5 ms·

I've got no idea at what magnitude I should start worrying. I would assume, and hope, that if my phone (which is otherwise on silent) is blaring, it must be a b

by dfxm12 5y ago

I've got no idea at what magnitude I should start worrying. I would assume, and hope, that if my phone (which is otherwise on silent) is blaring, it must be a big deal. Maybe for some people a 4.3 is a big deal, but not for all...

leeoniya 5y ago
> I've got no idea at what magnitude I should start worrying ask your building inspector
BurningFrog 5y ago
You start worrying at 5.0.
- rectang 5y ago
  It depends how close you are to the epicenter, of course. Your figure seems about right to me: I think a 5.0 near an epicenter would be pretty violent. But I've never been near an epicenter — only on the outskirts.
  - djrogers 5y ago
    It also depends on what type of ground you're on. I've been in 5+ earthquakes in a house built on solid rock (Los Angeles area hills), and a 4.5 down in the valley. Being on loose ground makes it feel much worse.
  - ryantgtg 5y ago
    Every time I feel an earthquake in LA, my first question is, “was that a small one near me or a big one far away?”
    - antod 5y ago
      You get a feel for that with the shaking frequency and/or gap between different sets of waves (P & S waves). No discernable gap and higher jerkier frequency usually means closer, a longer rolling feeling with separated phases that might last longer usually means further away. Just like sound or ocean waves the higher frequencies attenuate out quicker over distance.
dharmab 5y ago
If you live in an earthquake zone you quickly learn what a 2, 4, 6 feel like. It is a gossip topic in your community like the weather.
- zinekeller 5y ago
  I think that although (estimated) magnitude is helpful, Japan's system also calculates the (estimated) intensity from the earthquake for your local area. Not always correct (but this tends to be rare), but usually within +/-1 of the Shindo scale (which is their local intensity scaling). Seems that ShakeAlert doesn't compute (yet, hopefully) the estimated intensity in your area.
- Ancapistani 5y ago
  If you live in an area with frequent earthquakes, yes. I live near the New Madrid. There aren't frequent earthquakes here at all, but historically when we do have one... it's a big one.
- cgriswald 5y ago
  This isn't my experience at all and I've lived in the Bay Area nearly half my life. I have a vague idea of what a mag 4 earthquake feels like, and that's about it.
  - deleted 5y ago
    [deleted]
  - antod 5y ago
    Yeah that makes sense, people talk about what magnitude x "feels" like, but they're really describing an earthquakes intensity rather than magnitude. You don't directly "feel" the magnitude. Any given magnitude quake is going to feel very different for people in different situations - eg how far away, how deep, soil conditions, how tall the building they are in etc... Magnitude is related to how much energy is released - useful for seismologists and records, while intensity is related to ground acceleration and subjective effects which is useful for structural engineers and the public caught in one. eg that 6.2 magnitude Christchurch quake mentioned elsewhere still managed to produce some of the highest ever recorded vertical ground accelerations despite releasing a tiny fraction of what a really big quake can do.
kevinmchugh 5y ago
Distance from the epicenter matters as well. I was 6 miles from a 4.9 last month, my first real earthquake. It was unsettling and concerning (including for the people I was on zoom with) but that was it. Nothing fell off the walls, iirc no fatalities or buildings demolished. The scale is logarithmic. My rule of thumb is that 5 is where things start to get much more dangerous.
- Enginerrrd 5y ago
  Where I'm from, (Just a few miles from where this one was) we don't really start to worry until 7+.
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
klenwell 5y ago
We had had an earthquake in low 5's here a couple years earlier. That was nerve-wracking but didn't do any damage. So I think I was gauging my reaction (mostly instinctively) off that. Actually, I just looked up the previous earthquake: https://earthquake.usgs.gov/earthquakes/eventpage/ci38457511/executive https://earthquake.usgs.gov/earthquakes/eventpage/ci38457511... That one was a 7.1! Significantly larger than I remembered but more distant. I must have been thinking of an earlier earthquake.

by dfxm12 5y ago

leeoniya 5y ago

> I've got no idea at what magnitude I should start worrying ask your building inspector

BurningFrog 5y ago

You start worrying at 5.0.

rectang 5y ago
It depends how close you are to the epicenter, of course. Your figure seems about right to me: I think a 5.0 near an epicenter would be pretty violent. But I've never been near an epicenter — only on the outskirts.
- djrogers 5y ago
  It also depends on what type of ground you're on. I've been in 5+ earthquakes in a house built on solid rock (Los Angeles area hills), and a 4.5 down in the valley. Being on loose ground makes it feel much worse.
- ryantgtg 5y ago
  Every time I feel an earthquake in LA, my first question is, “was that a small one near me or a big one far away?”
  - antod 5y ago
    You get a feel for that with the shaking frequency and/or gap between different sets of waves (P & S waves). No discernable gap and higher jerkier frequency usually means closer, a longer rolling feeling with separated phases that might last longer usually means further away. Just like sound or ocean waves the higher frequencies attenuate out quicker over distance.

dharmab 5y ago

If you live in an earthquake zone you quickly learn what a 2, 4, 6 feel like. It is a gossip topic in your community like the weather.

zinekeller 5y ago
I think that although (estimated) magnitude is helpful, Japan's system also calculates the (estimated) intensity from the earthquake for your local area. Not always correct (but this tends to be rare), but usually within +/-1 of the Shindo scale (which is their local intensity scaling). Seems that ShakeAlert doesn't compute (yet, hopefully) the estimated intensity in your area.
Ancapistani 5y ago
If you live in an area with frequent earthquakes, yes. I live near the New Madrid. There aren't frequent earthquakes here at all, but historically when we do have one... it's a big one.
cgriswald 5y ago
This isn't my experience at all and I've lived in the Bay Area nearly half my life. I have a vague idea of what a mag 4 earthquake feels like, and that's about it.
- deleted 5y ago
  [deleted]
- antod 5y ago
  Yeah that makes sense, people talk about what magnitude x "feels" like, but they're really describing an earthquakes intensity rather than magnitude. You don't directly "feel" the magnitude. Any given magnitude quake is going to feel very different for people in different situations - eg how far away, how deep, soil conditions, how tall the building they are in etc... Magnitude is related to how much energy is released - useful for seismologists and records, while intensity is related to ground acceleration and subjective effects which is useful for structural engineers and the public caught in one. eg that 6.2 magnitude Christchurch quake mentioned elsewhere still managed to produce some of the highest ever recorded vertical ground accelerations despite releasing a tiny fraction of what a really big quake can do.

kevinmchugh 5y ago

Distance from the epicenter matters as well. I was 6 miles from a 4.9 last month, my first real earthquake. It was unsettling and concerning (including for the people I was on zoom with) but that was it. Nothing fell off the walls, iirc no fatalities or buildings demolished. The scale is logarithmic. My rule of thumb is that 5 is where things start to get much more dangerous.

Enginerrrd 5y ago
Where I'm from, (Just a few miles from where this one was) we don't really start to worry until 7+.

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

klenwell 5y ago

We had had an earthquake in low 5's here a couple years earlier. That was nerve-wracking but didn't do any damage. So I think I was gauging my reaction (mostly instinctively) off that. Actually, I just looked up the previous earthquake: https://earthquake.usgs.gov/earthquakes/eventpage/ci38457511/executive https://earthquake.usgs.gov/earthquakes/eventpage/ci38457511... That one was a 7.1! Significantly larger than I remembered but more distant. I must have been thinking of an earlier earthquake.