Mr. Kipper
World Geography (3)
28 September, 1999

On this day in history, 28 September 1999, the students in Mr. Swinney’s 3rd period Honours World Geography class were privileged to/subjected to watching yet another educational video in the Nova series, this one entitled “Killer Quake.” In 1994 at 4.31 am, a 6.5 magnitude earthquake shook Los Angeles. It was scary because they thought earthquakes like that couldn’t happen so far from the San Andreas fault. It seems the quake had travelled under an entire mountain range to get there. The ground shook for only six seconds, but 57 people were killed and 9,000 were injured. Andrea Donellan and her team of seismologists later discovered that its epicentre was located in the San Fernando Valley in a community called Northridge. Most earthquakes leave a rift in the earth revealing the fault’s location, but this was no ordinary earthquake: no sir! It was caused by an unhappy thing known as a “blind thrust” fault. You can’t see them. You just know they’re there when they make earthquakes. And... there are as many as 100 of these things right under Los Angeles!

Apparently, they’re caused because the Pacific and North American tectonic plates are irritating each other. Lots of stress occurs because of irregularities in the shapes of the plates which cause not only sliding motion, but head-on collision.  Because of this phenomenon, the area buckled and the crust cracked, causing many little offshoot cracks-- blind thrust faults-- from the San Andreas fault. There was an earthquake in L.A., the Witte earthquake, caused by a blind thrust fault on 6 May 1987. The city has had, in the past six years, one major earthquake per year.

For a final frightening note, the Alesian Park fault (which is the biggest underneath the city) is located in L.A.’s most densely populated area. From what research seismologists have been able to do, it’s very close to its breaking point and pretty much overdue for a damaging earthquake! Isn’t that scary? For Californians, it seems the question is not if an earthquake will occur, but when.