On October 17, 1989, at 5:04:15 p.m. a magnitude 6.9 earthquake severely shook the San Francisco and Monterey Bay regions. The epicenter was located at 37.04° N. latitude, 121.88° W. longitude near Loma Prieta peak in the Santa Cruz Mountains, approximately 9 miles northeast of Santa Cruz and 60 miles south-southeast of San Francisco. I was on my way home from work stopped at traffic light in Pittsburg. I first wondered what was wrong with my car, it was shaking. When I noticed that the light was swaying and there was no wind I knew something was wrong. It wasn’t until I got home and turned on the T.V. that I discovered the extent of disaster.
Since the great earthquake of 1906, no major quake has been centered near a densely urbanized part of the San Francisco Bay region. Although the 1989 Loma Prieta quake killed more than 40 people in the region’s urban core, it was centered in mountainous country 50 miles south of San Francisco. In 1995, when a quake of the same magnitude struck Kobe, Japan, another bayside urban area thought to be well prepared for earthquakes, more than 6,000 people died and the damage amounted to $100 billion. Had the Loma Prieta quake been centered in San Jose, Oakland, or San Francisco, similar losses could have occurred.
I think most of us have become rather complacent over the years. Unlike the Midwest, where even I can tell you there will be tornadoes ever spring, or the southeast and gulf states where hurricanes are seen coming well in advance of hitting land fall, earthquakes are not predictable. About as close as they can currently get is a probability. There is a probability of more than 99% that in the next 30 years Californians will experience one or more magnitude 6.7 or greater quakes, potentially capable of causing extensive damage and loss of life. For powerful quakes of magnitude 7.5 or greater, there is a 46% chance of one or more in the next 30 years—such a quake is twice as likely to occur (37%) in the southern half of the State than in the northern half (15%).
Smaller magnitude earthquakes are more frequent than larger quakes. According to the new forecast, about 3 magnitude 5 or greater quakes will occur in the California region per year, and a magnitude 6 or greater quake about every 1.5 years. These numbers do not include aftershocks that follow larger quakes—including them would roughly double the expected number of magnitude 5 or greater quakes.
For the entire California region, the fault with the highest probability of generating at least one magnitude 6.7 or larger earthquake is the southern San Andreas (59% in the next 30 years). For northern California, the most likely source of such a quake is the Hayward-Rodgers Creek Fault (31% in next 30 years).
There are 5 faults that run through Contra Costa that would shake Oakley in varying degrees depending on the magnitude and a 6th that could also provide a substantial shaking. The Green Valley fault runs through north-central county, the Greenville fault runs along the imaginary border separating east and central county, the Mount Diablo fault, the Northern Calaveras fault runs through south-central county and the Northern Hayward running through west county. The 6th fault is a combination of the Rodgers Creek and North Hayward. The North Hayward ends in Suisun Bay. The southern end of the Rodgers Creek fault begins in Suisun Bay.
If the Greenville fault where to shake at a 6.9, same as the Loma Prieta, what would it do to Oakley?
Are you prepared for the next one. It could be tomorrow or 30 years from now. The Assocation of Bay Area Governments was the source for these maps. It is an excellent site for earthquake information . Prepare yourself , family and home for the next one.