1,721,184 research outputs found
Estimates of Vs30 Based on Constrained H/V Ratio Measurements Alone
No full text"One more use of H/V of microtremors is described by S. Castellaro and F. Mulargia. They propose a method to infer the ever-needed Vs 30 by fitting the observed H/V spectrum to the theoretical one computed under assumption taht noise wavefield is composed of the fundamental mode Rayleigh waves. The authors find their technique superior and more informative than all popular array methods, allowing detection of deviations from 1-D subsoil geometry over lengths of a few meters!" (CASSIDY J., MUCCIARELLI M., HERAK M. 8eds.), Increasing Seismic Safety by Combining Engineering Technologies and Seismological Data, p.2
Seismic hazard estimates using ill-defined macroseismic data at site
No full textA 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
Seismic hazard assessment and site effects evaluation at regional scale.
No full textNATO Science Series IV, Kluwe
Are different M = a + bI0 relationships due to a statistical bias?
No full textRelationships between magnitude and macroseismic intensity are widely used, even though intensity is a non-metric observable. Several proposed relationships for the Italian and surrounding regions show a significant correlation of the parameters of the widely used functional form M = a + bI0 This could suggest either the common dependence on a third variable or that the different proposed relationships are due to a pivotal phenomenon around average values, mainly driven by data sampling and uncertainties. Synthetic simulations lend support to the last hypothesis.JCR Journalope
Codes, models and reality: reductionism vs. holism in a review of microzonation studies in the Umbria-Marche region
No full textIn the 10 years since the Umbria-Marche earthquake, several microzonation studies were carried out in the two
regions. In the immediate aftermath of the event, the focus was on the epicentral area and toward emergency intervention
and reconstruction plans. In the following years, regional and national projects aimed to transfer the
lessons learned to other towns. Usually, those two kinds of microzonation studies are referred to as «simplified»
and «detailed». The difference is more subtle, and leads to the question of whether a microzonation study can
be tackled following a reductionist approach, i.e. leaving different experts taking care of a limited subject (geology,
geophysics, seismology, geotechnics, structural engineering). The impression looking back at 10 years of
studies is that a holistic approach would be more appropriate to describe a system (structure-soil-bedrock) that
is non-linear, inhomogeneous, and presenting feedback among its components. A second problem that emerges
is the link with codes and practitioners. During the past 10 years the seismic code has been changed and a new
version is on arrival. The last proposed version of the code is based on a parameter (Vs30) that is discussed in
the same country where it was first adopted, and introduces a parameter (acclivity) that appears to be a secondor
third order problem with respect to others that are completely disregarded (e.g., 2-d site effects). A possible
explanation for this mismatch between codes, models and reality is that our knowledge of distribution and amplitude
of site effects is biased by selective under-sampling. Being driven by damage, and paying less attention
to a uniform distribution of studied sites and situations, we act like a drunk man looking of his lost keys under
a street lamp, not because he is sure that he lost them there, but because the light is there.JCR Journalope
Seismotectonic characteristics of Aegean-type faults: insights from palaeoseismological investigations in the Mediterranean Region.
No full textHVSR prospections in multi-layered environments: an example from the Tyrnavos Basin (Greece)
No full textThe Tyrnavos Basin (Central Greece) is an E-W trending graben bordered by two major antithetic sets of right-stepping dip-slip normal faults that began forming during Middle Pleistocene as a consequence of the N-S extension which affected the whole Aegean Region. This Quaternary structure is superimposed on the Pliocene-Early Pleistocene NW-SE trending Larissa Basin, approximately 700-800 m deep. Seismic activity is instrumentally well documented within and surrounding the investigated area. Based on structural, morphotectonic and palaeoseismological data, several structures previously characterised as active faults have been investigated by applying the HVSR method. This method is commonly used to map the thickness of sedimentary layers in a basin based on the variation of the fundamental 1-D frequency. The polyphased structural evolution and the consequently complex geological setting do not allow for the contouring of a unique continuous surface. We therefore developed a new interpretation technique for statistically significant HVSR peaks, in order to obtain 2-D sections that can be interpreted in a seismic-like fashion. We applied this technique across the major active faults bordering the basin. The results confirm their occurrence at depth and document the important vertical component of displacement
Magnitude distribution of linear morphogenic earthquakes in the Mediterranean Region: insights from palaeoseismological and historical data
No full textWe analyse the earthquake magnitude distribution of 'linear morphogenic earthquakes' that reactivated dip-slip normal faults within the Mediterranean Region. Information on past events is obtained following two distinct methodological approaches: the geological one (morphotectonic investigations and palaeoseismological excavations) and the historical one (contemporaneous descriptions and surveys of coseismic ruptures). In order to homogenize the different datasets, and therefore enabling a comparison, we calculate moment magnitudes (Mw) starting from seismic moments (M0) estimates. The cumulative distributions thus obtained for the two datasets show differences that a series of non-parametric tests suggests to be statistically significant. Coseismic displacements are systematically overestimated for strong (Mw>6.5) historically-based earthquakes and for moderate (5.0-6.0) palaeoseismologically-observed events. Also concerning the rupture length, the geological information generally provides larger values for moderate earthquakes. The possible causes of this discrepancy and the consequences in using the two datasets for seismic hazard assessment analyses are also discussed
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