Date: Tuesday, June 13th, 2006
Time: 6:00 p.m.-Social Hour; 7:00 p.m.-Dinner; 7:45 p.m.-Presentation
Location: Steven’s Steak House, 5332 Stevens Place, Commerce, California
Cost: $35 per person with reservations, $40 at the door, $15 for students with a valid Student ID
Reservations: Please call (323) 889-5366 or email firstname.lastname@example.org
SPEAKER: Bill Cotton, Cotton Shires & Associates
TOPIC: Earthquake-Induced Ground Failures: A Historical Perspective Using the Great San Francisco Earthquake of 1906 as a Starting Point
The Great San Francisco Earthquake of 1906 (M 7.8) was the first earthquake in the United States to be carefully documented and studied by field geologists. Detailed post-earthquake field data were compiled and published in the California State Earthquake Investigation Commission’s “Lawson Report” in 1908. While most of the scientific interest was focused on the effects of surface fault rupture and ground shaking, landslides and other forms of ground failure were also well documented. With the exception of lateral spreading in the low-lying regions of the Bay area, earthquake-induced ground failures such as landslides were considered “minor effects”, mainly because they were confined to the unpopulated mountain regions. Today, the urban population in the greater San Francisco Bay area stands at nearly 10 million, and the mountainous landslide terrain has now become highly populated. Anticipating the potential adverse impact of a rapidly expanding population into uncharted hillsides, Youd and Hoose of the USGS (PP 993) reviewed the 200-year-old records of major northern California earthquakes and published their findings in 1978. Much of their work was concentrated on a more detailed analysis of the Lawson report, with an expanded effort at defining the locations and specific types of ground failures relative to the modern urban environment.
The Bay area hillsides were again tested in October of 1989 when the M 6.9 Loma Prieta earthquake struck the region. Again, ground failures were widespread with extensive lateral spread failures around the margin of the San Francisco Bay and numerous damaging landslides in the epicentral area of the Santa Cruz Mountains. The present probabilistic earthquake forecast is 62% for a M 7.0 event situated on one of the areas major faults within the next 25 to 30 years. Smart money places this event along the Hayward fault in the east Bay area of Oakland/Berkeley. Numerous large landslides exist in the developed portion of the east Bay hillsides. Displacement analyses indicate that large regions of these hillsides are highly vulnerable to moderate to strong seismic ground shaking. It is reasonable to expect that the cost of earthquake-induced landslide damage will exceed several billion dollars when the next large magnitude earthquake strikes the densely urbanized hillsides of the Bay region.