OT: Earthquakes: What Do You Know About Subduction?

[RutgersRaRa]

With today's earthquake getting many of us amped up, let's springboard off the event and do a deeper dive into what you geologists and others know about earthquakes. Given that earthquakes are typically the result of tectonic plates shifting, which forces one plate below or above the other, and given that the epicenter was "in" Lebanon, how far below the surface did the friction occur between the two plates to cause the surface to vibrate the way it did? IIRC, the earth's crust is not what moves, the plates below it do. And, how many feet of one plate would be forced under the other to generate an earthquake such as we experienced today?

Holy crap, just as I posted that we got an aftershock in Bedminster!!

 

[RUBigFrank]

Some deep shit

 

[nutfromSEC117]

 

[RUBOB72]

Yes another one at 6 pm but there have about 10-12 since first one.

 

[RutgersRaRa]

Yes another one at 6 pm but there have about 10-12 since first one.

I didn't feel the earlier aftershocks, but this one was like a three-second blast whose intensity was similar to the initial shock of the first quake.

 

[ashokan]

I read CA quakes are more likely to be acute in one discrete area (like San Fran).
The east coast is older and settled-in geologically so seismic waves are more dispersed (safer) and travel farther. Today's quake was felt in Boston.

 

[Kbee3]

I've felt none of them. Must be the ganja.

 

[Shelby65]

I read CA quakes are more likely to be acute in one discrete area (like San Fran).
The east coast is older and settled-in geologically so seismic waves are more dispersed (safer) and travel farther. Today's quake was felt in Boston

East coast is older ? So in its beginning, ‘before’ the west coast, what was in that space the west coast later comprised geologically ? Nothing ? Was the earth not spherical yet ? Was it shaped like Pac-Man ?

Time travelers would have fallen off the earth if they ventured west of the Rockies ?

 

[WhichReligionIsRight]

With today's earthquake getting many of us amped up, let's springboard off the event and do a deeper dive into what you geologists and others know about earthquakes. Given that earthquakes are typically the result of tectonic plates shifting, which forces one plate below or above the other, and given that the epicenter was "in" Lebanon, how far below the surface did the friction occur between the two plates to cause the surface to vibrate the way it did? IIRC, the earth's crust is not what moves, the plates below it do. And, how many feet of one plate would be forced under the other to generate an earthquake such as we experienced today?

Holy crap, just as I posted that we got an aftershock in Bedminster!!

The US Eastern Seaboard isn’t a subduction zone. The tectonic plates are in the middle of the Atlantic Ocean and along the West Coast. There are fault zones everywhere, including the Ramapo Fault. The earthquakes were probably related to some settling of the Appalachian Mountains.

 

[WhichReligionIsRight]

I read CA quakes are more likely to be acute in one discrete area (like San Fran).
The east coast is older and settled-in geologically so seismic waves are more dispersed (safer) and travel farther. Today's quake was felt in Boston.

The US West Coast lies on the boundary of two tectonic plates so is prone to be more frequent and intense shocks. In addition, there is a lot of sediment sitting on top of the bedrock out west many more active (and ever-changing) faults. But I would wager that a 6.9 Earthquake hitting NJ would do comparable amounts of damage as has occurred in California - maybe worse because earthquake-resistant building codes are enforced in California.

 

[Joey Bags]

This was a relatively rare intraplate quake. We are in the middle of the North American Crayton, which is comprised of old, dense rock. When a quake happens inside this region it’s like a bell ringing, and can be felt extremely far away from the center.

The fault lines like New Madrid and those in NJ are extremely old, and tend to produce quakes based on external pressures to the plate boundaries hundreds or thousands of miles away. Another theory revolves around fluid build up under the plate itself which releases pressure via ancient faults from long ago.

 

[ashokan]

East coast is older ? So in its beginning, ‘before’ the west coast, what was in that space the west coast later comprised geologically ? Nothing ? Was the earth not spherical yet ? Was it shaped like Pac-Man ?

Time travelers would have fallen off the earth if they ventured west of the Rockies ?

The oldest rocks in the world come from Newfoundland. Eastern area of Canadian shield and North America has ancient metamorphic rock. Scotland and America used to be joined together and separated 60 million years ago. Earth has been a very dynamic place geologically. Newer rock comes from middle of ocean. In some places you find the oldest rocks on top of newer rocks because of the churn/collision forces. Old rocks resurface from below to overlap newer rocks. The Scottish highlands and Appalachians are from the same mountain range.

CA used to be a passive geological continental zone but it transitioned into an active margin with a lot of sedimentary rock typical of land that used to be under an ocean (as much of CA was)


"Precambrian rocks in Newfoundland and Labrador include some of the oldest rocks on Earth, dating back to 3.8 billion years ago (Ga). The Precambrian sedimentary, igneous, and metamorphic rocks of this province make up the eastern part of the Canadian Shield. Laurentia (North America) was surrounded by shallow seas of the Iapetus Ocean, covering part of the Island of Newfoundland. Other parts of Newfoundland were located off the coast of Gondwana at this time, and they preserve rare fossils of soft-bodied animals."

http://paleoportal.org/index.php?globalnav=time_space&sectionnav=state&name=Newfoundland%20and%20Labrador

 

[ashokan]

AN interesting Youtube vid shows how older rock ends-up on top of newer rock (12 minutes in). It also shows how Scotland and Loch Ness were created. Loch Ness has is one of those straight line formations that are also in Newfoundland

 

[Shelby65]

Is it not true that all areas of earth are equally old but only the geologic ages of the surface lands differ ?

Tectonic actions reshape the surface but there was always something in the area you describe as west. The age of the earth is the same everywhere.

I know what Ashokan meant but I dont think he phrased it accurately. He didn’t mention rocks.

 

[RUTGERS95]

I read CA quakes are more likely to be acute in one discrete area (like San Fran).
The east coast is older and settled-in geologically so seismic waves are more dispersed (safer) and travel farther. Today's quake was felt in Boston.

more to do with type of surface rock, clay, surface water, etc etc than age as but you are right, there are some 'older' areas due to plate movement (I forget the term they used when learning this in school).

it's all quite fascinating really

 

[RUTGERS95]

Is it not true that all areas of earth are equally old but only the geologic ages of the surface lands differ ?

Tectonic actions reshape the surface but there was always something in the area you describe as west. The age of the earth is the same everywhere.

I know what you meant but I dont think you phrased it accurately. You didn’t mention rocks.

yes

 

[Source]

Believe it or not, one of the worst earthquakes in the U.S. and East Coast history occurred in Charleston, South Carolina in 1886. Most earthquakes, as stated in this thread, are interplate earthquakes. But there is a far more devastating and rare type quake called an intraplate earthquake where the energy build up provides a far more devasting punch. This is what happened in Charleston on August 31, 1886.

But the people of New Brunswick and Rutgers were sympathetic. They put on a charity baseball game that brought back local players from town teams and Rutgers as far back as the 1850s. Over 800 watched "old fashioned" baseball and had a great time including D.D. Williamson, an original 1869 Rutgers football player.

According to the September 11, 1886 Daily Fredonian (of New Brunswick), "The proceeds of the game will net nearly $100, and Mayor Strong will forward the amount to Charleston to-day. The following contributions have been sent to Cashier Campbell of the First National Bank'; Dr. John Woodbridge $5.00; Rev. W.J. McKnight $5.00; Three Little Girls $3.00; Lieut. J.T. Huneycutt $2.50; Terrill & Hoagland $2.00 Dr. Austin Scott (five years prior to being Rutgers President) $2.00
Total: $19.50”

 

[ashokan]

Is it not true that all areas of earth are equally old but only the geologic ages of the surface lands differ ?

Tectonic actions reshape the surface but there was always something in the area you describe as west. The age of the earth is the same everywhere.

I know what Ashokan meant but I dont think he phrased it accurately. He didn’t mention rocks.

I learn this stuff falling asleep to youtube vids - the good ones wake-me up lol.
All I know since the quake is that seismic waves travel further in the Northeast because the rock under NE is "old, cold and dense" - its been settled, layered and healed-up different from CA.

" More than 150,000 people reported feeling the New Jersey earthquake, some from several hundred miles away, according to the United States Geological Survey, which collects reports of shaking. While the number of reports reflects the population density of the area, it also highlights a fundamental geological difference between the tectonically active West Coast and the East Coast, which is covered by old faults that occasionally get reactivated.

The underlying rock in the East Coast is old, cold and dense, and the faults have had time to heal, meaning that seismic waves travel farther than on the West Coast, where the crust is broken up by faults."

Why the New Jersey earthquake was felt several hundred miles away​

https://www.washingtonpost.com/science/2024/04/05/earthquake-new-jersey-new-york-why/

 

[Source]

East Coast earthquakes aren’t common, but they are felt by millions. Here’s what to know​

East Coast earthquakes aren't common, but they are felt by millions. Here's what to know

Earthquakes large enough to be felt by a lot of people are relatively uncommon on the East Coast. Since 1950 there have only been about 20 quakes with a magnitude above 4.5, according to the United States Geological Survey.

apnews.com