Recent earthquakes like the MJMA 7.2 Hyogo-ken Nambu earthquake and the M 7.4 Kocaeli earthquake demonstrate once again the need to include detailed soil investigation into hazard evaluation, that is the need of microzonation. Seismic hazard assessment conducted at a regional scale generally does not consider soil effects but for the choice of attenuation law that can be soft soil or rock. But the relevant role of seismic hazard in the assessment of seismic coefficients for the definition of the actions in seismic codes must be properly considered. That is to say, the level of protection of buildings is proportional to a definite level of hazard (generally is considered the ground motion with 10% probability of exceedence in 50 years). When a microzonation is performed this criterion cannot be ignored, therefore a clear linkage must be established between hazard (regional scale) and microzonation. The crucial point is represented by the reference motion (or input motion) to be used for site effects analysis, that must be compatible with the regional seismic hazard. In this paper three different approaches for reference motion evaluation are analysed: probabilistic, stochastic and deterministic. Through the case history of Fabriano microzonation the three approaches are compared. It is shown that each approach presents advantages and disadvantages with respect to another. For example the probabilistic approach (the reference motion is directly derived from the expected response spectra for a given return period) is correctly linked with hazard, but produces an overestimation in short periods range, while the deterministic approach correctly simulates the wave propagation, but it ends with a kind of conditional probability. Till now clear criteria to choose the right approach does not appear to exist and the expert experience is of fundamental importance.
Regional and local seismic hazard assessment
Marcellini A;Daminelli R;
2001
Abstract
Recent earthquakes like the MJMA 7.2 Hyogo-ken Nambu earthquake and the M 7.4 Kocaeli earthquake demonstrate once again the need to include detailed soil investigation into hazard evaluation, that is the need of microzonation. Seismic hazard assessment conducted at a regional scale generally does not consider soil effects but for the choice of attenuation law that can be soft soil or rock. But the relevant role of seismic hazard in the assessment of seismic coefficients for the definition of the actions in seismic codes must be properly considered. That is to say, the level of protection of buildings is proportional to a definite level of hazard (generally is considered the ground motion with 10% probability of exceedence in 50 years). When a microzonation is performed this criterion cannot be ignored, therefore a clear linkage must be established between hazard (regional scale) and microzonation. The crucial point is represented by the reference motion (or input motion) to be used for site effects analysis, that must be compatible with the regional seismic hazard. In this paper three different approaches for reference motion evaluation are analysed: probabilistic, stochastic and deterministic. Through the case history of Fabriano microzonation the three approaches are compared. It is shown that each approach presents advantages and disadvantages with respect to another. For example the probabilistic approach (the reference motion is directly derived from the expected response spectra for a given return period) is correctly linked with hazard, but produces an overestimation in short periods range, while the deterministic approach correctly simulates the wave propagation, but it ends with a kind of conditional probability. Till now clear criteria to choose the right approach does not appear to exist and the expert experience is of fundamental importance.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
