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On July 4th, 2019, as millions of Southern Californians looked forward to fireworks and other celebrations, earthquake shaking rumbled across much of California, causing tall buildings in the Los Angeles region to sway noticeably. 

Ridgecrest Earthquake Epicenter

Earthquake scientists quickly pinpointed the epicenter of the first earthquake in the sequence in the high desert about 150 miles north of Los Angeles, within a remote United States Navy Base at China Lake, adjacent to the town of Ridgecrest. 

Scientists conversing by US Army helicopter

Damage from the July 4th event, estimated at magnitude 6.4, was mostly restricted to Ridgecrest, China Lake, and nearby Trona. 

nightly view of highway with large cracks from earthquake and car in the distance.


Felt Map 2019 Ridgecrest Earthquake

The Mainshock - 8:19 pm local time on July 5th, 2019 

With a magnitude of 7.1, the Ridgecrest mainshock, as it is known, was the largest earthquake to strike Southern California in 20 years, causing damage to nearby communities already impacted by the earthquake the day before. Waves from this powerful earthquake rocked population centers across Southern California.


Road Damage from the Ridgecrest, CA Earthquake

Seismic Network

The Ridgecrest earthquakes and their aftershocks were recorded by a conventional seismic network that had been expanded over the previous decade as part of the development of the ShakeAlert Earthquake Early Warning system. The California Integrated Seismic Network comprises thousands of sophisticated seismometers throughout California that transmit data in real-time to a central hub, where they are processed and analyzed by both real-time systems and teams of experts. 

ShakeAlert sensor station being serviced by USGS personnel

ShakeAlert Improves

In July 2019, the ShakeAlert Earthquake Early Warning System was operational in industrial settings, for example slowing and stopping trains in California. Analysis of data from the 2019 Ridgecrest earthquake sequence resulted in technical improvements to ShakeAlert, revision of alert delivery thresholds, and streamlining of the content in alert messages. 

Image shows a map of the earthquake area with seismic stations overlaid

Public alerting via apps and the Wireless Emergency Alert System began in California in October 2019 and in Oregon and Washington in 2021.  

Green logo for the ShakeAlert earthquake early warning system
ShakeAlert Is Not Earthquake Prediction

Rich Data Set

Scientists continue to analyze the rich data set to address key questions in earthquake science, including what factors control the timing and location of aftershocks, and how the ground shakes close to large earthquakes. 

Investigations of the Ridgecrest Sequence have exploited data from seismic networks, geodetic networks, satellites and more. Complementing conventional seismic networks that have grown in sophistication, the scientific community also embraces additional technologies that allow earthquake shaking to be recorded in far greater detail than previously possible. One such technology was borrowed from the oil patch: simple “nodal” seismometers that have been used for many years to acquire seismic data for industry, primarily oil and gas exploration. These simple instruments have been used increasingly in recent years for scientific investigations of earthquakes and faults.

A nodal seismometer can be easily deployed for a month in a closely...

A nodal seismometer can be installed quickly, literally stuck into the ground, where conventional seismometers are much more expensive, and can take hours to install. Earthquake scientists increasingly use dense deployments of nodals to record earthquakes which creates far more sampling than is possible with conventional networks. Data from nodal deployments were used, for example, to better understand the structure of sub-surface fault zones in the Ridgecrest area. 

two people working with instruments in an arid area

Newer Technology

A newer technology, also developed first for industry applications, involves so-called Distributed Acoustic Sensing systems that turns unused fiber optic cables into earthquake recording devices. With sophisticated technology, signals along the full length of a cable can be interrogated to obtain a record of earthquake shaking at any point along a cable. Whereas any seismometer records shaking at a point, a Distributed Acoustic Sensing system records shaking along a linear array, capturing shaking data in unprecedented detail. 

Advances in seismic instrumentation are leading to collection of unprecedented volumes of seismic data, the analysis of which poses a challenge for the scientific community. The migration of seismology into the modern big-data era has impelled development of new analysis techniques, including machine-learning and artificial intelligence. 

2019 Ridgecrest Earthquake Sequence - M7.1 Seismologists

Discoveries Continue

Since its earliest days as a modern scientific field, advancements in earthquake science have long been spurred by significant earthquakes. Data recorded from earthquakes allow scientists to explore earthquakes and their effects in ever-greater detail. 

Five years after the 2019 Ridgecrest earthquakes rocked the California high desert, the scientific community continues to collect and analyze an increasing range of data streams to improve our understanding of earthquakes and the hazard they pose. 

Video Transcript
Surface faulting from the M7.1 Searles Valley earthquake

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