industry better suited for building for earthquakes now than before.
Earthquakes are a powerful and destructive force that flatten cities and claim lives. Again, the construction industry is uniquely positioned to take advantage of modern technology that can save lives and cities alike.
