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Can a 7.8 Earthquake Hit the Bay Area? Here's the Science Behind It

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The magnitude 7.8 earthquake that rocked parts of Turkey and Syria on Monday, killing more than 23,000 people, resembles a threat that Californians could potentially face. The same type of fault runs across most of the state. Here’s the science behind these huge earthquakes and how to be prepared.

What makes a big earthquake?

Earthquakes result from a slip along a fault line, a geological term for a crack in Earth’s crust. Basically, two slabs of rock suddenly and violently slip past one another, radiating energy in all directions in the form of seismic waves that cause the shaking that people experience. The Turkey earthquake occurred along the East Anatolian fault, a strike-slip fault — where two tectonic plates slide past each other horizontally — that measures hundreds of miles long. The portion that ruptured is at least 100 miles long. Essentially, the longer the length of the fault that ruptures, the larger the magnitude of the earthquake it produces. And the larger the population surrounding the fault lines, the more devastation is caused by the earthquake.

“You’re not necessarily seeing stronger ground motions, but you’re seeing a longer duration of ground motion and a greater area that is exposed to the most extreme shaking just because more of the fault is involved in producing the shaking,” said Austin Elliott, a research geologist at the U.S. Geological Survey’s Earthquake Science Center based in Mountain View’s Moffett Field in the South Bay.

We have several long faults in the Bay Area that are capable of producing strong earthquakes similar to what happened in Turkey. A strike-slip quake can occur along the San Andreas Fault, for example. The fault line runs 800 miles long from the Salton Sea in Southern California to Cape Mendocino through the Peninsula and San Francisco and along the North Coast.

“Tectonically and seismologically, the earthquakes we expect in California are very similar to the earthquakes that have just happened in Turkey,” said Elliott, but, “geographically and demographically, the situation is different.”

The San Andreas Fault is largely offshore as it goes north, and is distant from some of the major population centers, Elliott said. Other faults that run through cities, like the Hayward Fault, the Rodgers Creek Fault and the Calaveras Fault, are also capable of large earthquakes, potentially involving more communities in the temblor.

Scientists have calculated about a 30% chance that the Hayward Fault will “break big” (PDF) — with a magnitude 6.7 event or bigger — within 30 years. The “HayWired” scenario from the USGS projects that in the aftermath of a magnitude 7.0 quake in Hayward, 2,500 people would need immediate rescue.

“We still consider the Hayward Fault to be the one with the highest probability of producing a large event in the Bay Area in years and decades to come,” said Roland Bürgmann, a UC Berkeley seismologist. ”The damages will be tremendous given the continuing exposure, despite all the great efforts made to mitigate the impact.”

Scientists use triangulation to find the epicenter of an earthquake, collecting seismic data from at least three locations. Every earthquake is recorded on numerous seismographs located in different directions.

Improved building codes and infrastructure

The Bay Area has experienced multiple large-scale earthquakes in history. The 1857 earthquake in Central California was an estimated magnitude 7.8, the 1868 Hayward Fault quake was a magnitude 6.8, and the famous 1906 San Francisco earthquake was at a 7.9 magnitude along the San Andreas Fault. In comparison, the Loma Prieta earthquake of 1989 was a magnitude 6.9.

“Each new earthquake teaches us more about what works and what doesn’t work in constructing buildings and infrastructure,” said Elliott.

The Bay Area has strong building standards and codes, some of the strictest in the world as far as seismic preparedness, he said. Its built environment is generally well-prepared to withstand the earthquakes seismologists expect in the region. That said, there are still a lot of vulnerable facilities and structures that require seismic retrofitting.

“It really takes building codes, planning by all the different agencies and communities involved to be more and more ready,” said Bürgmann.

Earthquake prep from a geologist’s perspective

To prepare for a big earthquake, Elliott recommends using sites like Earthquake Country Alliance, which has a wealth of preparedness information. Homeowners should make sure their homes are properly braced and bolted to their foundations. California has grant programs to help to improve the structural stability of your home.

At home, look around your space and brace things like bookshelves, televisions and furniture that could be toppled by heavy shaking. Have shoes next to your bed so that if it’s dark and there’s glass on the floors, you don’t step on it and hurt yourself. And don’t forget to prepare your emergency kit.

After an earthquake, emergency services will be swamped. So it’s important to try to be self-sufficient by having your emergency supplies in hand and knowing basic first aid. Fire departments, paramedics and hospitals are going to be spread thin. So making sure you have your first aid kit within reach is important.

Stay connected with your neighbors and friends during this time. “Your neighbors or your friends may live in more vulnerable buildings than you do or vice versa,” said Elliott. “And you may want to be conscious of that as well in your planning.”


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