What would a really “Big One” look like?

People who live anywhere along the Earth’s tectonic plate boundaries (the so-called “ring of fire” know that at any time  “the big one” – a really, really large, damaging earthquake – could happen. The largest earthquake in recorded history was a 9.5 event along the coast of Chile in 1960. The second largest was a 9.2 along the southern coast of Alaska in 1964. Since January, 1700, only six events have occurred that were 9.0 or larger – one of them as recently as 2004 in Sumatra, Indonesia.

The “Biggest One” we could imagine would be a 9.9 earthquake, which would release 10 raised to the power (1.5*4/10) = 4 times as much energy as the Alaskan event in 1964.

The fault length from such an event would also be about 4 times longer, or 4,000 km. Although earthquake experts don’t expect an earthquake of this size, one of the places it could occur would be along the Aleutian/Alaska subduction zone. The entire zone would have to rupture in one earthquake, which earthquake scientists believe has ever happened.

If it did happen, the earthquake would cause strong shaking for 5 minutes or more (bigger earthquakes release their energy over a larger area and for a longer period of time). If the idea of a five-minute earthquake frightens you, remember that some of the energy will be traveling from hundreds of miles away. In most cases, only the 10 - 15 seconds of shaking that originates from the part of the fault nearest you will be very strong.

References:

• Earthquake Project Questions
• John Lahr, USGS
• Aleutian/Alaska Subduction Zone
• Putting Down Roots in Earthquake Country