As Mother Nature rains havoc upon us today #OTD in 1857 was The Fort Tejon Earthquake. It was the last time "The Big One" occurred on the central-southern San Andreas Fault with a M7.9 rupturing from Parkfield to couple dozen miles (or so) northwest of The Cajon Pass.
The earthquake would have continued rupturing southeast towards Imperial County, but the 1812 event, commonly known as The Wrightwood Earthquake, occurred, which "stopped" and "prevented" The San Andreas Fault from further rupturing.
The 1857 event is known as The Fort Tejon Earthquake, because that is where the most notable destruction occurred in sparsely populated Southern California.
Summary of events by way of newspaper "Los Angeles Star" indicates:
Many large aftershocks with several being described, "as strong as the first earthquake."
Damage reported in the San Fernando and San Gabriel Valleys.
No major damage reported in what is modern day #DTLA.
Many large aftershocks with several being described, "as strong as the first earthquake."
Damage reported in the San Fernando and San Gabriel Valleys.
No major damage reported in what is modern day #DTLA.
A repeat of the 1857 earthquake will likely result in moderate to severe damage in The Santa Clarita Valley, Antelope Valley, parts of The San Fernando and San Gabriel Valleys, and Inland Empire. The L.A. Basin (DTLA, Eastside, north OC) will likely see moderate to major damage.
Liquefaction will be another problem. Reporting in the "Los Angeles Star" suggest liquefaction occurred in the San Gabriel Valley and San Bernardino area.
It will not be surprising if damage as a result of liquefaction occurs 50-100 miles away from the San Andreas Fault not unlike what resulted in 1989 Loma Prieta in The Marina District or 1985 and 2017 Mexico City.
Exactly how bad will damage be in a repeat of the 1857 earthquake? Well, based on 1857 contemporaneous accounts and what we've since learned about seismology and geology, we have a decent idea of what to expect, but, there is only going to be one way of finding out for sure.
The last time, by the way, there was a major earthquake on The San Andreas Fault between The Cajon Pass and Salton Sea was ~1680.
From Parkfield to The Salton Sea, yes, we are currently within the time frame of when a major earthquake can reoccur on The San Andreas Fault. The mean recurrence interval on The SAF is about 105 years. Of course, average, mean and medium doesn’t mean, "always right on time."
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