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Strong quakes in Puerto Rico (1 Viewer)


bjdeming

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Per the USGS Earthquake Map, Puerto Rico has had these today (at the time of writing, most recent listing last:

M6.4, M5.6, M5.0, M4.5, M5.6, 4.5, 4.6.

They're all shallow, too, and apparently just off the coast. The 6.4 caused small (0.1-foot) tsunami. Per the Miami Herald, local news reports 1 dead, 1 injured, and extensive damage.

And yesterday, reportedly an M5.8 knocked down a local natural landmark.

Hopefully, all the energy for this episode has been released. Looking at the maps accessible via the USGS map link, it looks to me as though like anything bigger would cause tsunami problems for the Caribbean rather than the Gulf.
 

bjdeming

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OK, not all of them are offshore, per this source. (This is a different set of seismologists, so their magnitude values may not correspond to those from the USGS, but the difference will probably be slight; this does show that there are a lot of smaller earthquakes ongoing, too.)
 

WesL

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They have had a rough few days.

Here is some updated info from USGS -

On Jan. 7, a magnitude 6.4 earthquake struck the region at 4:24 am local time (08:24:26 UTC). Significant damage is possible. Over the past several weeks, hundreds of small earthquakes have occurred in the Puerto Rico region, beginning in earnest with a M 4.7 earthquake late on December 28 and a M 5.0 event a few hours l

The magnitude 6.4 earthquake was widely felt. According to ShakeMap, strong to very strong shaking occurred across parts of Southern Puerto Rico closest to the event and moderate shaking occurred across the rest of the island. The NOAA Tsunami Warning System states no tsunami warning or advisory. The USGS summary page on this earthquake includes an aftershock forecast. Aftershocks will continue near the mainshock.

Over the past several weeks, hundreds of small earthquakes have occurred in this same region, beginning in earnest with a M 4.7 earthquake late on December 28 and a M 5.0 event a few hours later. Since the M 4.7 event, over 400 M 2+ earthquakes have occurred in this region, ten of which were M 4+, including today’s M 6.4 event and yesterday's 5.8 quake. The preliminary location of today's 6.4 earthquake is within about 7.5 miles (12 km) of the January 6, 2020, M 5.8 earthquake. The proximity of these events to Puerto Rico, and their shallow depth, mean that dozens of these events have been felt on land, though with the exception of the latest two earthquakes, the M 6.4 and the M 5.8, none are likely to have caused significant damage.

The January 6 and 7, 2020, M 5.8 and M 6.4 earthquakes offshore of southwest Puerto Rico occurred as the result of oblique strike slip faulting at shallow depth. At the location of this event, the North America plate converges with the Caribbean plate at a rate of about 20 mm/yr towards the west-southwest. The location and style of faulting for the event is consistent with an intraplate tectonic setting within the upper crust of the Caribbean plate, rather than on the plate boundary between the two plates.

Tectonics in Puerto Rico are dominated by the convergence between the North America and Caribbean plates, with the island being squeezed between the two. To the north of Puerto Rico, North America subducts beneath the Caribbean plate along the Puerto Rico trench. To the south of the island, and south of today’s earthquake, Caribbean plate upper crust subducts beneath Puerto Rico at the Muertos Trough. The January 6 earthquake, and other recent nearby events, are occurring in the offshore deformation zone bound by the Punta Montalva Fault on land and the Guayanilla Canyon offshore.

 

WesL

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Still a lot of shaking going on in PR. 64 earthquakes over Magnitude 2.5 in the last 24 hours.

Link to live map -
1578498313636.png
 

Lori

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I’ve a friend with family there, communication is still iffy from Hurricane Maria, this has helped matters to their already compromised infrastructure! Prayers for PR!!
 

bjdeming

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Here are some updates from PR on the StormCarib site.

And the USGS reported today that there's a slight chance of a stronger shock. They are also deploying more sensors.

If there's any good news here, it's that the big quake happened on a strike/slip fault: sideways motion, for the most part (there were some small tsunami reported). This isn't the vertical movement associated with subduction zone megaquakes.

Wonder if the Arecibo telescope was affected. I had just read, around the end of the year, that they had finally got it fully operational again after Maria. A quake in 2014 damaged it, but that was on the northern side of the island. Haven't been able to find anything about it in the online news.
 
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bjdeming

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I know this is a heads-up (or heads-ducked) weather situation today, but also in the last 3-1/2 hours Puerto Rico has had an M5.9 plus six quakes that were M4.0 or more.

The geology and tectonics of this region are SO complicated. But that's not the usual pattern after a large earthquake. The USGS has their sensors on the island and were installing them yesterday, per the site linked above. Hopefully they can get them up and running ASAP and get a little more insight into what is happening just offshore and/or underneath this active area.

Puerto Rico has been hit by what scientists call an earthquake swarm, which is a series of earthquakes rather than the usual pattern of one dominant earthquake followed by aftershocks," John Vidale, a seismologist at the University of Southern California, told USA TODAY.

"We don’t well understand why the larger earthquakes continue for a while," he said. "It may have to do with slow slip on faults in the area or perhaps the hydrology of the fault system."

-- Source
 

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