1,721,008 research outputs found
Sensitivity analysis of directivity effects on PSHA
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Near-Source Seismic Demand and Pulse-Like Records: a Discussion for L’Aquila Earthquake
No full textRupture directivity effects in ground motion are known since many years to both seismologists and earthquake engineers, i.e. in sites that are in a particular geometrical configuration with respect to the rupture, the velocity fault-normal signals may show a large pulse which occurs at the beginning of the record and contains the most of energy. The results are waveforms different from ordinary ground motions recorded in the far field or in geometrical conditions not favorable with respect to directivity. Current attenuation laws are not able to capture such effect well, if at all, and current probabilistic seismic hazard analysis is not able to predict the resulting peculiar spectral shape. Moreover, it is believed that structures with dynamic behavior in a range of periods related to the pulse period may be subjected to underestimated seismic demand. In the paper this is investigated and increments in both elastic and inelastic seismic actions are quantified using a large dataset of records, from the next generation attenuation project (NGA), in which a fraction is comprised of velocity pulses identified in other studies. These analyses employ recently developed tools and procedures to assess directivity effects and to quantify the associated threat in terms of seismic action on structures. Subsequently, the same tools are used in one of the first attempts to identify near-source effects in the data recorded during a normal faulting earthquake, the mainshock of the recent Abruzzo (central Italy) sequence, leading to conclude that pulse-like effects are likely to have occurred in the event, that is (1) observation of pulse-like records in some near-source stations is in fair agreement with existing predictive models, (2) the increment in seismic demand shown by pulse-like ground motion components complies with the results of the analysis of the NGA data, and (3) seismic demand in non-impulsive recordings is generally similar to what expected for ordinary records. The results may be useful as a benchmark for inclusion of near-source effect in design values of seismic action and structural risk analysis
Comparing Short-Term Seismic and COVID-19 Fatality Risks in Italy
No full textRisks assessment and risks comparison are basic concepts for emergency management. In the fields of earthquake engineering and engineering seismology, the operational earthquake loss forecasting (OELF) is the research frontier for the assessment of short‐term seismic risk. It combines seismicity models, continuously updated based on ground‐motion monitoring (i.e., operational earthquake forecasting), with large‐scale vulnerability models for the built environment and exposure data. With the aim of contributing to the discussion about capabilities and limitations of OELF, the study presented aims at comparing the OELF results and the fatality risk (based on fatality data) related to coronavirus 2019 (COVID‐19) that, at the time of writing, is perceived as very relevant and required unprecedented risk reduction measures in several countries, most notably Italy. Results show that, at a national scale in Italy, the COVID‐19 risk has been higher than the seismic risk during the two pandemic waves even if, at the end of the so‐called lockdown, the evolution of the pandemic suggested the possibility (not realized) of reaching a situation of comparable seismic and COVID‐19 risks in a few weeks. Because the two risks vary at a local scale, risks comparison was also carried out on a regional basis, showing that, before the beginning of the second wave, in some cases, the seismic risk, as assessed by means of OELF, was larger than the pandemic one
Operational earthquake loss forecasting: a retrospective analysis of some recent Italian seismic sequences
No full textOperational earthquake forecasting (OEF) relies on real-time monitoring of seismic activity in an area of interest to provide constant (e.g., daily) updates of the expected number of events exceeding a certain magnitude threshold in a given time window (e.g., 1 week). It has been demonstrated that the rates from OEF can be used to estimate expected values of the seismic losses in the same time interval OEF refers to. This is a procedure recently defined as operationalearthquakelossforecasting (OELF), which may be the basis for rational short-term seismic risk assessment and management. In Italy, an experimental OELF system, named MANTIS-K, is currently under testing. It is based on weekly rates of earthquakes exceeding magnitude (M) 4, which are updated once a day or right after the occurrence in the country of an M 3.5+ earthquake. It also relies on large-scale structural vulnerability and exposure data, which serve to the system to provide continuously the weekly expected number of: (1) collapsed buildings, (2) displaced residents, and (3) casualties. While the probabilistic basis of MANTIS-K was described in previous work, in this study OELF is critically discussed with respect to three recent Italian seismic sequences. The aim is threefold: (1) illustrating all the features of the OELF system in place; (2) providing insights to evaluate whether if it would have been a useful additional tool for short-term management; (3) recognizing common features, if any, among the losses computed for different sequences
Markovian modeling of seismic damage accumulation
No full textAnalysis of civil structures at the scale of life-cycle requires stochastic modeling of degradation. Phenomena
causing structures to degrade are typically categorized as aging and point-in-time overloads. Earthquake effects
are the members of the latter category this study deals with in the framework of performance-based
earthquake engineering (PBEE). The focus is structural seismic reliability, which requires modeling of the
stochastic process describing damage progression, because of subsequent events, over time. The presented
study explicitly addresses this issue via a Markov-chain-based approach, which is able to account for the
change in seismic response of damaged structures (i.e. state-dependent seismic fragility) as well as uncertainty
in occurrence and intensity of earthquakes (i.e. seismic hazard). The state-dependent vulnerability issue
arises when the seismic hysteretic response is evolutionary and/or when the damage measure employed
is such that the degradation increment probabilistically depends on the conditions of the structure at the time
of the shock. The framework set up takes advantage also of the hypotheses of classical probabilistic seismic
hazard analysis, allowing to separate the modeling of the process of occurrence of seismic shocks and the
effect they produce on the structure. It is also discussed how the reliability assessment, which is in
closed-form, may be virtually extended to describe a generic age- and state-dependent degradation process
(e.g. including aging and/or when aftershock risk is of interest). Illustrative applications show the options to
calibrate the model and its potential in the context of PBEE
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