Understanding Earthquakes

There's definitely a whole lotta shakin' goin' on every day on our planet. The National Earthquake Information Center says there are about 55 earthquakes a day around the world — that's 20,000 a year. Fortunately, most are too weak to cause damage, but stronger quakes, depending on location and other factors, can cause casualties, injuries, and property damage.

A quake occurs when two chunks of Earth beneath the surface, or tectonic plates, suddenly slip past each other and release large amounts of pent-up energy. The surface of the slip is called a fault.

Perhaps the most famous fault in the world is the San Andreas, which stretches about 750 miles (1,200 kilometers) from northern California to the Mexican border. It was even the topic of a Hollywood movie named for it. But there are thousands of other faults around the world.

So of course, everyone wants to know if scientists can predict earthquakes. The short answer is no. Recent smartphone apps can only provide a few seconds of warning for a specified area, and scientists can estimate the likelihood of a fault rupturing sometime over the next few decades, but no one is able to predict exactly when an earthquake will occur.

However, researchers around the globe, including some from JPL, are building a growing body of information about earthquake probabilities, behaviors, and effects .

After the Shaking Stops

JPL scientists have pioneered methods to measure the way the surface of Earth's crust deforms. Their work helps us understand how earthquake faults behave before, during, and after a quake. Measurements of crustal deformation are now used in California earthquake forecast models developed by the California and U.S. Geological Surveys.

After any quake, the first priority is to help any affected communities. For example, a research team led by JPL developed a way to map earthquake damage using remote sensing satellite technology. This can save precious time for disaster response teams by showing which areas are hardest hit. The mapping technology has been used after several earthquakes, including the 2020 Puerto Rico quake.

After two 2019 quakes near Ridgecrest, California, JPL and Caltech geophysicists determined that causes for large earthquakes can be more complex than had been assumed. They determined that a domino-like effect can happen, with interconnected faults triggering other faults and then putting pressure on a nearby major fault.

Sometimes an undersea earthquake triggers a tsunami, a series of giant waves that gain height and speed as they roll toward land. In 2004, a very large earthquake beneath the Indian Ocean near Indonesia triggered an enormous tsunami that caused 230,000 deaths in 14 countries. It's considered one of the deadliest natural disasters ever recorded. After that, a team of scientists from JPL and Sapienza University in Italy developed a new way to help improve tsunami warning systems, based on how a tsunami disturbs a part of Earth's atmosphere.

And a JPL-managed GPS system can infer seafloor movements from onshore land displacements, which helps in calculating the size and direction of a tsunami.