Benchmarks in a seismically active zone

[jfc]

I moved to LA from rock solid stable Chicago a couple of months ago and the little earthquake today got me thinking. Since LA is on a different techtonic plate than the rest of the country, which apparently moves northwards 2 inches per year, how do they set the coordinates on permanent benchmarks? Are they resurveyed every once in a while, or does everything on the Pacific plate just stay the same relative to itself.

How about projects that straddle the plates? Wouldn't railroads or pavements buckle with the differential movement? Someone in my office was saying that City Hall is 12 feet closer to San Francisco than when it was built in the 20s.

 

[kevo_55]

You are correct, the benchmarks are in some sort of constant motion and will change over time.

While I don't have any good answers for you, you might want to check this website out: http://www.nehrp.gov/

This is the basis of all structural seismic design.

 

[Casey]

I think they just eye-ball it.

 

[sehad]

I think they just eye-ball it.

Now you know that no engineer would ever do that

 

[Dexman1349]

Now you know that no engineer would ever do that

lol, but a surveyor might...

 

[EM_PS]

^^ Puh-leeezee!! are there any engineers who truly 'get' geodesy & GNSS? Oh right, they're referred to as geomatic engineers (more typ as surveyors)

jfc, the control networks are likely reobserved at least on a yearly basis by NGS or whoever maintains the geodetic networks, similar to vertical benchmarks in New Orleans area, which continues to subside over time.