Wednesday April 18, 1906 – 100 years ago today, a great earthquake occurred along the San Andreas fault, the epicenter of which was quite close to the City of San Francisco. More recently, other earthquakes have occurred in the same area: 1979 Coyote Lake, 1984 Morgan Hill and 1989 Loma Prieta earthquakes. All of these facts are well-known, and aren’t necessarily new news. Not until some recent work that is, by geologist David Wald and associates. The paper, entitled “Source Study of the 1906 San Francisco Earthquake,” compares the events using data from a 100+ year old seismograph that just happened to record both earthquakes.
Below – This is the seismogram data showing both quakes:
One great value of old seismographs is that we can make quantitative comparisons of 1906 with the 1989 Loma Prieta earthquake. Fortunately, the same seismograph instrument at Gottingen, Germany was operating during both earthquakes.
If the Loma Prieta (M~7.0) trace looks smaller, it is because the 1906 (M~7.8) earthquake released approximately 16 times more energy:
Because we have much more extensive information about the ground motion that accompanied the 1989 earthquake, we can work backwards and infer what the ground motions must have been like in 1906.
We expect that the shaking in the next 1906-type earthquake will probably not be much more intense than the shaking felt in 1989 near the epicenter of the Loma Prieta earthquake, but it will last longer — perhaps 45 to 60 seconds or more. Strong shaking in the Loma Prieta earthquake lasted only about 15 seconds. In a repeat of the 1906 earthquake, the region experiencing intense shaking will also be much more widespread than in the Loma Prieta event, affecting areas all along the rupture.
Studying the little Loma Prieta pips on the upper traces and recalling the massive travesty that was the 1989 event, makes one wonder how bad it will be if the energy of the 1906 event were to occur today. My estimation is that damage and casualties would be 100 times worse than 1989.
Now, I don’t want to get into predicting the future, but when (not if) this quake happens in San Francisco, and the devastation is on an order of magnitude to compare to New Orleans last year, just watch the weeping, wailing Friscoites blame the administration for everything that happened – that is, unless the administration happens to be a Democratic one.
Paraphrasing the Bard: “What fools these liberals be.”
Click on WikiPedia for more information about the 1906 event.
Sun’s out, and so are trappings of spring
With immigration reform, homeland security and national defense looming as the most vital and important items on the congressional agenda, Rep. Jane Harman (D – CA 36) thinks that the “unprecedented attack” on Roe v. Wade eclipses those issues. 
Often I look at the logs that are recorded when someone accesses our blog. Often I see weird things in the search strings that direct traffic to us. I decided to share some of this weirdness with you.
