Portola Valley's Sheldon Breiner, a geophysicist and long-time member of the town's Geologic Safety Committee, hopes local residents were shaken up a little by the Aug. 24 earthquake in Napa County.
That's because Mr. Breiner predicts that a larger earthquake is very likely headed our way.
He says that there is a 60 to 70 percent chance of an earthquake on the San Andreas fault, the one that runs through Woodside and Portola Valley, within the next two decades.
That quake, he says could be as powerful as 8.0 on the moment magnitude scale, which Mr. Breiner explains has replaced but is similar to the previously used Richter scale. Both scales are logarithmic, which means that a 7.0 earthquake is 10 times as powerful as the recent 6.0 Napa County earthquake, and an 8.0 earthquake is 100 times as strong.
Mr. Breiner will share some of his knowledge about earthquakes at a free public talk on Tuesday, Sept. 9, at the Historic Schoolhouse in the Portola Valley Town Center, at 7:30 p.m. The talk is titled "Earthquakes: all you ever wanted to know but were too shaken to ask."
Mr. Breiner says he will explain what causes earthquakes, what will happen in an earthquake and why, how earthquakes are observed and measured, and what, if anything, we can do about them.
"If you ever had questions about this important California phenomenon, be there," he says. "Some will get answered."
Mr. Breiner says that modern seismic codes mean many local buildings should escape major damage in an earthquake. Older buildings can be retrofitted to be safer, including by adding things such as triangular bracing, which can withstand the type of shaking caused by an earthquake.
The way that the earth shakes in a quake leads to another of Mr. Breiner's earthquake tips: how to tell how far away the epicenter of a quake is. The first shock in an earthquake is sharp and travels at 2.5 miles per second. The secondary shock travels more slowly, at 1.5 miles per second, he says. Counting or timing the number of seconds between the two shocks and multiplying by 5 results in a rough estimate of how many miles away the earthquake's center is, he says.
Mr. Breiner's tips for preparing for an earthquake, which he has written about in a blog he calls "Fault Lines," include the following:
• Have an emergency first-aid kit, water, food, flashlights, spare batteries and a radio as part of an emergency preparedness kit.
• To avoid tied-up local phone lines, as soon as possible report your status to someone who lives outside the area, and who your friends and family know to also check in with.
• Make sure your water heater is strapped in and a turn-off tool is attached to the outdoor gas meter.
A precaution reinforced by the early morning timing of the recent earthquake is to safeguard your bedroom, where most people spend at least eight hours a day, Mr. Breiner says. "You are more likely to be in bed than any other single place at the time of an earthquake."
Avoid glass-framed or heavy pictures and heavy vases near a bed. Fasten heavy bookcases firmly to the studs in the wall.
Seismic waves, he says, can abruptly move the walls of the room, leaving an unattached bookcase or other heavy object momentarily stationary in space. The abrupt return of the walls could then slam the bookcase across the room causing serious damage.
Keep a flashlight handy near the bed, he says.