Once again, there was front page news in the SF chronicle on earthquakes. Every few months, we get a new study saying essentially the same thing: Hayward Fault has earthquakes on average 140 years apart (based on the last 5). The last big one was 1868, so its time to be concerned. Most likely, the earthquake will be 6-7 range based on statistics, but there are more homes on the Hayward than any other fault in the Bay Area.

What this new study shows is the rate of uninsured along the fault. 95% of residences along the fault are NOT insured, exposing millions to some serious risk. But if Bear Stearns taught us anything, the government will pick up the tab.

Other than that, the info on shaking hasn’t changed much since our April talk on the Hayward Fault.

More Info
USGS Press Release
1868 Hayward Alliance (Preparation and Safety)
Predictive Intensity Map along Hayward Fault

This past weekend, 6 DtaS attendees strapped on their boots and hit the trail. Considering the recent 5.6 quake last week, what better time to learn about faults here in the Bay Area?

Six of us hit the dusty trail in Los Trancos Open Space Preserve. It was a docent led hike and our leader was quite knowledgeable. Over the course of the 2-3 mike hike (click the link to see a virtual tour of the hike), we were learned about basic earthquake science, with a eye on the 1906 quake. Many after effects of the 1906 quake were still visible, from tree trunks growing sideways to flat earthquake “benches” formed on the side of the hill. Most fascinating was the view from the hillside…you could see how the San Andreas snaked toward San Francisco, especially into Crystal Spring reservoir.

This hike is offered once a month. Check out the calender on Los Trancos’ website for more information.

Last week’s inaugural event was a tremendous success. About 35 people learned about the Hayward fault, it’s destructive capability and the techniques being used to find out more.

For those of you who missed out: videos, pics, and Jack’s presentation have been posted on the Past Cafes page. You can download the video or watch it online.

See you in a few weeks!

Here are something interesting links for the earthquake fanatic:

Nor Cal USGS

Real Time Earthquake Maps (California-Nevada)

Real-time Shaking Maps for California earthquakes of Magnitude 3.5 and larger

1906 San Francisco Earthquake ShakeMaps

Earthquake Probabilities for the San Francisco Bay Area
USGS and other scientists conclude that there is a 62% probability of at least one magnitude 6.7 or greater quake, capable of causing widespread damage, striking the San Francisco Bay region before 2032.

General Quake Info
Earthquake basics and educational material; geological and historical information; links to professional and amateur organizations; online access to earthquake data.

Hazards & Preparedness
How to prepare your home, business and family for earthquake hazards; earthquake probabilities; shaking hazard maps; liquefaction hazard and earthquake engineering.

Earthquake Research
Current research activities and results in seismology, crustal structure and deformation, geology and borehole physics.

UC Berkeley Quake Site

Historical Earthquake Intensity Information

1868 Hayward Earthquake History:
http://www.museumoflocalhistory.org/pages/list.php?topic=earthquake
http://www.sfmuseum.org/hist1/1868eq.html
http://www.sfmuseum.org/hist4/68oakl.html
http://seismo.berkeley.edu/faq/1868_0.html
http://cires.colorado.edu/~bilham/HaywardCreep.html

California Department of Insurance - California Earthquake Information

California Reader: Stories about earthquakes

Hayward Fault Tour
A website showing the surface expressions of the Hayward Fault.

Paleoseismology, Hayward Fault, California
A large, widely damaging earthquake will occur on the Hayward fault in the future. That much we know. What we don’t know is when.

Predictive Intensity Map for 1868 Hayward Fault
This is the intensity distribution we would expect for a repeat of the 1868 earthquake which was a M=7.0 event on the Hayward fault.

Finally there is a great Google Earth Flyover of the Hayward fault put together by Jim Lienkaemper, a USGS geologist. Map showing active fault traces within the Hayward Fault Zone, including a virtual tour of the Hayward fault in the east San Francisco Bay Region that can be viewed in the Google Earth.

Magnitude 9 quakes are generally caused by subduction events. There are 40,000 km of subduction boundaries around the Pan Pacific Rim. Seismologists have been studying these subduction zones to identify high risk areas for high mag quakes. Why? A mag 9.0 quake caused the 2004 tsunami in Indonesia, killing over 300K.

Earthquake science utilizes all sorts of data, earth temperature, geologic features, physics, even historical data. When you boil down the search for the next big one, we always end up at a question of probability.

Looking at all this data, they have identified a number of troubling (ie high probability) subduction zones. One big problem, the Sumatran-Andaman earthquake that caused the 2004 tsunami did NOT occur in a likely zone.

What does that mean? Most likely, our understanding of “danger” subduction zones is by no means refined. That doesn’t mean we should abandon our study of these zones, but frankly admitting our lack of knowledge in this area seems right on.
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