California's 7.1 earthquake–and how earthquakes work

Earthquakes are naturally destructive effects of our planet's constantly changing surface. Thousands of them happen every day.

A powerful magnitude 7.1 temblor rocked Southern California at 8:19 PT on July 5, 2019, just 34 hours after a magnitude 6.4 earthquake hit the same region. This is the largest in decades, with the last temblor this large—the magnitude 7.1 Hector Mine earthquake—striking the Mojave Desert in 1999.

This latest event was widely felt, causing several fires and damage to buildings and roads in Ridgecrest and nearby, but reports on the impacts are still emerging. Aftershocks are expected to continue, with a 27 percent chance that as many as two earthquakes of magnitude 6 or higher could occur within the next week.

About earthquakes

Earthquakes, also called temblors, can be so tremendously destructive that it’s hard to imagine they occur by the thousands every day around the world, usually in the form of small tremors. See the latest earthquakes and learn how to stay safe during these disastrous events.

Earthquakes 101 Earthquakes can leave behind incredible devastation, while also creating some of the planet's most magnificent formations. Learn about the geophysics behind earthquakes, how they are measured, and where the most powerful earthquake ever witnessed occurred.

Where do most earthquakes occur?

Some 80 percent of all the planet's earthquakes occur along the rim of the Pacific Ocean, called the "ring of fire" because of the preponderance of volcanic activity there, as well. Most earthquakes occur at fault zones, where tectonic plates—giant rock slabs that make up Earth's upper layer—collide or slide against each other.

These impacts are usually gradual and unnoticeable on the surface; however, immense stress can build up between plates. When this stress is released quickly, it sends massive vibrations, called seismic waves, often hundreds of miles through the rock and up to the surface. Other quakes can occur far from faults zones when plates are stretched or squeezed.

Earthquake magnitude ratings and their impacts

Scientists assign a magnitude rating to earthquakes based on the strength and duration of their seismic waves. A quake measuring 3 to 4.9 is considered minor or light; 5 to 6.9 is moderate to strong; 7 to 7.9 is major; and 8 or more is great.

On average, a magnitude 8 quake strikes somewhere every year, and some 10,000 people die in earthquakes annually. Collapsing buildings claim by far the majority of lives, but the destruction is often compounded by mud slides, fires, floods, or tsunamis. Smaller temblors that usually occur in the days following a large earthquake can complicate rescue efforts and cause further death and destruction.

Loss of life can be avoided through emergency planning, education, and the construction of buildings that sway rather than break under the stress of an earthquake.

Warning: Some of the photos below contain graphic imagery.