Big Sur landslide highlights earthquake vulnerability of magnificent California coast

By David Jacobson, Temblor

Check your hazard rank

This image shows the landslide that occurred in Big Sur over the weekend. Some suggest this stretch of road may remain closed for months as 35-40 feet of dirt is currently covering Highway 1. (Photo by John Madonna – AP)


Over the weekend, a massive landslide in Big Sur left part of Highway 1 covered in 35-40 feet of dirt, with some reports stating that the section of road may remain closed for months. Fortunately, no one was hurt in the incident, as this part of highway has been closed almost continuously since January due to smaller landslides caused by California’s unusually wet winter and spring. This stretch of California is an extremely popular tourist destination because of its spectacular views of the Pacific Ocean and steep cliffs. However, now the area is completely cut off, with Caltrans wondering if the road is even still there or if it will have to be completely rebuilt.

This Google Earth image shows the same location as the first image in this post. By comparing the two, the magnitude of the landslide becomes evident.


While this is an isolated incident, it also highlights the earthquake vulnerability of the Big Sur coastline. In the event of a large earthquake, it is highly likely that numerous landslides will block Highway 1, which will make getting supplies in and people out that much more difficult. According to the California Geological Survey, this entire stretch of California is very susceptible to landslides because of high angle slopes and weak rock.

These images show Mud Creek before and after the landslide over the weekend. This part of the California coast has already been impacted by landslides due to an unusually wet winter and spring. Because of this, businesses throughout Big Sur have been severely impacted. (Photos from: Google Earth and the AP)


Even though this part of Northern California is not very seismically active, the San Gregorio Fault runs straight through Big Sur. The San Gregorio Fault, is a large right-lateral strike-slip fault which runs nearly parallel to the San Andreas, until they merge northwest of the Golden Gate. Based on investigations, the San Gregorio last ruptured 220-700 years ago, prior to Spanish missionary arrival. A repeat of such an event would exceed M=7.0, and would trigger violent shaking throughout Northern California. The threat of such an earthquake, as well as quakes on smaller faults in the area was one of the factors that prompted PG&E to last year announce that the Diablo Canyon nuclear power plant would be closed. This plant in San Luis Obispo, is California’s last nuclear power plant, and sits mere kilometers from active faults.

This Temblor map shows the location of the landslide over the weekend as well as nearby faults. The San Gregorio Fault to the north of the landslide is capable of generating M=7+ earthquakes.


To gain a greater understanding of what could happen to the Big Sur coastline in a large earthquake, we need only look at what happened in the November 2016 Kaikoura, New Zealand earthquake. This M=7.8 quake resulted in over 10,000 landslides, several of which blocked New Zealand’s Highway 1, which is not completely open six months after the earthquake. The isolation which has befallen Kaikoura, has been devastating as the town is highly dependent on tourism, and with significant closures, many businesses have either closed or seen significant decreases in profits. Furthermore, the fact that the damaged stretch of highway is not completely open more than six months after the earthquake illustrates how long it can take for clearing and repairs to be completed. The image below shows one of the landslides that blocked New Zealand’s State Highway 1, and the resemblance to the Big Sur coast is quite evident.

This picture shows one of the many landslides that blocked State Highway 1 in New Zealand in the November 2016 Kaikoura earthquake. (Photo from: Environment Canterbury)


Because Big Sur, like Kaikoura, is so heavily dependent on tourism, at least one resort has refused to let road closures impact business. The Post Ranch Inn, north of the landslide has been using helicopters to bring in guests since April to cope with the closed highway. However, not all resorts have been so lucky, as some have seen reservations decrease by over 50%. If such hardship has hit resorts from the recent landslides, who know what would happen to them if the number of slides increased into the thousands. What all of this shows is that we are lucky to have such natural beauty, created by faults, but that the faults can also quickly take it away.

The video below shows the extent of the Big Sur landslide


New York Times
Gary D. Simpson, Stephen C. Thompson, J. Stratton Noller, and William R. Lettis, The Northern San Gregorio Fault Zone: Evidence for the Timing of Late Holocene Earthquakes near Seal Cove, California, Bulletin of the Seismological Society of America, Vol. 87, No. 5, pp. 1158-1170, October 1997.