Home / 80 Frequently Asked Questions About Earthquakes and Their Answers

It takes a very specific geological event to create an earthquake. Here's how it happens: The ever-present movement of the tectonic plates beneath the Earth's crust causes occasional collisions that release energy, essentially a grinding between two plates. This results in an earthquake. Most quakes tend to occur along fault lines (boundaries between plates) because this is where most movement occurs, plate-to-plate.

The United States Geological Survey defines an earthquake as such: "Earthquake is a term used to describe both sudden slip on a fault, and the resulting ground shaking and radiated seismic energy caused by the slip, or by volcanic or magmatic activity, or other sudden stress changes in the earth." Simply stated, this type of disaster involves the events underneath the surface of the Earth that lead up to the quake and the actual quake itself.

Like most natural disasters, quakes require certain environmental circumstances to be in place for them to occur. Again quoting the United States Geological Survey, "An earthquake is caused by a sudden slip on a fault. The tectonic plates are always slowly moving, but they get stuck at their edges due to friction. When the stress on the edge overcomes the friction, there is an earthquake that releases energy in waves that travel through the Earth's crust and cause the shaking that we feel."

There is a very simple bit of advice to remember if you find yourself caught in a quake. This is from the Centers for Disease Control and Prevention, which published findings on the safest way to survive a quake. "DROP down onto your hands and knees before the earthquake knocks you down. This position protects you from falling but allows you to still move if necessary. COVER your head and neck (and your entire body if possible) underneath a sturdy table or desk. If there is no shelter nearby, get down near an interior wall or next to low-lying furniture that won't fall on you, and cover your head and neck with your arms and hands. HOLD ON to your shelter (or to your head and neck) until the shaking stops. Be prepared to move with your shelter if the shaking shifts it around."


Quakes can occur just about anywhere. In fact, almost every state in the United States has recorded incidences of earthquakes occurring. However, some states and regions are more prone to such disasters than others. The ten states in the U.S. that receive the most earthquakes are:

  • Alaska
  • California
  • Hawaii
  • Nevada
  • Washington State
  • Idaho
  • Wyoming
  • Montana
  • Utah
  • Oregon

Earthquakes occur as a natural, though disastrous phenomenon. They are caused by a sudden slip, below the Earth's surface, along a fault line. A fault line is a place where two tectonic plates meet. These plates are slowly moving, and sometimes they grind along each other, causing a shift of rock and a resulting quake to occur.

The Richter Scale is a special measurement designation used to determine the intensity and severity of an earthquake. According to the USGS, "Earthquakes are recorded by a seismographic network. Each seismic station in the network measures the movement of the ground at that site. The slip of one block of rock over another in an earthquake releases energy that makes the ground vibrate. That vibration pushes the adjoining piece of ground and causes it to vibrate, and thus the energy travels out from the earthquake hypocenter in a wave." Earthquakes are measured by their magnitude on a scale of 0 to, essentially, infinity. The highest magnitude earthquake ever recorded ranked at 9.5 on the Richter Scale.

Most small earthquakes only last for a few seconds, but more intense earthquakes can last for several minutes. A quake rarely lasts longer than a few minutes. However, such events can cause massive, even catastrophic devastation in those minutes.

It's not easy to prepare for a quake because such events are not easy to predict. Ready.gov, a government-funded and run disaster preparedness website, says this about preparing for such an event: "Practice drop, cover, and hold on with family and coworkers. Create a family emergency communications plan that has an out-of-state contact. Put together a stash of non-perishable foods, cleaning supplies, and water for several days, in case services are cut off in your area. Secure heavy items in your home like bookcases, refrigerators, televisions and objects that hang on walls. Store heavy and breakable objects on low shelves."

In the United States, the most commonplace for quakes to occur is in California. This is because two tectonic plates meet in California, the Pacific Plate, and the North American Plate. The major fault line that is formed by the plates is called the San Andreas Fault. It's important to keep in mind that, though earthquakes tend to occur in specific regions where tectonic plates meet, quakes can occur at any location and at any time. For example, only eight states in the U.S. have not recorded a quake event (at least not between 1973 and 2003). These are Wisconsin, Vermont, North Dakota, Maryland, Iowa, Florida, Delaware, and Connecticut. As for the remaining 42 states, frequency of quake events ranges anywhere from West Virginia, which has just one quake on record, to Alaska, which has 12,053 earthquakes on record for the 1973 to 2003 recording period.

The "epicenter" (as one would normally think of it) in an earthquake is not called that, though such a term does have its place in quake nomenclature. According to the United States Geological Survey, "An earthquake is what happens when two blocks of the Earth suddenly slip past one another. The surface where they slip is called the fault or fault plane. The location below the Earth's surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the Earth is called the epicenter."

One of the most common natural disasters to occur on Earth, earthquakes can happen almost anywhere, at any time. They are highly unpredictable, as there is no "season" for quakes like there is for many other natural disasters. Quake tremors can occur at any time of the year and at any time of the day or night. They can occur under any weather conditions. They cannot be predicted, at least not more so than a few minutes out from the first tremor. Given how common earthquakes are and their potential for being particularly devastating to established urban areas, it's important to prepare for them and to know how to respond when one occurs.

Possibly, yes. Fracking intentionally causes small quakes, and this process has been linked to larger quakes. A magnitude four quake in Texas some years ago was linked to nearby fracking. Also, detonating a nuclear warhead is another human-created cause of quakes. Detonating such an immense payload causes a seismic shift that is so immense it is comparable to an earthquake. Quoting Michigan Technological University, "The largest underground explosions, from tests of nuclear warheads (bombs), can create seismic waves very much like large earthquakes. This fact has been exploited as a means to enforce the global nuclear test ban, because no nuclear warhead can be detonated on Earth without producing such seismic waves."

While large earthquakes are relatively common in the United States, early warning systems implemented by the United States Geological Survey provide alerts to help Americans take shelter. Furthermore, more durable building methods and well-established emergency response systems help save lives and reduce fatalities during U.S.-based quakes. This is why relatively few Americans die in quakes, compared to other countries that experience similar-magnitude quakes. The most powerful earthquake to strike the United States occurred in Alaska in 1964. This quake was a magnitude 9.2 that struck Prince William Sound and killed 139 people.

The million-dollar question, are quakes increasing in intensity and frequency? In the paper, geophysicist Paul Lundgren of NASA's Jet Propulsion Laboratory in Pasadena, California, said, "We've seen that relatively small stress changes due to climate-like forcings can effect microseismicity. A lot of small fractures in Earth's crust are unstable. We see also that tides can cause faint Earth tremors, known as microseisms. But the real problem is taking our knowledge of microseismicity and scaling it up to apply it to a big quake, or a quake of any size that people could feel, really. Climate-related stress changes might or might not promote an earthquake to occur, but we have no way of knowing by how much." The short answer is that scientists simply do not know if earthquakes will get worse or not. Regardless, individuals and families need to understand how to prepare for an earthquake and what to do should one occur.

The main cause is a shifting of tectonic plates that create a sudden movement of stone beneath the Earth's surface.

What you do after a quake depends on where you are and the type of environment/risks you have around you. According to the City of Portland's official warning system on quakes, "Evacuate if you are in a tsunami hazard zone. Walk inland or to higher ground as soon as it is safe to do so. Do not wait for official notification. Stay away from the coast until officials permit you to return. Check for injuries. Do not move seriously-injured persons unless they are in immediate danger. Check for hazards such as fires, gas leaks, downed utility lines and fallen objects. Clean up any potentially harmful materials spills. Expect aftershocks. Aftershocks following large earthquakes can be large and damaging."

Most scientists maintain that quake prediction is inherently impossible, though some argue that advances in technology could lead to the effective and reliable prediction of earthquakes.

The National Earthquake Information Center locates about 20,000 quakes across the plant each year, or 55 quakes per day.

Approximately 55 significant, notable earthquakes occur on planet Earth each day, but the location of those quakes vary, region to region. For example, California, a quake-prone state in the U.S., experiences about 100 micro-quakes every day. Compare that to other states in the U.S. that may only experience a quake once every several years.

Many organizations provide advice on quakes. The agreed-upon rule of thumb is best put by the CDC: "DROP down onto your hands and knees before the earthquake knocks you down. This position protects you from falling but allows you to still move if necessary. COVER your head and neck (and your entire body if possible) underneath a sturdy table or desk. If there is no shelter nearby, get down near an interior wall or next to low-lying furniture that won't fall on you, and cover your head and neck with your arms and hands. HOLD ON to your shelter (or to your head and neck) until the shaking stops. Be prepared to move with your shelter if the shaking shifts it around."

Earthquakes are unique in that they are a literal shaking of the Earth beneath our feet. Earthquakes are vibrations coming up through the Earth's crust that cause shaking on the surface. Sometimes the shaking feels like it is going back and forth. Sometimes it is entirely erratic and without a pattern.

While the 1964 Great Alaska Earthquake was the worst U.S.-based quake, it was only the second-worst earthquake ever recorded internationally. The worst quake ever recorded was in Bi-Bio Chile. It was a 9.5 magnitude quake, whereas the Alaska quake was a 9.2. The Chile quake occurred in 1960.

According to Brooklyn College, the key is in the convergent plate boundaries. According to the college's report: "At convergent plate boundaries, where two continental plates collide earthquakes are deep and also very powerful. In general, the deepest and the most powerful earthquakes occur at plate collision (or subduction) zones at convergent plate boundaries."

Quakes are most likely to occur where two plate boundaries meet. On Planet Earth, that includes places primarily along the rim of the Pacific Ocean, including states and countries along the western Americas, plus China, Japan, Russia, North and South Korea, and various islands along the fringes of the Pacific Ocean.

While there is no scientific consensus that either confirms or denies it, some believe that dogs possess such sensitive hearing that they can pick up the faint scraping and grinding of rocks beneath the surface of the Earth that precede an earthquake.

Seismographs begin alarming us of an earthquake just a few seconds before the actual tremors set in, which is all the warning we usually have before a quake occurs.

Earthquakes are unique in that they are a literal shaking of the Earth beneath our feet. Earthquakes are vibrations coming up through the Earth's crust that cause shaking on the surface. Sometimes the shaking feels like it is going back and forth. Sometimes it is entirely erratic and without a pattern.

Absolutely. In 1960, the largest earthquake ever recorded hit Chile. This magnitude 9.5 quakes caused 1,600 deaths in Chile. Though the earthquake did not occur anywhere near the United States, the earthquake caused a tsunami that traveled across the Pacific Ocean and hit Hawai'i. Thirty-five-foot waves crashed on the island of Hilo and killed 61 people.

Like many other types of waves, quake waves bend when they pass through different materials, which is part of why quake tremors and the direction they travel are so unpredictable.

A fault refers to the fracture along the blocks of crust on either side of two tectonic plate boundaries. A fault line is where most quakes occur.

The Richter Scale is a special measurement designation used to determine the intensity and severity of an earthquake. According to the USGS, "Earthquakes are recorded by a seismographic network. Each seismic station in the network measures the movement of the ground at that site. The slip of one block of rock over another in an earthquake releases energy that makes the ground vibrate. That vibration pushes the adjoining piece of ground and causes it to vibrate, and thus the energy travels out from the earthquake hypocenter in a wave." Earthquakes are measured by their magnitude on a scale of 0 to, essentially, infinity. The highest magnitude earthquake ever recorded ranked at 9.5 on the Richter Scale.

Earthquakes can happen at any time and with very little warning. Experts recommend that if you're already inside when an earthquake strikes, stay inside. Do not run outside or to other rooms during an earthquake. Staying put and seeking cover offers the best chance at avoiding injury. Don't stand in a doorway or near a window. Seek shelter underneath something sturdy, such as a table. If you have children or elderly relatives living with you, help them seek refuge first. Earthquake tremors are usually short-lived. Seek shelter and cover and wait it out.

Aftershocks are complicated. Small, unnoticeable aftershocks can occur for days, months, even years after a major earthquake. But most serious earthquakes produce just a handful of aftershocks that come about shortly after the main tremors recede.

There is no such thing as earthquake weather. It is a myth.

Earthquakes are measured on the Richter scale, a numerical scale used to express the magnitude of a quake. A destructive quake typically has a magnitude of 5.5 to 8.9, with quakes above 8.9 being quite rare and particularly destructive.

Earthquakes and volcanos are both caused by the movement of tectonic plates.

California by far, with Alaska in second place.

According to the United States Geological Survey, "The deepest earthquakes occur within the core of subducting slabs – oceanic plates that descend into the Earth's mantle from convergent plate boundaries, where a dense oceanic plate collides with a less dense continental plate and the former sinks beneath the latter."

Seismologists are Earth scientists who specialize in geophysics. They study the genus and propagation of the seismic waves that create earthquakes.

Yes. A transform plate boundary is simply a type of plate boundary where plates slide horizontally past each other. As the plates rub against each other, huge stresses on the rocks can cause portions of the rock to break, resulting in quakes.

Yes, a volcanic eruption can indeed cause an earthquake, though volcano-caused quakes are usually not as intense as quakes caused by movement along tectonic plate boundaries.

From the USGS, "An earthquake is caused by a sudden slip on a fault. The tectonic plates are always slowly moving, but they get stuck at their edges due to friction. When the stress on the edge overcomes the friction, there is an earthquake that releases energy in waves that travel through the Earth's crust and cause the shaking that we feel."

Three seismographs are needed to locate a quake.

Earthquakes are arguably one of the most destructive natural disasters, often because of the other disasters that they can cause. Earthquakes can trigger landslides and mudslides along hilly terrain, especially in areas with water-soaked soils. Earthquakes can also cause buildings to collapse, disrupting gas, electricity, and telephone service. Earthquakes can also cause fires and even tsunami waves.

Low-pitched rumbles, rattling windows, car alarms, small trembles, crumbling concrete, and a shaking, shifting sound are the noises generally associated with earthquakes.

A quake or tremor that results in a sudden and violent shaking of the ground is the key defining factor of an earthquake.

The highest magnitude is essentially infinite in terms of potential quakes. However, since recording began, the highest magnitude that has occurred was a 9.5 magnitude quake in Chile that occurred in 1960.

When an earthquake occurs, stop, drop, cover, and hold on. This is the immediate response one should take to a quake because one usually does not have much time to prepare for such a disaster.

In this question, "worst" refers to the quake with the highest death toll, even if it was not the highest magnitude quake. According to Our World in Data, the deadliest earthquake ever recorded took place in Shaanxi, China, in 1556. It's estimated to have killed about 830,000 people.

Technically, Yes. However, earthquakes are far more common and likely in some regions than others.

Not one that seismographs have recorded, but it is almost certain that one has occurred in world history.

Geologists use the seismic waves created by an earthquake to measure the quake's epicenter. The epicenter is located by measuring the difference between the arrival time of different types of waves.

Most disasters of this nature last just a few seconds. However, that does not mean one can come out of cover after the initial tremors recede, as aftershocks are quite common in earthquakes. Should a quake strike, one should not come out of the shelter until local responders and authorities say it is safe to do so, unless they live in a tsunamis-risk zone.

Michigan Technological University published an excellent classification system of different magnitude earthquakes. According to their data, a quake event that measures a 5.5 magnitude or higher can cause significant damage.

You can feel anything above a 2.5 magnitude quake, but such quake events usually only cause minor damage.

Seek cover! Drop down low to the ground and try to take cover underneath a stable surface.

A magnitude 4.0 quake can be felt as far as 60 miles away from the epicenter. A magnitude 5.5 quake can be felt 300 miles away from the epicenter. The higher the magnitude of the quake, the further away its tremors can be felt.

Quake tremors travel very fast. The rupture speed of the average tremor is 5,600 to 6,700 miles per hour. For context, most bullets only travel at about 1,700 miles per hour.

The United States Geological Survey defines aftershocks as such: "Aftershocks are smaller earthquakes that occur in the same general area during the days to years following a larger event or "mainshock." They occur within 1-2 fault lengths away and during the period of time before the background seismicity level has resumed. As a general rule, aftershocks represent minor readjustments along the portion of a fault that slipped at the time of the mainshock. The frequency of these aftershocks decreases with time. Historically, deep earthquakes (>30 km) are much less likely to be followed by aftershocks than shallow earthquakes."

There are some simple rules to follow during a quake regarding what not to do. For example, do not run outside or to other rooms during quake tremors. Avoid areas of a building that are right next to exterior walls. Windows, facades, and architectural details are often the first parts of the building to collapse.

There is no such thing as quake season. Statistically speaking, there is an equal distribution of quakes throughout the year and in all types of weather.

If a building collapses during a quake, no floor is a safe floor. However, being on a higher floor increases the chances of survival during such an event. Conversely, being lower to the ground makes evacuation easier after the quake. Simply stated, it's more important to seek cover and protect oneself on whatever floor they are on during a quake than to go looking for a safer floor.

Some animals might be able to sense the initial tremors that come right before a quake occurs. While some scientific papers have been published, the research is still inconclusive and is awaiting peer review.

No. If you are inside during a quake, stay inside. Don't run outside during a quake. Don't run at all during a quake. You are much safer by staying inside and seeking shelter underneath a table.

Such waves are usually called "Seismic Waves."

The best place to seek shelter during a quake is in the center of a room under a sturdy desk or table, not near windows or exterior walls.

According to National Geographic, "A powerful earthquake can cause landslides, tsunamis, flooding, and other catastrophic events. Most damage and deaths happen in populated areas. That's because the shaking can cause windows to break, structures to collapse, fire, and other dangers. Geologists cannot predict earthquakes.”

Earthquakes are unique in that they are a literal shaking of the Earth beneath our feet. Earthquakes are vibrations coming up through the Earth's crust that cause shaking on the surface. Sometimes the shaking feels like it is going back and forth. Sometimes it is entirely erratic and without a pattern. The vibrations of the shifting tectonic plate boundaries are what causes the shaking sensation of earthquakes.

Sometimes, yes. This is not a common or frequent natural event, but it has occurred. Regional earthquakes greater than magnitude six have been identified as a cause point for nearby volcanic events.

Yes. Thousands of earthquakes are recorded on planet Earth each year.

This is a tricky question to answer because the answer is both yes and no. Quoting the United States Geological Survey experts, "A temporary increase or decrease in seismicity is part of the normal fluctuation of earthquake rates. Neither an increase nor decrease worldwide is a positive indication that a large earthquake is imminent. According to long-term records (since about 1900), we expect about 16 major earthquakes in any given year. That includes 15 earthquakes in the magnitude 7 range and one earthquake magnitude 8.0 or greater. In the past 40-50 years, our records show that we have exceeded the long-term average number of major earthquakes about a dozen times."

Quakes cause immense destruction and serious damage to infrastructure. When a magnitude five or above quake occurs in an urban area (with the epicenter of the quake occurring in an urban center), the earthquake can destroy the entire infrastructure of that urban area. Some countries (like the United States) have created advanced technologies and building methods to protect buildings and infrastructure from quakes. Other countries, however, are still at high risk of experiencing serious damage from such disaster events.

Another term for this is "foreshock." A foreshock is a quake that occurs before a larger seismic recording occurs. A foreshock can be a good warning that major quake tremors are just around the corner.

Cities at high risk for quakes are:

  • Tokyo, Japan
  • Jakarta, Indonesia
  • Los Angeles, California
  • Quito, Ecuador
  • Osaka, Japan
  • San Francisco, California
  • Lima, Peru
  • Tehran, Iran
  • Istanbul, Turkey

The entire nation of Japan rests in an active seismic area. Japan records the most quakes of any country.

For the most part, quake events tend to cause fires because tremors damage residential and business gas and electrical lines. That can create natural gas leaks and the downing of power lines, both of which can cause fires.

Not with any kind of predictability or reliability. Quakes come and go. Some years have more quakes than others. However, there is no way of proving if quakes are becoming more common and more intense than they once were.

Unfortunately, no. According to the USGS, "We cannot prevent natural earthquakes from occurring but we can significantly mitigate their effects by identifying hazards, building safer structures, and providing education on earthquake safety. By preparing for natural earthquakes we can also reduce the risk from human induced earthquakes."

It's possible. The USGS has recorded a few instances of serious quakes in Texas, Oklahoma, and other states directly linked to seismic disruptions caused by fracking explosions. From the USGS, "The largest earthquake known to be induced by hydraulic fracturing in the United States was a M4 earthquake in Texas. In addition to natural gas, fracking fluids and saltwater trapped in the same formation as the gas are returned to the surface. These wastewaters are frequently disposed of by injection into deep wells. The injection of wastewater and saltwater into the subsurface can also cause earthquakes that are large enough to be damaging. Wastewater disposal is a separate process in which fluid waste from oil and gas production is injected deep underground far below ground water or drinking water aquifers. The largest earthquake known to be induced by wastewater disposal was a M5.8 earthquake that occurred near Pawnee, Oklahoma in 2016." That's one argument for finding alternative, sustainable, and renewable forms of energy production.


Sources:

https://earthquake.usgs.gov/learn/glossary/?term=earthquake

https://www.cdc.gov/disasters/earthquakes/during.html#

http://www.geo.mtu.edu/UPSeis/why.html

https://www.ready.gov/earthquakes

ttps://www.usgs.gov/natural-hazards/earthquake-hazards/science/science-earthquakes?qt-science_center_objects=0#qt-science_center_objects

https://climate.nasa.gov/news/2926/can-climate-affect-earthquakes-or-are-the-connections-shaky/

https://www.usgs.gov/faqs/why-are-we-having-so-many-earthquakes-has-naturally-occurring-earthquake-activity-been?qt-news_science_products=0#qt-news_science_products

https://earthquake.usgs.gov/data/oaf/overview.php

https://www.usgs.gov/faqs/what-depth-do-earthquakes-occur-what-significance-depth?qt-news_science_products=0#qt-news_science_products

https://www.usgs.gov/faqs/what-earthquake-and-what-causes-them-happen?qt-news_science_products=0#qt-news_science_products

https://ourworldindata.org/the-worlds-deadliest-earthquakes

http://www.geo.mtu.edu/UPSeis/magnitude.html

https://www.usgs.gov/natural-hazards/earthquake-hazards/science/animals-earthquake-prediction?qt-science_center_objects=0#qt-science_center_objects

https://kids.nationalgeographic.com/science/article/earthquake#

https://www.usgs.gov/faqs/can-we-cause-earthquakes-there-any-way-prevent-earthquakes?qt-news_science_products=0#