San Benito Geology: The Great San Benito ShakeOut

This is the first in a series of six monthly articles about the geology of San Benito County. The first topic is earthquake safety, designed to coincide with the Great California ShakeOut statewide drill on Thursday, Oct. 18.

This article was contributed by Jim Ostdick.

Way back in the 20th Century, on the first day of my very first college geology course, as I reached the classroom door, I saw a weathered index card taped in place at eye level. On the card, scribbled in the professor’s handwriting, was a quotation by American historian Will Durant. It excited me, it scared me a little, and it triggered my inner skeptic.

“Civilization exists by geological consent, subject to change without notice.” – Will Durant

Then and there, I was primed and ready to learn.

Some of us are old enough to remember where we were at 5:04 p.m. on October 17, 1989. Game 3 of the World Series was at Candlestick Park, with the San Francisco Giants down 0-2 to the Oakland A’s in the highly touted “Battle of the Bay.” Al Michaels was the ABC announcer at the time and in the middle of his opening segment, the 6.9 magnitude Loma Prieta earthquake rocked Candlestick and the entire San Francisco Bay region.  Here is a YouTube clip of that crazy moment.

The quake was centered near Loma Prieta Peak in the Forest of Nisene Marks State Park close to Aptos in Santa Cruz County. Twenty-five years later, BenitoLink published an article commemorating the effects of the shock on downtown Hollister. Read about it here.

Civilization is stubborn and life itself is resilient, so predictably, just about all of the destruction here and in Santa Cruz and San Francisco has been repaired. However, we cannot forget the 62 lives lost and the $5 billion worth of property damage from 1989. Seismologists estimate there is a “62% probability that at least one earthquake of magnitude 6.7 or greater will occur on a known or unknown San Francisco Bay region fault before 2032.” Are you prepared?

For the last ten years, Californians have participated in annual earthquake readiness drills called The Great California ShakeOut. The drills can be practiced at home, in schools, and at work. Statistics are collected and kept for comparison in several regions of the state. To participate in this year's drill, please click on the above link and find out how to report. Try it. It’s exciting, it’s a little scary, and it will trigger your inner skeptic.

Skepticism is a primary tool of the scientist. It is the opposite of blind faith. By thinking critically about a problem, we compare what we already know to what others have discovered and address how it applies to us. This is how we learn. To get ready for this year’s Great San Benito ShakeOut, I recommend a resource published by the U.S. Geological Survey called “Putting Down Roots in Earthquake Country.” It includes a set of seven steps to earthquake safety, which I will summarize below.

Seven Steps to Earthquake Safety

“Earthquakes in the Bay Area are inevitable, but damage from them is not! Steps you can take before, during, and after earthquakes will help make you and your family safer and reduce your injuries, damage, and losses.” – Putting Down Roots in Earthquake Country

1.) Identify potential hazards in your home: Falling objects cause the most injuries in earthquakes. Secure heavy furniture, art, mirrors, home electronics, water heaters, gas pipes, glassware, china, combustibles.

2.) Create a disaster preparedness plan: Practice Drop, Cover, and Hold On. Identify safe places in your home, places to take cover, how to protect yourself if wheelchair bound. Establish a safe meeting place outside the home,  who are your out of area contacts, where will the kids go if they are separated from you?

3.) Create disaster kits: Bottled water, snacks, medications, flashlights, spare eyeglasses, pet food and leashes. What are your personal needs? Disaster kits are available from the Red Cross.

4.) Identify your building’s potential weaknesses and begin to fix them: Does your home or place of work need retrofitting? Conduct a structural safety quiz (see Step 4 on the Earthquake Country website).

5.) Protect yourself during earthquake shaking: Drop, Cover, and Hold On. Do you live in a floodplain or downstream of a dam? What is your escape route? Plan ahead!

6.) After the quake, check for injuries and damage: Train your family or housemates in First Aid and CPR. Check for gas leaks and structural damage.

7.) When safe, continue to follow your disaster preparedness plan: Aftershocks happen! Establish communication with the outside, ration food and water, determine where to seek shelter.

San Benito County is experiencing a period of rapid growth and new residents may not be familiar with living in earthquake country. Please share this information with them and offer the benefits of your experience and planning. After a strong earthquake, emergency services and cell phone coverage may be interrupted. As well as preparing yourself and your family for a disaster, offering reasonable aid to someone in need is an important part of being a good citizen.

For more information, including local links, consult the San Benito County Office of Emergency Services.



Jim Ostdick

Jim Ostdick is a retired Earth Science teacher and travel writer. A resident of San Juan Bautista since 2005, Ostdick's primary interests are California geology, energy conservation, outdoor recreation, and human-powered travel. He is the author of Palomino and the Dream Machine: A Retired Dude's Bicycle Tour Around the Lower Forty-Eight United States (, 2015) and Palomino Nation: My 2016 Crazyass Walk Across America (, 2017). Palomino Dream blog Palomino and the Dream Machine Palomino Nation