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  • English  (5)
  • 2005-2009  (5)
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  • English  (5)
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  • 1
    Unknown
    Amsterdam ; Boston : Elsevier
    Keywords: DDC 620/.001/51 ; LC TA330
    Pages: Online-Ressource (viii, 353 pages)
    Edition: 2nd Edition
    ISBN: 9780444517869
    Language: English
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  • 2
    Publication Date: 2023-06-16
    Description: The Aegean region overlies a complex tectonic regime that experiences a wide diversity of earthquake behaviour, with enormous disparity in focal mechanism and spatio-temporal distribution. Multiple random earthquake simulations, via Monte Carlo simulation, offer the opportunity to analyse seismic hazard across the Aegean, whilst still allowing for uncertainty in various parameters such as frequency-magnitude relation, maximum magnitude (Mmax) and attenuation relation. They may also enable meaningful determination of hazard (in terms of Peak Ground Acceleration (PGA) and MSK Intensity) with exceedence probabilities significantly smaller than those currently used in standard probabilistic seismic hazard assessment (PSHA) techniques. In addition, these simulations can also be used to conduct sensitivity analyses that will act as a verification process, allowing assumptions regarding the seismic hazard parameters to be continually tested. A catalogue of earthquakes in the Aegean (1900-1999AD) is used as a basis for fitting appropriate models of spatial distribution, frequency-magnitude relation and maximum-magnitude. This has been achieved by random re-sampling of the catalogue, and by random sampling from a Gutenberg-Richter relation fitted to the observed data. Simple hazard analyses for five cities within the Aegean have been undertaken using the earthquake simulations. PGA has been determined using appropriate attenuation relations, and its variability quantified. For each site, the PGA with a 10% probability of exceedence in 50 years is largely consistent with those of current hazard analyses. This may give the user additional confidence in the hazard determined for lower exceedence probabilities.
    Language: English
    Type: info:eu-repo/semantics/conferenceObject
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  • 3
    Publication Date: 2023-06-16
    Description: The selection of specific uniform seismic source zones for use in probabilistic seismic hazard analysis is often controversial. Recognizing that a consistent approach to source model development is not always possible, as the information available relating to geology and seismotectonics can vary from region to region, the K-means algorithm for hierarchical cluster analysis can be used to partition regions based on observed seismicity. The Aegean [incorporating Greece, Albania, Former Yugoslav Republic of Macedonia (F.Y.R.O.M.), southern Bulgaria and western Turkey], with its varied seismotectonics and generally high seismicity, is used as an important area ofseismicity in which to develop and demonstrate the application of K-means. Two types of algorithm are considered. The first is a point-source K-means that can be used to partition a catalogue of earthquake hypocentres. The second is a novel line-source development of the algorithm, appropriate in seismology as these are analogues for the traces of active faults, which is then applied to a catalogue of known fault ruptures in the Aegean. The common problems of the K-means methodology are also addressed. Ensemble analyses are used to identify better choices of initial estimates for the cluster centres. A cluster quality index is used to identify the optimum number of clusters, and its robustness assessed when considering different subsets of the observed earthquake catalogue. An alternative approach is also implemented: Monte Carlo seismic hazard analysis is used to compare models with different numbers of clusters with the observed seismicity of the 20th century. Considerable variation is found in the optimum number of clusters identified either by the quality index or by stochastic seismic hazard analysis. Ultimately the K-means partitions of seismicity are developed into source models and their representation of Aegean seismotectonics assessed. The result is that models containing between 20 and 30 clusters emerge as the most appropriate in capturing the spatial variation in hypocentral distribution and fault type in the Aegean.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 4
    Publication Date: 2023-06-16
    Language: English
    Type: info:eu-repo/semantics/article
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  • 5
    Publication Date: 2023-06-16
    Description: Applying alternative and different approaches to seismic hazard assessment is instructive. It allows learning from the different outcomes of the different approaches. These outcomes may be mutually reinforcing or diverge, suggest further study and research is needed, or provide new insights into old problems. Herein Java island-scale seismic hazard will be considered by applying different probabilistic approaches to hazard assessment. Results from two distinct methods are provided for Java: 1) primary zoning using K-means partitioning of seismicity into spatial clusters (progressed into zones) which are then developed into seismic hazard maps using Monte Carlo earthquake catalogue simulation, and 2) extreme value analysis applied at a matrix of points throughout a zoneless Java. The latter approach has been used before, the former adopts seismicity partitioning into spatial clusters prior to Monte Carlo modelling and is novel. The earthquake catalogue analysed is NEIC (1973-2006). This catalogue is homogenised to the moment magnitude scale MW and Poisson declustering of fore- and after-shocks applied. The completeness threshold is around 4.9 MW. Shallow earthquakes down to 80 km depth contribute most to the hazard and are partitioned into 1 to K trial clusters of seismicity by minimising the total within cluster distance from seed centroids. Repeated trials produce an optimum partition. A variety of indices can be invoked to try to quantify cluster quality for a given K; in addition to this, it is decided to seek the best value of K by testing the influence of K on ensuing seismic hazard analyses. Monte Carlo synthesis generates synthetic catalogues for each K value, from which peak ground acceleration (PGA) hazards are calculated and compared against results from the observed catalogue to choose acceptable K values. To summarise the results, seismic hazard maps are constructed for two acceptable values of K (8 and 27) for Java from the Poisson declustered catalogue of shallow earthquakes using the Boore, Joyner, Fumal attenuation law. Not surprisingly the smaller value of K with 8 clusters (progressed to zones) produces the smoother hazard map. All of the maps indicate highest hazard around the Sunda Strait and a general expectation in Java Island of 100-300 cm s-2 with one-in-ten chance of exceedance in 50 years.
    Language: English
    Type: info:eu-repo/semantics/conferenceObject
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