Written by: Lisa Stelzner
Primary Source: Daily Dose of Science Blog
In 1964, when the Good Friday quake occurred in Alaska at a magnitude of 9.2 (the most powerful earthquake recorded in North America), scientists didn’t know that earthquakes were caused by plate tectonics. This seems crazy now, since it doesn’t seem like very long ago, but earthquake science is very new. A geologist named George Plafker had already mapped some of the geology of Alaska and was sent by the USGS to Alaska right after the earthquake, since he was relatively “nearby” in Seattle. The earthquake was so huge that parts of the coast lifted 38 feet, while other parts subsided 8 feet. Fisherman witnessed how far the tides went out (a tsunami wiped out villages afterward).
Plate tectonics was a new theory in the 1960s, but had not suggested a method for how earthquakes occurred that agreed with any physical evidence. Scientists knew the seafloor was spreading and new crust was forming, but did not know what happened to old crust, unless the Earth was simply expanding. Dr. Plafker came up with the low-angle thrust fault idea after seeing the quake aftermath in Alaska, stating that plates are colliding and sliding under one another in places and caused a fault zone. The Pacific Plate and North American Plate meet on land in Alaska and deformation can be witnessed by humans, unlike uplift that occurs on the ocean floor.
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