New Challenges in Seismic Design - Earthquake Engineering for Structural Design - page 14

1.4.3 Tasksof EngineeringSeismology

While Seismology is involved with the phenomena produced in the Earth interior,
Engineering Seismology relates the phenomena produced at the Earth surface,
directly affecting the buildings situated in seismic areas.
- Determination of influence of traveled path and attenuation curves.
- Effects of site condition types.
- Description of spatial movements, directivity, incoherence, etc.
- Modification of ground motions due to topographic irregularities and
alluvial valleys.
- Effects of soil liquefaction.
- Establishing the main ground motion types.
- Digitalization of recorded accelerations, velocities and displacements.
- Establishing the dominant natural period of ground motions.
- Determination of ground motion duration.
- Determination of number of significant pulses.
- Characteristics of near-field and far-field earthquakes
A basic aspect is related to the general information concerning the seismic
region, which is developed by means of the following activities:
- Preparing data concerning these historical earthquakes in regions where
earthquakes occurred in the past.
- Examining the movements of tectonic plates in regions with very intense
seismic activity.
- Evaluating the potential of strong ground motions occuring in regions with
moderate seismic activity.
- Controlling quiescent regions, containing hidden inactive faults, which are
determined by using modern prospecting, but which can be transformed in
to active faults.
A second aspect is related to the information concerning source characteristics,
which is devoted to evaluate:
- Focal mechanism type, considering the presence of the tectonic plate
boundaries, in case of inter-plate earthquakes, and the existing faults in a
plate, in case of intra-plate earthquakes.
- Focal depth, knowing the great differences between surface and deep
sources.
- Directivity of the fault ruptures along an existing fault, knowing the
tendencies of plate movements.
- Spatial characteristics of ground motions.
A very important aspect is related to this information concerning the
geotechnical localconditions, which is faced to establish:
-

Stratification in horizontal and vertical planes, soil layer thickness.

- Dynamic properties of these soil layers.

- Hydrological regime of the regions, related to the influence on

amplification of ground motions.