Estimation of the seismic hazard parameters for various sites in Greece using a probabilistic approach

International audienceThe probabilistic approach that was recently introduced by Kijko and Graham (1998,1999) was applied for the estimation of seismic hazard for various sites in Greece in terms of peak ground acceleration (PGA) and peak ground velocity (PGV). These sites represent geographically cities of Greece among which are the capital of Greece and some others with high, intermediate and low seismicity. The approach allows the use of earthquake catalogues with incomplete reported historical and complete instrumental data, the consideration of different magnitude thresholds, and the incorporation of magnitude uncertainties. One of the advantages of the method is that it does not require any determination of seismic zones. The estimated values of PGA for return periods of 476 years were grouped in 4 categories, the same ones used in the seismic hazard map for the New Seismic Code of Greece. Comparison results were quite interesting and very encouraging concerning the reliability of this probabilistic approach

A method for Bayesian estimation of the probability of local intensity for some cities in Japan

Seismic hazard in terms of probability of exceedance of a given intensity in a given time span,was assessed for 12 sites in Japan.The method does not use any attenuation law.Instead,the dependence of local intensity on epicentral intensity I 0 is calculated directly from the data,using a Bayesian model.According to this model (Meroni et al., 1994),local intensity follows the binomial distribution with parameters (I 0 ,p ).The parameter p is considered as a random variable following the Beta distribution.This manner of Bayesian estimates of p are assessed for various values of epicentral intensity and epicentral distance.In order to apply this model for the assessment of seismic hazard,the area under consideration is divided into seismic sources (zones)of known seismicity.The contribution of each source on the seismic hazard at every site is calculated according to the Bayesian model and the result is the combined effect of all the sources.High probabilities of exceedance were calculated for the sites that are in the central part of the country,with hazard decreasing slightly towards the north and the south parts

Spatial distribution of the seismic hazard parameters in the seismogenic sources of Japan

Με την εφαρμογή δύο διαφορετικών προσεγγίσεων έγινε η εκτίμηση των παραμέτρων σεισμικότητας στις σεισμογενείς πηγές της Ιαπωνίας. Οι μέθοδοι αυτές είναι α)η μέγιστη πιθανοφάνεια και β) η στατιστική Bayes. Αμφότερες οι μέθοδοι μπορούν να εκτιμήσουν το μέγιστο δυνατό μέγεθος του σεισμού Μ , την ποσότητα που β είναι η κλίση της καμπύλης της σχέσης της συσωρευτικής κατανομής των σεισμών και τον μέσο ρυθμό y[ των σεισμών. Στην παρούσα εργασία επικεντρώνουμε το ενδιαφέρον μας στην εκτίμηση των δύο πρώτων παραμέτρων ερευνώντας για την ύπαρξη πιθανού μοντέλου της γεωγραφικής τους κατανομής στις σεισμογενείς περιοχές τις Ιαπωνίας. Δύο είναι οι βασικές υποθέσεις για την αποδοχή των μεθόδων που εφαρμόζονται: 1) ότι οι σεισμοί ακολουθούν κατανομή Poisson και 2) ότι ισχύει ο νόμος Gutenber-Richter. Οι μέθοδοι επιτρέπουν τον υπολογισμό του σφάλματος για τα μεγέθη των σεισμών. Γενικά δείχθηκε ότι οι τιμές Μ είναι διαφορετικές και μεγαλύτερες από τις παρατηρημένες τιμές Mmax . Οι τιμές της παραμέτρου που υπολογίστηκαν βρέθηκαν ότι είναι πολύ χαμηλές για τις σεισμογενείς ζώνες 2 και 7. Αυτό σε συνδυασμό με τις παρατηρήσεις άλλων ερευνητών μας οδηγούν στο συμπέρασμα ότι στις περιοχές αυτές είναι πιθανή η γένεση μεγάλου σεισμούThe seismicity parameters in the seismogenic zones of Japan are estimated by the application of two different approaches. These are the maximum likelihood method as well as the Bayesian estimator is invoked in order to check the validity of the results. Both methods allow us to estimate the maximum regional (possible) earthquake M , the well known value β (b=ßloge) which is the slope of the magnitude-frequency relation and the mean activity rate /[ of the seismic events. The present study is focused in the first two parameters searching for any pattern on their geographical distribution through the sources of Japan. Two are the main assumptions adopted for both methods: 1) the seismic events are of Poissonian character and 2) the magnitude-frequency law is governed by Gutenberg-Richter type. The methods allow to account the influence of uncertainties of the earthquakes magnitude. Taking into account these properties we found that the values of M are different and bigger than the observed M^*x . The estimated b-values show very low values in the seismogenic sources 2 and 7. In comparison with other measurements from other authors these two sources suggested to be areas with very high probability for an large earthquake occurrenc

Evaluation of the seismic hazard parameters for selected regions of the world: the maximum regional magnitude

Parameters of seismic hazard are estimated by the application of the maximum likelihood method. The technique is based on a procedure which utilizes data of different quality, e.g., the ones where the uncertainty in the assessment of the magnitudes is great and those where the magnitudes are computed with great precision. In other words, the data were extracted from both historical (incomplete) and recorded (complete) files. The historical part of the catalogue contains only the strongest events, whereas the complete part can be divided into several subcatalogues each one assumed to be complete above a specified threshold magnitude. Uncertainty in the determination of magnitudes has also been taken into account. The method allow us to estimate the seismic hazard parameters which are the maximum regional magnitude, Mmax , the activity rate, l, of the seismic events and the well known b-value, the slope of the magnitude-frequency relationship. The parameter b, which is interrelated to b (b = bloge), is also obtained. All these parameters are of physical significance. The mean Return Periods, RP, of earthquakes with a certain lower magnitude M ³ m are also determined. The method is applied in some regions of the circum-Pacific belt, which includes various tectonic features, and where catastrophic earthquakes are known from the historical era. The seismic hazard level is also calculated as a function of the form q(Mmax , RP7.5 ) and a relative hazard scale (defined as an index K) is defined for each seismic region. According to this, the investigated regions are classified into five groups of very low, low, intermediate, high and very high seismic hazard levels. This classification is useful for both theoretical and practical reasons and provides a picture of quantitative seismicity

Evaluation of the seismic hazard parameters for selected regions of the world: the maximum regional magnitude

Parameters of seismic hazard are estimated by the application of the maximum likelihood method. The technique is based on a procedure which utilizes data of different quality, e.g., the ones where the uncertainty in the assessment of the magnitudes is great and those where the magnitudes are computed with great precision. In other words, the data were extracted from both historical (incomplete) and recorded (complete) files. The historical part of the catalogue contains only the strongest events, whereas the complete part can be divided into several subcatalogues each one assumed to be complete above a specified threshold magnitude. Uncertainty in the determination of magnitudes has also been taken into account. The method allow us to estimate the seismic hazard parameters which are the maximum regional magnitude, Mmax , the activity rate, lˆ, of the seismic events and the well known b-value, the slope of the magnitude-frequency relationship. The parameter b, which is interrelated to b (b = bloge), is also obtained. All these parameters are of physical significance. The mean Return Periods, RP, of earthquakes with a certain lower magnitude M ³ m are also determined. The method is applied in some regions of the circum-Pacific belt, which includes various tectonic features, and where catastrophic earthquakes are known from the historical era. The seismic hazard level is also calculated as a function of the form q(Mmax , RP7.5 ) and a relative hazard scale (defined as an index K) is defined for each seismic region. According to this, the investigated regions are classified into five groups of very low, low, intermediate, high and very high seismic hazard levels. This classification is useful for both theoretical and practical reasons and provides a picture of quantitative seismicity

Time independent seismic hazard analysis of Greece deduced from Bayesian statistics

International audienceA Bayesian statistics approach is applied in the seismogenic sources of Greece and the surrounding area in order to assess seismic hazard, assuming that the earthquake occurrence follows the Poisson process. The Bayesian approach applied supplies the probability that a certain cut-off magnitude of Ms = 6.0 will be exceeded in time intervals of 10, 20 and 75 years. We also produced graphs which present the different seismic hazard in the seismogenic sources examined in terms of varying probability which is useful for engineering and civil protection purposes, allowing the designation of priority sources for earthquake-resistant design. It is shown that within the above time intervals the seismogenic source (4) called Igoumenitsa (in NW Greece and west Albania) has the highest probability to experience an earthquake with magnitude M > 6.0. High probabilities are found also for Ochrida (source 22), Samos (source 53) and Chios (source 56)