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21.
Significantly different estimates of seismic hazard may result for the same site as aneffect of different methodological choices underlying the adopted procedures. In orderto explore this aspect, two approaches devoted to probabilistic seismic hazard assessment are considered for the evaluation of hazard in a seismic area in Northern Italy. In particular, results of a standard procedure are compared with those obtained by an innovative approach. Fundamental features of this last methodology are the extensive use of intensity data relative to seismic effects observed at the site of interest during past earthquakes and the basic role attributed to the parameterisation of uncertainty which affects the considered pieces ofinformation. The analysis indicates that the new approach supplies results significantlydifferent from those obtained from standard methodology and that these differences strongly depend on strategies adopted for data processing and for the management of uncertainties which affect input parameters. 相似文献
22.
--A distribution-free statistical approach is proposed for tackling the problem of regionalization devoted to the study of magnitude-intensity relationships in the Mediterranean area. The training-set constitutes a compilation of more than 2000 earthquakes which occurred in the Mediterranean region since the end of the nineteenth century, when instrumental data became available, with epicentral or maximum intensity S VI and MS magnitude values. Firstly an empirical magnitude-intensity correspondence has been computed for each intensity class by using the entire data set in the assumption of homogeneity at the regional scale. Residuals of such relation have been analyzed by a distribution-free statistical approach in order to evaluate the opportunity of a regionalization able to locally improve the performances of magnitude-intensity relationships. The analysis indicates that data concerning larger earthquakes (intensity S VII) do not suggest the opportunity of zonation, and that unbiased estimates of macroseismic magnitude can also be obtained in the assumption that magnitude-intensity correspondences are uniform over the entire Mediterranean area. Therefore, better constrained relations determined for the entire Mediterranean region should be preferred to ill-defined local ones. As concerns smaller events (intensity VI), the procedure suggests that medium/small-scale lateral variations (on a wavelength lower than 102 km) should be taken into account if an efficient estimate of magnitudes from maximum observed intensity is pursued, but that data presently available are not sufficient to suggest any reliable zonation of the area under study. 相似文献
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—?A new approach is proposed to the seismic hazard estimate based on documentary data concerning local history of seismic effects. The adopted methodology allows for the use of “poor” data, such as the macroseismic ones, within a formally coherent approach that permits overcoming a number of problems connected to the forcing of available information in the frame of “standard” methodologies calibrated on the use of instrumental data. The use of the proposed methodology allows full exploitation of all the available information (that for many towns in Italy covers several centuries) making possible a correct use of macroseismic data characterized by different levels of completeness and reliability. As an application of the proposed methodology, seismic hazard estimates are presented for two towns located in Northern Italy: Bologna and Carpi. 相似文献
25.
Maria-Jose Jiménez Dario Albarello Mariano García-Fernández 《Bulletin of Earthquake Engineering》2016,14(7):1849-1867
In many countries such as Spain earthquake databases still mainly comprise macroseismic data from felt effects. The full exploit of this information is of basic importance for seismic risk assessment and emergency planning, given the strict link between macroseismic intensity and damage. A probabilistic procedure specifically developed to handle macroseismic data, mostly relying on site information and seismogenic-source free, has been applied to evaluate seismic hazard in SE-Spain (Alicante-Murcia region). Present seismicity is moderate-low with largest magnitudes slightly over Mw5.0. The historical record includes very destructive earthquakes, maximum EMS98 intensities reaching IX–X and X in the nineteenth century (e.g., Torrevieja 1829 earthquake). Very recently, two events in the area on 11 May 2011 (Mw4.5, Mw5.2) killed nine people, injured 300, and produced important damage in the city of Lorca. Regional hazard maps for the area together with specific hazard curves at selected localities are obtained. Results are compared with the maximum observed intensities in the period 1300–2012, and with the values in the seismic hazard map from the Spanish Building Code in force. In general, the maximum felt intensity values are closer to the hazard values calculated for 2 % probability of exceedance in 50 years, using felt and expected intensity. The intensity-based probabilistic hazard maps obtained through the applied approach reduce the inherent smoothing of those based on standard probabilistic seismic hazard assessment approaches for the region, allowing identifying possible over- or sub-estimates of site hazard values, providing very valuable information for risk reduction strategies or for future updates of the building code hazard maps. 相似文献
26.
B. Pace D. Albarello P. Boncio M. Dolce P. Galli P. Messina L. Peruzza F. Sabetta T. San�� F. Visini 《Bulletin of Earthquake Engineering》2011,9(1):199-230
After the April 6th 2009 L’Aquila earthquake (M
w
6.3), where 306 people died and a further 60,000 were displaced, seismic microzoning investigations have been carried out
for towns affected by a macroseismic intensity equal to or greater than 7 MCS. Based upon seismotectonic data, historical
seismicity and strong motion records, we defined input spectra to be used in the numerical simulations of seismic microzoning
in four key municipalities, including the town of L’Aquila. We adopted two main approaches: uniform hazard response spectra
are obtained by a probabilistic seismic hazard assessment introducing some time-dependency for individual faults on the study
area; a deterministic design spectrum is computed from magnitude/distance pairs extracted by a stationary probabilistic analysis
of historical intensities. The uniform hazard spectrum of the present Italian building code represents the third, less restrictive,
response spectrum to be used for the numerical simulations in seismic microzoning. Strong motions recordings of the main shock
of the L’Aquila sequence enlighten the critical role played by both the local response and distances metric for sites located
above a seismogenic fault; however, these time-histories are compatible with the uncertainties of a deterministic utilization
of ground motion predictive equations. As recordings at very near field are rare, they cannot be neglected while defining
the seismic input. Disaggregation on the non-Possonian seismotectonic analysis and on the stationary site-intensity estimates
reach very similar results in magnitude-distance pairs identification; we interpret this convergence as a validation of the
geology-based model by historical observations. 相似文献
27.
Relative motion of the Adriatic with respect to the confining plates: seismological and geodetic constraints 总被引：3，自引：0，他引：3
28.
Alternative interpretations of horizontal to vertical spectral ratios of ambient vibrations: new insights from theoretical modeling 总被引：2，自引：1，他引：1
Different positions exist about the physical interpretation of horizontal to vertical spectral ratios (HVSR) deduced from
ambient vibrations. Two of them are considered here: one is based on the hypothesis that HVSR are mainly conditioned by body
waves approaching vertically the free surface, the other one assumes that they are determined by surface waves (Rayleigh and
Love, with relevant upper modes) only. These interpretations can be seen as useful approximations of the actual physical process,
whose reliability should be checked case-by-case. To this purpose, a general model has been here developed where ambient vibrations
are assumed to be the complete wave field generated by a random distribution of independent harmonic point sources acting
at the surface of a flat stratified visco-elastic Earth. Performances of the approximate interpretations and complete wave
field models have been evaluated by considering a simple theoretical subsoil configuration and an experimental setting where
measured HVSR values were available. These analyses indicate that, at least as concerns the subsoil configurations here considered,
the surface-waves approximation seems to produce reliable results for frequencies larger than the fundamental resonance frequency
of the sedimentary layer. On the other hand, the body waves interpretation provides better results around the resonance frequency.
It has been also demonstrated that the HVSR curve is sensitive to the presence of a source-free area around the receiver and
that most energetic contribution of the body waves component comes from such local sources. This dependence from the sources
distribution implies that, due to possible variations in human activities in the area where ambient vibrations are carried
on, significant variations are expected to affect the experimental HVSR curve. Such variations, anyway, only weakly affect
the location of HVSR maximum that confirms to be a robust indicator (in the range of 10%) of the local fundamental resonance
frequency. 相似文献