DECAY PARAMETERS OF AFTERSHOCK SEQUENCES GLOBALLY DISTRIBUTED

The evaluation of the parameters c and k of the decay law of the aftershocks in an earthquake sequence has been carried out in this study. For this reason 170 seismic sequences globally distributed, during the time period 1964-1986, were performed. All of them modelled well by Omori’s law. We estimated that the mean global values of and parameters , are 0.660+0.181 and - 0.341+0.090, respectively. The values of these parameters are also estimated for different regions of the world, west and east part of circum-Pacific rim, as well as for the Eurasia belt.The parameters c and k calculated for the various regions of the world found to be spread around the global average, although admittedly few exceptions to this generalization are also observed to exist

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

Seismicity assessment for the different regions in and around Turkey based on instrumental data: Gumbel first asymptotic distribution and Gutenberg-Richter cumulative frequency law

International audienceThe evaluation of the seismicity in 24 seismic regions, in which Turkey and adjacent areas divided, is carried out. For this purpose two methods are adopted. The first is the "whole process" which follows the Gutenberg and Richter distribution frequency-magnitude law, while the second one is the "part process" which is well known as the theory of extreme values. This theory was developed by Gumbel in order to solve many geophysical problems. The first asymptotic distribution of extremes was used in the present study. The advantage of the method is that it does not required analysis of the whole data set. It uses, instead, the sequence of earthquakes with the largest magnitudes in a set of predetermined equal-time intervals. The parameters a and b were estimated from both methods. For the goodness of fit, to the Gutenberg-Richter frequency-magnitude law, the maximum likelihood approach is applied. The b-values calculated from Gutenberg and Richter frequency-magnitude law, reveal a better fit to the tectonic environment of the 24 seismic regions of Turkey and its surroundings examining in this study. On the other hand b-values evaluated from Gumbel's first distribution, do not adjust to the particular tectonics of the 24 seismic regions. The modal value a1/b adopted from Gutenberg-Richter for the 24 seismic regions were calculated, as well. An effort made to correlate the tectonics of the area with the spatial distribution of the various computed seismic parameter, while maps were produced for this purpose. These maps provide a detail image of seismicity and local tectonics for the whole investigated area. The results showed that the Aegean arc and the North Anatolian fault zone ranked among to the first positions between the 24 seismic regions researched

Seismic hazard for selected sites in Greece: A Bayes-ian estimate of seismic peak ground acceleration, Natural Hazards

Abstract. A procedure for estimating maximum values of seismic peak ground acceleration at the examined site and quantiles of its probabilistic distribution in a future time interval of a given length is considered. The input information for the method are seismic catalog and regression relation between peak seismic acceleration at a given point and magnitude and distance from the site to epicenter (seismic attenuation law). The method is based on Bayesian approach, which simply accounts for influence of uncertainties of seismic acceleration values. The main assumptions for the method are Poissonian character of seismic events flow and distribution law of Gutenberg-Richter's type. The method is applied to seismic hazard estimation in six selected sites in Greece