New Madrid 1811-1812 Seismic Series > 6.0 Earthquakes

[bugalou]

I threw together this graphic to attempt to show the magnitude of the 1811-1812 New Madrid earthquakes. This graphic shows all earthquakes that occurred during this event that were > 6.0 along with the time and date in which they occurred.   I think many people forget this event wasn't just a single strong earthquake, it was many! Having such major quakes occur in such a small period of time, just a couple months, is part of what makes the New Madrid seismic zone so unique (along with being an intraplate fault system that can produce major earthquakes). While most other earthquakes have lots of aftershocks, some powerful, the events that happened here are pretty unusual in the amount of strong quakes produced.  Keep in mind this is ignoring the hundreds of smaller aftershock quakes that occurred for several months afterwards, many over 5.0. Part of the reason for all of this may be related to the how the stresses here are built up. Newer research shows it may actually be mantle flow creating the the stress on the fault system and not purely pressure from the lithospheric plate movement.

Needless to say a series like this occurring today would likely be the biggest natural disaster in US history.

[VandyMachine]

If that happened today. Middle Tennessee would get hammered too. No one around here even thinks of that as a possibility. Does Nashville even have earthquake building codes?

[NismoWx]

If that happened today. Middle Tennessee would get hammered too. No one around here even thinks of that as a possibility. Does Nashville even have earthquake building codes?

No, they don't. And I'd venture to guess that 99% of homeowners don't have EQ coverage, either.

[Thundersnow]

It gave me pause when I was once on a tour of a historic home in Franklin (just south of Nashville). It was built in the early 1800s (completed in 1809, I think it was). There were these bolts on the exterior wall with star-shaped nuts/caps that someone asked about.

The person who knew the history of the home said these were earthquake bolts for rods running through the walls and structure. They were put in to shore up the house after the structural damage from the 1811-1812 earthquakes. 

I then imagined the scope of the catastrophe in this area if such an event happened today.

[kevin]

Theoretically, if this were to happen today, what would be the outcome and what makes you think it would be the worst natural disaster in US history?

[StormNine]

Theoretically, if this were to happen today, what would be the outcome and what makes you think it would be the worst natural disaster in US history?

Widespread damage across Tennessee with severe to even catastrophic impacts for West TN and even into Middle TN (especially if you are on river sediment/unconsolidated tornado). Moderate damage all the way to at least Interstate 75 because there is no major mountain range to absorb the energy of the secondary waves. 

Impacts will vary depending on the location of the epicenter and intensity. If there is active river flooding then that will have more negative impacts. 

Widespread Disruption to the Economy (bridges knocked out, roadways destroyed, etc).

Widespread Power Issues

Widespread Damage/FEMA needs for at least 6 states

Now research is lowering the chance of a M6.0 earthquake in our lifetime still around 20-40%, but it is still a chance and is still something to clearly watch/prep.

Everyone should have a 4-7 day disaster prep/kit and not just for earthquakes but even derecho or tornado impacts could cause a need for an extended disaster kit.

   

[NismoWx]

Theoretically, if this were to happen today, what would be the outcome and what makes you think it would be the worst natural disaster in US history?

You should read the book 8.4 by Peter Hernon.   It was written 20+ years ago so some of the population/demographics data is inaccurate now, but it gives you a good idea of what might actually happen.

Complete fiction, of course, but it's a good read. I've actually read it a few times.

8.4 https://a.co/d/8KfcRjK

Sent from my SM-S908U using Tapatalk

[InMemphis]

I did a book report in 7th grade on 8.4 and it paints a downright scary picture for the Memphis area.

[bugalou]

Theoretically, if this were to happen today, what would be the outcome and what makes you think it would be the worst natural disaster in US history?

One aspect not mentioned is if bridges across the MS river stay standing. The i40 bridge was seismically retrofited and others to the north and south were built with seismicity in mind. They would likely survive a single event, but I am not sure if they would withstand what happened in in 1811/1812 even with the extra bits. The old bridge in Memphis may not survive a single event.  These bridges going down would be devastating for the entire country and cause shortages of goods from coast to coast, especially if more than one failed. It would also likely lead to a lot problems getting people help locally.

The good news is an 1811/12 event will more than likely not happen in our lifetime, but a ~6.0 is very possible, upwards of 40% by 2050. The "big" events like shown above seem to happen about ever ~400 years based on current research. That said, new faults that are related to the overall process going on here have been found in recent times (~past 3 decades) under eastern AR around Marked Tree, as well as in south eastern AR.  All of these may produce earthquake series all on their own with very little historic dating of events.  There is proof though the fault in SE AR has produced at least one major quake though in as there are big sand blows shown in soil studies that are too large to have been caused by quakes from the New Madrid fault.