Below 5 you only need to worry about objects in your immediate vicinity.
Old/poorly built buildings start collapsing at about 6.
Above 8, almost any building can collapse.
Old/poorly built buildings start collapsing at about 6.
Above 8, almost any building can collapse.
In California and Japan, decades of stringent building codes mean that most structures are likely to be safe agaist even large quakes, in the sense that occupants should survive, even if the structure itself is not repairable.
Along the central and eastern US, and in large parts of rural China, Iran, Iraq, and Turkey, amongst other areas, building codes, geology, and general preparadness and awareness (or lack) can make even comparatively small quakes deadly.
From the Rockies east, the US is underlayed by largely-intact limestone and a thick crust which can propagate seere ground movement hundreds of kilometers, up to 1,000 km or more. By comparison, along th USwest coast, being 100--200 km from an epicentre usually renders even a large quake largely harmless (though it may still be felt). Additionally, construction standards in the central/eastern US and other regions mentioned above tend to result in far more severe structural damage. Rescue, aid, and shelter capabilities may also be limited.
(In California, the principle geological hazard is fill or other soils prone to liquefaction, which can greatly amplify movement locally. Landslides may also be a concern. In mountains, rockslides.)
The guidelines 323 gives are useful for California and Japan. Elsewhere, comparable damage might occur a magnitude below those given.
Why? Because we never get earthquakes here, so there were no lifted edges or holders! Then suddenly we get a small quake, and they all came crashing down.
I'm aware of workplaces in which all furniture > 4 ft in height requires building maintenance to move as it's bolted to walls.
https://en.m.wikipedia.org/wiki/2011_Christchurch_earthquake
Anecdotally, I heard to level Downtown Los Angeles completely it will have to be hit with some absurd Earthquake like a 9.0
Seattle buildings built in the last 3 decades are explicitly designed to survive extreme earthquakes. Most of the risk is in the 1970s and earlier infrastructure, quite a lot of which has been torn down to make room for the massive growth of Seattle.
What magnitude is that? (The highest they're designed to survive)
Seattle has a couple ~7.0 earthquakes every century, so the city has experience with strong earthquakes and everything old that is still standing has at least some ability to resist earthquakes (survivor bias). The last big earthquake was in 2001 (magnitude 6.8).
> isn't the strength that is the problem so much as the kinds of loads different earthquakes put on structures.
Interesting, didn't know.