For the prior video feature in this series covering the proper marketing of properties in areas of the state susceptible to seismic hazards, click here.

Indirect earthquake damage

When an earthquake occurs, one fault slides against, underneath or on top of another. This direction can be vertical, horizontal or somewhere in between.

The San Andreas Fault is a transform fault, meaning it does not subsume land to another fault, nor is it subsumed. Rather, the two plates — the North American and Pacific Plate — move past each other, in a horizontal fashion. When this occurs, observers on the ground may not notice the evidence the fault movement leaves behind, but from the air it is clearly visible.

In addition to the initial shaking of the ground and potential damage to buildings and property, earthquakes cause a lot of indirect damage as well. Earthquakes can manifest and cause:

  • ground failure, which refers to landslides and liquefaction (when loose, wet or sandy soil shifts during the shaking and causes building foundations to sink or move);
  • tsunamis, large waves caused by earthquakes, volcanic eruptions or underwater landslides; and
  • dam failure, which results in localized flooding.

Areas susceptible to inundation due to dam failure caused by an earthquake are also noted on the NHD Statement as a potential flooding area. [See RPI Form 314 §5]

Therefore, even if a property is not located near a fault, it may be located in an area where an earthquake may indirectly damage it. These areas are identified in geologic maps, available at local city planning departments.

The ground shakes — then shakes some more

There have been 54 major earthquakes in California since 1900, defined as an earthquake of at least magnitude 6.5, and/or causing loss of life or property damage greater than $200,000, according to the California Geological Survey.

The last major earthquake was a magnitude 6.5 and occurred on December 22, 2003 in San Simeon, causing substantial damage in nearby Paso Robles.

With 54 major earthquakes over the past 115+ years, one major earthquake occurs on average every 2.1 years. Therefore, it appears California is well overdue for a major earthquake.

Where will the next big earthquake occur?

Statistically, the next “Big One” (of around magnitude 8.0) will likely occur along the southern end of the San Andreas Fault.

Most of California’s populated areas are located in or near an earthquake hazard zone. The exception is California’s Central Valley, encompassing cities like Fresno and Sacramento (property lying east of I-5 north of Delano and south of Redding). Here, you are as safe as you can be (in California) from earthquakes.

The West Coast of the United States is particularly susceptible to earthquakes, as it lies alongside the western edge of the North American Plate, where it butts up against the Pacific Plate. Students of Geology may recall the Ring of Fire, which encircles much of the Pacific Ocean. California makes up a significant portion of the ring, though its main symptom is earthquakes, rather than the volcanoes experienced in much of the Pacific.

Can scientists predict earthquakes?

The ability to predict earthquakes does exist, but the warning time is short and California has yet to fully implement an alert system.

It works like this: There are two types of waves that occur when an earthquake strikes. The shear waves or “S” waves cause the shaking that is so destructive to property. However, several seconds before the “S” wave hits, a mostly silent primary wave, or “P” wave, arrives. Dogs and other animals sensitive to sound can detect P waves, but human ears usually cannot.

Earthquake predicting technologies alert the user when a “P” wave is detected.

This gives the user a few seconds to head for cover, turn off a gas stove, exit an elevator or complete any last-second preparations. The warning time depends on how deep the quake is and how far the epicenter is from the user.