Feature Of The Month - Loma Prieta Quake

The Seismic Safety Zone

Loma Prieta Quake

Fourteen Years & Counting

Don Eck - Contributing Editor

It seems the Loma Prieta quake of 1989 woke a lot of people up not to mention that it also surprised a number of people.

From the Stanford News.

“If there's one thing that major quakes like Loma Prieta reveals, its that each one holds its own surprise says Greg Beroza, an associate professor of geophysics at Stanford.”

In the case of the Oct. 17, 1989, Loma Prieta quake, there were some surprises - the fault slipped in a different way than it did in previous major earthquakes, such as the 1906 quake, and the damage it caused led scientists to look for new and different fault structures that are sure to be in the Bay Area.

Using data gathered during the quake and in studies performed over the past five years, geophysicists have learned that the Bay Area is riddled with a much more complex web of earthquake faults than what was previously understood.

Greg Beroza analyzed seismic waves generated during the quake, and Stanford colleague Paul Segall made measurements of the change in position of certain benchmarks on the earths surface to show that much of the motion during the Loma Prieta quake was vertical motion typical of reverse or thrust faults.

One of the things that alarmed the scientist was the uneven damage seen in the Bay Area. Damage to the Cypress elevated freeway structure in Oakland was so much greater than expected at that distance from the epicenter that it led some scientists to speculate that seismic energy was reflected off horizontal rock layers or faults deep in the earths crust.

The question now begs to be answered is this. Are there unknown faults in the Bay Area that are capable of generating a major quake on their own meaning can they cause a major quake without the assistance of a nearby known fault? Are earthquake faults of the San Francisco Bay Area linked miles below the Bay? Is stress transmitted from one fault to the next - and if so, how? Could, transmitted stress explain the apparent "pairing" of major quakes in the region during the 1800s and early 1900s - and does this mean an East Bay shock is due to follow the San Andreas fault-based-earthquake of 1989?

The answer to those questions would appear to be no because at present time those quakes haven't occurred. That doesn't mean they won’t occur. There is no time schedule that quakes follow. They have their own time schedule to which we the people are not privileged to know.

Questions or Comments - Contact Don Eck

E-Mail: donleck@sbcglobal.net

April 28, 2004

Hollister, CA


	The Seismic Safety Zone Loma Prieta Quake Fourteen Years & Counting Don Eck - Contributing Editor It seems the Loma Prieta quake of 1989 woke a lot of people up not to mention that it also surprised a number of people. From the Stanford News. “If there's one thing that major quakes like Loma Prieta reveals, its that each one holds its own surprise says Greg Beroza, an associate professor of geophysics at Stanford.” In the case of the Oct. 17, 1989, Loma Prieta quake, there were some surprises - the fault slipped in a different way than it did in previous major earthquakes, such as the 1906 quake, and the damage it caused led scientists to look for new and different fault structures that are sure to be in the Bay Area. Using data gathered during the quake and in studies performed over the past five years, geophysicists have learned that the Bay Area is riddled with a much more complex web of earthquake faults than what was previously understood. Greg Beroza analyzed seismic waves generated during the quake, and Stanford colleague Paul Segall made measurements of the change in position of certain benchmarks on the earths surface to show that much of the motion during the Loma Prieta quake was vertical motion typical of reverse or thrust faults. One of the things that alarmed the scientist was the uneven damage seen in the Bay Area. Damage to the Cypress elevated freeway structure in Oakland was so much greater than expected at that distance from the epicenter that it led some scientists to speculate that seismic energy was reflected off horizontal rock layers or faults deep in the earths crust. The question now begs to be answered is this. Are there unknown faults in the Bay Area that are capable of generating a major quake on their own meaning can they cause a major quake without the assistance of a nearby known fault? Are earthquake faults of the San Francisco Bay Area linked miles below the Bay? Is stress transmitted from one fault to the next - and if so, how? Could, transmitted stress explain the apparent "pairing" of major quakes in the region during the 1800s and early 1900s - and does this mean an East Bay shock is due to follow the San Andreas fault-based-earthquake of 1989? The answer to those questions would appear to be no because at present time those quakes haven't occurred. That doesn't mean they won’t occur. There is no time schedule that quakes follow. They have their own time schedule to which we the people are not privileged to know. Questions or Comments - Contact Don Eck E-Mail: donleck@sbcglobal.net April 28, 2004 Hollister, CA thome \| Hazard Awareness \| Don's Corner \| Feature Of The Month - Loma Prieta Quake \| Fault Of The Month \| Useful Links \| Earthquake Prediction \| Home Retrofitting \| Earthquake Insurance \| Poem Of The Month \| Field Trip Story \| Professional Insurance Services