Earthquake engineering for structural design

Earthquake Engineering for Structural Design

This chapter provides a basic understanding of earthquakes, by first discussing the causes of earthquakes,
then defining commonly used terms, explaining how earthquakes are measured, discussing the distribution
of seismicity, and, finally, explaining how seismicity can be characterized.
Earthquakes are broad-banded vibratory ground motions, resulting from a number of causes
including tectonic ground motions, volcanism, landslides, rockbursts, and man-made explosions. Of
these, naturally occurring tectonic-related earthquakes are the largest and most important. These are
caused by the fracture and sliding of rock along faults within the Earth’s crust. A fault is a zone of the
earth’s crust within which the two sides have moved — faults may be hundreds of miles long, from one
to over one hundred miles deep, and are sometimes not readily apparent on the ground surface.
Earthquakes initiate a number of phenomena or agents, termed seismic hazards, which can cause significant
damage to the built environment — these include fault rupture, vibratory ground motion
(i.e., shaking), inundation (e.g., tsunami, seiche, dam failure), various kinds of permanent ground failure
(e.g., liquefaction), fire, or hazardous materials release. In a particular earthquake event, any particular
hazard can dominate, and historically each has caused major damage and great loss of life in particular

Earthquakes are complex multidimensional phenomena, the scientific analysis of which requires
measurement. Prior to the invention of modern scientific instruments, earthquakes were qualitatively
measured by their effect or intensity, which differed from point to point. With the deployment of
seismometers, an instrumental quantification of the entire earthquake event — the unique magnitude
of the event — became possible. These are still the two most widely used measures of an earthquake,
and a number of different scales for each have been developed, which are sometimes confused


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