Distance, km

FIGURE 18.2 Attenuation curve developed by Mualchin and Jones [2].

the depth of the crust is fairly constant, the size of the earthquake is usually controlled by the length of the fault.

Magnitude is not particularly revealing to the structural engineer. Engineers design structures for the peak accelerations and displacements at the site. After every earthquake, seismologists assemble the recordings of acceleration versus distance to create attenuation curves that relate the peak ground acceleration (PGA) to the magnitude of earthquakes with distance from the fault rupture (Figure 18.2).

All of the data available on active faults is assembled to create a seismic hazard map. The map has contour lines that provide the peak acceleration based on attenuation curves that provide the reduction in acceleration due to the distance from a fault. The map is based on deterministic derived earthquakes or on earthquakes with the same return period.

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