Close-up of a fractured road due to an earthquake


Short-period seismic stations ready to be deployed as part of a temporary array



Earthquake Hazards

Earthquakes are recurrent demonstrations that the Earth is indeed an active planet. These sudden releases of energy pose several hazards to our natural and built environment. There are different hazards depending on the local conditions of the rupture and the geographic area: buildings may crumble, cracking in bridge supports or even casualties among population. In coastal areas, powerful offshore earthquakes could trigger a tsunami, a series of massive waves that would flood the shoreline within minutes; damage or destroy roads, bridges and utility lines; and likely cause many injuries and deaths. 

The first main earthquake hazard (danger) is the effect of ground shaking. Buildings can be damaged by the shaking itself or by the ground beneath them settling to a different level than it was before the earthquake (subsidence). 


The term site effect is generally used to refer to wave propagation in the immediate vicinity of the site, as opposed to the propagation effects, which refer to the complete path from the source to receiver. Site effects can include modification of seismic waves by the local sedimentary cover, particularly where this local cover is not representative of the total path from the epicenter, the effect of alluvial valleys or basins, effect of local topography, and effects of the water table. 

Site effects play a very important role in characterizing seismic ground motions because they may strongly amplify seismic motions just before reaching the surface of the ground or the basement of man-made structures. 

Recently, a large number of studies have focused in developing tools to asses potential site effects using as a proxy the shear-wave velocity of the topsoil (first tens of meters). In this regard, passive seismic methods (H/V spectral ratio, MASW) have proven their usefulness to derive such results in urban areas. 

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