Re: Experts split over quake risk

The article only mentions one of three sources of error-
the GPS measurements themselves. Getting down to
millimeters per year is tricky. Any individual GPS measurement
may have a meter error, but repeating many times over
years can you into sub-centimeter.

Another source of noise is ambient (as opposed
to systematic) ground movement. The more people look
the more they see "micro-movements" like the ground swelling
after a rainy period, topographic settling and all kinds of things.
One can account for these by observing for many years,
watching at grids of stations rather individual stations
among other things.

A third situation is that spatial pattern of ground deformation
may be spread out and complicated. In southern CA you have
islands of relatively little internal movement bordered by zones
of larger deformation. Sometimes these are call micro-plates.
This geography has to worked out for Missouri too.

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