Geology Reference
In-Depth Information
4.11.6 Seismicity
4.11.6.1 Principles
Design against earthquake loading is an issue that needs to be
considered in many parts of the world, depending upon the impor-
tance of the project and risks from any potential damage. In some
locations, because of inherently low historical seismicity (UK) or
severity of other design issues (e.g. typhoon wind loading in Hong
Kong), seismicity might be largely ignored for design other than for
high-risk structures like nuclear power plants. Elsewhere, seismicity
needs to be formally assessed for all structures and taken into
account for design.
4.11.6.2 Design codes
Many countries have design codes for aseismic design and these are
generally mandatory. Nevertheless, it is often prudent to carry out an
independent check and in particular to consider any particular aspects
of the site that could affect the impact of an earthquake. For example,
the local soil conditions might have the potential to liquefy. These
issues are considered in more detail in Chapter 6.
Design codes, where well written and implemented, reduce the
earthquake risks considerably. The USA, for example, has a high
seismic hazard in some areas but fatalities are few and this can be
attributed to good design practice and building control. China
also has a high seismic hazard in some areas, but earthquakes
commonly result in comparably large loss of life, which might be
attributed to poor design and quality of building. Structures can
be designed to withstand earthquake shaking, and even minor
improvements in construction methods and standards of building
control (quality of concrete, walls tied together, steel reinforce-
ment, etc.) can prevent collapse and considerably reduce the likely
loss of life (Coburn & Spence, 1992).
4.11.6.3 Collecting data
first stage is to consider historical data on earthquakes, which are
available from many sources, including the International
Seismological Centre, Berkshire, and the US Geological Survey.
These historical data can be processed statistically using appropriate
empirical relationships to give probabilistic site data
The
-
for example, of
peak ground acceleration over a 100 or 1,000-year period. This can be
done by considering distance from site of each of the historical earth-
quake data or linked to some source structure (such as possible active
faults). Dowrick (1988) addresses the process well, and some guidance
is presented in Chapter 6. In some cases, estimates are made of the
 
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