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Geologists say Alaska quake caused by huge rupture

If so, what caused the rupture?

Plate techtonics. Surely you've heard of that concept. The entire Pacific Plate is rotating counter-clockwise (which is easily demonstrated by rock correlation).

Nobody greases the wheels, though, and when the plate catches against the adjacent plates and breaks loose all at once, everything bounces.

After giving a presentation at a geologists convention a few years ago, I was interviewed by the "Science Editor" of the local, big city newspaper. It became readily apparent after just a few minutes that this journalist had little or no scientific background. Although I tried as best as I could, you can't teach someone scientific "lingo" in a 20 minute interview. His article, published the next day, had a couple of quotes from me, but they were hardly in context and so badly reconstructed as to make them almost unrecognizable.

I also found out that the author of an article rarely ever constructs the headline. That is another editor's job. So, if that person understands even less about the subject, there is no telling what might happen. Let me give you an example from a trade publication: "Elf's 20-Year Experience Confirms Effectiveness of Smart Pigs." If you don't know about international oil companies and oil pipeline maintainence you would have no idea what the article was about!

So back to this thread. An earthquake (seismic shaking) is the manifestation of an energy release. Earthquakes can be caused by several different sources. Some of the more obscure sources are meteorite impacts and man-made nuclear explosions. Volcanic eruptions or subterranean movement of magma also causes earthquakes. You could even argue that a large truck or train passing by your house causes the ground to shake!

But for most purposes, earthquakes are related to movement of the earth's crust along more-or-less defined zones called faults. The recent Alaskan earthquake was caused by the release of energy stored in the crustal plates adjacent to the Denali Fault Zone. When the rocks there could no longer contain the stress and strain being put upon them by the subtle movement of the great crustal plates, the subsequent failure produced offset along the fault. The time it took the plates to move represent the duration of the quake. In this case the offset was measured at the earth's surface in the form of ground rupture. The ground rupture was measured to shift one side of the fault zone (relative to the other side) as much as 26 +/- feet. That's A LOT of movement. By way of comparison, the Northridge earthquake in the 1994 in Southern California caused a 1-foot vertical offset in the local foothills. The 1906 San Francisco earthquake had documented offset of about 20 +/- feet. Most of the "rupture" in the Northridge quake occurred at depth, along the faults associated with the earthquake. It could only be measured with instruments.