Archive for September, 2004|Monthly archive page


Well, the Parkfield earthquake finally seems to have happened.
Parkfield‘s a town in California, adjacent to the San Andreas Fault. The particular segment of the San Andreas running through the area has had earthquakes on an unusually regular schedule since the 19th century — a magnitude 6 about once every twenty to thirty years. Prior to yesterday, the last one was in 1966; it was believed that the next one would happen by the mid-90s, but it failed to materialize. That was the closest I’ve ever seen to an official North American earthquake prediction, and it didn’t pan out; of course, it was a probabilistic prediction, not an absolute one, but nonetheless it turned into an example of just how unpredictable earthquakes are.
Well, now, the suspense is over. No one hurt, fortunately, and after a decade I think we can just call it fashionably late.


And now, an equation-display solution that actually works

A little online discussion turned up a free Java applet that does pretty much exactly what I need — given a LaTeX equation handed to it as a parameter, it renders the equation. Using Java seems like overkill, but I’ll take a conceptually-inelegant solution that works over a conceptually-elegant one that doesn’t.

So, here we go:

The applet’s hosted on my webspace at U of M; it’s pretty small, but all the same I’d prefer it if people would grab their own copies rather than using mine, bandwidth being a limited resource and all. The one clunky aspect is having to fiddle with the applet size in pixels; still, that’s something I can live with.

Update: Well, it turns out that the applet won’t run unless it’s locally hosted — it should work now, though.

Er, let’s try that again…

Well, that was an embarassing example of how hard it is to get these things to work. TypePad added a bunch of hard line breaks to my MathML, which may be why it didn’t render — I think I’ve successfully turned that option off, though. One more try:




Putting equations on the web is, as everyone knows, a royal pain in the ass.

I’ve been researching this, both for course purposes and potentially for this log, and it seems that the only widely-supported solution is a bunch of little gif files. That’s deeply irritating — for one thing, on TypePad, I’d have to upload, and keep track of the names of, a dozen little files for each post — hardly worth the hassle, and the equations would end up being editable online.

Then there’s MathML. Just for grins, here’s a MathML equation:




(cribbed from a test page). It’ll probably work OK in Mozilla — but anyone else is going to need a plugin, which may or may not work. And it’s still a hassle to generate; there are various LaTeX to MathML converters out there, but It’d rather just type LaTeX (which is a nice compact format for equations, and one that I know) directly into the browser; the MathML source is rather bloated and hard to edit by hand.

Anyone out there have any better ideas?

Abstracts: not an art form

Here’s the abstract I submitted last week (pre-vacation) for the fall AGU meeting. The writing style of abstracts always makes me cringe; what makes me cringe even more with conference abstracts is having to write them before the results are really in. Since the abstract deadline’s three months before the meeting, the choice is between presenting slightly stale material or being noncomittal about the results in the abstract; I usually end up opting for the latter, but it still makes me uneasy.

Mantle Fabric Beneath Ontario: Results From the CNSN, FEDNOR and

Andrew W. Frederiksen, Soo-Kyung Miong, and David Eaton

The basement of the province of Ontario is Precambrian, consisting of the Archean Superior Province in the north and west, which abuts on the Proterozoic Grenville Orogen. The Grenville, which forms the southeastern edge of the Canadian Shield, is the result of extensive crustal shortening and deformation during the interval 1.3-0.98 Ga. The degree to which this crustal deformation is reflected in the underlying mantle is uncertain, though LITHOPROBE detection of a preserved subduction zone (Calvert et al., 1995) in the Superior indicates that relict Precambrian features are preserved below the crust. A number of permanent CNSN stations (e.g., SADO, GAC, KGNO, etc.) are located on or near the Grenville, and have large archives of teleseismic data available; the deployment of the dense POLARIS network on the Grenville in southern Ontario provides higher-resolution constraints, and has more recently been extended by FEDNOR stations in the Superior province. We present preliminary analyses of the FEDNOR data for SKS splitting and crustal thickness, along with a more detailed examination of receiver functions in the Grenville for upper-mantle structure. The SKS results for the Superior Province show fast directions to be largely in-line with absolute plate motion, in contrast with previously-presented results for the Grenville; receiver functions on a transect across Southern Ontario indicate ubiquitous fine anisotropic layering which varies laterally over distance scales of less than 200 km.

Term, again

Here at the University of Manitoba, classes officially start tomorrow. Summer’s when I get to bask in a gloriously irregular and nocturnal schedule; now that I’m regular classes, it’s time to resume regular hours.

This semester, I’ll be teaching two courses: one old and one new. The old one’s the first course I was handed upon my arrival at the U of M two years ago: 7.206 Introductory Geophysics. It’s mostly an applied course, covering the various geophysical methods used in oil and mining exploration, environmental studies, and engineering. What those methods do is characterize the subsurface — that is, provide information about what’s underground. For instance, a DC resistivity system puts electrical currents into the ground, and measures the resulting voltage; since V=RI, the result depends on the distribution of conductive regions in the ground (as well as on the placement of electrodes); a gravimeter measures variations in gravity from place to place (a fiddly business), which are caused by variations in density in the rock. The course is a grab bag of theory, case studies, practical exercises, and data analysis, and will for most of the geology students be the only geophysics course they ever take.

The new one’s a graduate course, with a probable enrollment of two; it’s a theoretical seismology course. I’ve never given such a course before, and I’m going to run it as a reading course with weekly meetings. I’m a bit apprehensive about this one, since I’ve never done this sort of thing before, but I think it can work; I know the material well enough to do a fair bit of improvising.

Now, the thing is, I’m still rather dubious about my own teaching abilities. As a Ph.D. student I had very limited teaching opportunities, and I’ve never really had any formal teaching instruction. I’ve mostly concentrated on structure and clarity, perhaps at the expense of liveliness — as a student there was nothing I hated more than a course too disorganized to follow. I think my courses may be a bit of a snooze as a result (though I haven’t caught too many people actually snoozing in class, something I used to do a lot of myself). If anyone actually in my courses is reading, feel free to let loose with suggestions or criticisms; the one universal in my course evaluations is “talk louder!”, so I’m forseeing a lot of lozenges in my future as I try to put that into effect.