A bit more on Parkfield

So what was all that behind the recent Parkfield entry? Here is a bit of explanation:

Earthquakes sometimes happen on faults, but not always

Most of the impressive earthquakes of the last few decades have happened on previously unrecognized faults. This has left some of us wondering whether the whole "earthquake fault" thing might be misconcieved. Parkfield occured on the part of the San Andreas Fault that it should have; but it was late. Or was it. As noted in the post the 1922 event might not have been on the SAF. If the 1922 event was on some other fault (unrecognized?) then the period at Parkfield looks alot more like 35 years and the recent event was right on time.

Predicting the future is hard

The Parkfield prediction is the only prediction that the USGS has ever made or is likely to make. They got it wrong despite the apparent simplicy of the Parkfield segment behavior. The regularity of the series is pretty striking, but whether it is regular at 22 years or 35 years is completely dependent on where the 1922 event was and that is something that we are not likely to ever be able to determine.

Earthquake risk is risky

All of earthquake risk thinking is based on the notion that earthquakes happen on recognized faults in ways that are similar from event to event. If you can't count on earthquakes occuring on faults that you know about, the problem is much harder.

Earthquake physics is very complex. I don't know how it compares in a technical sense to the complexity of the climate system or any other Earth systems. But it does give one pause as we think about trying to make decisons based on predictions.

Aside
For more on the issues surrounding prediction see Sarewitz et al. 2000
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Parkfield, at last

Well it finally happened. 13 years late, but better late than never (I think).



In the early 1980s, earthquake scientist predicted that a magnitude 6.0 earthquake would occur on the Parkfield segment of the San Andreas fault by 1993. This was based on the fact that the Parkfield segment of the SAF seemed to have failed in very similar events, at regular intervals, over the last 150 years or so. (Events occured in 1857, 1881, 1901, 1922, 1934, and 1966.)

Aside
Lots of jingo in that, let me parse it a bit.

"segment of the SAF"

the San Andreas Fault is not perfectly straight and while on average the whole thing must slip at about the relative rate of slip between the North American and Pacific plates, different parts stick and slip at different times.

"seems to"

science waffle for "the timing isn't perfect, but it ain't bad either"

"very similar events"

similar events to a seismologist is one in which the same part of the fault slips about the same amount - roughly the size of the earthquake is area that slips times the amount that it slips.

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In response to this prediction, the Parkfield Experiment was designed and implemented. Essentially that meant that alot of instruments were installed along that segment of the fault and then we waited. I was a graduate student during the time of the window at Parkfield and it was a long slow death. It had to happen, but no one could say when.

Now it has but not as it was expected: Previous events had initiated in the North and propogated south. This one started in the south and went north. Previous events had been preceeded by a pretty good fore shock (about magnitude 5). This one had no warning. Finally there is the issue of the timing. 22 years has long been accepted as the period at Parkfield, but as Chris Scholz points out the event prior to the 1966 (the event prior to this one) occured in 1934 which is 32 years. The interval since 1966 is 38 years. Allan Lindh has suggested that the 1922 event may have occured off of the SAF; if that is so then the interval is more like 35 years since 1901.

Aside
Note that the "suggested" link above will go away by about 13 October 2004. If you are a Chronicle of Higher Education subscriber it will always be available here. If you are not a subscriber, send me email and I will get you the text.
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Road Kill

Lots of posts to write (the parkfield earthquake, the early evolution of tenure, science in the national parks, self censurship), but tonight I think I will take on a realtive short one - Road Kill.

In driving around Westchester County these days, my completely unscientific monitoring indicates that road kill is up by a bunch. I am pretty sure I saw a coyote (not wylie enough) by the Taconic on Saturday as well as a hawk (rather ruffled) further up the road. Mostly though it has been an increase in the number of racoons (big ones) and squirrels. (I hit a possum a week or so ago, my first known kill.) Haven't seen many dead skunks in the middle of the road or elsewhere for that matter.

So the question is - Why the increase? Is it seasonal? (I think yes). My guess (yes it is a guess, not an estimate) is that it has to do with increased foraging activity in preparation for the coming winter. It would be easy to explain my not having observed this before because I didn't have a girlfriend that lived in the country before this year. (well that depends on how you count - I was working on having one last year at this time, but we hadn't gotten to the point where I could make observatons about road kill).

A few other observations on the megafauna upstate. There are a lot of deer! They are bold, but 9-14 year old girls don't like me to throw rocks at them to send them out of the yard; however, they will volunteer to chase them. There are reports of black bears - they have definitely returned to Black Rock Forest. I expect it was wolves that kept the deer in check and they are definitely not prowling the backyards of Westchester County. I have heard coyotes in the dusk.

I don't really know what to think about what would amount to the predator / prey relations of an ecosystem such as Westchester, especially the lands surrounding the reservior system. It certainly looks to me like automobiles are a postive factor with respect to controlling the vermin population. I doubt that they are enough of a factor to replace whatever other predators might have done, but I really don't know. With respect to the deer, a top predator is definitely needed. Humans could be that too, but the 9-14yo girl factor is a real problem.

Aside
Zora is completely saturated with my scientific lessons (although she was intrigued when I suggested I could show her how to make up data; but then lost interest when I started adding error to our invented points) - so I am having to really bite my tonge with respect to her assigned evaporation experiment. I haven't discussed road kill with her.
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