6 ms·

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

by 323 5y ago

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.

lostlogin 5y ago
Christchurch, New Zealand was smashed by a 6.2. Pretty much as you say, older and poorly designed building didn’t fare well, and the earlier 7.2 earthquake wouldn’t have helped. It was a very shallow earthquake too. https://en.m.wikipedia.org/wiki/2011_Christchurch_earthquake https://en.m.wikipedia.org/wiki/2011_Christchurch_earthquake
- quartesixte 5y ago
  Earthquake codes in California mitigate a lot of the intensity of a shake and its damage. Anecdotally, I heard to level Downtown Los Angeles completely it will have to be hit with some absurd Earthquake like a 9.0
  - njarboe 5y ago
    The strike slip fault system in most of California can produce earthquakes up to about 8.0. Subduction zone earthquakes that occur in many places, like Northern California up to Alaska, Chile, Japan, etc, can produce 9+ earthquakes. 10 and above only occur during large impact events. So California can have buildings "earthquake proofed" for much lower cost than say Seattle and they come at higher frequency. That may be one of the reasons that California's infrastructure is pretty well prepared for coming earthquakes while Seattle will have major damage when the next 9.0 hits in 0-400 years.
    - jandrewrogers 5y ago
      The most dangerous fault line in Seattle, both in terms of earthquake and tsunami risk, is the eponymous system of shallow thrust faults[0] that run through the middle of the city and historically have produced ~7.0 earthquakes. 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. [0] https://en.wikipedia.org/wiki/Seattle_Fault https://en.wikipedia.org/wiki/Seattle_Fault
      - hsod 5y ago
        There’s also a healthy local trade in earthquake retrofitting. After the nisqually quake the city got pretty serious, a lot of old buildings downtown were severely damaged
      - cutemonster 5y ago
        > designed to survive extreme earthquakes What magnitude is that? (The highest they're designed to survive)
        jandrewrogers 5y ago
        The modern building codes are derived from a 9.0 subduction zone model. I've heard people say that building standards derived from this model should work for just about any type of earthquake up to around 8.0-8.5 even if not specifically modeled; I have no idea how true that is but it seems plausible. Building codes are not defined just by the strength of the earthquake but also the earthquake type, depth, soil etc. It isn't the strength that is the problem so much as the kinds of loads different earthquakes put on structures. 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).
        cutemonster 5y ago
        Thanks! > isn't the strength that is the problem so much as the kinds of loads different earthquakes put on structures. Interesting, didn't know.
      - aaomidi 5y ago
        After living in an apartment constructed in 2019 in the Seattle area...see I want to believe you but I just can't.
  - clairity 5y ago
    a number of years ago, i worked in one of the downtown LA office towers when a 5.x earthquake hit. it was a jolt and rumble, and looking out the window, we saw the other towers nearby swaying back and forth. then we realized we were also swaying back and forth. it was unnerving to say the least. the little engineer in me eventually kicked in to point out that that engineered-in flexibility was what kept us from breaking apart and crashing into the ground.
dredmorbius 5y ago
This depends greatly on building codes, structure contents, and local geology. 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.
- ecpottinger 5y ago
  Here in Ontario we had a small quake caused by a rock slide in Lake Ontario, almost no damage was seen. But my friend in Bowmanville said her grand mother lost tens of thousands of dollars in custom plates that she has displayed on ledges all around her house. 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.
  - dredmorbius 5y ago
    That'd be "awareness and preparedness". I'm aware of workplaces in which all furniture > 4 ft in height requires building maintenance to move as it's bolted to walls.

by 323 5y ago

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.

lostlogin 5y ago

Christchurch, New Zealand was smashed by a 6.2. Pretty much as you say, older and poorly designed building didn’t fare well, and the earlier 7.2 earthquake wouldn’t have helped. It was a very shallow earthquake too. https://en.m.wikipedia.org/wiki/2011_Christchurch_earthquake https://en.m.wikipedia.org/wiki/2011_Christchurch_earthquake

quartesixte 5y ago
Earthquake codes in California mitigate a lot of the intensity of a shake and its damage. Anecdotally, I heard to level Downtown Los Angeles completely it will have to be hit with some absurd Earthquake like a 9.0
- njarboe 5y ago
  The strike slip fault system in most of California can produce earthquakes up to about 8.0. Subduction zone earthquakes that occur in many places, like Northern California up to Alaska, Chile, Japan, etc, can produce 9+ earthquakes. 10 and above only occur during large impact events. So California can have buildings "earthquake proofed" for much lower cost than say Seattle and they come at higher frequency. That may be one of the reasons that California's infrastructure is pretty well prepared for coming earthquakes while Seattle will have major damage when the next 9.0 hits in 0-400 years.
  - jandrewrogers 5y ago
    The most dangerous fault line in Seattle, both in terms of earthquake and tsunami risk, is the eponymous system of shallow thrust faults[0] that run through the middle of the city and historically have produced ~7.0 earthquakes. 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. [0] https://en.wikipedia.org/wiki/Seattle_Fault https://en.wikipedia.org/wiki/Seattle_Fault
    - hsod 5y ago
      There’s also a healthy local trade in earthquake retrofitting. After the nisqually quake the city got pretty serious, a lot of old buildings downtown were severely damaged
    - cutemonster 5y ago
      > designed to survive extreme earthquakes What magnitude is that? (The highest they're designed to survive)
      - jandrewrogers 5y ago
        The modern building codes are derived from a 9.0 subduction zone model. I've heard people say that building standards derived from this model should work for just about any type of earthquake up to around 8.0-8.5 even if not specifically modeled; I have no idea how true that is but it seems plausible. Building codes are not defined just by the strength of the earthquake but also the earthquake type, depth, soil etc. It isn't the strength that is the problem so much as the kinds of loads different earthquakes put on structures. 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).
        cutemonster 5y ago
        Thanks! > isn't the strength that is the problem so much as the kinds of loads different earthquakes put on structures. Interesting, didn't know.
    - aaomidi 5y ago
      After living in an apartment constructed in 2019 in the Seattle area...see I want to believe you but I just can't.
- clairity 5y ago
  a number of years ago, i worked in one of the downtown LA office towers when a 5.x earthquake hit. it was a jolt and rumble, and looking out the window, we saw the other towers nearby swaying back and forth. then we realized we were also swaying back and forth. it was unnerving to say the least. the little engineer in me eventually kicked in to point out that that engineered-in flexibility was what kept us from breaking apart and crashing into the ground.

dredmorbius 5y ago

This depends greatly on building codes, structure contents, and local geology. 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.

ecpottinger 5y ago
Here in Ontario we had a small quake caused by a rock slide in Lake Ontario, almost no damage was seen. But my friend in Bowmanville said her grand mother lost tens of thousands of dollars in custom plates that she has displayed on ledges all around her house. 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.
- dredmorbius 5y ago
  That'd be "awareness and preparedness". I'm aware of workplaces in which all furniture > 4 ft in height requires building maintenance to move as it's bolted to walls.