Seismic Ground Motion - Dynamic Behavior of Concrete and Seismic Engineering - page 97

This chapter deals with the characterization of seismic stresses using values
suited to para-seismic design, and details the ways in which these values are
estimated and the way they are used to predict future earthquakes using either
empirical or more physical models.
3.2.2. Accelerometer networks
Several thousand accelerometers are in operation all over the world. Organized
as regional networks, they are sometimes installed as low span very dense local
networks, or installed inside a wide range of civil engineering works (buildings,
dams, nuclear power stations and geo-technical works). Generally, there are two
kinds of instrument: “open field” instruments, intended for recording the ground
motion (or seismic action); and “structure” instruments, used for recording the actual
seismic behavior of the monitored structure.
Until the last decade, the only purpose of the latter instrumentation was to
improve para-seismic knowledge and safety regulation. Telecommunications
advances have, however, allowed two other uses in quasi-real time: real time alert
generation in the case of big distant and remote earthquakes (like the Pacific
subduction area earthquakes and their effects in Mexico) and crisis management to
make a chart of the most severely hit areas in a very short time, for co-ordination
and decision-making in relief efforts (for example, gas network management in
Taiwan in 1999 - Tokyo Gas manages over 3,000 stations on its own behalf, or
high-speed trains - Shinkansen in Japan and Mediterranean TGV in France).
The most important open field networks, as far as volume is concerned, have
been installed in the Pacific area, notably Japan, Taiwan, California and Mexico.
Europe and countries around the Mediterranean with a few exceptions are somewhat
behind, but efforts have been made to create new networks (such as the RAP in
France) or to improve them (as in Italy).
Structure instrumentation is far less widespread, and the data obtained is
typically under-used, for reasons probably arising from “community cultures” that
are more or less modeling confident. Whilst glaring gaps in the networks still exist
in Europe, the USA and Japan have started their own consistent and sustained
instrumentation programmes. Their results are not always easy to “import” into
Europe because of differences in building processes, particularly when modeling
ancient buildings.