Hi All. I hope you find this as interesting as I did. "Scientists studying earthquakes now know temblors of significant magnitude were relatively common during the 1800s in the Bay Area. Between 1836 and 1906 there were 17 earthquakes of magnitude 6.0 and greater. Seven of those earthquakes were of magnitude 6.5 or greater.
After the 8.3-magnitude 1906 earthquake, there was only one quake, that was 6.0 over the next 73 years. It wasn't until a 6.0 shook Gilroy in 1979 that significant activity resumed. Scientists believe the 1906 was of such great power, it served to relieve pressure on faults around the Bay Area for the next seven decades.
Now scientists fear that the tension is beginning to mount again. Livermore experienced a 6.0 in 1980, Morgan Hill had a 6.3 in 1984 and the Loma Prieta quake registered in at 6.9 10 years ago yesterday. While the Loma Prieta quake was major, it did little to relieve pressure from faults outside the Santa Cruz Mountains, Schwartz said.
More recently, a 5.0 was recorded in Bolinas on Aug. 17 along the San Andreas fault. It was the same segment that moved so powerfully in 1906. It's the continual movement of the Earth's plates moving against each other that causes energy to build. With the rapid development of the Bay Area over the last several decades, officials now fear a potential wave of earthquakes will cause dire damage to life and property.
. While housing popped up all over the county, there was little attention paid to the geological history of building sites, including landslide history Kojan said.
"Once a slide occurs, it is a permanently weakened condition," he said. "About 30 percent of the land area in Marin east of the San Andreas is undermined by landslides," he said.
Kojan explained that once an area has slid, it is never as strong again, no matter how much time passes. Stabilization of landslide areas is possible, but costly, the geologist said. An earthquake's timing also can be crucial. If it occurs during the rainy season the wet soil is more likely to slide than during the summer.
Those who do not prepare are foolish, experts say. "We are at ground zero," the USGS's Schwartz said. "We have the highest seismic activity of any urban center in the country and we will have an earthquake. It's just a question of when, where and how large." Take Care. Don in creepy town.