M4.7 Earthquake Hits Puerto Rico in Rare and Frightening Swarm of More Than 1,100 Quakes

[Elderberry]

Strange Sounds 1/3/2020

A 4.7-magnitude earthquake hit Puerto Rico on January 2, 2020 in the latest of a rare string of quakes that has frightened many in the U.S. territory.
“We haven’t stopped shaking. It’s the first time something like this happens,” said the emergency management director for the southern coastal town of Ponce.

The most recent quake occurred eight miles south of Guayanilla at a shallow depth of four miles and was felt in the capital of San Juan and elsewhere in Puerto Rico. It was reported by more than 320 people on the USGS website.

The quake swarm began on December 28, with a M4.7 followed by a M5.1 tremor that hit near Puerto Rico’s south coast and sent dozens of panicked people into the streets.

These first two jolts made goods fall off supermarket shelves, created cracks in homes, and triggered a large rock to fall and block a road. No injuries were reported.

Meanwhile, more than 1,100 earthquakes have been recorded in that region. Most have not been felt, except for a M4.2 on December 31 and that of yesterday.
Officials baffled by the Puerto Rico earthquake swarm

“I’ve spent 29 years with Puerto Rico’s Seismic Network, and it’s the first time I observe this kind of activity,” director Víctor Huérfano told The Associated Press. “There’s no way to predict when it’s going to end, or if it’s going to lead to a major event.“

“In general, the force behind all of this is the North American plate and the Caribbean plate squeezing Puerto Rico,” he said.

More: https://strangesounds.org/2020/01/puerto-rico-earthquake-swarm-2019-2020.html


Earthquake swarm in Puerto Rico 2019-2020.

[Smokin Joe]

All this time, wasted effort, has been over a typo....

The biggest threat is Global Worming.



More seriously, I wonder if there is a magma chamber on the move...

[Victoria33]

bkmk

[Elderberry]

4.5 quake hits Puerto Rico amid rare seismic activity

660 City News by DáNica Coto 1/2/2020

https://www.660citynews.com/2020/01/02/4-5-quake-hits-puerto-rico-amid-rare-seismic-activity/

“I’ve spent 29 years with Puerto Rico’s Seismic Network, and it’s the first time I observe this kind of activity,” director Víctor Huérfano told The Associated Press. “There’s no way to predict when it’s going to end, or if it’s going to lead to a major event.”

He said the flurry of quakes have been extremely superficial and have occurred along three faults in Puerto Rico’s southwest region: Lajas Valley, Montalva Point and the Guayanilla Canyon.

“In general, the force behind all of this is the North American plate and the Caribbean plate squeezing Puerto Rico,” he said.

A similar cluster of quakes occurred last year along Puerto Rico’s northwest coast following a 6.0-magnitude earthquake in late September that led to more than 1,200 quakes in that area, Huérfano said.

One of the largest and most damaging earthquakes to hit Puerto Rico occurred in October 1918, when a 7.3-magnitude quake struck near the island’s northwest coast, unleashing a tsunami and killing 116 people.

[GtHawk]

“I’ve spent 29 years with Puerto Rico’s Seismic Network, and it’s the first time I observe this kind of activity,” director Víctor Huérfano told The Associated Press. “There’s no way to predict when it’s going to end, or if it’s going to lead to a major event.“


Odd that just a little further down they have another quote from him

A similar cluster of quakes occurred last year along Puerto Rico’s northwest coast following a 6.0-magnitude earthquake in late September that led to more than 1,200 quakes in that area, Huérfano said.

[roamer_1]

More seriously, I wonder if there is a magma chamber on the move...

Alright Joe... I dunno how geology intersects tectonics, but could it not be true that these swarms are healthy? That they are a relieving of pressure? I thought in general that the wicked quakes come when things can't move, and pressures can build up... Wouldn't then a series of smaller quakes indicate movement that is relieving the pressures needed for a larger quake?

[Elderberry]

I would think that when a long period of time goes by with very little quake activity, It must mean there is very little movement. Then when a lot of little quakes occur, then there is movement between the plates. So when the little quakes stop occurring, does it mean the movement has stopped or does it mean that energy is now building up for a large quake?

[DB]

Alright Joe... I dunno how geology intersects tectonics, but could it not be true that these swarms are healthy? That they are a relieving of pressure? I thought in general that the wicked quakes come when things can't move, and pressures can build up... Wouldn't then a series of smaller quakes indicate movement that is relieving the pressures needed for a larger quake?

That's a mixed bag. When some place moves often and someplace else not far way doesn't the strain increases in that locked location increasing the odds of something big happening.

[roamer_1]

That's a mixed bag. When some place moves often and someplace else not far way doesn't the strain increases in that locked location increasing the odds of something big happening.

 

[Smokin Joe]

Alright Joe... I dunno how geology intersects tectonics, but could it not be true that these swarms are healthy? That they are a relieving of pressure? I thought in general that the wicked quakes come when things can't move, and pressures can build up... Wouldn't then a series of smaller quakes indicate movement that is relieving the pressures needed for a larger quake?

You are right in that small quakes relieve stresses in a less catastrophic fashion. It could be a good thing, o long as those stresses relieved aren't transferred into a major fault. The Island is pretty much crisscrossed with faults, so a little movement might cause a lot of reshuffling, creating the swarm of quakes. 
Geologic Map showing (known) faults: https://mrdata.usgs.gov/geology/pr/map-pr.html

The black lines are faults, and there are a lot of them.

The island is adjacent to the Puerto Rican Trench, and composed primarily of volcanic and volcaniclastic rocks, the latter technically sedimentary rocks formed by and from ejecta from volcanoes or eroded volcanic rock, surrounded by a halo of carbonate rock (likely Limestone) formed by marine organisms.

The primary question is one of whether this is simply part of the usual bump and grind along plate boundaries, or if something deeper is on its way. Without additional data indicating volcanic activity, chances are, with the complex nature of the fault network there it is just stress relief along multiple faults caused by a plate shift.
The question then, is where did that stress go, and is it now bound along a major fault and building for later release in a stronger event?
For Puerto Ricans, it is likely much better to have multiple small quakes than one big one, as the damage will be less and fewer people will be injured.

[roamer_1]

You are right in that small quakes relieve stresses in a less catastrophic fashion. It could be a good thing, o long as those stresses relieved aren't transferred into a major fault. The Island is pretty much crisscrossed with faults, so a little movement might cause a lot of reshuffling, creating the swarm of quakes. 
Geologic Map showing (known) faults: https://mrdata.usgs.gov/geology/pr/map-pr.html

The black lines are faults, and there are a lot of them.

The island is adjacent to the Puerto Rican Trench, and composed primarily of volcanic and volcaniclastic rocks, the latter technically sedimentary rocks formed by and from ejecta from volcanoes or eroded volcanic rock, surrounded by a halo of carbonate rock (likely Limestone) formed by marine organisms.

The primary question is one of whether this is simply part of the usual bump and grind along plate boundaries, or if something deeper is on its way. Without additional data indicating volcanic activity, chances are, with the complex nature of the fault network there it is just stress relief along multiple faults caused by a plate shift.
The question then, is where did that stress go, and is it now bound along a major fault and building for later release in a stronger event?
For Puerto Ricans, it is likely much better to have multiple small quakes than one big one, as the damage will be less and fewer people will be injured.

Right... I kinda get all that - Like river ice at the beginning of breakup... One big chunk will break off and take a bunch of littler chunks with it... But not only can all those chunks get balled up downstream, putting weight on an edge that was otherwise fine, but where they broke off is now exposed, and that edge may not be willing to resist like it had before... Thus @DB 's complications... All you can be sure of is that the river will continue to apply pressure, good, bad, or indifferent...

[Smokin Joe]

Right... I kinda get all that - Like river ice at the beginning of breakup... One big chunk will break off and take a bunch of littler chunks with it... But not only can all those chunks get balled up downstream, putting weight on an edge that was otherwise fine, but where they broke off is now exposed, and that edge may not be willing to resist like it had before... Thus @DB 's complications... All you can be sure of is that the river will continue to apply pressure, good, bad, or indifferent...

A great analogy. Chances are that if one plate stopped in a fixed position on the globe, the momentum of the rest would create even more catastrophic events than all of them jostling for position.

[roamer_1]

A great analogy. Chances are that if one plate stopped in a fixed position on the globe, the momentum of the rest would create even more catastrophic events than all of them jostling for position.

@Smokin Joe @DB

Thanks