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What Are the Effects of Earthquakes on Buildings? Dangers, Facts & FAQ
Ed Malaker
Last updated:
Earthquakes are dangerous natural phenomena that can cause a considerable amount of damage to homes and other structures. If you are in an area that experiences many earthquakes or live along the coastline, you are likely concerned about the effects of earthquakes on buildings. Keep reading as we provide you with information that will help you avoid shoddy construction practices and other problems when choosing a home, so it will take less damage in the event of an earthquake.
How Does an Earthquake Affect a Structure?
Earthquake effects on structures:
It Creates Inertia Forces: Inertia causes much damage to a building when an earthquake occurs. Inertia is the measurement of force pulling or pushing on a stationary object. The ground starts to rumble when an earthquake occurs, but the roof remains at rest. Since the walls connect the ground to the roof, they will begin pulling and pushing when an earthquake occurs, which can cause damage to the ceiling joints and the ceiling itself, possibly leading to a cave-in. The walls’ pushing and pulling can also damage each floor, especially where they attach to the wall. The more the ground rumbles, the higher the inertia, resulting in even more damage.
It Creates Stiffness Forces: Stiffness forces are the internal forces in columns and beams that hold up a structure. As these items push and pull on the roof as the ground shakes, internal forces can form, which can warp the columns and beams or move them out of place. Short beams cannot handle as much stress and strain as large ones and create weak points in the structure. It also causes an uneven distribution of weight.
It Produces Horizontal and Vertical Shaking: Earthquakes will cause your house to move up and down and shake horizontally in all directions. Many structures can handle vertical loads and the up-and-down movement of the ground, but fewer homes can withstand the inertia created when the house shakes horizontally, as there is usually not much in the way of support. Masonry, including cement and brick walls, are particularly prone to damage from horizontal movement during an earthquake. These walls often develop large cracks or fall completely during an event.
It Causes Other Effects: Unfortunately, ground shaking is not the only problem that earthquakes cause. For example, an earthquake in the ocean could cause a tsunami that brings flooding and water damage, often completely destroying many homes in the area. Landslides are another major problem often caused by earthquakes. The soil can engulf your home, and in many cases, the landslide can lift the house off the foundation and carry it away.
The 10 Things to Consider When Choosing a House in an Earthquake-Prone Area
1. Soft-Story Buildings
A soft-story building has less resistance or stiffness on the lower floors than on the floors above it due to longer or fewer columns adding support. Many times, this occurs when there is a parking garage on the lower levels of an office building. Many dance halls and similar businesses will have an open first floor with apartments or offices upstairs, creating a soft-story building, especially when the ceiling on the first floor is higher than on the other building levels.
2. Short Columns
Short columns are usually a part of a non-bearing brick wall and restrict lateral displacement of the frame and increase rigidity.
3. Inadequate Reinforcement Detailing
Reinforcement-detailing mistakes can cause damage to buildings in earthquake-prone areas. Improper spacing and bar size of the rebar inside cement columns and other parts of the building can cause weak spots that fail when an earthquake occurs, which enables the cement beams to crack, shear, or buckle, possibly resulting in the collapse of the building.
Image Credit: Angelo_Giordano, Pixabay
4. Nonstructural Damage
While nonstructural damage shouldn’t endanger the stability of a building and isn’t a big cause for concern, it can create other dangers, like falling walls or plaster. For instance, a small earthquake might crack a wall in a bedroom. It might stay that way for many years before suddenly falling and leaving a large hole that you need to repair.
5. A Discontinuous Force-Resisting System
A discontinuous force-resisting system has support columns that don’t extend to the foundation. All vertical elements that support the lateral force of a building must continue to the foundation, or extreme damage can occur during an earthquake, often resulting in the complete collapse of the first floor and any floors that don’t have adequate support.
6. A Strong Beam But Weak Column
When you have support columns weaker than the beams, they will fail first in the event of an earthquake, which can lead to the collapse of a building. If the column is stronger than the beam, the beam will collapse first, which will cause damage to the floor but leave the building standing in many cases.
7. Inadequate Detailing
Inadequate drainage provisions, expansion joints, and other items can cause significant damage during an earthquake. Expansion joints, which often hold new additions to an older structure, are especially prone to breaking and might even result in the addition falling away, which might damage other structures.
Image Credit: bridgesward, Pixabay
8. Poor-Quality Concrete
Low-quality concrete without much tensile and shear strength is especially prone to damage during an earthquake, as it will easily shatter and crumble even when the reinforcing rebar is adequate, resulting in more damage.
9. Inferior Materials
Besides concrete, many other materials used in construction must be of good quality, especially in an earthquake-prone area. Items like dirt and rock foundations, cinder blocks, and clay bricks must be high quality, or they will be more prone to failure during an earthquake. The proper installation of these items is also essential.
Image Credit: Simunovic, Shutterstock
10. Densely Populated Areas
Living in a densely populated area is another risk in an earthquake-prone area, as other buildings might fall and damage yours. The denser the population, the more you need to worry about properties that you have no control over.
Where Do Most Earthquakes Occur?
Most people associate earthquakes with California and the west coast, and while many earthquakes do occur here, they can occur almost anywhere in the country. Utah, Colorado, Wyoming, Idaho, and Montana all experience frequent earthquakes on the western side of the U.S. Oklahoma is a central state that receives several hundred small earthquakes each year. Eastern states that receive earthquakes include Arkansas, Missouri, Illinois, Kentucky, South Carolina, New York, and Maine.
Image Credit: Angelo_Giordano, Pixabay
How Are We Improving Buildings to Survive an Earthquake?
The USGS National Strong Motion Project has outfitted more than 250 structures with seismic sensory devices to study the effects that earthquakes have on them to help improve building techniques in the future. The data that these devices can detect includes the earthquake’s strength, the building’s movement and type, and the location of any damage. These devices demonstrate what kind of damage occurs most frequently, so we can take steps to add support in these areas.
What Happens After an Earthquake Occurs?
After an earthquake, an inspector will usually come to assess the damage and perform several tasks:
Look for and take note of any visible or hidden damage.
Write down the extent of the damage, and take pictures to help accurately document it.
Consider if the damage threatens any other nearby structures.
Determine if the building is safe to occupy.
After the inspection, the building inspector will usually provide a colored tag:
A green tag means the building is safe to enter and occupy, and you can return to life as usual.
A yellow tag indicates that the building is damaged and unsafe to live in for an extended time without repairs, but it is safe enough that occupants can retrieve their belongings to help minimize their loss.
A red tag indicates that the building received severe damage and is no longer safe to occupy. It can collapse at any moment, so you will not be able to retrieve any belongings, and local authorities will likely demolish the building as is.
Summary
The effects of an earthquake on buildings can be devastating. Inertia and other forces can tear apart a building, especially if it uses low-quality building materials. Structures with a soft story or short columns will take more damage if an earthquake occurs. Programs like the USGS National Strong Motion Project are working to study the effect of earthquakes on structures so building techniques can improve. This means we should see less damage occurring in the future. Remember that earthquakes can occur almost anywhere in the country. Always research the area where you are looking to buy to see if earthquakes occur there, and look into the history of a building before you purchase it to see if it has already suffered damage that might make it weaker if another earthquake occurs.
Ed Malaker is an experienced writer who has brought his knowledge to a wide range of blogs, including home improvement, guitars, computer programming, tools, fitness, and pets. If you don't catch him writing, you can usually find Ed working in the garden or taking on DIY projects around the house. Ed’s also a talented musician, spending time composing music for independent films or helping people fix their guitars.
Ed Malaker
