Fault Displacement Hazard Analysis Based on Probabilistic Seismic Hazard Analysis for Specific Nuclear Sites

Permanent ground displacements/deformations caused by earthquakes can seriously challenge the safety of the nuclear power plants. The state-of-the-art hazard analysis methods provide a fault displacement hazard curve, i.e., the annual probability of given measure of displacement will be exceeded. The evaluation of ground displacement hazard requires great effort, empirical evidence, and sufficient data for the characterization of the fault activity and capability to cause permanent surface displacement. There are practical cases when the fault at the site area revealed to be active, and, despite this, there are no sufficient data for the evaluation of permanent ground displacements hazard and for judging on the safety significance of permanent ground displacement. For these cases, a methodology is proposed that is based on the seismotectonic modelling and results of the probabilistic seismic hazard analysis. The method provides conservative assessment of the annual probability of fault displacement that allows the decision whether permanent displacement hazard is relevant to nuclear power plant safety. The feasibility and applicability of the method is demonstrated for the Paks site, Hungary.

A New Approach For Physically-Based Probabilistic Seismic Hazard Analysis For Portugal

Probabilistic seismic hazard analysis (PSHA) is nowadays the more complete analysis method to estimate the seismic input for structural analysis. However, it is strongly influenced by seismogenic parameters and attenuation equations. Here PSHA using empirical Green’s functions (EGFs) with 2 + 2 variables is carried out, which are correlated through the moment magnitude. This combination, already known as “physically-based PSHA (pb-PSHA)”, is an original approach that should be disseminated because it provides a good alternative in countries where the seismogenic zones and attenuation equations are not well known. The proposed model is based on linear faults, random, periodic, impulsive, linear source functions, and a punctual hypocentre. Differential equations are explained. Results are shown in terms of new seismic parameters, specific return periods and ground accelerations. The studied country is Portugal. It appears to the authors that no study has been published about pb-PSHA for Portugal.

Probabilistic Seismic Hazard Analysis of Sitamarhi near Bihar-Nepal Region

This article presents the results of a probabilistic seismic hazard analysis (PSHA) for Sitamarhi, Bihar considering the region-specific maximum magnitude and ground motion prediction equation (GMPEs). North Bihar region is one of the seismically unstable areas in India facing several destructive earthquakes for the Himalayan Mountains that was created by the collision of Indian and Eurasian plate. The Gutenberg-Richter (G-R) seismic hazard parameter ‘a’ and ‘b’ have been evaluated by considering the available local earthquake data. Earthquake data were collected from the United States geological survey (USGS), Indian Meteorological Department (IMD), New Delhi, Seismotectonic Atlas of India (GIS 2000) within 500 km radius of the study area, and 62 seismotectonic sources were identified and considered in this study. Seismic source zones for the region have been defined based on large-scale geological features, which are used for assigning the maximum possible earthquake potential. Estimated PGA values are 0.89 g and 0.61 g for the 2% and 10% probabilities of exceedance in 50 years. The results showed that West Patna fault and Sitamarhi Fault are the two main faults, which contribute maximum in the peak ground acceleration (PGA) values for Sitamarhi region.

Seismic hazard for the Trans Adriatic Pipeline (TAP). Part 1: probabilistic seismic hazard analysis along the pipeline

The design of critical facilities needs a targeted computation of the expected ground motion levels. The Trans Adriatic Pipeline (TAP) is the pipeline that transports natural gas from the Greek-Turkish border, through Greece and Albania, to Italy. We present here the probabilistic seismic hazard analysis (PSHA) that we performed for this facility, and the deaggregation of the results, aiming to identify the dominant seismic sources for a selected site along the Albanian coast, where one of the two main compressor stations is located. PSHA is based on an articulated logic tree of twenty branches, consisting of two models for source, seismicity, estimation of the maximum magnitude, and ground motion. The area with the highest hazard occurs along the Adriatic coast of Albania (PGA between 0.8 and 0.9 g on rock for a return period of 2475 years), while strong ground motions are also expected to the north of Thessaloniki, Kavala, in the southern Alexandroupolis area, as well as at the border between Greece and Turkey. The earthquakes contributing most to the hazard of the test site at high and low frequencies (1 and 5 Hz) and the corresponding design events for the TAP infrastructure have been identified as local quakes with MW 6.6 and 6.0, respectively.

Accounting for Epistemic Uncertainty in Site Effects in Probabilistic Seismic Hazard Analysis

ABSTRACT A probabilistic seismic hazard analysis performed for rock conditions and modified for soil conditions using deterministic site amplification factors does not account for uncertainty in site effects, which can be significant. One approach to account for such uncertainty is to compute a weighted average amplification curve using a logic tree that accounts for several possible scenarios with assigned weights corresponding to their relative likelihood or confidence. However, this approach can lead to statistical smoothing of the amplification curve and possibly to decreased computed hazard as epistemic uncertainty increases. This is against the expected trend that higher uncertainty leads to higher computed hazard, thus reducing the incentive for practitioners to characterize soil properties at a site. This study proposes a modified approach in which the epistemic uncertainty is captured in a plot of amplification factors versus period. Using a case history, the proposed method is shown to improve the issue with the weighted average method for at least two oscillator periods and to yield similar results for two other periods in which the highlighted issue is less significant.