The first of this week’s three late posts. Sorry again!
Jeopardy! category: SCIENCE & GEOMETRY (19-10-2015)
$1600 clue: Scientists use triangulation to locate this, the point on the Earth’s surface right above a seismic event
The gist: “Bang” in the middle. OK, maybe earthquakes don’t really make a “bang,” you’re sure likely to hear at least one as debris falls if you’re anywhere near the epicenter (or epicentre, for us Canadians). While frequently thought of as the origin or “starting point” of an earthquake, it of course isn’t, as this clue makes clear – an epicentre is by definition on the Earth’s surface, while the hypocentre is the point underground where the energy build-up that causes an earthquake is first released. Nonetheless, for human purposes the epicentre tends to be a much more useful concept, since barring significant underground construction it tends to be where the most damage occurs.
When an earthquake begins, the released seismic waves go out in all directions from the hypocentre, and are transformed (that is, slowed down) by various irregularities in the Earth’s composition, most notably the liquid outer core, which affects the compressional P-waves (think ripples on a pond) and the transverse S-waves (think waves on a beach) differently. Using at least three detectors (hence triangulation) at different points around the Earth, seismologists are able to calculate the epicentre of an earthquake based on the waves’ travel times at different places on the Earth’s surface. Such information can be crucial in sending relief efforts to places likely to be have been hit most hard.
The clue: Although “epicentre” has entered the lexicon generally as a synonym for “centre,” I suspect most people still associate it at least to some degree with earthquakes, so any clue about a point in space and earthquakes will probably bring to mind epicentre. I’d say this clue is probably significantly easier than either of the two earlier clues, but maybe that’s just me.
In Jeopardy!: 16 clues in the J!Archive have an epicentre (but with the American spelling), if you will. Twelve of them mention earthquakes as well. Two mention atomic explosions, which also have epicentres, also known as “ground zero” (since atomic explosions usually occur in the air, the line from an explosion to the epicentre goes down, while the line from a hypocentre to an epicentre goes up).