The main purpose of a site effect survey is to estimate the degree of amplification of the ground accelerations as a function of vibration (i.e. an earthquake) at a specific location. This is very important when constructing buildings and facilities for any purpose.
The phenomenon of seismic wave propagation on the surface of soils and soft rocks, as well as sedimentary basins and topographic structures, has in the past caused heavy damage and loss of human life. In places where no strong vibrations have been recorded, it is possible to estimate expected land fluctuations using analytical models.
To perform the calculations, information is required on the velocity of shear waves for each layer in the subsurface and the spatial distribution of soft deposits above the base rock. In particular, we are interested in identifying which major reflectors exist (the surface of rock layers that return seismic waves) and how deep they are. It is important to note that the geological layers are not necessarily uniform in space or thickness and their seismic speeds may change over short distances. Moreover, due to geological structure, the orientation of the subterranean strata varies, and sometimes they are not continuous due to the presence of deep faults.
Geological (e.g. drilling) and geophysical tools (e.g. refraction) exist for determining these parameters, but their use in urban areas is often complicated and expensive and the results are not necessarily suitable for characterizing the seismic effects on the surface of the site.
Therefore, a local seismological site effect survey enables the calibration and verification of an underground model constructed by integrating all existing information. Furthermore, a seismological survey that includes the recording and processing of background noise and weak earthquakes and the study of the relevant properties of the subsurface strata make it possible to identify the strata that influence the movement of the seismic waves in the subsoil while addressing frequencies that are important for planning and construction purposes.
The course of the data acquisition may take a period from 1 week to 2 months, depending on the amount of ambient background seismic noise that reaches the area. Data processing and model building may take up to 1 month.
Contact us to design a survey for your site.