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Originally Posted by liat91
Before San Francisco builds more high density stuff all over the place, you might want to think about that major fault line that runs under it.
Imagine the damage an active major strike-slip fault would do under Manhattan. Even Tokyo doesn’t have this sort of fault under it, as I believe they wouldn’t have built such a city of that magnitude over it.
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Strike-slip is a pretty common type of fault, and not even the worst.
Thrust faults in subduction zones are capable of greater magnitude earthquakes and bigger tsunamis: the 1960 Valdivia (Chile) quake (9.5), the 1964 Alaska quake (9.2), the 2004 Indian Ocean earthquake (9.1-9.3) and tsunami, and the 2011 Tohuku quake in Japan (9.1) and tsunami were all megathrust earthquakes.
Strike-slip faults don't generally produce those magnitudes, and because the ocean floor doesn't drop or rise as with thrust earthquakes in subduction zones, the tsunamis are usually much smaller as well. The 1906 San Francisco quake is estimated at 7.9, which is the same as or smaller than the earthquake that devastated Tokyo in 1923 (est. 7.9-8.2). The 1989 Loma Prieta quake, centered south of San Francisco, was 6.9.
As to Tokyo specifically, the city was wiped out in 1707 by a megathrust earthquake estimated between 8.6 and 9.3, and then again in 1923 as noted above. You don't need a strike-slip fault to wipe out a city; the thrust faults do a better job of that.
As for faults directly beneath Tokyo, there's at least one, according to
this article:
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The fault line that runs beneath Tokyo is kilometres closer to the surface than seismologists realized, according to a new survey. That could be worrying news to residents waiting for the next 'big one' to hit the city, as quakes occurring at a shallow depth tend to cause more shaking and damage to buildings than deeper ones.
Tokyo is among the most densely populated earthquake zones in the world, with some 33 million people living and working in the conurbation. In 1923, around 105,000 people in the city were killed by a huge magnitude 7.9 quake.
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