New Challenges in Seismic Design - Earthquake Engineering for Structural Design - page 12

1.4 SEISMOLOGY VERSUSENGINEERING SEISMOLOGY
1.4.1 Seismologists and Engineers
The seismological and engineering approaches are typical for the difference
between science and application (Smith, 2001).
The science of Seismology is involved with the study of tectonic plate
movements associated to important earthquakes. The seismologists , as Earth
scientists, are specialized in geophysics and they are devoted to analyze the genesis
and propagation of seismic waves in geological materials. Some of them study the
relation between faults, stress and seismicity, others interpret the mechanisms of
rupture from seismic wave data, others integrate geoscientific information in order
to define zones of seismicity, and finally others collaborate with engineers trying to
minimize the damage caused to construction. But the physicists working in this
field use conceptions and methodologies different from that used by engineers.
They have also the privilege of proposing, testing and discarding erroneous
hypotheses. The explanation of earthquake generation is an example of this
approach. From chemical reactions to the continental drift or Earth expansion, all
types of hypotheses were used without any consequence for these incorrect
assertions. Now, the causes of earthquakes being clarified and the Theory of Plate
Tectonics is accepted by all scientists, the interest of seismologists is mainly
concentrated in understanding the faults, positions and movements, remaining in
the field of qualitative description of phenomena.
Structural Engineering is a field of engineering which deals with the design of
structural systems with the purpose of supporting and resisting various loading
conditions. A Structural Engineer is most commonly involved in the design of
buildings and other civil engineering structures. Contrary to the seismologist, the
structural engineers' activity must rely on proven principles and data, as wrong
hypotheses produce impermissible life and economic losses. For an engineer, the
approaches for the structural design must be quantitative. Forces caused by
earthquakes must be evaluated and the structure members are proportioned to have
a resistance greater than these forces. The main purpose of structural design is to
produce a suitable structure, even in the case of strong earthquakes. Reducing
future earthquake losses depends on the understanding and quantification of the
damaging effects of earthquakes. Using data from regional seismic networks, the
research in this area is devoted to discover how the characteristics of the
earthquake source, wave propagation effects and near-surface geological deposits
could control the strong shaking. Specific studies are also investigating the factors
which govern the susceptibility to ground failure from land sliding and
liquefaction. All these aspects are framed in the so-called earthquake hazard.
It can happen that the interests of seismologists and structural engineers
frequently overlap, but in different ways. Both are interested in knowing the
positions of active faults. The seismologists want to know how these faults move,
in function of their typology and characteristic, while the engineers are concerned