October 30th, 2007

Main

(no subject)

There are a number of things that give one a tactile experience of frequency-based filtering of waves.

Regardless, feeling it in earthquakes is still a unique experience.

Somewhere, a few miles under Milpitas and just to the right a bit, a large chunk of rock went "Wham!" this evening. A pretty sizable "Wham!", as such things go -- about 5.6 on the Richter scale.

When I was a young boy in Carmel, that wham is pretty much what the earthquakes there felt like, though not quite as hard -- I think the biggest one we had was in the high 4's. From what I recall, they made a pretty solid "Wham!" sound when they hit, though that may have been the collective sound of every tiny gap in the house between a bookshelf and a wall being slammed closed at the same time. And they were fierce, aggressive shaking, the sort a dog does to a toy.

This one, though, got filtered through 15 or 20 miles of several eons of accumulated San Francisco Bay mud, and all the high frequencies got damped out.

What was left was a gentle 1-2Hz shaking, which went through a gentle crescendo for about 20 seconds, and then just as gentle a decrescendo for 20 seconds. No suddenness, no sharpness to the shaking. Still a sense of quite a lot of energy in it, but all spread out and with all the sharp edges smoothed out.

This all meant that my first coherent thought afterwards (after the "how much is this going to grow?" thoughts, and then "good, not that big" ones that followed) was putting those pieces together and realizing, "Oh, ..., that must have been a big one whereever it was centered."