San Andreas Fault consists of three sections, wherein two are static and one slow-moving. A new study from Columbia University's Lamont-Doherty Earth Observatory in Palisades, New York, found that the relatively calm central section of the fault is also capable of producing large earthquakes similar to those created by other sections.
Researchers backtracked the geological record of the fault and found that it has experienced earthquakes of magnitude 7 or higher, which is the same as the 1906 San Francisco earthquake. The findings add to the risk of a Big One happening in the future that may have been long overdue.
A sign posted at the San Andreas Fault, separating the Pacific and the North American tectonic plates near Parkfield, California on July 12, 2019 in a remote part of California but one of the most heavily studied quake areas in the world.
Three Main Sections of the 800-Mile San Andreas Fault
Most of the big earthquakes in California have either happened in the northern or southern parts of the state, such as in San Francisco or Los Angeles, local news outlet KCBX reported. On the other hand, Central California was thought to be at lower risk and has been relatively earthquake-free in the past, except for the 1925 Santa Barbra earthquake.
The infamous 800-mile long San Andreas Fault in California is composed of the northern section that produced the 7.9-magnitude 1906 San Francisco earthquake, the slow-moving and calmer central section, and the southern sections that produced the deadly 6.7-magnitude 1994 Northridge earthquake near Los Angeles.
According to Newsweek, the 1906 San Francisco claimed more than 3,000 lives, while the 1994 earthquake in LA claimed 57 people. In contrast, the central section of the fault is not static, and parts of its plates move past each other in slow motion that scientists thought that this creeping section of the fault avert the production of pressure build-ups and negate opportunities for large earthquakes.
But the findings of the new study, titled "History of Earthquakes Along the Creeping Section of the San Andreas Fault, California, USA," published in the journal Geology, say otherwise. Now, researchers believe that it is building energy for another large earthquake that is commonly referred to as the "Big One."
Central Section of San Andreas Fault Experienced Large Earthquakes in the Past
According to MailOnline, researchers drilled and removed rocks two miles below the surface of the central section of the fault that is believed to have hosted many major earthquakes in the past. They subjected these rocks to a chemical analysis method to gauge the heating of the rocks in prehistoric times and predict how strong the earthquakes would be.
They found evidence that these earthquakes could be as strong as magnitude 7, which means that large earthquakes were indeed possible in the central section and that people should be aware of it. These earthquakes are estimated to occur every 20 years, a pattern that could help experts estimate an incoming quake.
Scientists have set up an observatory above the Parkfield city and a two-mile deep borehole that extracts the cores used in the study to study the ground. They also noted in their study that there were biomarkers in sediment in the fault line from this area to the southern border of the central fault that are hundreds to thousands of years old.
According to Pratigya Polissar and Heather Savage, there are several altered compositions of highly disturbed sedimentary rock that are 10,000 feet below, with evidence that more than 100 earthquakes occurred. They pointed out that the fault looks like it jumped by more than five feet with at least a magnitude of 6.9.
They believe that there are larger quakes in the quiet zone and hope to detect them as they conduct further studies and improve detection methods.
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