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Damn damn damn, a major subduction zone earthquake is not what this week needed. Red pager alert - likely high damage for large population.
A subduction zone is when an oceanic tectonic plate is slipping under another tectonic plate. This particular region is a messier story. 
The tl;dr is this was a big (M8.1), deep (70km) earthquake that produced very strong to violent over a wide region for tens of seconds.
The half-duration is currently estimated at 37.35s: That means it took over 37sec for the fault to slip & tear. The shaking lasted longer.
Pager Alerts are automated notices of estimated casualties & damage based on impacted cities. This is a Red Alert: large population exposed
In tiny mercies, the worst shaking was confined to smaller towns the coast: under a million people felt severe or worse shaking.
It also looks like the earthquake didn't have a lot of vertical motion:
A tsunami warning is in play nearby (tsunami.gov), but minimal vertical movement means it was small (~1.5m on local buoys)
Unfortunately, a quirk of geology (sediment-filled basin) means any earthquake shaking is amplified in Mexico City.
All this happened an hour ago (how dare I go offline & silence alerts?!) & we won't get proper damage assessments until morning.
Multiple tips of "earthquake lights" videos. <3
Thar be contested science; no widespread agreement on explanation.
Thar be contested science; no widespread agreement on explanation.
Earthquake lights have moved from myth to phenomena thanks to widespread video. Something about big quakes can ionize the atmosphere.
Main theories
1. Breaking rocks releases ionized oxygen
2. Breaking quartz generates piezoelectric field
3. Grinding rocks generates voltage
1. Breaking rocks releases ionized oxygen
2. Breaking quartz generates piezoelectric field
3. Grinding rocks generates voltage
Ionization, piezoelectricity, & triboluminescence all observed on small scales in lab setting, but... real life is complicated.
But... we're in an enormous geomagnetic storm, thunderstorms are everywhere in the region, & damaged electrical grids can spark like fiends.
With all the satellites overhead storm-watching, hopefully one with the right gear was overhead for more data on the lights.
Nice to see Mexico's earthquake early warning system being useful! (California, please fully fund your system.)
Earthquake early warning systems don't predict earthquakes. They trigger off initial sharp P-wave to warn of impending S- & surface waves
P-waves are faster than S-waves. Farther from epicenter, P-waves race ahead so time-gap between P- & S-waves grows, increasing warning time.
Although 10-90sec warning doesn't sound like much, it's enough to pause surgery, lock subways, pull over, flee kitchen, toggle dams, & more.
In places with robust building codes, heart attack is one of the leading causes of death during an earthquake. Any warning helps mitigate.
Q: Why is depth changing?!
A: Revisions as more data rolls in. I outsourced explaining to Steve. Thread:
A: Revisions as more data rolls in. I outsourced explaining to Steve. Thread:
Early warning applied tonight in Mexico:
As with all disaster warning systems, false positives carry a huge risk of undercutting credibility. Every success makes me happy.
Q: Did the hurricanes trigger the earthquake?
A: No, too far apart
Q: Can hurricanes ever trigger earthquakes?
A: ...maybe? Research unclear
A: No, too far apart
Q: Can hurricanes ever trigger earthquakes?
A: ...maybe? Research unclear
Preliminary research indicates possibility of hurricanes triggering earthquakes. Maybe.
smithsonianmag.com/smart-news/hur…
news.nationalgeographic.com/news/2011/11/1…
smithsonianmag.com/smart-news/hur…
news.nationalgeographic.com/news/2011/11/1…
Q: Will M8 Mexico earthquake trigger California's Big One ?
A: No, too far away
Q: Will it trigger aftershocks?
A: Yes, stress redistributes
A: No, too far away
Q: Will it trigger aftershocks?
A: Yes, stress redistributes
When a fault slips, it releases stress on bit that moved, but increases stress on locked ends.
More stress = more risk
Exe: 2010 in a Baja
More stress = more risk
Exe: 2010 in a Baja
Aftershocks exponentially decrease in magnitude & frequently as stress redistributes in the region and surrounding faults readjust.
Q: Does any of this relate to seeing Irma's seismic signature?
A: Not really, but that's a cool story. Thread:
A: Not really, but that's a cool story. Thread:
Ugh misplaced tweet adrift from thread:
Seismic waves are sound waves (simplification lie), so once quake detected, notification races ahead
Seismic waves are sound waves (simplification lie), so once quake detected, notification races ahead
Last night's Mexico earthquake placed in historical context: quakes trace out shape of the subducting slab.
Mexico City is in a sediment-filled basin. Seismic waves of any nearby earthquake amplify in the geologic goo.
Amplification effect is so bad that historical geophysicists mistook Mexico City for quake epicenter because it had worst shaking.
Q: What's the different between the seismic signal of a hurricane and an earthquake?
A: Shape & energy.
A: Shape & energy.
Seismic waves travel globally, even when humans can't feel them. Impact on well water levels in Virginia:
Huh. All the aftershocks so far are ~M5, largest was M5.7. I would've expected a M7 & a few M6 in the first few hours.
Seismograph emphasizes the logarithmic scale: M8.1 is 250x bigger amplitude than M5.7, releasing 3980x more energy.
Oh cool! Quake early warnings racing ahead of fast P-wave (purple), slower damaging S-waves (yellow). via @ffloresm
Another nice visualization out of Puerto Rico on hurricane vs earthquake seismic signals:
