Nearly all earthquakes are caused by continental plates getting stuck on oceanic plates and then getting abruptly unstuck.
Eighty miles from the shore and ten thousand feet below the surface of the sea, the hand of a geological clock is somewhere in its slow sweep. All across the Northwest, seismologists are looking at their watches, wondering how long we have, and what we will do, before geological time catches up to our own.
The Cascadia fault line remained hidden from us for so long because we couldn’t see deep enough into the past. It poses a danger to us today because we haven’t thought deeply enough about the future. That’s no longer a problem of information; we now understand very well what the Cascadia fault line will someday do.
Seismologists know that how long an earthquake lasts is a decent proxy for its magnitude.
The 1989 earthquake in Loma Prieta, California, which killed 63 and caused six billion dollars’ worth of damage, lasted about fifteen seconds and had a magnitude of 6.9. A thirty-second earthquake generally has a magnitude in the mid-sevens. A minute-long quake is in the high sevens, a two-minute quake has entered the eights, and a three-minute quake is in the high eights. By four minutes, an earthquake has hit magnitude 9.0.
An earthquake from the Cascadia fault line is predicted to be a high magnitude one lasting minutes.
The Cascadia’s average amount of time between earthquakes is 243 years. That timespan is dangerous both because it is too long—long enough for us to unwittingly build an entire civilization on top of our continent’s worst fault line—and because it is not long enough. Counting from the last earthquake in 1700, we’re now 315 years into a 243 year cycle.
How should a society respond to a looming crisis of uncertain timing but of catastrophic proportions that it’s completely not prepared for?
There’s no sugarcoating it. The earthquake itself will be devastating. Then, depending on location, people will have much less than an hour to flee before the tsunami, which follows a quake, smashes ashore to complete the devastation. “When that tsunami is coming, you run. You protect yourself, you don’t turn around, you don’t go back to save anybody. You run for your life.” That’s the advice of a safety policy official.
We’re insulated from nature, living in what would have been a dream world to our ancestors, taking for granted things they couldn’t imagine. But nature is always there, and we often forget. It’s like our cuddly cat coming home with a mouse or a bird that it’s hunted and killed for us. We forget that a cat is part of nature
I found this information in a New Yorker Magazine article that’s worth reading if you want to know more about the Cascadia fault line.