4 ms·

I'm in Brooklyn and felt it while on a call with an NJ resident who was the first to say "are we having an earthquake??" Do earthquakes have a propagation spee

I'm in Brooklyn and felt it while on a call with an NJ resident who was the first to say "are we having an earthquake??" Do earthquakes have a propagation speed? Might she have felt it before me?

pxx 3y ago
Yes, the speed of sound (through the earth, so faster than the speed of sound in air); yes. In California, typically usgs has earthquakes posted before I can feel them. They didn't have this one a few minutes after I felt it, so I feel like automatic earthquake detection is off in this area of the US.
- andrewla 3y ago
  Same experience -- felt a shaking; thought maybe a heavy truck had passed by for a second, then saw that all the monitors were swaying. Checked USGS and saw nothing, so figured it was nothing, because on the west coast they have the reports up lickety split. Half hour later everyone's phone started buzzing with the automated alert.
- gcr 3y ago
  I received the earthquake alert about 45 minutes after it occurred.
  - cj 3y ago
    The Apple alert came in at 12:05pm warning of aftershocks but not the primary event.
- Lance_ET_Compte 3y ago
  In the Bay Area, everyone gets an SMS message that says an earthquake is coming. I've felt/heard the shaking 10-20 seconds later. Some industrial equipment shuts down to avoid damage.
  - nashashmi 3y ago
    We felt it at 10:26 am ET. And an alert was sent to everyone at 11:24 am that an earthquake is coming. And then another one alerting for possibility of aftershocks. No aftershocks felt.
pmx 3y ago
They travel in waves through the rock!
atrus 3y ago
Everything has a propagation speed :P, but yes she probably felt it before you, then her signal made it to you faster than the Earthquake did. https://xkcd.com/723/ https://xkcd.com/723/
jedberg 3y ago
Yes. There is an excellent XKCD on the topic: https://xkcd.com/723/ https://xkcd.com/723/ But in summary, the speed is slower than light, so yes you can find out through telecom faster than it getting to you.
pseudolus 3y ago
The earthquake was centered in NJ.[0] Propagation speed would be a function of the depth. [1] [0] https://www.google.com/maps/place/40%C2%B040'58.8%22N+74%C2%B045'10.8%22W/@40.683004,-75.4121796,9z/data=!4m4!3m3!8m2!3d40.683!4d-74.753?entry=ttu https://www.google.com/maps/place/40%C2%B040'58.8%22N+74%C2%... [1] https://www.britannica.com/science/seismic-wave https://www.britannica.com/science/seismic-wave
deleted 3y ago
[deleted]
aragonite 3y ago
> Might she have felt it before me? Surface waves yes, body waves not necessarily. But surface waves are more destructive.
ortusdux 3y ago
The west coast states have the MyShake early warning system, which sends out automated alerts for 4.5+ quakes. https://earthquake.ca.gov/ https://earthquake.ca.gov/
hi 3y ago
Same thing happened to me. I was on a facetime with someone in Brooklyn, but I was a 2 hour drive north outside of NYC and it took what felt like 30 seconds to propagate over that 200km.
paxys 3y ago
Earthquakes propagate very slowly (around 2-8 miles/sec). That's how systems like ShakeAlert can send out early warning notifications. This one, for example, happened 40+ miles from NYC proper, so residents could have had like 20 seconds notice if the service operated here. People further up or down the coast could have had multiple minutes.
slingnow 3y ago
Do you think that earthquakes transmit instantaneously? Why would they not have a propagation speed like everything else in the universe?
- School-Cotton 3y ago
  I assume they meant “propagation speed that is substantially slower than light in a vacuum” since that is less than 50ms between any two points on earth.
- triceratops 3y ago
  On the earth the speed of light as is good as instantaneous.
  - quesera 3y ago
    > On the earth the speed of light as is good as instantaneous. Frustrated network architects would disagree!
eggy 3y ago
Sure given the epicenter was in NJ and closer than Brooklyn. I am from Brooklyn, but live in Nyack, NY, and I felt it here. Nyack is 40mi from epicenter, Brooklyn ~60mi. But your experience could be different based on the structure you are in, floor elevation, and existing soil and ground conditions.
Glant 3y ago
People in my town in southern NH reported feeling it about 20 minutes after it happened
spike021 3y ago
Yes. Last time there was a fairly large one in the SF Bay Area I happened to be on the phone with some relatives about 40 miles away and I felt an earthquake a moment before they did.
cossatot 3y ago
Earthquake waves have several propagation speeds, because there are different types of waves. The fastest is called the P-wave, which is a compressional (longitudinal) wave, similar to a sound wave, with a velocity of ~5-8 km/s for typical continental bedrock. The second fastest is the S-wave, or shear wave, which is about 65% of the P-wave speed. These waves produce relatively little displacement at the surface (except for close to the epicenter of large earthquakes) but are important seismologically. Then, there are the surface waves, which are caused by the interaction of the S-waves with the surface (in a way that I don't 100% understand). These travel about 90% of the S-wave speed, but they have the biggest displacements at the surface and therefore are the main ones that you feel and that cause damage. The surface wave displacements also get amplified in wet or loose soil, so the ground shaking and seismic damage is also much greater areas on top of sediment rather than bedrock. Areas on a river, lake or coast where the land has been extended into the water by dumping fill dirt are the worst--ground shaking is really bad and they are very prone to liquefaction. The difference between the arrival times (at any given point on earth) of the different phases of seismic waves is a function of the distance from the earthquake itself (the hypocenter) and the observation site. It is close to linear in Euclidian distance relatively near the earthquake hypocenter, but becomes more nonlinear farther from the earthquake, because the wave speeds are faster at depth (denser rock) so the travel paths of the wave fronts (the ray paths) are nonlinear. These differences in arrival times are one of the main ways of locating the hypocenter of an earthquake given observations from seismometers at multiple sites. It's essentially triangulation, except with time differences instead of angles--this is done through solving a system of equations. Additionally, S-waves can't pass through liquids, so there is the 'S-wave shadow zone' that occupies a large fraction of the side of the earth opposite an earthquake where there are no primary S-wave arrivals--S-waves are blocked by the liquid outer core. This is how we found out that the outer core is liquid!
- bobthepanda 3y ago
  Early warning systems also work by detecting P and S waves as close to the epicenter as possible.
- neurostimulant 3y ago
  Ground liquefaction is scary. Happened in Palu, Sulawesi a while ago. You can see houses moving as if they're on wheels: https://www.youtube.com/watch?v=J_egBKj1W08 https://www.youtube.com/watch?v=J_egBKj1W08
mannykannot 3y ago
Three and a half hours later, a collective yawn from the west coast passed over the epicenter.

I'm in Brooklyn and felt it while on a call with an NJ resident who was the first to say "are we having an earthquake??" Do earthquakes have a propagation speed? Might she have felt it before me?

pxx 3y ago

Yes, the speed of sound (through the earth, so faster than the speed of sound in air); yes. In California, typically usgs has earthquakes posted before I can feel them. They didn't have this one a few minutes after I felt it, so I feel like automatic earthquake detection is off in this area of the US.

andrewla 3y ago
Same experience -- felt a shaking; thought maybe a heavy truck had passed by for a second, then saw that all the monitors were swaying. Checked USGS and saw nothing, so figured it was nothing, because on the west coast they have the reports up lickety split. Half hour later everyone's phone started buzzing with the automated alert.
gcr 3y ago
I received the earthquake alert about 45 minutes after it occurred.
- cj 3y ago
  The Apple alert came in at 12:05pm warning of aftershocks but not the primary event.
Lance_ET_Compte 3y ago
In the Bay Area, everyone gets an SMS message that says an earthquake is coming. I've felt/heard the shaking 10-20 seconds later. Some industrial equipment shuts down to avoid damage.
- nashashmi 3y ago
  We felt it at 10:26 am ET. And an alert was sent to everyone at 11:24 am that an earthquake is coming. And then another one alerting for possibility of aftershocks. No aftershocks felt.

pmx 3y ago

They travel in waves through the rock!

atrus 3y ago

Everything has a propagation speed :P, but yes she probably felt it before you, then her signal made it to you faster than the Earthquake did. https://xkcd.com/723/ https://xkcd.com/723/

jedberg 3y ago

Yes. There is an excellent XKCD on the topic: https://xkcd.com/723/ https://xkcd.com/723/ But in summary, the speed is slower than light, so yes you can find out through telecom faster than it getting to you.

pseudolus 3y ago

The earthquake was centered in NJ.[0] Propagation speed would be a function of the depth. [1] [0] https://www.google.com/maps/place/40%C2%B040'58.8%22N+74%C2%B045'10.8%22W/@40.683004,-75.4121796,9z/data=!4m4!3m3!8m2!3d40.683!4d-74.753?entry=ttu https://www.google.com/maps/place/40%C2%B040'58.8%22N+74%C2%... [1] https://www.britannica.com/science/seismic-wave https://www.britannica.com/science/seismic-wave

deleted 3y ago

[deleted]

aragonite 3y ago

> Might she have felt it before me? Surface waves yes, body waves not necessarily. But surface waves are more destructive.

ortusdux 3y ago

The west coast states have the MyShake early warning system, which sends out automated alerts for 4.5+ quakes. https://earthquake.ca.gov/ https://earthquake.ca.gov/

hi 3y ago

Same thing happened to me. I was on a facetime with someone in Brooklyn, but I was a 2 hour drive north outside of NYC and it took what felt like 30 seconds to propagate over that 200km.

paxys 3y ago

Earthquakes propagate very slowly (around 2-8 miles/sec). That's how systems like ShakeAlert can send out early warning notifications. This one, for example, happened 40+ miles from NYC proper, so residents could have had like 20 seconds notice if the service operated here. People further up or down the coast could have had multiple minutes.

slingnow 3y ago

Do you think that earthquakes transmit instantaneously? Why would they not have a propagation speed like everything else in the universe?

School-Cotton 3y ago
I assume they meant “propagation speed that is substantially slower than light in a vacuum” since that is less than 50ms between any two points on earth.
triceratops 3y ago
On the earth the speed of light as is good as instantaneous.
- quesera 3y ago
  > On the earth the speed of light as is good as instantaneous. Frustrated network architects would disagree!

eggy 3y ago

Sure given the epicenter was in NJ and closer than Brooklyn. I am from Brooklyn, but live in Nyack, NY, and I felt it here. Nyack is 40mi from epicenter, Brooklyn ~60mi. But your experience could be different based on the structure you are in, floor elevation, and existing soil and ground conditions.

Glant 3y ago

People in my town in southern NH reported feeling it about 20 minutes after it happened

spike021 3y ago

Yes. Last time there was a fairly large one in the SF Bay Area I happened to be on the phone with some relatives about 40 miles away and I felt an earthquake a moment before they did.

cossatot 3y ago

Earthquake waves have several propagation speeds, because there are different types of waves. The fastest is called the P-wave, which is a compressional (longitudinal) wave, similar to a sound wave, with a velocity of ~5-8 km/s for typical continental bedrock. The second fastest is the S-wave, or shear wave, which is about 65% of the P-wave speed. These waves produce relatively little displacement at the surface (except for close to the epicenter of large earthquakes) but are important seismologically. Then, there are the surface waves, which are caused by the interaction of the S-waves with the surface (in a way that I don't 100% understand). These travel about 90% of the S-wave speed, but they have the biggest displacements at the surface and therefore are the main ones that you feel and that cause damage. The surface wave displacements also get amplified in wet or loose soil, so the ground shaking and seismic damage is also much greater areas on top of sediment rather than bedrock. Areas on a river, lake or coast where the land has been extended into the water by dumping fill dirt are the worst--ground shaking is really bad and they are very prone to liquefaction. The difference between the arrival times (at any given point on earth) of the different phases of seismic waves is a function of the distance from the earthquake itself (the hypocenter) and the observation site. It is close to linear in Euclidian distance relatively near the earthquake hypocenter, but becomes more nonlinear farther from the earthquake, because the wave speeds are faster at depth (denser rock) so the travel paths of the wave fronts (the ray paths) are nonlinear. These differences in arrival times are one of the main ways of locating the hypocenter of an earthquake given observations from seismometers at multiple sites. It's essentially triangulation, except with time differences instead of angles--this is done through solving a system of equations. Additionally, S-waves can't pass through liquids, so there is the 'S-wave shadow zone' that occupies a large fraction of the side of the earth opposite an earthquake where there are no primary S-wave arrivals--S-waves are blocked by the liquid outer core. This is how we found out that the outer core is liquid!

bobthepanda 3y ago
Early warning systems also work by detecting P and S waves as close to the epicenter as possible.
neurostimulant 3y ago
Ground liquefaction is scary. Happened in Palu, Sulawesi a while ago. You can see houses moving as if they're on wheels: https://www.youtube.com/watch?v=J_egBKj1W08 https://www.youtube.com/watch?v=J_egBKj1W08

mannykannot 3y ago

Three and a half hours later, a collective yawn from the west coast passed over the epicenter.