Probabilistic Seismic Hazard Assessment of Egypt

En este estudio se ha llevado a cabo una evaluación de la peligrosidad sísmica probabilista para Egipto en términos de los valores de la aceleración pico del suelo (PGA) y la aceleración espectral (SA). También se presentan curvas de peligrosidad, espectros uniformes de diseño, y resultados de desagregación para las ciudades más importantes, enfocado a la mejora del conocimiento sobre ingeniería de terremotos en la región. Se han realizado cálculos en términos de valores de PGA y SA, para condiciones de roca y suelo, para una probabilidad de superación del 39.3%, 10% y 5% en 50 años (periodos de retorno de 100, 475 y 975 años, respectivamente). Se calcularon también las curvas de peligrosidad y los espectros uniformes de respuesta y diseño para 31 ciudades en Egipto, las cuales se han dibujado y comparado con los valores contemplados en el más reciente código de construcción sismorresistente en Egipto (ECP-201, 2011).In the present study, a probabilistic seismic hazard assessment for Egypt is carried out in terms of peak ground acceleration (PGA) and spectral acceleration (SA) values. Hazard curves, uniform and design hazard spectra, and deaggregation results for the most important cities, are also presented, focused on improving the current earthquake engineering knowledge in the region. Seismic hazard computations in terms of PGA and SA values, for both rock and stiff-soil site conditions, with 39.3%, 10% and 5% probability of exceedance in 50 years (return periods of 100, 475 and 975 years, respectively) were performed. Hazard curves and uniform hazard spectra for thirty-one cities in Egypt were computed and plotted against the PGA values considered in the most recent Egyptian building codes (e.g., ECP-201, 2011).Tesis Univ. Jaén. Departamento de Física. Leída el 24 de octubre de 2017

Seismic Hazard Assessment and Its Uncertainty for the Central Part of Northern Algeria

This study presents a probabilistic seismic hazard assessment for the central part of northern Algeria using two complementary seismic models: a fault-based model and a gridded seismicity model. Two ground-motion attenuation equations were chosen using the Pacific Earthquake Engineering Research Center Next-Generation models, as well as local and regional ones. The ranking method was used to assess their ability to gather accurate data. To account for epistemic uncertainty in both components of the assessment, the seismic hazard was computed using a logic tree approach. Expert judgment and data testing were used to evaluate the weights assigned to individual ground-motion prediction equations. The seismic hazard maps depicted the obtained results in terms of spectral accelerations at oscillation periods of 0.0, 0.2, and 1.0 s, with 10% and 5% probabilities of exceedance in 50 years, and for soil types B, B/C, C, and C/D, as defined by the National Earthquake Hazards Reduction Program. From the analysis, the uncertainty is expressed as both a 95% confidence band and the coefficient of variation (COV). Annual frequencies of exceedance and hazard curves were estimated for the selected cities, as well as uniform hazard spectra for the previously quoted probabilities of exceedance and the soil types considered. Peak ground acceleration values of 0.44±0.17 g and 0.38±0.06 g were reported for the B/C soil type in the cities of Algiers and Blida, respectively, for a return period of 475 years. Seismic maps for the selected return periods depicting the classification of the estimated values are also displayed in terms of very high, high, medium, low and very low degrees of reliability. Furthermore, a seismic hazard disaggregation analysis in terms of magnitude, distance, and azimuth was carried out. The primary goal of such analyses is to determine the relative contribution of different seismic foci and sources to seismic hazard at specific locations. Thus, for each studied city, for the considered return periods and for the soil type B/C, the so-called control or modal earthquake was estimated. At Algiers, events with magnitudes Mw 5.0–5.5 and distances of less than 10 km contribute the most to the mean seismic hazard over a 475-year period. However, for the same return period, those events with Mw 7.0–7.5 and located between 10 and 20 km away contribute the most to the seismic hazard at Tipaza

Probabilistic Seismic Hazard Assessment for United Arab Emirates, Qatar and Bahrain

A probabilistic seismic hazard assessment in terms of peak ground acceleration (PGA) and spectral acceleration (SA) values, for both 10% and 5% probability of exceedance in 50 years, has been performed for the United Arab Emirates, Qatar, and Bahrain. To do that, an updated, unified, and Poissonian earthquake catalog (since 685 to 2019) was prepared for this work. Three alternative seismic source models were considered in a designed logic-tree framework. The discrimination between the shallow and intermediate depth seismicity along the Zagros and the Makran regions was also considered in this assessment. Three alternative ground-motion attenuation models for crustal earthquakes and one additional for intermediate-depth ones have been selected and applied in this study, considering the predominant stress regime computed previously for each defined source. This assessment highlights that the maximum obtained hazard values are observed in the northeastern part of the studied region, specifically at Ras Al-Khaimah, Umm Al-Quwain, and Fujaira, being characterized by mean PGA and SA (0.2 s) pair values equal to (0.13 g, 0.30 g), (0.12 g, 0.29 g), and (0.13 g, 0.28 g), respectively, for a 475-year return period and for B/C National Earthquake Hazards Reduction Program (NEHRP) boundary site conditions. Seismic hazard deaggregation in terms of magnitude and distance was also computed for a return period of 475 years, for ten emirates and cities, and for four different spectral periods

Western Mexico seismic source model for the seismic hazard assessment of the Jalisco-Colima-Michoacan region

The Mexican subduction zone, the Gulf of California spreading center, as well as the triple junction point around the Jalisco and the Michoacan Blocks, represents the most active seismogenic belts inducing seismic hazard in the Jalisco-Colima-Michoacan region. Herein, considering such seismotectonic setting, we develop a new seismic source model for the surrounding of Jalisco-Colima-Michoacan to be used as an input in the assessment of the seismic hazard of the region. This new model is based on revised Poissonian earthquake (1787-2018) and focal mechanism (1963-2015) catalogs, as well as crustal thickness data and all information about the geometry of the subducting slabs. The proposed model consists of a total of 37 area sources, comprising all the three different possible categories of seismicity: shallow crustal, interface subduction, and inslab earthquakes. A special care was taken during the delimitation of the boundaries for each area source to ensure that they represent a relatively homogeneous seismotectonic region and to include a relatively large number of earthquakes that enable us to compute as reliable as possible seismicity parameters. Although the sources were delimited following the standard criteria of assessing the probabilistic seismic hazard, they are also characterized in terms of their seismicity parameters (annual rate of earthquakes above Mw 4.0, b-value, and maximum expected magnitude), mean seismogenic depth, as well as the predominant stress regime. The proposed model defines and characterizes regionalized potential seismic sources that can contribute to the seismic hazard at the Jalisco-Colima-Michoacan region, providing the necessary information for seismic hazard estimates

Seismic and Geodetic Crustal Moment-Rates Comparison: New Insights on the Seismic Hazard of Egypt

A comparative analysis of geodetic versus seismic moment-rate estimations makes it possible to distinguish between seismic and aseismic deformation, define the style of deformation, and also to reveal potential seismic gaps. This analysis has been performed for Egypt where the present-day tectonics and seismicity result from the long-lasting interaction between the Nubian, Eurasian, and Arabian plates. The data used comprises all available geological and tectonic information, an updated Poissonian earthquake catalog (2200 B.C.–2020 A.D.) including historical and instrumental datasets, a focal-mechanism solutions catalog (1951–2019), and crustal geodetic strains from Global Navigation Satellite System (GNSS) data. The studied region was divided into ten (EG-01 to EG-10) crustal seismic sources based mainly on seismicity, focal mechanisms, and geodetic strain characteristics. The delimited seismic sources cover the Gulf of Aqaba–Dead Sea Transform Fault system, the Gulf of Suez–Red Sea Rift, besides some potential seismic active regions along the Nile River and its delta. For each seismic source, the estimation of seismic and geodetic moment-rates has been performed. Although the obtained results cannot be considered to be definitive, among the delimited sources, four of them (EG-05, EG-06, EG-08, and EG-10) are characterized by low seismic-geodetic moment-rate ratios (<20%), reflecting a prevailing aseismic behavior. Intermediate moment-rate ratios (from 20% to 60%) have been obtained in four additional zones (EG-01, EG-04, EG-07, and EG-09), evidencing how the seismicity accounts for a minor to a moderate fraction of the total deformational budget. In the other two sources (EG-02 and EG-03), high seismic-geodetic moment-rates ratios (>60%) have been observed, reflecting a fully seismic deformation

Crustal Strain and Stress Fields in Egypt from Geodetic and Seismological Data

The comparison between crustal stress and surface strain azimuthal patterns has provided new insights into several complex tectonic settings worldwide. Here, we performed such a comparison for Egypt taking into account updated datasets of seismological and geodetic observations. In north-eastern Egypt, the stress field shows a fan-shaped azimuthal pattern with a WNW–ESE orientation on the Cairo region, which progressively rotated to NW–SE along the Gulf of Aqaba. The stress field shows a prevailing normal faulting regime, however, along the Sinai/Arabia plate boundary it coexists with a strike–slip faulting one (σ1 ≅ σ2 > σ3), while on the Gulf of Suez, it is characterized by crustal extension occurring on near-orthogonal directions (σ1 > σ2 ≅ σ3). On the Nile Delta, the maximum horizontal stress (SHmax) pattern shows scattered orientations, while on the Aswan region, it has a WNW–ESE strike with pure strike–slip features. The strain-rate field shows the largest values along the Red Sea and the Sinai/Arabia plate boundary. Crustal stretching (up to 40 nanostrain/yr) occurs on these areas with WSW–ENE and NE–SW orientations, while crustal contraction occurs on northern Nile Delta (10 nanostrain/yr) and offshore (~35 nanostrain/yr) with E–W and N–S orientations, respectively. The comparison between stress and strain orientations over the investigated area reveals that both patterns are near-parallel and driven by the same large-scale tectonic processes