All of My Faults Are Stress Related

I’ve been awakened by an earthquake, but it was only M 4. I can’t imagine what it would have been like to be in San Francisco 103 years ago this morning, when a M 8-ish earthquake struck at 5:12 am. Shaking ten times stronger than the Loma Prieta earthquake – I couldn’t stand up in M 7 quake; would a M 8 knock a person out of bed?

And it was one thing to experience a M 7 earthquake in the daytime, as a geologist who knew just how nearby the Pacific Plate was, and how fast it moved, and what it could do. Did people in 1906 remember the Hayward quake of 1868, nearly 40 years before? Or would the foreshock have been the only warning, a rumbling bring people out of dreams and into a nightmare?

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Image source: USGS photographic library. Photo by G.K. Gilbert, from USGS Bulletin 324.

During the earthquake, the San Andreas Fault broke from south of San Jose to the Mendocino triple junction, 296 miles to the north. The USGS estimates that offset varied from around 8 feet along the southern part of the fault to as much as 28 feet near the north end. Today, the actual rupture is hard to pick out – when I led Stanford intro geology students to see the fault in the early 90′s, I had to wave my arms vaguely and try to convince the students that somewhere in the poison oak was something that would have been really impressive in 1906. Point Reyes National Seashore has a trail with a re-created fence showing the offset. (It’s fun to stand with one foot on the North American plate and one on the Pacific plate, and try to imagine the movement.)

It’s fun to imagine the slip. But I wouldn’t want to be there the next time it goes.

Other remembrances:
SF Gate: Rare photos of S.F.’s 1906 disaster
About.com geology

Comments

#1 Janne
April 18, 2009

Here in Japan a second scale (“shindo” – shake degree) is widely used and is the one normally reported in the media when an earthquake occurs; if the magnitude is reported at all, it’s a parenthetical aside. The idea with it is that it tells you the approximate magnitude of effect at a given point on the surface, rather than the energy of the earthquake. People tend to understandably be rather more interested in that of course.

What’s your thoughts on a scale like that, and do you have any idea why a similar scale isn’t used more widely elsewhere?
#2 Tony
April 18, 2009

Earthquake early warning technology is available now and in use in some fire stations and schools in the Bay Area and Palm Springs — but not enough! Check out our blog at http://www.seismicwarning.com/SWSblog
#3 alufelgi
April 19, 2009

In my opinion the largest threat for California are cataclysms and ecological catastrophes. Not important is how many money we have because one tragedy can us take all.
#4 Heraclides
April 20, 2009

Good timing posting this. I picked up a ex-libris hardback copy of Winchester’s A crack in the edge of the world (for 50 cents), which I hope to be the next book I read, after the trashy thriller I’ve almost finished. Any comments on the book by people knowledgeable about the science or event is most welcome.

I’ve felt quite a few 4+ since they’re pretty common (there have been 10 of M≥4.0 in NZ since March 28th for example), but have only felt 7+ from a distance (New Zealand has had over 15 “shallow” earthquakes ≥7.0 since 1848). One thing that strikes me about the 1906 quake, from what little I know about it, was the size of the area affected and the extent of the damage.

(Disclosure: I’m not a geologist!)
#5 retired Principal
April 23, 2009

I just read Furnace of Creation-Cradle of Destruction, A Journey to the Birthplace of earthquakes, Volcanoes, and Tsunamis, by Roy Chester. Its an ok book, but in it I found these howlers, the first quite OT:
on p. 66 he writes that during the great SF quake, there were horizontal displacements up to 10.5 km!! I’m trying to imagine a cowboy on a horse, watching a barn approach from several km to the south, and march by, going out of sight to the north! I found a source on the web that gives this figure for the displ. since the Miocene!
on p. 83, he says the 1960 tsunami struck Hilo, HI with a wave 90 m high. I live in HI, and have seen film of that tsunami destruction; 540 homes and 61 lives were lost, but the wave height was closer to 9-10 m, over 30 ft., but an order of magnitude smaller than his figure.
on p. 101 we read that the mid-ocean ridge rises to 3000 m above sea level!
on pp. 146 and 150, discussing the fauna around the deep sea spreading center “smokers”, he twice refers to “muscles”.
He has a typo I have only seen before on the internet, loosing for losing.
The author was apparently a top-notch marine geochemist. The book is published (2008)by the American Management Association, strangely enough. Perhaps they commissioned it; he does address management and mitigation techniques towards the end. They seem to be in the book publishing business without benefit of any editors.
I tried to find any geology or earth science sites that might have reviewed this book, but no luck.
#6 Sally
April 25, 2009

On a different tack, I believe the woman in the photo is famous botanist Alice Eastwood, who was engaged to G.K. Gilbert until his untimely death ended their romance. She is well known for rescuing important type specimens from the California Academy of Science after that earthquake.

Nice to discover your site…
#7 Kim Hannula
April 25, 2009

Sally – thank you for identifying the woman in the photo! I’ll need to make note of that to mention when I show that photo in classes. (That she’s a famous botanist more than being Gilbert’s fiancee.)

Janne – In the US, the Mercalli intensity serves that purpose – how much damage, rather than the energy released. Maybe we would be better off using that as the main way we talk about earthquakes to the public – I don’t know.

Heraclides – I’ve read Crack in the Edge of the World. I’m not an historian, and a lot of the book dealt with the history of San Francisco before and after the earthquake, so I don’t have the background to comment on a lot of the book. The basic geology, at least, is solid. I haven’t worked on the San Andreas Fault (just lived near it), so I don’t know whether the people doing research right now would agree with all the ways he described it.
#8 Heraclides
April 25, 2009

Thanks Kim. Once I get these grant proposals out of the way, I might be able to tackle it…
#9 Sally
April 26, 2009

Here’s a link to a good bio of Alice and a caption for that photo: at Pomona, and another link to bio info and her papers at Harvard. She retired at 90! An inspiration… Worth a look.
#10 opony szczecin
April 26, 2009

grand kanyon junior…
#11 Sparky
May 11, 2009

We had a 5.3 magnitude earthquake in the UK last year. It woke my parents up, but I don’t understand what caused it, since the epicentre was near Lincoln, but that’s nowhere near any plate boundaries I know about.
????
#12 desiree
May 26, 2009

im a ten year lod girl doing an esay and ive sited this site but theres no way to copy it on a doucument