The magnitude 5.1 earthquake that occurred around midnight on March 29 east of Los Angeles was a reminder of the unstable geologic conditions in Western states. Its epicenter was in a densely populated residential area of La Habra, Calif., just a quarter-mile from Sonora High School.
The U.S. Geological Survey has an experimental early warning system in place. Unfortunately, the warning time was limited to four seconds, not nearly enough to alert the public, let alone giving people time to adopt the “drop-cover-hold” position recommended during this type of event.
The L.A. area dodged a bullet last week, as there were no casualties reported. Because the quake was caused by movement of the bedrock along the Puente Hills Fault, one of the many breaks in the earth’s crust in California, 38 aftershocks occurred.
Lucy Jones is a senior science adviser for risk reduction with the USGS. Her advice is good for any place in the U.S., including our area which felt a smaller quake recently: Pay attention to where you place your children’s beds. Heavy items like a bookcase can fall on them and injure or kill them.
Many remember the heartbreaking scene of a mother burying her son, 12-year old Pete Fulghum. The child died when a wall collapsed on him during the Raleigh, N.C., tornado of 1988. As we are much more likely to see a tornado than a quake, Jones’ recommendation to watch for stability around the living areas is very applicable to North Georgia as well.
Stability of the ground around residential areas is another matter. On March 22, a mudslide tore into the town of Oso, Wash., with the ferociousness of a tsunami, burying houses under 40 feet of debris and killing dozens. It resulted from the collapse of an entire hillside, previously known to be unstable because it consisted mainly of sand deposited by streams during the last ice age. The deposits were hundreds of feet thick and weakened by heavy rain. What looked like a pleasant hillside turned out to be a sand pile waiting to surge into the valley.
Hall County sits on solid bedrock, but erosion has carved some steep cliffs with thick layers of clay soil on top. The tragedy in Washington points out that one should carefully evaluate where to build a house, and avoid the hazards of unstable slopes.
Rudi Kiefer, Ph.D., is a professor of physical science and director of sustainability at Brenau University. His column appears Sundays and at gainesvilletimes.com.