On Earthquakes

On March 12, 2011, in General, by Neil Stevens

When a person feels an earthquake, it tends to come in one of two varieties. There’s the brief, sharp jolt that comes from being near a minor earthquake, where one receives the localized high-frequency waves, and there’s the low rumbling that comes from being further away a larger earthquake, where one receives the low-frequency waves that travel further. Earthquakes strong enough to defy these two categories, strong enough to matter and close enough to be felt fully, are rare.

Throughout my entire life, there has been only one earthquake that left me with genuine concern for my surroundings, if only for a couple of seconds. This is true despite my living my entire life in earthquake country, apparently across town from an offshoot of the mighty San Andreas itself. That earthquake was an otherwise unremarkable earthquake in 2005. About 16 miles away from me a magnitude 4.9 earthquake struck Yucapia. This earthquake lasted just long enough, and shook just hard enough, that as it went on I was concerned for serious damage if it lasted too long or got any stronger. Fortunately it was only a 4.9 and did no such thing. However when it started I was sitting right where I am right now, at my desk. Though at the time I used a plain, old 6 foot plastic table as a desk, its top warped from my old, heavy computer resting on it for years. That warping, combined with the shaking, was causing a cup I had on the desk to slide.

When you’re used to earthquakes, they don’t cause you to panic. But when they hit, any sensible person will pause and evaluate the situation. That’s what I did when this one hit. I remember sitting there, staring at my cup as it shook, and realizing that this could be a big one. I had a moment of genuine surprise before I finally grabbed my cup to keep it from falling. And then, as the shaking continued, I got seriously concerned… just in time for the shaking to stop, and life to go on.

And remember: this was a magnitude 4.9 earthquake about 16 miles from me. Very close, but not especially strong. No damage. So when we see that Tokyo was perhaps 200 miles from the Sendai earthquake, and did enough damage to start a few fires, it’s shocking. A magnitude 5 earthquake will give you a neat story if you’re close enough to it. A magnitude 6 earthquake can possibly be life-changing if you’re very close, but otherwise it’s just a brief rumble. A magnitude 9 earthquake is beyond comprehension in its destructive power.

And it’s a genuine tribute to modern engineering that Japan suffered as little direct earthquake damage as it did from that incredible Sendai earthquake. Unfortunately, unlike California with our major faults running through the Bay area and all over southern California, Japan’s islands leave it surrounded by offshore earthquakes. So not only does Japan have to take the earthquakes themselves, but the tsunamis after (it’s for a reason we use the Japanese name for those, even when they strike America or Indonesia), and tsunamis are most destructive to islands. And while it’s hard to get useful, hard facts from the press, my understanding is that the flooding was a major contributing factor to the nuclear reactor explosion in Fukushima prefecture.

We can prepare all we want, but a wall of water will do what it wants. Forces that smash up buildings to rubble in seconds just will not be stopped. Earthquakes can be mitigated, as Japan and California have, with drastic improvements to civil and structural engineering. With a tsunami, the best we can do is give warning before it hits, sorry to say.

So while earthquakes are a fact of life for me, a magnitude 9 quake is a one-off, terrible event. But even then, without the threat of tsunami, it would not be nearly so bad as it was. So my best wishes go to everyone hit by it all in Japan, and I hope California residents realize how much better it is that our fault lines are onshore, not off.

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