A big one like this one in Chile on the New Madrid would absolutely obliterate Memphis and St. Louis
Fortunately the New Madrid Seismic Zone is physically incapable of generating an 8.8 magnitude earthquake.
Not so fortunate, especially considering that the shaking of New Madrid earthquakes of 1811-1812 was
ten times larger in area than the 1906 San Francisco earthquake and three times larger than the 1964 Alaska earthquake. Also, given how little is known about the actual fault system underlying this region, it's not possible to say that this zone is physically incapable of generating an 8.8 earthquake. The New Madrid quakes had a greater intensity over a greater area than any earthquake in recorded history (before 1973, at least) except for the three great earthquakes of India to which it was comparable and this was with a surface wave magnitude of only
7.5 on the Richter scale for the December 16, 1811 quake. Due to the harder, colder, drier and less fractured nature of the rocks in the earth’s crust in the central United States, earthquakes in this region shake and damage an area approximately 20 times larger than earthquakes in California and most other active seismic areas. Even though large earthquakes occur much less frequently in the NMSZ than in California, the long term average quake threat, in terms of square miles affected per century, is about the same because of the approximately 20 times larger area affected in the central United States
Most recent studies seem to indicate the NMSZ may be dying out, though have not gotten much media attention.
Overdue versus dying out.
The NMSZ appears to be about 30 years overdue for a magnitude 6.3 quake because the last quake of this size occurred 100 hundred years ago at Charleston, Missouri, on Oct. 31, 1895 (it was a magnitude 6.7). A magnitude 6.3 quake near Lepanto, Arkansas, on Jan. 5, 1843, was the next prior earthquake of this magnitude. About 75 percent of the estimated recurrence time for a magnitude 7.6 earthquake has elapsed since the last quake of this size occurred in 1812.
Pretty clear you haven’t read any of the more recent scientific literature on the NMSZ.
The actual estimated magnitudes magnitudes of the 1811-1812 quakes were greatly exaggerated some decades ago, but people still cling to them; the best recent estimates are by Susan Hough, USGS; The largest of the shocks is esitmated at Moment Magnitude 7.5, with others at 7.3, 7.0, and 7.0.
That’s still a substantial quake, but nowhere near the M 8-9 estimates you unfortunately see repeated again and again.
An 8.8 magnitude eartquake is indeed absolutely physically impossible in the NMSZ; such quakes ONLY occur and only CAN occur in subduction zones, because you need a sufficient planar area of the rupture zone to generate such massive magnitudes. NMSZ isn’t a subduction zone, and therefore, can’t. The same is true of the San Andreas - it can’t reach 8.8 either based on the simple physics of how long it is and the potential surface area of a rupture.
It’s true that the nature of the Midwest allows sesimic energy to propagage much further than in places like California.
But recent GPS work on the NMSZ indicates little motion and little stress building up:
http://www.sciencedaily.com/releases/2009/03/090313145956.htm
“New Madrid Fault System, U.S., May Be Shutting Down
ScienceDaily (Mar. 20, 2009) — The New Madrid fault system does not behave as earthquake hazard models assume and may be in the process of shutting down, a new study shows.
“A team from Purdue and Northwestern universities analyzed the fault motion for eight years using global positioning system measurements and found that it is much less than expected given the 500- to 1,000-year repeat cycle for major earthquakes on that fault. The last large earthquakes in the New Madrid seismic zone were magnitude 7-7.5 events in 1811 and 1812.”
Doesn’t mean there’s no earthquake threat in the Midwest (including other areas like the Wabash River, etc.) or from the NMSZ, but people tend to get a bit breathless and overexcited telling each other how New Madrid will destroy the Midwest.
If you’re talking about threats that don’t get enough attention the earthquake threats to places like Salt Lake City, Albuquerque, etc. probably are the ones that need hype at this point.