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Caltech’s Earthquake Specialists Shed Light On ‘Big One’ Ahead of Thursday’s Great ShakeOut Event

There is a 97.45 percent chance of a major earthquake within 30 miles of Pasadena within the next 50 years. Thursday, Pasadenans will prepare for that day

Published on Wednesday, October 19, 2022 | 6:13 am

Photo of Northridge Earthquake of 1994 response by Red Cross. [Photo by Jeanette Ortiz-Osorio / American Red Cross]
The next big earthquake in California is only a matter of when.

“It will happen,” Caltech Seismologist and Research Professor of Geophysics, Dr. Egill Hauksson said. “We know that it will occur because the Pacific and North America Plates keep moving past each other at a steady speed.”

Even though earthquake research has come a long way, scientists still can’t say exactly when the next large earthquake will strike California. 

“We know where the biggest earthquakes occur (on the mapped faults) but we have no idea when it will occur,” Dr. Hauksson said. 

The US Geological Survey (USGS) database shows that there is a 97.45 percent chance of a major earthquake within 30 miles of Pasadena within the next 50 years.

International ShakeOut Day is October 20, when millions of people worldwide will participate in earthquake drills at work, school, or home. Here in Pasadena, people in government offices, businesses and schools throughout Los Angeles County will stop everything for a minute Thursday to “drop, cover and hold on” during a statewide earthquake preparedness drill at 10:20 a.m. (Click here for more)

Pasadena is sandwiched between the Raymond fault to the south, the Eagle Rock fault to the west and the Sierra Madre fault to the north along the mountain front. These faults all move very slowly, Dr. Hauksson added.

And, of course, the southern portion of the San Andreas fault – the world’s longest fault that runs through almost the whole length of California – has been identified as the most likely source of a very large earthquake in the state. 

This portion slices through Los Angeles County along the north side of the San Gabriel Mountains.

A computer simulation constructed through a collaborative effort between the U.S. Geological Survey and the Southern California Earthquake Center shows that a magnitude 7.8 scenario earthquake would rupture 186 miles from Bombay Beach at the edge of the Salton Sea in the south to Lake Hughes northwest of Palmdale in the north. 

Pasadena, south of that fault line, could experience maximum shaking – and major damage – if that scenario ever occurs.

“It could happen any time, or not for a very long time,” Dr. Hauksson said. “The damage from such an earthquake was modeled as part of the ShakeOut project. It will be very damaging and could disrupt our way of life for months.”

In time for International ShakeOut Day on Thursday, Dr. Hauksson said both Caltech and JPL are researching faults, how they move, and what kind of damage the Big One could cause in affected areas.

“Caltech and JPL scientists collaborate on earthquake research,” he said. “JPL develops and launches satellites to measure the movements of the plate as well as deformation of the ground by earthquakes. These data are analyzed jointly by Caltech and JPL researchers.”

At the Caltech Seismological Lab, Dr. Hauksson and his team are working to acquire, analyze and model data pertaining to the structure and dynamics of the earth as well as other planetary bodies. The data comes from many sources: regional and global seismic networks, in-house analytic facilities such as high pressure mineral physics, oceanic research cruises, remote sensing equipment including radar and GPS, and geologic field mapping. Currently, the team incorporates all aspects of geophysics and earthquake geology including the structure of regional crusts, the physics of earthquakes, and even the structure, chemistry, and convective flow of the earth’s interior.

The Southern California Earthquake Data Center (SCEDC) also operates at the Caltech Seismological Lab. The SCEDC is the primary archive of seismological data for southern California.

“We are pretty good at predicting the effects of earthquakes,” Dr. Hauksson said. “We can give probabilities of how often and how strongly a certain place will shake in California. This is useful for planning of land use and infrastructure.”

At JPL, scientists using satellite data are building a growing body of information about earthquake probabilities, behaviors, and effects. It has pioneered methods of measuring the way the surface of Earth’s crust deforms, and its work helps other scientists understand how earthquake faults behave before, during, and after a quake. 

The scientists may not be able to predict when an earthquake could happen, but by knowing how the faults behave, they are able to advise developers and urban planners on what kind of structures could withstand a strong earthquake, or whether those structures should be built or not in a particular area.

After any quake, the first priority is to help any affected communities. A research team led by JPL has 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. This mapping technology has been used and tested after several earthquakes, including the 2020 Puerto Rico quake.

With all the faults that either sandwich Pasadena or are close to it, the Crown City has a very high earthquake risk. It has experienced a total of 6,478 earthquakes since 1931. 

The largest earthquake within 30 miles of Pasadena was the Northridge earthquake that recorded a 6.7 magnitude in 1994.

For more information about Caltech’s Seismological Lab, visit

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