5 ms·

A reduction in seismic noise is a boon for geoscientists

85 points by mmaia 7y ago

ASalazarMX 7y ago
TL;DR: Cities in lockdown cause less background noise in seismometers.
- elliotec 7y ago
  Thanks, yeah this isn't like fewer earthquakes, it's less non-tectonic movement so we can hear the earthquakes better.
pwinnski 7y ago
Weekdays are now at similar levels to weekends previously. Somewhat amazing.
jofer 7y ago
Not such a great thing if you're doing ambient noise seismology, though! You win some, you lose some... (For background, you can also use the noise from trucks/etc as a seismic source to probe the structure of the subsurface. It's much more computationally intensive and, well, noisy, but it actually works!)
- TheGallopedHigh 7y ago
  That’s quite interesting. It would be great if you explain a bit more about it. Namely, this is only used for locations close roads? Can other natural occurrences of sound give the same result? Can the same source that’s moving give a better picture of what’s below by that fact that it’s moving? Ie setup at different locations, so to speak.
  - jofer 7y ago
    Sorry I never noticed this! More or less any source of noise that's loud enough and is coupled to the ground works. In fact, a lot of what winds up being a good source is actually things like ocean waves -- not just man-made noise. Ideally, you want a clear "spike" of noise at a lot of locations and not necessarily a moving source. However, something like a truck/train hitting bumps at different locations along the road could definitely do a nice job of that. At any rate, the basic idea is to look at cross correlations of the waveforms -- any noise that is clearly correlative at different seismic stations is used. Take all of this with a grain of salt -- I work in an adjacent field and not exactly this one.
Zelphyr 7y ago
I know almost nothing about seismology or geology so forgive my naiveté here: Could the lack of movement caused by everybody staying home actually inadvertently induce greater than normal seismic events? By that I mean I'm wondering if all of our moving around normally may be like nano events that cumulatively ease pressure on fault lines? Almost like all of our movements sort-of force the faults to gently slip all the time instead of making giant movements, thus releasing an earthquake. But if we're not moving around much then that pressure starts to build up.
- dogsgobork 7y ago
  I doubt the rumblings of our transportation activity has much impact on earthquakes. The energy put out by a jetliner landing or the heaviest of trucks rolling by is minuscule, and typically earthquakes occur at depths measured in kilometers. Our seismic sensors are only several meters in depth, or at the surface, making them more susceptible to the seismic noise of our small man-made sources.
  - lmilcin 7y ago
    Seismic activity at a low level is triggered by much smaller forces. A small shock like a truck can cause two pieces of rock that are in tension to move against each other, causing a tremor. Same way as water can be overheated or supercooled when there is no trigger present, impurity or shock that will localize the start of reaction, the Earth crust can store a little bit of extra energy when there is not enough trigger. This is only temporary effect, after some time the level will come back even without increase in human activity. When human activity is restored what you can expect is seismic activity above normal levels, for some time until the stored energy is dissipated.
    - pixl97 7y ago
      Human locomotion activity is still tiny in those regards. A much bigger effect is the amount of water we pump and move which is very heavy and can directly induce earthquakes.
s0rce 7y ago
Can we use globally distrusted sensitive seismometer data to determine if lockdowns/shelter-in-place is working? Presumably we should see similiar decreases. I wonder if the USGS makes this data public. Any experts know? Seems like some traces are available (Here is the SF East Bay - https://earthquake.usgs.gov/monitoring/seismograms/9 https://earthquake.usgs.gov/monitoring/seismograms/9) but I'm not sure how to interpret this or where the older data is. Edit: the article mentioned a relevant tweet https://twitter.com/celestelabedz/status/1243306005456289792/photo/1 https://twitter.com/celestelabedz/status/1243306005456289792...
anigbrowl 7y ago
I'm not missing the air pollution either.

85 points by mmaia 7y ago

ASalazarMX 7y ago

TL;DR: Cities in lockdown cause less background noise in seismometers.

elliotec 7y ago
Thanks, yeah this isn't like fewer earthquakes, it's less non-tectonic movement so we can hear the earthquakes better.

pwinnski 7y ago

Weekdays are now at similar levels to weekends previously. Somewhat amazing.

jofer 7y ago

Not such a great thing if you're doing ambient noise seismology, though! You win some, you lose some... (For background, you can also use the noise from trucks/etc as a seismic source to probe the structure of the subsurface. It's much more computationally intensive and, well, noisy, but it actually works!)

TheGallopedHigh 7y ago
That’s quite interesting. It would be great if you explain a bit more about it. Namely, this is only used for locations close roads? Can other natural occurrences of sound give the same result? Can the same source that’s moving give a better picture of what’s below by that fact that it’s moving? Ie setup at different locations, so to speak.
- jofer 7y ago
  Sorry I never noticed this! More or less any source of noise that's loud enough and is coupled to the ground works. In fact, a lot of what winds up being a good source is actually things like ocean waves -- not just man-made noise. Ideally, you want a clear "spike" of noise at a lot of locations and not necessarily a moving source. However, something like a truck/train hitting bumps at different locations along the road could definitely do a nice job of that. At any rate, the basic idea is to look at cross correlations of the waveforms -- any noise that is clearly correlative at different seismic stations is used. Take all of this with a grain of salt -- I work in an adjacent field and not exactly this one.

Zelphyr 7y ago

I know almost nothing about seismology or geology so forgive my naiveté here: Could the lack of movement caused by everybody staying home actually inadvertently induce greater than normal seismic events? By that I mean I'm wondering if all of our moving around normally may be like nano events that cumulatively ease pressure on fault lines? Almost like all of our movements sort-of force the faults to gently slip all the time instead of making giant movements, thus releasing an earthquake. But if we're not moving around much then that pressure starts to build up.

dogsgobork 7y ago
I doubt the rumblings of our transportation activity has much impact on earthquakes. The energy put out by a jetliner landing or the heaviest of trucks rolling by is minuscule, and typically earthquakes occur at depths measured in kilometers. Our seismic sensors are only several meters in depth, or at the surface, making them more susceptible to the seismic noise of our small man-made sources.
- lmilcin 7y ago
  Seismic activity at a low level is triggered by much smaller forces. A small shock like a truck can cause two pieces of rock that are in tension to move against each other, causing a tremor. Same way as water can be overheated or supercooled when there is no trigger present, impurity or shock that will localize the start of reaction, the Earth crust can store a little bit of extra energy when there is not enough trigger. This is only temporary effect, after some time the level will come back even without increase in human activity. When human activity is restored what you can expect is seismic activity above normal levels, for some time until the stored energy is dissipated.
  - pixl97 7y ago
    Human locomotion activity is still tiny in those regards. A much bigger effect is the amount of water we pump and move which is very heavy and can directly induce earthquakes.

s0rce 7y ago

Can we use globally distrusted sensitive seismometer data to determine if lockdowns/shelter-in-place is working? Presumably we should see similiar decreases. I wonder if the USGS makes this data public. Any experts know? Seems like some traces are available (Here is the SF East Bay - https://earthquake.usgs.gov/monitoring/seismograms/9 https://earthquake.usgs.gov/monitoring/seismograms/9) but I'm not sure how to interpret this or where the older data is. Edit: the article mentioned a relevant tweet https://twitter.com/celestelabedz/status/1243306005456289792/photo/1 https://twitter.com/celestelabedz/status/1243306005456289792...

anigbrowl 7y ago

I'm not missing the air pollution either.