An earthquake is the sudden and intense shaking of the ground that occurs when sections of the topmost layer of the earth’s mantle, known as tectonic plates, suddenly slip past one another, generating energetic shocks known as seismic waves. Depending on its intensity, an earthquake can cause significant structural damage to buildings and even trigger other environmental disasters such as fires and tsunamis. The National Earthquake Information Center records about 20,000 earthquakes that happen around the globe each year and approximately 55 per day.
Earthquakes can be either tectonic, volcanic, collapse, or explosion, depending on what triggered their occurrence. Tectonic earthquakes occur due to geological forces generated from the movement of tectonic plates, while volcanic earthquakes are triggered by volcanic activities. Meanwhile, collapse earthquakes occur as a result of shock waves generated during the collapse of underground caverns and mines. Earthquakes caused by the detonation of nuclear or chemical devices are known as explosion earthquakes.
In terms of casualties, the earthquake that occurred in Shaanxi, China, in 1556 is considered the deadliest ever recorded, with an estimated death toll of about 830,000 people.
Understanding the science of earthquakes requires an explanation of the earth's structure. The earth’s surface consists of four major layers: the inner core, outer core, mantle, and crust. The topmost layers are the crust and the upper part of the mantle, which constitute the earth’s lithosphere. The lithosphere is not a single piece. It consists of 15 pieces of large rock slabs known as tectonic plates.
Tectonic plates constantly move as they float over thick layers of molten rocks in the earth’s mantle. The edges of the plates, known as plate boundaries, are made up of several faults, fractures, or cracks. Since plate boundaries are rough, they usually get stuck while the plates move. An earthquake occurs when friction between the plates builds up, causing their edges to unstick at a fault. This slip results in the sudden release of energy that causes the shaking felt on the surface.
Earthquakes typically happen in three phases: foreshocks which occur at the same location before the larger earthquakes, the actual earthquake referred to as the mainshock, then aftershocks which are smaller earthquakes that occur in the same area after the mainshock. Each phase of an earthquake can only be properly identified after the full sequence of the earthquake has occurred.
The location below the earth’s surface where the earthquake starts is called the hypocenter, while the point it happens on the surface is called the epicenter. Furthermore, the frequency, type, and size of earthquakes experienced in an area over a particular period are known as the area’s seismic activity.
Earthquakes are generally considered naturally occurring geological events. However, over the years, scientific research has linked the occurrence of earthquakes with certain human activities such as:
Mining: Mass removal of materials from the earth’s crust during mining can result in a sudden collapse that can trigger an earthquake. An example of this is the 2007 mining-induced earthquake that occurred at the Crandall Canyon coal mine in Utah, which led to the death of six miners.
Operation of dams and water reservoirs: Valleys behind dams cover a wide area of land, which, when filled, can substantially change the stress load of the crust beneath it due to the weight of the water. The earliest recorded example of this is a 1945 earthquake that occurred in areas around Lake Mead located in Nevada and Arizona.
Fracking: This is the shorter term for hydraulic fracturing, which is a method of extracting petroleum or natural gas by breaking through rock formation through the injection of fluids at high pressure.
Wastewater injection: This is a method of disposing of salty or polluted water by injecting it into deep underground wells, away from any source of drinking water. The majority of wastewater in the U.S are byproducts of oil and gas extraction.
These activities either cause earthquakes of lesser scale or accelerate the occurrence of more serious earthquakes.
The size of an earthquake is known as its magnitude, which depends on the level of seismic waves released during the earthquake. Seismographs record magnitude on a logarithmic scale. The stronger the force of the earthquake, the higher the value it has on the scale. For example, a magnitude five earthquake is approximately ten times less violent than a magnitude 6 and 100 times less powerful than a magnitude seven. The average person rarely notices an earthquake of magnitude below 2.5. However, earthquakes greater than magnitude seven may cause extensive damage. The largest earthquake ever recorded was a magnitude 9.5 earthquake that occurred in Chile in 1960. The 1964 Great Alaska earthquake was the most powerful recorded earthquake in U.S. history, with a magnitude of 9.2.
The intensity of an earthquake is measured differently from its magnitude, as varying degrees of shaking may be noticed in different areas around the epicenter where an earthquake occurs. Therefore, an earthquake’s intensity depends on where the measurement is taken. Meanwhile, an earthquake has a single magnitude value that is independent of the location of the measurement. Intensity scales such as the Modified Mercalli Scale are used to measure the shaking and physical impacts of an earthquake in a particular place. The Modified Mercalli Scale uses values from I to X to represent an earthquake's intensity. Higher numbers from VIII indicate that an earthquake significantly damaged structures. In contrast, lower values typically correspond to how noticeable an earthquake was to individuals. Several earthquakes occur yearly, but only a small percentage are powerful enough to be noticed or to cause damage.
When an earthquake occurs, it is difficult to predict the amount of damage it will cause. The most common effect of an earthquake is the intense shaking and vibration of the ground. Depending on the earthquake's intensity, the shaking can cause substantial structural damage to buildings, roads, and other infrastructures. The local conditions where the earthquake occurs will determine the nature and scope of the effects. For instance, multi-story buildings tend to sustain more severe damage than smaller ones. Similarly, building damage is more frequent and severe in areas with soft sediments or soils.
Structures built on soft sediments also face the risk of liquefaction, in which the soil beneath them becomes fluid, making the building collapse or sustain substantial damages. This happens because the intense shaking of water-saturated sediments can cause the grains to break apart and stop supporting one another. The sediment turns to mud and flows as water between the grains keeps them apart.
Ground shaking resulting from earthquakes can also trigger landslides because the shaking weakens loose rocks and other materials, causing them to slide down slopes of land without control. Additionally, because of the damage that ground shaking causes to electrical and gas lines, fires are frequently linked to earthquakes. However, in recent times, utility operators can lessen pipeline pressure and break electrical circuits to limit the danger of fires during earthquakes.
Finally, large earthquakes that occur below ocean floors can displace a large volume of water, causing another kind of natural disaster known as Tsunamis. Tsunamis have massive waves and forces that can run ashore and devastate nearby areas and places far away from the tsunami's source. An example of this is the 1964 Tsunami, resulting from a magnitude 9.2 earthquake that occurred in the Gulf of Alaska, which caused damage and loss of life in several places, including Alaska, Hawaii, California, Oregon, and Washington.
Located in the South Central region of the country, Texas has a land area of 268,596 square miles and a population exceeding 29.1 million as of 2020, making it the second-largest U.S. state by both area and population. Texas is generally considered one of the U.S states with earthquake hazards, and according to research by Texas higher institutions, human activities, such as oil and gas extraction, may have contributed to the state’s earthquake risk. In areas like the Gulf Coast and Northeast Texas, most earthquake epicenters occur near active petroleum fields and wastewater injection wells.
Between 2010 and 2015, the state experienced 83 earthquakes greater than magnitude 3, causing an average of 11 injuries per year and over thirteen million dollars in annual loss of properties. Texas earthquake hazards are, however, considered small when compared to other states, like California, Missouri, Montana, South Carolina, and Washington, which have experienced earthquakes of magnitudes exceeding 7 in the past. The largest earthquake in Texas history is a magnitude six that occurred on 16 August 1931 around the town of Valentine, located southeast of El Paso. Below is a list of other notable earthquakes that have occurred in Texas since 1990, including their magnitudes.
|July 20, 1991||3.6||Falls City|
|April 9, 1993||4.3||Fashing|
|April 14, 1995||5.7||Alpine|
|March 24, 1997||3.8||Alice|
|May 31, 1997||3.4||Commerce|
|October 30, 2008||3.0||Dallas-Fort Worth|
|May 16, 2009||3.0||Dallas-Fort Worth|
|April 25, 2010||3.9||Alice|
|Sep 11, 2011||4.4||Snyder|
|Oct 20, 2011||4.8||Fashing|
|May 17, 2012||4.8||Timpson|
|Jan 25, 2013||4.1||Timpson|
|Sep 2, 2013||4.3||Timpson|
Texas earthquakes do not usually cause fatalities or extensive damage. Even the one that occurred in Valentine only badly damaged frame houses, brick chimneys, and a schoolhouse with sections built of cement blocks and bricks.
Between 2005 and 2009, the majority of the earthquake epicenters in Texas were either in the cities of Amarillo, Lubbock, San Antonio, Austin, Dallas, Alpine, Houston, or El Paso.
Earthquakes can be difficult to navigate without proper preparation. Though evacuation may seem like an option, it is not possible in many instances, considering how unexpected earthquakes are. However, considering the following tips can help Texas residents prepare for earthquakes before they happen.
Draw up an earthquake response plan and practice it. With a properly prepared and practiced emergency response plan, everyone knows what to do when an earthquake occurs. This can reduce the risks of an earthquake causing serious injuries or fatalities. It is important for an emergency response plan to include a communication method for the family during the earthquake, as well as the maintenance of emergency supplies kits. Such kits should be kept in easy-to-access locations and contain essential items, including water, non-perishable foods, a flashlight, whistles, and first-aid equipment.
Secure your home and its contents. It is essential that people verify that the home and other buildings they stay in are resistant to the effects of earthquakes. Shocks generated during earthquakes can cause significant structural damage to a building and its content or collapse the building totally in extreme situations. Texas residents can secure their homes and their contents ahead of an earthquake by:
Adhering to local and state seismic building standards and construction code requirements for structures to withstand disasters.
Making structural changes such as anchoring their structures to their foundation, reinforcing masonry walls, installing earthquake-resistant bracing systems for mobile homes, and foundation bolting. It is also essential to reinforce exterior features, like decks, canopies, and garage doors. Keep in mind most structural work requires approval by an engineer.
Bracing overhead light fixtures, using strong latches or bolts on cabinets, bolting tall furniture to wall studs, and keeping large or heavy items close to the floor.
Set up your vehicle for earthquakes. The intense shaking can result in debris falls, collapsing buildings, and bulking bridges, which can cause significant damage to vehicles on the road. Consider the following tips in equipping a vehicle in preparation for an earthquake emergency:
Always have a vehicle emergency kit. The pack should include a first aid kit and manual, flashlight, fire extinguisher, water, and non-perishable foods.
Consider weather forecasts and road conditions when planning long trips. It is advisable to avoid driving in bad weather except if it is necessary.
Always have enough gas in the vehicle in case the situation requires an evacuation. However, avoid carrying spare gas in a vehicle’s trunk.
Ensure that the vehicle is in good condition, serviced, and properly maintained.
Prepare your finances to handle earthquake emergencies. It is critical to be financially prepared for any emergency. Access to financial resources is required for sustenance and/or evacuation during an unfolding emergency. Likewise, the aftermath of an earthquake can come with lingering financial issues caused by the destruction of valuables, as well as personal injuries sustained during the disaster. Here are some helpful tips on how to prepare one's finances before the earthquake:
Verify that the insurance policy for your property covers all potential natural disaster damages.
Develop a savings plan specifically for emergency circumstances, including earthquakes.
Make copies of important financial documents and identifications such as insurance policies, social security numbers, credit card numbers, and bank account numbers. Make sure the documents are stored in a secure location but at the same time are easily accessible.
Consider the safety of your pets. During an emergency like an earthquake, pets will be more dependent on their owners for their safety and well-being. The following tip can help in keeping pets safe if an earthquake occurs:
Put an evacuation plan in place for the pets, considering that many public shelters and hotels may not accept pets during an emergency.
Develop a buddy system. Plan with neighbors, friends, or relatives to make sure that someone is available to care for or evacuate your pets if you are unable to do so.
Pet owners should create an emergency kit for each pet. The kit should include water, food, sanitation products, medicine, first-aid equipment, and toys.
Always have a recent picture with the pet for identification in case it gets lost.
Though earthquakes are usually unexpected and unpredictable, early warning services can alert residents moments before the earthquake begins. The early warning systems’ effectiveness depends on the type of the shock waves the earthquake produces. There are two types of waves generated during an earthquake: the P waves and the S waves. The P waves are weaker than the S waves but travel faster. Because of that, warning services can notice them earlier and then alert residents sooner.
Early warning systems and services are very useful. They can minimize the secondary effect of earthquakes. By alerting utility providers to cut out supplies to areas that can be affected, fires can be prevented. Similarly, residents get a little extra time to coordinate their earthquake emergency response.
The Integrated Public Alert & Warning System (IPAWS) is an emergency alert system in Texas that provides authenticated and life-saving information to the public during earthquake emergencies. Emergency alerts are usually transmitted through several communication media, including mobile phones, radio, and television. Texas currently has 52 countries and 15 cities that are authorized public alerting authorities. It is important to always be attentive to earthquake alert systems as, apart from early warnings, they provide valuable information that can guide residents' movement during and after an earthquake.
The predominant risk associated with earthquakes in Texas is the damage or collapse of unreinforced structures. Though earthquakes have historically done little damage in Texas, there is still the concern that larger earthquakes above magnitude seven may occur at some point in time. Furthermore, smaller earthquakes may still cause damage. There is also the risk of the effects of earthquakes that happen in nearby states. For example, earthquakes in 1811-1812 Missouri-Tennessee caused some damage in the Dallas-Fort Worth area. Similarly, the effects of earthquakes in Oklahoma can be felt in the Texas Panhandle area. Secondary effects of earthquakes, like liquefaction, Tsunamis, and Volcanoes, do not typically occur in Texas.
The most vulnerable areas in Texas include the West, where earthquakes of around magnitude 6 occurred in 1931 and 1995, and the Panhandle, where at least seven earthquakes of magnitude four or higher have occurred since 1900.
What to do once the shaking from an earthquake begins depends on where the person is during this unexpected event. If at home or in some other building or structure then the following tips apply:
As soon as the ground begins to shake, get down on one's hands and knees to avoid being knocked down by the earthquake shock.
For protection from falling debris, cover the head and neck with your arms. When it is possible to safely move away from falling objects, crawl to a safer location or seek cover.
Hold on to anything sturdy that one can move with until the shaking stops.
If operating a gas stove, turn off the stove immediately and take cover at any sign of shaking.
If in bed when the intense shaking begins, do not leave the bed. Instead, protect your head by covering it with a pillow to reduce the risk of sustaining injuries from falling objects or debris.
Avoid standing in a doorway, as doorways do not protect from being knocked to the ground or from falling objects, which are the most likely source of injuries during an earthquake.
Avoid staying close to the windows.
Avoid using the elevators as the building’s power may go out, and the sprinkler systems can be triggered.
Take pets indoors and maintain direct control of them.
For people outdoors during the earthquake, it is important to move in the open, away from buildings, streetlights, and utility wires. If this is not possible, especially in a city setting, duck inside a building immediately to avoid falling debris.
When in a moving vehicle during an earthquake:
Recognize the first signs of earthquake Common signs include ground jolting and shaking, things falling, and cracks.
Pull over the side of the road as quickly as possible. Also, keep an eye on the traffic as some drivers may panic.
Avoid parking under bridges, signs, power lines, trees, or any other hazards that can fall on the car. Also, avoid parking close to buildings and gas stations.
Do not park close to expansion joints on elevated highways and bridges because concrete slabs of the highway or bridges can fall off due to the shocks generated by the earthquake.
Turn off the vehicle engine and apply the handbrake, then stay in the vehicle till the shaking stops completely. Using the handbrake prevents the vehicle from rolling back and forward.
Stay in the car if a powerline falls on it and wait till a qualified person removes it. Call 911.
Exit the vehicle immediately if you smell gasoline, as this might indicate a leak that can cause the vehicle to ignite or explode.
Several steps can be taken to address damages caused by an earthquake and prevent further casualties.
For homes and families:
Look out for fallen objects and falling debris.
If the building is damaged, look out for a safe way out and go to an open space, away from damaged areas.
There is a possibility of being trapped in the debris. If this happens, try not to move or kick up dust.
Call or text for assistance if you have access to a cell phone. If there is no phone around, tap on a pipe or wall, shout or use a whistle to alert rescuers.
Once safe, keep an eye on local news reports for emergency information and instructions.
Be cautious when cleaning up a building after an earthquake. Always wear protective clothing, including long pants, a long-sleeved shirt, and sturdy shoes.
Clean up spilled medications, bleach, gasoline, or other flammable liquids immediately.
If away from home, return when authorities say it is safe to do so.
Check yourself for injuries and get first aid, if necessary, before helping injured or trapped persons.
Look out for and extinguish small fires. Fire is the most common hazard after an earthquake.
Expect aftershocks after the initial earthquake. If this happens, make sure to follow through with the safety procedures again.
Dial 911 immediately if you suspect a gas leak.
Seek the services of professionals to inspect the building's structure and utilities.
Avoid roaming around damaged areas and rubble. Never use a lighter or matches around such areas
In the aftermath of the earthquake, pets’ behavior may change in response to the stressful situation, making them defensive and aggressive. Consult a veterinarian if the animal’s change in behavior persists beyond a reasonable period.
For those in vehicles after the earthquake:
Exit the vehicle when the shaking stops. Do not forget to locate the emergency supplies in the car.
Examine the car and the surroundings for damages and determine whether or not it is safe to drive.
Communicate with friends and loved ones to make sure they are OK and to coordinate the next course of action.
Tune in to the local radio station for warnings and updates, including the information about the extent of the earthquake, safe evacuation routes, rescue efforts, and directions for people who have been injured.
Beware of aftershocks from the earthquake. They can easily dislodge damaged buildings and other structures that have not already collapsed.
Avoid driving over large cracks in the road. This can get the vehicle stuck.
Do not drive beneath bridges with visible cracks or structural damage. Be cautious of all overhanging objects, bridges, signs, walls, and overpasses, even if there is no visible damage.
Be aware of the possibility of landslides on the road.
When driving along a coastal road in a vicinity where a tsunami is a possibility, get to higher ground as soon as possible.
Here are tips that can help Texas residents recover their expenses following the earthquake:
Depending on their financial situation, Texas residents affected by earthquakes can apply for government-funded unemployment, healthcare, and food benefits. The federal government collaborates with affected state and local governments by providing assistance through the Federal Emergency Management Agency (FEMA), following a disaster declaration made by the President. Depending on the severity of the situation and the type of declaration made by the President, disaster assistance may extend to legal services, debris removal, and counseling programs.
Persons whose buildings have been rendered inhabitable due to the disaster can apply for interim housing pending repairs.
Be mindful of contractor scams and price gouging.
Check for tax reliefs associated with disaster-hit areas.
To aid in filing an insurance claim, take photographs or videos of the damages sustained by the property and belongings.