Are You Ready for a Big Earthquake?

It’s a fact. Millbrae residents live within a mile or two of the San Andreas Fault.

So what does this mean when it comes to earthquakes?

According to Tom Brocher, director of the U.S. Geological Survey Earthquake Science Center based in Menlo Park, “a repeat of the 1906 earthquake on the San Andreas Fault will cause violent levels of shaking in Millbrae.”

Brocher spoke to a group of 15 participants at an earthquake safety and preparedness workshop this past Wednesday evening at the , leading a discussion about earthquake hazards in Millbrae as well as other earthquake topics, including the types of damage earthquakes typically cause and what people can do to prepare for a big earthquake.

As part of Brocher's work with the Earthquake Science Center, the flagship research center for the USGS in the western United States for more than 50 years, he has hosted dozens of workshops like this for the public because “I like educating people on what a large earthquake is like and how they can prepare for it,” he said.

The Earthquake Science Center is the largest USGS research center in the West and houses extensive research laboratories, scientific infrastructure, and library facilities. Scientists in Menlo Park conduct a wide array of both basic and applied science, usually in collaboration with scientists from outside the Center.

During the workshop, Brocher showed the group that the area east of Highway 101 is predominantly landfill and is expected to shake harder and have more liquefaction than other parts of Millbrae.  

He also pointed out that the area west of El Camino Real is generally not prone to liquefaction.

Brocher then went over lessons learned from the 1906 San Francisco and 1989 Loma Prieta earthquakes, and simple and inexpensive measures people can all take to prepare for earthquakes and to mitigate the impact of earthquakes on their lives.

When asked what the biggest earthquake myth is, Brocher said, “That we will all be injured by the earthquake.”

In fact, all of us will be unharmed by the earthquake, he said, “but we must be prepared to survive for a few days without much help as the fire and police department will have large issues to cope with.”

Experts say it is very likely there will be a damaging San Francisco Bay Area earthquake in the next 30 years and that it will strike without warning.

Still, Brocher says there’s a lot of misinformation out there about earthquakes.

Test your knowledge about earthquakes with the following list of FAQs, dispelling common earthquake myths, compiled from the U.S. Geological Survey’s Earthquake Hazards Program’s website.

Can you predict earthquakes?

 No. Neither the USGS nor Caltech nor any other scientists have ever predicted a major earthquake. They do not know how, and they do not expect to know how any time in the foreseeable future. However based on scientific data, probabilities can be calculated for potential future earthquakes. For example, scientists estimate that over the next 30 years the probability of a major EQ occurring in the San Francisco Bay area is 67% and 60% in Southern California.

Can animals predict earthquakes?

The earliest reference we have to unusual animal behavior prior to a significant earthquake is from Greece in 373 BC. Rats, weasels, snakes, and centipedes reportedly left their homes and headed for safety several days before a destructive earthquake. Anecdotal evidence abounds of animals, fish, birds, reptiles, and insects exhibiting strange behavior anywhere from weeks to seconds before an earthquake. However, consistent and reliable behavior prior to seismic events, and a mechanism explaining how it could work, still eludes us. Most, but not all, scientists pursuing this mystery are in China or Japan.

Can some people sense that an earthquake is about to happen?

There is no scientific explanation for the symptoms some people claim to have preceding an earthquake, and more often than not there is no earthquake following the symptoms.

Is there earthquake weather?

In the 4th Century B.C., Aristotle proposed that earthquakes were caused by winds trapped in subterranean caves. Small tremors were thought to have been caused by air pushing on the cavern roofs, and large ones by the air breaking the surface. This theory lead to a belief in earthquake weather, that because a large amount of air was trapped underground, the weather would be hot and calm before an earthquake. A later theory stated that earthquakes occurred in calm, cloudy conditions, and were usually preceded by strong winds, fireballs, and meteors.

There is no such thing as "earthquake weather." Statistically, there is approximately an equal distribution of earthquakes in cold weather, hot weather, rainy weather, etc. Very large low-pressure changes associated with major storm systems (typhoons, hurricanes, etc) are known to trigger episodes of fault slip (slow earthquakes) in the Earth’s crust and may also play a role in triggering some damaging earthquakes. However, the numbers are small and are not statistically significant.

Do solar flares or magnetic storms (space weather) cause earthquakes? 

 Solar flares and magnetic storms belong to a set of phenomena known collectively as "space weather". Technological systems and the activities of modern civilization can be affected by changing space-weather conditions. However, it has never been demonstrated that there is a causal relationship between space weather and earthquakes. Indeed, over the course of the Sun's 11-year variable cycle, the occurrence of flares and magnetic storms waxes and wanes, but earthquakes occur without any such 11-year variability. Since earthquakes are driven by processes in the Earth's interior, they would occur even if solar flares and magnetic storms were to somehow cease occurring.

Are there more earthquakes in the morning/in the evening/at a certain time of the month? 

 Earthquakes are equally as likely to occur at any time of the day or month or year. The factors that vary between the time of the day, month, or year do not affect the forces in the earth that cause earthquakes.

Can the ground open up during an earthquake?

Shallow crevasses can form during earthquake-induced landslides, lateral spreads, or other types of ground failures. Faults, however, do not open up during an earthquake. Movement occurs along the plane of a fault, not perpendicular to it. If faults opened up, no earthquake would occur because there would be no friction to lock them together.

Will California eventually fall off into the ocean?

No. The San Andreas Fault System, which crosses California from the Salton Sea in the south to Cape Mendocino in the north, is the boundary between the Pacific Plate and North American Plate. The Pacific Plate is moving northwest with respect to the North American Plate at approximately 46 millimeters per year (the rate your fingernails grow). The strike-slip earthquakes on the San Andreas Fault are a result of this plate motion. The plates are moving horizontally past one another, so California is not going to fall into the ocean. However, Los Angeles and San Francisco will one day be adjacent to one another.

Why are we having so many earthquakes? Has earthquake activity been increasing? Does this mean a big one is going to hit?

The NEIC now locates about 20,000 earthquakes each year, or approximately 55 per day.  Because of the improvements in communications and the increased interest in natural disasters, the public now learns about earthquakes more quickly than ever before.

According to long-term records (since about 1900), we expect about 16 major earthquakes in any given year, which includes 15 earthquakes in the magnitude 7 range and one earthquake magnitude 8.0 or greater. In the past 38 years, from 1973 through 2011, our records show that we have exceeded the long-term average number of major earthquakes only 8 times, in 1976, 1990, 1995, 1999, 2007, 2009, 2010 and 2011.

The year with the largest total was 2010, with 24 earthquakes greater than or equal to magnitude 7.0. In other years the total was well below the 16 per year expected based on the long-term average:  1989 only saw 6, while 1988 saw only 7 major earthquakes.