11 January 2009
Well, if I can say something without jinxing it, it appears as though our two weeks of winter may be over. Not but what it won’t be grey and rainy for a while yet, but the incipient buds are swelling more greenly on their socially networked branches. The leaves cluttering the sidewalks are from the sweetgums, and most of them only just fell within the last month. We’ve had some sunny warmth here and there, and while I haven’t seen any hummingbirds yet, the Steller’s Jays have been joined by squads of robins.
But the thing that really brought a sense of seasonal change for me was at the end of the cold snap we had in December. Hardly seems fair of me to use that term, when Fairbanks has been pretty chilly by comparison, but people take notice when we get a weeks worth of heavy frosts in Corvallis. At any rate, on about 29 December, I woke to find cirrus clouds covering most of the sky, and causing a strong, beautiful 22 1/2 degree halo around the Sun. I’ve long since given up any pretensions to being able to photograph such phenomena, so I contented myself with staring upward for several blocks on the way to work.
16 August 2007
Well, no tsunami yesterday, completing the trifecta of non-disasters. The potential here was anulled rather quickly, but it took a while longer to clear things in Chile. We did, however, have another earthquake last night. This one was centered, as nearly as I can tell, just a few miles northwest of our house. Also, again last night the clouds were at just the right elevation to be spectactularly illuminated by the 21 July fissure.
12 August 2007
Last night at work we had customarily clear skies and a pretty good crowd for the Perseid meteor shower, which peaked in the early morning hours today (HST). The shower was good but not spectacular: without trying particularly hard I saw about a dozen meteors, including a couple of near-bolides. I saw a few meteors as Perseus rose on Friday night, too, and we’ll probably see more tonight as the shower tapers off.
3 August 2007
Title of this post notwithstanding, I still prefer Dewey Decimal.
The 21 July eruption on Kilauea is still going strong, though I haven’t been anywhere I can see it recently. So far, looks like a fairly small amount of lava has been erupted, and it isn’t headed toward my house.
Meanwhile, an encroaching hazard of another kind is receiving somewhat less media attention. Election reform and in particular electronic voting machine oversight seem to be low on the list for discussion, compared with number of dollars raised by candidates.
As I prepare for a talk at work tomorrow night on the history & philosophy of science (I think I hear the yawns starting already), I ran across an outstanding optical illusion on APOD a couple weeks back. As they say, it is a good example of how good we think our perceptions are contrasted with how good they actually are. Or perhaps something deeper, say Benjamin Cohen’s example of teaching his engineering students about what we can perceive and what we can’t.
25 July 2007
Stargazing was pretty good the last couple of nights. Even with the remnants of Cosme on Saturday, we managed to have clear skies all four nights. But the highlight on Sunday and Tuesday nights were definitely the clear skies all the way down to Kilauea. Based on the update from HVO, we had one of the best views anyone has gotten of the fissure eruptions that started on 21 July.
We even dragged a couple of Dobsonian telescopes over to the picnic tables at the back of the parking lot and trained them on the eruption. Based on our back-of-the-envelope calculations, the eruption subtended an angle of about one degree (half as wide as my thumb, held at arm’s length) and was about forty miles away. That made the visible part of the flow about a mile long, but please note that the error bars on that number are large–nearly the size of the envelope itself.
24 October 2006
As befits an earthquake whose aftermath was less than the 24-hour news channels made it out to be, this post will be less than initially promised. First of all, though, the HVO Current Eqs Map is up and running, though it is a little slow due to heavy traffic. Also, they have the seismograph readings from the Hualalai instrument station (closest to the quake).
I noticed that many media figures, including Hawai`i County Civil Defense officials, referred repeatedly to the magnitude of the quake on the Richter scale. While Richter’s 1935 system (based upon the much-abused scale for measuring star brightnesses, also called magnitudes; that’s a completely different rant) was designed for a specific purpose, it worked pretty well and had a catchy name, so it got pressed into greater service. Also, he was at CalTech when he developed it, and therefore had a lot of reputation to throw around. The Richter scale measures the amount of energy released during an earthquake, and was originally designed for use with a specific instrument at a specific location, but later rejigged for use pretty much wherever you wanted.
A less specific scale of similar utility, a sort of metric system of magnitude if you will, called moment magnitude, was developed in 1979. This new scale was designed to agree closely with the Richter scale, and it is logarithmic in the same way. In both scales, two earthquakes with an increase of one magnitude (4 to 5, say) means the amplitude of shaking is ten times as great at the same distance from both quakes. Likewise, a quake of 5 releases about 32 times as much energy compared with a quake of 4 on both the Richter and moment magnitude scales. Thus, the differences between the scales are pretty much mathematical (as shown here) but as a non-representative sample, I know more seismologists who use moment magnitude than Richter magnitude. These same seismologists do confess that they often use Richter when dealing with the lay public or media, however, because it is much better known. If you really want to get tricky, you can look at centroid moment tensors, which look cool on maps. Unfortunately, the Hawai`i one isn’t big enough to show up on the map they have on the web, but here is the raw centroid moment tensor stuff, for the truly geeked-out. So, use whichever scale you like, unless of course you’re talking about deep earthquakes, in which case, the body wave is a better measurement. Figure it out yourself. Here’s a pretty good description of the various kinds of scales for measuring the amount of energy released, courtesy of the HVO again.
My second point in all of this is that I can’t figure out why hypocenter never caught on the way epicenter has. Google ‘political epicenter,’ and you get over a million hits. Try it for ‘political hypocenter,’ and you get one percent of that. People often use epicenter when they actually mean ‘right where the dang thing happened,’ though. To clarify (and anyone who knows more Greek than I should feel free to display that at this time) the hypocenter is the point way down deep in the Earth where the rupture actually happens (cf hypodermic needle). The epicenter is the point on the surface of the Earth directly above that point (cf epidermis). For the topologically challenged, if you drew a line from the center of the Earth to the hypocenter and kept going until you start blinking really hard, you’d be at the epicenter. That spot doesn’t necessarily feel the greatest effects of the quake, or suffer the greatest damage, either. Those can vary greatly depending on the kind of soil or rock in the immediate neighborhood. Cracks, sinkholes, building collapses and so on do not reliably indicate the epicenter, and are almost never indicative of the hypocenter. Common depths for earthquakes are either 5-10km or about 30km, depending on location and type. All of which is to say that there can be a big difference between hypocenter and epicenter, and the word we use less usually designates the more important point, seismically.
All of this is by way of saying that scientific terms certainly get appropriated, and not always in the way they were intended. Without getting all literal and inflexible and stuff, these two examples might be a case where some clarification from the science-types would be useful in the fray of general discourse.
P.S. Hypocenter apparently is also used to designate the spot right underneath a nuclear bomb detonated in the air. An even less fun place to be than the previous definition.
16 October 2006
At about 7:10 yesterday morning, we felt a pretty good earthquake at our house. Living, as we do, on an active volcano and about five miles as the `alala flies from Pu`u O`o (the active vent on Kilauea), this isn’t that wierd. Except that I was standing outside in the road and I felt it pretty strongly, watching trees swaying back and forth. Our house is built with post-and-pier construction, common out here because the lots are frequently not all that level. It provides the added bonus, however, of doing the same thing the Japanese now spend millions designing their office buildings to do: shimmy so they don’t break. Elle reports that from her observations inside the house (under a doorway—don’t try to run outside, kids) she expected to hear dishes breaking as they cascaded to the floor, but in fact the shelves moved with the house. Our sum total damage was one box of cookies that fell off its shelf. The aftershock about ten minutes later was slightly less strong and definitely shorter–ten seconds, compared with nearly a minute for the first quake. A third felt aftershock at about 10:30a.m. was barely worth mentioning. Elle didn’t even wake up from her nap.
With all radio stations knocked out, our most expedient mode of getting information was to drive the firehouse in Volcano. Noni, the font of all wisdom, had already hear that it was relatively big (prelim 6.5 magnitude, see below) and centered near Pu`uanahulu, on the west side of the island. Subsequent reports would place the quake center offshore, but County Civil Defense did an excellent job of getting the word out that there was no forecast tsunami.
As it happened, not only was the quake not centered near us, our region of the island suffered the least damage. Waiakoloa Village was the closest place with a post office to the epicenter, and they got rocked pretty hard, although no reports of structural damage. But as of yesterday about noon, pretty much every road on the North side of the island was closed. Saddle road remained open, and the entire Ka`u district fared well, save for some rocks on the road in Ocean View. But if you’ve ever been to Ocean View, it would only be news if there weren’t rock on the road. Hamakua coast highway, Kawaihae, Hawi Mountain Road, and both the upper and lower roads from Waimea to Kona remain closed in various places. The Volcano Fire Department stayed true to ourselves (motto: Always Ready, Rarely Paged) but in fact, the Hawai`i Fire Department reported no calls for assistance received due to the earthquake.
The confusion over what roads were closed seems to have been the biggest impact yesterday. The Kona hospital was initially evacuated, but then reopened. A bunch of schools are closed today, and lots of buildings are being evaluated. Some places lost water or power yesterday, but many are back online. In short, no big deal.
Unfortunately, the Hawai`i Volcano Observatory ‘Current Eqs Map’ is down from excessive traffic, but if you want a map, the IRIS seisic monitor is very good. Hawaii Tribune Herald webpage has some photos, but registration is required beyond the ‘front page.’ Also check out the Center for the Study of Active Volcanos page on natural hazards in Hawai`i, which has some excellent preparedness information.
The promised (and truly forthcoming, but maybe not until tomorrow) post will contain information on the not-so-critical difference between ‘center,’ and ‘epi-center,’ and the slightly more important one between the Richter Scale magnitude and the moment magnitude.
So, with roads closed and various utilities crippled, what did we do? Settled in for a beautiful afternoon at home–the wind was blowing (oddly) out of the South, but skies were clear and temperature was right around 70. In fact, we dragged out our hand-crank pasta maker and made a batch of fresh fettucine. I’ll let you know how it tastes.