M7.7 Jamaica Quake: Surface Waves Coming Soon

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Discussion Overview

The discussion revolves around the Mw 7.7 earthquake that recently occurred near Jamaica, focusing on its seismic characteristics, potential impacts, and comparisons to other seismic events in the region. Participants explore the nature of the earthquake, its depth, and the tectonic settings involved, as well as the immediate responses and media coverage.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant reports detecting the earthquake on their seismograph, noting that surface waves have not yet arrived.
  • Several participants express concern about the earthquake's magnitude and proximity to Jamaica, questioning whether the epicenter is on the island.
  • There are no immediate reports of serious injuries or damages, although the quake was felt as far away as Miami.
  • Another participant mentions the earthquake's shallow depth of 10 km and provides geographical context regarding nearby locations and populations.
  • Some participants speculate on the relationship between this earthquake and a previous magnitude 6.4 earthquake in Puerto Rico, discussing the tectonic settings of both events.
  • One participant describes the Jamaican earthquake as primarily strike-slip with some oblique slip, while contrasting it with the Puerto Rican event, which involved back arc extensional motion.
  • There is a request for clarification on the term "back arc extensional motion," leading to a description of the geological features associated with this tectonic setting.

Areas of Agreement / Disagreement

Participants express varying degrees of concern regarding the earthquake's impact, with some emphasizing the lack of immediate damage reports while others highlight the potential for significant effects. There is no consensus on the relationship between the Jamaican and Puerto Rican earthquakes, as participants present differing views on their tectonic connections.

Contextual Notes

Participants reference various sources for information on the earthquake, but there are limitations in the data regarding the full extent of damage and the geological implications of the events discussed. The discussion includes assumptions about the relationship between tectonic events that remain unresolved.

davenn
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TL;DR
Jamaica quake
Mw 7.7 quake coming in on my seismograph now

http://www.sydneystormcity.com/seismograms.htm

The surface waves have not arrived yet ( at time of writing this) they will probably max out the display
 
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Gads, that's big. How close to the island is the epicenter, or is it ON the island?
 
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phinds said:
Gads, that's big. How close to the island is the epicenter, or is it ON the island?

from the USGS map ...

200128 M7.7 offshr Jamaica.jpg
 
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davenn said:
Summary:: Jamaica quake

The surface waves have not arrived yet ...
Yeah, there is always some delay of time on Jamaica ...

1580245868047.png
 
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Can't be too serious - hopefully. CNN international still covers the current farce in DC, German news channels have breaking news a) new Corona infections b) Jamaica 7.7 no damages reported so far, and another one has only the usual irrelevant news in the ticker. And @berkeman's link speaks of a possible 3ft (1m) tsunami.
 
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https://earthquake.usgs.gov/earthquakes/eventpage/us60007idc/executive
Fairly shallow at 10 km.
  • Lucea, Hanover, Jamaica125.9 km (78.2 mi) SSE, Population: 6289
  • Montego Bay, St. James, Jamaica139.1 km (86.5 mi) SE, Population: 82867
  • Niquero, Granma, Cuba140.3 km (87.1 mi) ENE, Population: 18771
I wonder how it relates to the Mag 6.4 earthquake in Puerto Rico. Seems to be same fault system.
https://earthquake.usgs.gov/earthquakes/eventpage/us70006vll/executive
https://www.usgs.gov/news/magnitude-64-earthquake-puerto-rico
 
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Astronuc said:
I wonder how it relates to the Mag 6.4 earthquake in Puerto Rico. Seems to be same fault system.

Same plate boundary, yes. But there's over 1000km between the 2 events, so kinda like asking if a quake
near Mexico City is related to a quake in Los Angeles.
The Puerto Rico was south of the plate boundary, by some 200km, but the Jamaican event was on the boundary.

The Jamaican event was primarily strike-slip, with a little oblique slip component
The Puerto Rican event was a back arc extensional motion (normal faulting)

so both events had a very different tectonic setting

Dave
 
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davenn said:
back arc extensional motion
Interesting. Please explain what that means. Or maybe a graphic.
 
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anorlunda said:
Interesting. Please explain what that means. Or maybe a graphic.

OK ... A belt of extensional tectonics is a very common feature behind (back from) a subduction
trench. Because of the extensional ( pulling apart) action the crust thins creating a basin and volcanism
is the common result, eg the Taupo Volcanic Zone (TVZ) in the North Island of New Zealand and many
other places around the world. The back arc basin can be on land or in the ocean depending on how
mature the island arc is.
di-5584-gns.jpg


in the caldera, you can see the faults that angle inwards from either side. These are the extensional
(normal) faults.

((I had another couple of images to upload, but the forum is on a go-slow again for me and refuses to
upload files I will do so when it starts working properly again)))https://en.wikipedia.org/wiki/Back-arc_basin
 
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A single normal fault
extension (normal) fault.jpg

now multiple versions of the above to form a basin with a thinned crust
basin faulting.jpg

Dave
 
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