At the end of June, the SCEC community marked the 30th anniversary of the Landers earthquake, which occurred on June 28, 1992. 

According to geologist Kerry Sieh, Landers was the largest earthquake to have occurred in the mainland United States in over 40 years. Significant damage occurred due to Landers, and many residents in the Mojave Desert experienced violent shaking. 

As part of the anniversary, SCEC hosted a webinar ​titled “Lessons, Lore, and Legacies of the 1992 Landers Earthquake” where SCEC scientists and members of the local community shared their perspectives on the earthquake (the recording is now available). So what is the legacy of Landers?
 

Damage done to a bowling alley in Yucca Valley due to the 1992 Landers Earthquake (Credit: NOAA)

Importance of Landers

Yehuda Ben-Zion, current director of SCEC, said the Landers earthquake “highlighted the importance of the Eastern California Shear Zone for the plate boundary deformation in southern California.” He also noted that some of the methods and techniques that were first used during Landers, such as InSAR, are now commonly used for many earthquakes and volcanic events. 

USGS seismologist Susan Hough said that the earthquake led to great improvements in seismic monitoring. “In 1992, most seismic recording instruments were either ‘weak motion’ or ‘strong motion’. They were designed to record either weak shaking or strong shaking on scale, but not both,” said Hough. “Over the years that followed, the network was upgraded with many more state-of-the-art instruments.”

The amount and extent of rupture in the Landers earthquake was surprising to the scientific community as the rupture happened over multiple faults, both mapped and unmapped. According to SDSU professor Thomas Rockwell, this earthquake illustrated the idea of cascading ruptures. 

“Various faults could link up to produce an earthquake that was larger than those that can be expected from the individual faults associated with that sequence,” he said. 

Because of the event, the scientific community also learned more about how large earthquakes can trigger other remote earthquakes. “We now explicitly model multi-fault ruptures in our system level earthquake forecasting models,” said Greg Beroza, co-director of SCEC.

Perspectives on Landers

On the 30th anniversary, some members of the SCEC community involved with Landers wanted to share their experience of the event and the work they did––and some fun stories!
 

Yehuda Ben Zion, Director of SCEC

“Back in 1992, I was a postdoc at Harvard, but was in South Pasadena when the Landers earthquake occurred. 

At the time, I was developing theoretical models for dynamic rupture and seismicity, while also conducting some observational research. With students and colleagues, we published several papers on seismic imaging of the Landers rupture zone, and properties of the seismicity and focal mechanisms before and after the earthquake. 

The large amplitude of the Landers surface waves woke me up. I quickly went outside the house to look around and listen, and I remember seeing flashing lights around downtown LA, perhaps produced by exposed electrical wires. For many minutes after the passage of the surface waves, I could hear water sloshing back & forth in nearby swimming pools.”

Greg Beroza, Stanford (Co-Director of SCEC)

“At the time, my work on earthquakes was focused on imaging the slip distribution in large earthquakes from seismograms close to the source of the earthquake. We did such a study for Landers, but it was one of the last studies of that type that I did. After the earthquake, and because of the earthquake, my research changed directions.

Prior to Landers, it was assumed that all aftershocks occurred on or near the fault that ruptured in the earthquake. In the case of Landers, there were small earthquakes triggered by the waves generated by Landers at distances of over 1000 km. This opened a new chapter in studies of earthquake interaction.

I was in Mexico City on my way back from the Mathematical Geophysics meeting when the earthquake occurred. I didn’t hear about it until Sunday evening when I got home. We weren’t so well-connected 30 years ago as we are today.”

Susan Hough, USGS Pasadena

“I arrived back from New York just in time to be jolted out of bed (metaphorically) by the earthquake. With the internet in its infancy, we all rushed to the office to look at the data and plan the scientific response. I was in the Caltech analysis room when the Big Bear aftershock hit––another good-sized jolt.  

I led the deployment of six portable seismometers after the 23 April, 1992 Joshua Tree earthquake and kept the instruments running over the months that followed. Most of the instruments were up and running on June 28, so I high-tailed it to the desert to retrieve data, which was a magnetic tape recording! I then analyzed it to show that the southernmost part of documented surface rupture had actually happened in early aftershocks, not the mainshock.”

Thomas Rockwell, San Diego State University

“Most of my work at the time of the Landers earthquake focused on resolving the timing of past earthquakes on Southern California faults, as well as slip rates. So, I collected all of my graduate students and we headed to the rupture after seeing an image of the offset highway on the morning news. This was, of course, after it woke me up! 

I initiated paleoseismic studies immediately after the earthquake which continued for several years, with funding from SCEC that supported many SDSU graduate students.

We established equipment to test for afterslip––we found none––and then started looking at potential trench sites. The fault was already swarmed with geologists from the USGS, CGS, Caltech, etc. and there was no coordination of activities. I think the chaos is one thing that started us thinking about coordinated post-earthquake response.”

John McRaney, Former Director of Administration at SCEC

“My work during Landers was mainly focused on getting financial resources to SCEC scientists to do research on the earthquake and its aftershocks. SCEC was only 17 months old at the time of Landers. 

The earthquake had a major impact on the center. The event made us aware that we needed to organize ourselves better for a future earthquake. We spent some time doing this and it helped us tremendously when the Northridge earthquake occurred in January 1994.

I was on holiday in Calgary on the morning of the earthquake. I heard the news on CNN and called back my boss at SCEC. He suggested I get home as soon as possible. 

At the Calgary airport, there were television news reporters filming everyone going to Los Angeles. So, my wife told one of the reporters I worked at SCEC and before I could refuse, I found myself being interviewed live on Canadian national television about the earthquake.”

Additional Reading:

1992 Landers Earthquake
The Very Long Reach of Very Large Earthquakes by Susan Hough
https://scedc.caltech.edu/earthquake/landers1992.html
https://www.usgs.gov/media/videos/pubtalk-52021-where-earthquakes-hide-desert
Special Webinar: Lessons, Lore, and Legacies of the 1992 Landers Earthquake (Recording now available)  

About the Author

Shreya Agrawal is an earth scientist and a journalist focusing on climate change, environmental and social issues and politics. She graduates from USC in 2023 with a dual bachelor's degree in Geological Sciences and English, and a masters degree in journalism. She hopes to better communicate science to the public and bridge gaps in science communication.