Earthquake Hazard Parameters Estimated in Crete Island and the Adjacent Area

—?Earthquake hazard parameters 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., those in which the uncertainty in the assessment of the magnitudes is great and those in which 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 sub-catalogues; each one assumed to be complete above a specified magnitude threshold. Uncertainty in the determination of magnitudes has also been taken into account. The method allows us to estimate the earthquake hazard parameters which are the maximum regional magnitude, M _max, the activity rate, λ, of the seismic events and the well known value β (b=β?log?e), which is the slope of the magnitude-frequency relationship. All these parameters are of physical significance. The mean return periods, RP, of earthquakes with a certain lower magnitude M?≥?m are also determined. The method is applied in the Island of Crete and the adjacent area, where catastrophic earthquakes are known from the historical era. The earthquake hazard of the whole area is divided in a cellular manner which allow the analysis of the localized hazard parameters and the representation of their regional variation. The seismic hazard analysis, which is expressed by: (a) The annual probability of exceedance of a specified value of magnitude and (b) the return periods (in years) that are expected for given magnitudes, for shallow events is finally performed for shallow events. This hazard analysis is useful for both theoretical and practical reasons and provides a tool for earthquake resistant design in both areas of low and high seismicity.     

Earthquake Hazard Parameters in Crete Island and its Surrounding Area Inferred from Bayes Statistics: An Integration of Morphology of the Seismically Active Structures and Seismological Data

-- The study addresses the evaluation of earthquake hazard parameters such as maximum regional magnitude (M_max) and the slope of Gutenberg-Richter law # (where b=# log e) for the Hellenic Wadati-Benioff zone and the overriding lithospheric plate in the area of Crete and its surroundings. The seismicity of the area is divided in a cellular (1.0° 2 1.0°) manner allowing analysis of the localized earthquake hazard parameters and graphical representation of their spatial variation. Our approach incorporates the recently updated earthquake catalogue for Greece and the adjacent areas, the consideration of the morphology of the deep seismically active structures in the studied area and use of a probabilistic procedure for estimating the earthquake hazard parameters.¶One of the main inconsistencies in the earthquake hazard assessment is the estimation of the maximum magnitude and the related uncertaint y. The Bayesian approach, applied in the present, is a straightforward technique for evaluating the earthquake hazard parameters and is based on the following assumptions: Poissonian character of seismic events flow, a frequency-magnitude law of Gutenberg-Richter's type with cutoff maximal value for estimated parameter and a seismic catalogue, having a rather sizeable number of events (i.e., 50 events at least per cell). For five cells in which the number of events is less than 50, an effort is made to produce synthetic data. The re-assessed parameters obtained from the synthetic data show no significant difference and the real data (of the five cells) are finally taken into account although the estimated uncertainty is high.¶For four random cells we constructed hazard curves showing the probabilities that a certain magnitude M will be exceeded in one year and the return periods (in years) that are expected for a given magnitude. These are particularly useful for the mapping of earthquake hazard in regions of either low or high seismic activity, as is Crete and the adjacent area.¶The obtained results show that the W and E parts of both subducting and overriding plates differ in the spatial distribution of all the estimated earthquake hazard parameters. The M_max distribution indicates strong coupling between the western portions of the interacting plates (M_max > 6.3) to the south of 36°N. The smaller values of M_max (M_max < 6.3) estimated in the SE part of the studied area indicate weak coupling between the eastern portions of the subducting and overriding plates.¶Values of b > 1.0 are found to the south and east of Crete for the Wadati-Benioff zone, and over the central part of the island and the area to the northeast of it (cell 11) for the continental wedge, which suggests nonuniform stress field and/or heterogeneous material.     

An estimate of probabilistic seismic hazard for five cities in Greece by using the parametric-historic procedure

A probabilistic procedure was applied to assess seismic hazard for the sites of five Greek cities (Athens, Heraklion, Patras, Thessaloniki and Volos) using peak ground acceleration as the hazard parameter. The methodology allows the use of either historical or instrumental data, or a combination of both. It has been developed specifically for the estimation of seismic hazard at a given site and does not require any specification of seismic sources or/and seismic zones. A new relation for the attenuation of peak ground acceleration was employed for the shallow seismicity in Greece. The computations involved the area- and site-specific parts. When assessing magnitude recurrence for the areas surrounding the five cities, the maximum magnitude, m_max, was estimated using a recently derived equation. The site-specific results were expressed as probabilities that a given peak ground acceleration value will be exceeded at least once during a time interval of 1, 50 and 100 years at the sites of the cities. They were based on the maximum peak ground acceleration values computed by assuming the occurrence of the strongest possible earthquake (of magnitude m_max) at a very short distance from the site and using the mean value obtained with the help of the attenuation law. This gave 0.24 g for Athens, 0.53 g for Heraklion (shallow) and 0.39 g Heraklion (intermediate-depth seismicity), 0.30 g for Patras, 0.35 g for Thessaloniki and 0.30 g for Volos. In addition, the probabilities of exceedance of the estimated maximum peak ground acceleration values were calculated for the sites. The standard deviation of the new Greek attenuation law demonstrates the uncertainty and large variation of predicted peak ground acceleration values.     

b-Values of two tectonic parts in the circum-pacific belt

Two different data sets have been applied to compute theb-parameter of the magnitude-frequency relation for two different areas in the circum-Pacific belt. These areas are: a) South America, Middle America and Mexico, b) all the remaining island arcs of the circum-Pacific belt, starting from Alaska and the Aleutian islands and proceeding southeastwards. The first data set spreads over 77 years, while the second one covers a 90-year period. In both cases the results clearly showed that theb-values are lower in the first of the above-mentioned areas, while respectively higher in the second. This is due to the tectonic conditions in these areas as estimated during the present work.     

Regional Variation of the ω - Upper Bound Magnitude of GIII Distribution in and Around Turkey: Tectonic Implications for Earthquake Hazards

Complete data set of earthquakes in Turkey and the adjacent areas has been used in order to compute the ω values in 24 seismic regions of Turkey. The parameter is obtained through Gumbel’s third asymptotic distribution of extreme values and is well known as upper bound magnitude. This is an interpretation that no earthquake magnitude greater than ω can occur in a region. The results also estimate the most probable magnitude for a time period of 100 years. The estimates of ω exceed the value of 7.00 in 20 of the 24 seismic regions. An effort is also made to find a relation between the magnitude and the length of a fault in the complicated tectonics of Turkey and the surrounding area. Earthquake hazard revealed as tables and maps are also considered for Turkey and the surrounding area.     

Probabilistic Appraisal of Earthquake Hazard Parameters Deduced from a Bayesian Approach in the Northwest Frontier of the Himalayas

A straightforward Bayesian statistic is applied in five broad seismogenic source zones of the northwest frontier of the Himalayas to estimate the earthquake hazard parameters (maximum regional magnitude M _max, β value of G–R relationship and seismic activity rate or intensity λ). For this purpose, a reliable earthquake catalogue which is homogeneous for M _W ≥ 5.0 and complete during the period 1900 to 2010 is compiled. The Hindukush–Pamir Himalaya zone has been further divided into two seismic zones of shallow (h ≤ 70 km) and intermediate depth (h > 70 km) according to the variation of seismicity with depth in the subduction zone. The estimated earthquake hazard parameters by Bayesian approach are more stable and reliable with low standard deviations than other approaches, but the technique is more time consuming. In this study, quantiles of functions of distributions of true and apparent magnitudes for future time intervals of 5, 10, 20, 50 and 100 years are calculated with confidence limits for probability levels of 50, 70 and 90 % in all seismogenic source zones. The zones of estimated M _max greater than 8.0 are related to the Sulaiman–Kirthar ranges, Hindukush–Pamir Himalaya and Himalayan Frontal Thrusts belt; suggesting more seismically hazardous regions in the examined area. The lowest value of M _max (6.44) has been calculated in Northern-Pakistan and Hazara syntaxis zone which have estimated lowest activity rate 0.0023 events/day as compared to other zones. The Himalayan Frontal Thrusts belt exhibits higher earthquake magnitude (8.01) in next 100-years with 90 % probability level as compared to other zones, which reveals that this zone is more vulnerable to occurrence of a great earthquake. The obtained results in this study are directly useful for the probabilistic seismic hazard assessment in the examined region of Himalaya.     

Probabilistic Seismic Hazard Assessment for Japan

A probabilistic seismic hazard assessment was performed for the Japanese islands and surrounding areas. Seismic hazard parameters characteristic of the seismic history of the regions were obtained. The probability of occurrence of a large M ≥ 7 earthquake within a 10- and 50-year period was also calculated. Regions of very high levels of hazard occur where the Pacific, Phillipine and Eurasian Plates meet. High probabilities of occurrence of a large M ≥ 7 earthquake within a 10- and 50-year period occur within the region where the Pacific Plate subducts with the Eurasian Plate.     

Application of a Bayesian Approach for Estimation of Seismic Hazard Parameters in Some Regions of the Circum-Pacific Belt

—?The maximum possible (regional) magnitude M_max and other seismic hazard parameters like β which is the slope of Gutenberg-Richter law, and λ which is the intensity (rate) of seismic activity are estimated in eight seismic regions of the west side of the circum-Pacific belt. The Bayesian approach, as described by (Pisarenko et?al., 1996; Pisarenko and Lyubushin, 1997, 1999) is a straightforward technique of estimating the seismic hazard. The main assumptions for the method applied are a Poissonian character of seismic events flow, a frequency-magnitude law of Gutenberg-Richter's type with cutoff maximum value for the estimated parameter and a seismic catalog, which have a rather sizeable number of events. We also estimated the quantiles of the probabilistic distribution of the “apparent” M_max for future given time-length intervals.