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Because the southern San Andreas fault is likely to experience ground-rupturing earthquakes at an average rate of one every 215 years or so — and because the last such earth-shaker in the southernmost section took place in 1726 — we’re about 80 years overdue, Blisniuk said.
Normally, earthquakes below magnitude 3 or so are rarely felt. However, smaller quakes from magnitude 2.0 can be felt by people if the quake is shallow (few kilometers only) and if people are very close to its epicenter and not disturbed by ambient factors such as noise, wind, vibrations of engines, traffic etc.
As a doctoral candidate in the Department of Earth and Planetary Sciences at Harvard University with a focus on understanding earthquake phenomena, the most common question people ask me is, “So, when is the next big earthquake going to happen?” Unfortunately, the answer is somewhat dissatisfying because the truth is, we really don’t know.
Assuming these two theories always held, you could predict when the next earthquake would happen based on 1) the location of greatest unrelieved strain, 2) the time since the last earthquake on the fault, and 3) precise knowledge of the fault zone (which we may never achieve for many areas).
Here are some quick tips. Place protective film over large windows, keep the blinds closed at night when everyone is sleeping, strap down the refrigerator, etc. Basically, strap down anything that is taller than it is wide. At home, the garage is probably the most unsafe room in the house.
The last megathrust earthquake hit on January 26th, 1700 (1700.071) which has been estimated to have been in the 8.7–9.2 level. The megathrust earthquake involved an average slip of 20 meters (66 ft). That was a very big move. Most quakes are under 2 feet.