reply to post by justsaying
Glad to be of some help. Just to make sure that mods know this is on-topic to some degree
, that report gives a lot of detail about possible
effects of a quake in the Arkansas region...
Now, back to your main point about Memphis. That city is a worry because of its low-lying position (relative to the river) and also and relatedly,
because of the risk of soil liquefaction combined with the high population density and a large number of buildings that aren't really designed to
withstand major quakes (or liquefaction events).
The USGS has some excellent info within its section entitled the Memphis Earthquake
. On that linked page, there are further links to more specific data and maps that detail the various quake-related hazards for
the Memphis region.
Any areas around there that have been artifically filled (ie "reclaimed" land) are basically unknown quantities because they're "geologically" so
recent and so historic data is lacking, but I for one wouldn't want to be living on Mud Island, for example. In the event of a big quake that will be
shaken pretty badly and I'd expect a lot of problems with the ground there.
The other problem with Memphis is that there is plenty of evidence in the region of the river changing course in the past. We could guess that most of
the time this was due to natural flood events, but on the other hand a major quake might also affect the river's course or at least cause significant
flooding. We only need to recall the tragic quake in Christchurch, New Zealand just a few weeks ago and the flooding there that resulted from
liquefaction and distrubances to the ground water table.
These are the sorts of things that the researchers took into account when they considered Memphis. Frankly I suspect they were cautious in their
estimates (which is fair enough), for the true outcome would be heavily dependant on so many factors, such as the time of year (in regards to river
height and hence ground water levels), the time of day (with daytime on a weekday generally considered the worst), and even the specific hour of the
day: a quake at peak hour in the morning would be very bad news indeed, as so many people would be on the roads or just arriving at work or school.
Much of these assessments would be applicable to other regions in the New Madrid fault region, and so studying the local conditions is well worthwhile
for anyone who lives in that part of the US of A.
My hope is that things will stay quiet for a good long while yet, giving both the authorities more time to prepare and people and govt agencies to
take action to retro-fit buildings and upgrade infrastrucures (where possible), in an attempt to reduce the potential impacts of any big quake.