The Great Southern California Shakeout thread

[NorthSideSox72]

The New Madrid Fault system is an odd one. It exists right in the middle of a plate, where it's difficult to get big earthquakes. But it's certainly there, and troublesome.

 

I've never really liked the studies I've seen on that one because most of them seem like they rate the recurrence interval too low, they tend to be a little too alarmist for the match I do in my head. I think about a 500 year recurrence interval for magnitude 8 events seems reasonable, and there are some numbers out there that say that. It's been 200 years since the last big one, but the last big one was a swarm of about 4 magnitude 7-8 events.

 

It's fairly likely that there will be a magnitude 6, slight damage, annoying type event on that system within the next 50-100 years. I think the next big one there is probably a couple hundred years off, but with faults, it's really hard to say that for sure. It could have a recurrence interval of 500 years, move 3 times in 200 years and then decide not to move again for 1500 years. You've got probably a 5% chance in the next 50-75 years of having another magnitude 8 event on that fault. On the other hand, the Southern San Andreas has probably a 95% chance of going within the next 50 years.

I realize I'm about to try to argue with a geologist about geology, but, I feel I should point this out.

 

A magnitude 6 event on the New Madrid, depending on depth, is likely to be a lot more than an annoyance. Its likely to be a killer. Unlike in Cali, the earth around the New Madrid is not a lot of broken rock - its a sandy-soil plain, basically. That means that the waves coming off the quake through the earth will dissipate much more slowly, and in fact in some areas will be amplified. Some of these "liquification zones" exist in Cali too of course, as I am sure you know. But the enture basin along the Mississippi in that area is one big flat liquification zone. Energy transference is much more efficient there, than in the angular and broken mountains in California. The zones of effect are pushed much further away from the epicenter.

 

According to the info disseminated by U of Memphis' school of geology when I lived down there, a mag 6 event, if near the southern end of the zone, could be deadly. It would cause fairly extensive damage in Memphis and much of the surrounding area. Obviously not on the scale of a 7 or 8 event, which would be truly catastrophic. But still lots and lots of damage, and human casualties would result, even from a 6.

 

 

[Balta1701]

Hey is our Aussie still in Australia? Because I'm in the background behind a blonde Australian reporter today.

[Balta1701]

If you've got a broadband connection, these are really, really cool computer simulations of the ground shaking associated with this event.