What does it feel like to experience an earthquake? Does the ground start rolling like an ocean wave or shake back and forth? Learn what factors affect what an earthquake feels like and how you can vicariously experience one.
What does an earthquake feel like?
Famous accounts from luminaries like Mark Twain, Charles Darwin, and John Muir provide valuable perspectives from the past. More recently, the LA Times collected reader memoirs of experiencing the Northridge quake. Today, extensive video footage from recent quakes like 2011’s massive M 9.1 Tohoku earthquake in Japan let us vicariously experience the tumult.
Earthquakes come in many different shapes and sizes. A number of factors will affect any specific earthquake experience. Let’s start with the biggest—earthquake strength. Scientists measure the power of an earthquake using a standard called “moment magnitude” (MW). It’s calculated by the ratio of shear stress to shear strain, the average amount of slip on the fault, and the total affected area of the quake.
All things equal, an earthquake with a higher MW rating will shake you a lot more than a quake with a lower rating. An M 4.0 earthquake could feel like a large truck driving by, while an M 8.0 quake could shake you so much you cannot stand.
Distance from the epicenter also strongly influences how an earthquake feels. According to the US Geological Survey, a bit of distance can create the difference between a “large jolt” and a “gentle bump.” Descriptions of magnitude numbers for earthquakes are always based on experiences near the epicenter.
Depth comes next. The strongest earthquake of 2018 barely registered on anyone’s radar because so few people felt it. The M 8.2 quake off the coast of Fiji occurred almost 350 miles below the surface of the earth. It struck too deep to trigger a tsunami, and spawned only small trembling on the sparsely populated nearby islands.
In California, the two most famous faults—San Andreas and Hayward—are both “transform” or “slip-strike” faults. The tectonic plates are sliding past each other. Earthquakes on strike-slip faults generally occur at shallower depths, but also tend to have lower magnitudes than those on convergent faults.
Geology and Earthquake Motion
Local geology—the soil and rocks—of a location can also greatly influence how an earthquake feels. Soft, thick, sediment can often amplify the shaking of an earthquake, making it feel stronger than its magnitude. If the soil is saturated with water, extreme shaking can also lead to liquefaction and massive damage.
Mexico City residents experience this phenomenon first-hand. Along with its spaghetti junction of continental tectonic plates, Mexico City is built on top of an ancient lakebed composed of sand, silt, and soft clay, and surrounded by mountains of bedrock. When earthquakes strike, the city acts like a “bowl of jelly” as amplified seismic waves bounce around the soft lake basin.
If personal accounts and videos aren’t enough to help you imagine what an earthquake feels like, visit Tokyo. The Tokyo Earthquake Simulation Center in the Ikebukuro Bosai-kan fire station offers the chance to experience two minutes of an earthquake at no charge. The Tokyo project also includes the largest earthquake simulator in the world, which shakes full, multistory buildings at magnitudes up to M 7.0.