18 ms·

I see earthquake reports (like this one) describe earthquake depth. What is the significance of it? Is it somehow actionable?

by xattt 3y ago

steanne 3y ago
https://en.wikipedia.org/wiki/Depth_of_focus_(tectonics) https://en.wikipedia.org/wiki/Depth_of_focus_(tectonics)
- xattt 3y ago
  Thanks! I must admit it’s hard to find an answer myself without the vocabulary.
  - acchow 3y ago
    This is where LLMs really shine.
    - dmix 3y ago
      That's a very good point, I was trying to google how buttons on a calculator communicate with the chips underneath, basically how contacts work, and Googling that kept giving me stuff about calculators not electronics, but ChatGPT gave me the perfect bullet point breakdown because it understood the context of my more general question. People often communicate/think in analogies to the underlying concepts.
deleted 3y ago
[deleted]
northwest65 3y ago
As somebody who has been through more than 10 thousand quakes, it's as significant as the force itself. 7.4 @ 300km deep you just yawn and roll over. @10km deep you pray your concrete roof tiles don't come through the ceiling and kill you in your bed... you basically just lie on top of your wife, give thanks for the time you did have, and hope for the best.
- furyofantares 3y ago
  > As somebody who has been through more than 10 thousand quakes What's this now?
  - iraqmtpizza 3y ago
    How many drops is this for you, Lieutenant? Thirty eight... simulated.
    - dredmorbius 3y ago
      <https://www.cactushugs.com/wp-content/uploads/2016/06/aliens-guy.jpeg https://www.cactushugs.com/wp-content/uploads/2016/06/aliens...> (For the uninitiated.)
  - rdl 3y ago
    There are a LOT of very small/deep/etc quakes in some places.
    - furyofantares 3y ago
      Sure, I see Riverside CA had over 6000 last year, though I doubt if someone who moved there two years ago would say they've "been through" over 10,000 quakes since, depending on their sensitivity, they might not have felt any of them, or maybe a dozen of them or something. I'm interested in specifics!
  - RowanH 3y ago
    Christchurch quake had 10's of thousands of aftershocks. A few people I know were rattled to the point they were shell shocked and just had to leave town - every tremor triggering off "could this be it" all over again.
    - EdwardDiego 3y ago
      For a long while, every damn heavy truck driving past the office got a few people going really silent and pensive.
lukan 3y ago
Well, imagine it like the distance you want to be away from a big explosion. The further away, the better. And the deeper it is, the further it is away from the ground, where humans are.
robocat 3y ago
A shallow 6 is very different from a deeper 7. My city Christchurch was fucked by a 6.2 or 6.3 - but it was both (a) shallow (5km) and (b) close to dense residential areas. Christchurch was near to the 7.1 Canterbury earthquake but that did much less damage as it was 10km deep and Christchurch wasn't on top of it (it mostly affected less dense rural properties in the region near Christchurch). Be careful not to think of earthquakes as a point - talking about epicentres and precise depth is very misleading. Earthquakes are a fault-sheet or wrinkles. Surface fault lines only show where the 3D rips through the solid earth meet the surface. Fault lines matter a bit especially since they indicate local shallowness, but I suspect we get distracted by them because they make spectacular news reports. Reality is complex. My parents house was right above the fault plane of the Canterbury fault - and their house came though mostly okay. I know lots of people very near the Christchurch quake and many of their houses were unrecoverably damaged.
- lamontcg 3y ago
  The Nisqually quake in Seattle was a 6.8 but it was 57km (35 miles) deep. It was also on the other side of Tacoma sort of in between Tacoma and Olympia. The depth of that quake made it a lot less severe than it could have been, only killed one person, but estimated it cost $1b to $4b in damages.
  - thijson 3y ago
    I remember how it felt, I thought I was sick, because I felt this rocking motion. I thought it was just me, then I stood up and saw a plant shaking, so I knew it was everything else that was shaking too. The amplitude slowly increased, reached a maximum, then decreased over the course of what seemed like a minute. It was a quite slow frequency, possibly due to the depth. This was from Portland.
    - lamontcg 3y ago
      I was on the 8th floor of a brick building in Seattle. If it had been a shallow quake I would be dead. There was a whole lotta motion. Can't remember what it damaged, though, other than some glass bottles on top of the refrigerator that fell off and shattered everywhere in the kitchen.
mastax 3y ago
Follow-up question. I understand how Richter Scale + depth could be useful, academically. But when communicating with the public, wouldn't it be easier to have a single number - rather than requiring the public to understand the relationship between two different quantities? Maybe: surface-equivalent Richter scale? Of course transitioning to a new standard would be even more confusing for a while. Edit: apparently there are many different scales in wide use already. https://en.wikipedia.org/wiki/Seismic_magnitude_scales https://en.wikipedia.org/wiki/Seismic_magnitude_scales
- kalleboo 3y ago
  In Japan for domestic quakes they always report the Shindo scale (based on surface peak ground acceleration) instead of Magnitude. It’s way more useful a measure IMHO and whenever I see western news report use M it tells me nothing about how bad the quake actually was. https://en.wikipedia.org/wiki/Japan_Meteorological_Agency_seismic_intensity_scale https://en.wikipedia.org/wiki/Japan_Meteorological_Agency_se...
  - astrange 3y ago
    We have a similar measure (MMI) in the US, but it's harder to report a local measure in a single article.
- brigandish 3y ago
  This is why the Shindo scale is favoured in Japan, as it addresses the effects on people and buildings in a particular area, so you can tell just by looking at what is shaking and how much to get an idea of the strength. The worst part of experiencing an earthquake, for me, is realising that anything can happen in the next moments, otherwise it's weirdly normal.
- ks2048 3y ago
  Also could take into account distance to the point of interest. So, in city X you have a number and city Y another.
  - 3y ago
doodlebugging 3y ago
I put together a little display of the earthquake action of the first 4-5 hours after the large event using data from the USGS site. [0] You can follow the action from event to event over the course of the first 22 events (about 4-5 hours I think). [0] https://postimg.cc/HckCRn1m https://postimg.cc/HckCRn1m It started near Hualien City with the magnitude 7.4 and then if you folow the blue lines you can see how it rattled NE-SW mostly along the coast for the first hour (6 events) then following the pink line you can see it popped at the NE end along the coast before a series of events that curved out into the sea to the E-SE for the next hour (5 events). That was followed during the third hour by 4 events oriented roughly NE-SW in green with all but one offshore to the NE. The fourth hour saw 4 more events almost complete the square in yellow. Things were quieting by then and the fifth hour only saw two events, both offshore in light blue with the series ending red with a single event offshore. I have a graph of activity showing the magnitude and depth versus the time of the event. You can see that the later events trend deeper and lower magnitude making them unlikely to be felt as much as the initial event and less likely to cause as much damage. [1] [1]https://postimg.cc/zyfdWhNT https://postimg.cc/zyfdWhNT To understand the timing of the events I have displayed them in an elapsed time versus magnitude display based on the initial event timing. [2] [2] https://postimg.cc/68w81VqG https://postimg.cc/68w81VqG You can see how the magnitude of the events tails off and they become less frequent with time. In the map view you can get a feel for the region's relaxation after the main quake and the other graph allows you to see how the event magnitudes decreased while the later events tended deeper.

I see earthquake reports (like this one) describe earthquake depth. What is the significance of it? Is it somehow actionable?

by xattt 3y ago

I see earthquake reports (like this one) describe earthquake depth. What is the significance of it? Is it somehow actionable?

steanne 3y ago

https://en.wikipedia.org/wiki/Depth_of_focus_(tectonics) https://en.wikipedia.org/wiki/Depth_of_focus_(tectonics)

xattt 3y ago
Thanks! I must admit it’s hard to find an answer myself without the vocabulary.
- acchow 3y ago
  This is where LLMs really shine.
  - dmix 3y ago
    That's a very good point, I was trying to google how buttons on a calculator communicate with the chips underneath, basically how contacts work, and Googling that kept giving me stuff about calculators not electronics, but ChatGPT gave me the perfect bullet point breakdown because it understood the context of my more general question. People often communicate/think in analogies to the underlying concepts.

deleted 3y ago

[deleted]

northwest65 3y ago

As somebody who has been through more than 10 thousand quakes, it's as significant as the force itself. 7.4 @ 300km deep you just yawn and roll over. @10km deep you pray your concrete roof tiles don't come through the ceiling and kill you in your bed... you basically just lie on top of your wife, give thanks for the time you did have, and hope for the best.

furyofantares 3y ago
> As somebody who has been through more than 10 thousand quakes What's this now?
- iraqmtpizza 3y ago
  How many drops is this for you, Lieutenant? Thirty eight... simulated.
  - dredmorbius 3y ago
    <https://www.cactushugs.com/wp-content/uploads/2016/06/aliens-guy.jpeg https://www.cactushugs.com/wp-content/uploads/2016/06/aliens...> (For the uninitiated.)
- rdl 3y ago
  There are a LOT of very small/deep/etc quakes in some places.
  - furyofantares 3y ago
    Sure, I see Riverside CA had over 6000 last year, though I doubt if someone who moved there two years ago would say they've "been through" over 10,000 quakes since, depending on their sensitivity, they might not have felt any of them, or maybe a dozen of them or something. I'm interested in specifics!
- RowanH 3y ago
  Christchurch quake had 10's of thousands of aftershocks. A few people I know were rattled to the point they were shell shocked and just had to leave town - every tremor triggering off "could this be it" all over again.
  - EdwardDiego 3y ago
    For a long while, every damn heavy truck driving past the office got a few people going really silent and pensive.

lukan 3y ago

Well, imagine it like the distance you want to be away from a big explosion. The further away, the better. And the deeper it is, the further it is away from the ground, where humans are.

robocat 3y ago

A shallow 6 is very different from a deeper 7. My city Christchurch was fucked by a 6.2 or 6.3 - but it was both (a) shallow (5km) and (b) close to dense residential areas. Christchurch was near to the 7.1 Canterbury earthquake but that did much less damage as it was 10km deep and Christchurch wasn't on top of it (it mostly affected less dense rural properties in the region near Christchurch). Be careful not to think of earthquakes as a point - talking about epicentres and precise depth is very misleading. Earthquakes are a fault-sheet or wrinkles. Surface fault lines only show where the 3D rips through the solid earth meet the surface. Fault lines matter a bit especially since they indicate local shallowness, but I suspect we get distracted by them because they make spectacular news reports. Reality is complex. My parents house was right above the fault plane of the Canterbury fault - and their house came though mostly okay. I know lots of people very near the Christchurch quake and many of their houses were unrecoverably damaged.

lamontcg 3y ago
The Nisqually quake in Seattle was a 6.8 but it was 57km (35 miles) deep. It was also on the other side of Tacoma sort of in between Tacoma and Olympia. The depth of that quake made it a lot less severe than it could have been, only killed one person, but estimated it cost $1b to $4b in damages.
- thijson 3y ago
  I remember how it felt, I thought I was sick, because I felt this rocking motion. I thought it was just me, then I stood up and saw a plant shaking, so I knew it was everything else that was shaking too. The amplitude slowly increased, reached a maximum, then decreased over the course of what seemed like a minute. It was a quite slow frequency, possibly due to the depth. This was from Portland.
  - lamontcg 3y ago
    I was on the 8th floor of a brick building in Seattle. If it had been a shallow quake I would be dead. There was a whole lotta motion. Can't remember what it damaged, though, other than some glass bottles on top of the refrigerator that fell off and shattered everywhere in the kitchen.

mastax 3y ago

Follow-up question. I understand how Richter Scale + depth could be useful, academically. But when communicating with the public, wouldn't it be easier to have a single number - rather than requiring the public to understand the relationship between two different quantities? Maybe: surface-equivalent Richter scale? Of course transitioning to a new standard would be even more confusing for a while. Edit: apparently there are many different scales in wide use already. https://en.wikipedia.org/wiki/Seismic_magnitude_scales https://en.wikipedia.org/wiki/Seismic_magnitude_scales

kalleboo 3y ago
In Japan for domestic quakes they always report the Shindo scale (based on surface peak ground acceleration) instead of Magnitude. It’s way more useful a measure IMHO and whenever I see western news report use M it tells me nothing about how bad the quake actually was. https://en.wikipedia.org/wiki/Japan_Meteorological_Agency_seismic_intensity_scale https://en.wikipedia.org/wiki/Japan_Meteorological_Agency_se...
- astrange 3y ago
  We have a similar measure (MMI) in the US, but it's harder to report a local measure in a single article.
brigandish 3y ago
This is why the Shindo scale is favoured in Japan, as it addresses the effects on people and buildings in a particular area, so you can tell just by looking at what is shaking and how much to get an idea of the strength. The worst part of experiencing an earthquake, for me, is realising that anything can happen in the next moments, otherwise it's weirdly normal.
ks2048 3y ago
Also could take into account distance to the point of interest. So, in city X you have a number and city Y another.
- 3y ago

doodlebugging 3y ago

I put together a little display of the earthquake action of the first 4-5 hours after the large event using data from the USGS site. [0] You can follow the action from event to event over the course of the first 22 events (about 4-5 hours I think). [0] https://postimg.cc/HckCRn1m https://postimg.cc/HckCRn1m It started near Hualien City with the magnitude 7.4 and then if you folow the blue lines you can see how it rattled NE-SW mostly along the coast for the first hour (6 events) then following the pink line you can see it popped at the NE end along the coast before a series of events that curved out into the sea to the E-SE for the next hour (5 events). That was followed during the third hour by 4 events oriented roughly NE-SW in green with all but one offshore to the NE. The fourth hour saw 4 more events almost complete the square in yellow. Things were quieting by then and the fifth hour only saw two events, both offshore in light blue with the series ending red with a single event offshore. I have a graph of activity showing the magnitude and depth versus the time of the event. You can see that the later events trend deeper and lower magnitude making them unlikely to be felt as much as the initial event and less likely to cause as much damage. [1] [1]https://postimg.cc/zyfdWhNT https://postimg.cc/zyfdWhNT To understand the timing of the events I have displayed them in an elapsed time versus magnitude display based on the initial event timing. [2] [2] https://postimg.cc/68w81VqG https://postimg.cc/68w81VqG You can see how the magnitude of the events tails off and they become less frequent with time. In the map view you can get a feel for the region's relaxation after the main quake and the other graph allows you to see how the event magnitudes decreased while the later events tended deeper.