Probabilistic Seismic Hazard Assessment for the Republic of Armenia
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Probabilistic Seismic Hazard Assessment for the Republic of Armenia EXPLANATORY NOTE for the Seismic Zonation Map at the Scale of 1:500,000 Based on the Probabilistic Seismic Hazard Assessment for the Republic of Armenia PROJECT# 7179350 Probabilistic Seismic Hazard Assessment for the Republic of Armenia EXPLANATORY NOTE FOR The Seismic Zonation Map at the Scale of 1:500,000 Based on the Probabilistic Seismic Hazard Assessment for the Republic of Armenia 2018 1 PROJECT# 7179350 Table of Contents Probabilistic Seismic Hazard Assessment for the Republic of Armenia .............................................................................. 1 Introduction .......................................................................................................................................................................... 3 Sources and Methodology .................................................................................................................................................... 4 1. Active fault Analysis ................................................................................................................................... 4 2. Map of earthquake source zones with maximum magnitude of seismogenic zones and earthquake recurrence intervals ................................................................................................................................... 15 3. Different seismo-tectonic models considered and the selected seismo-tectonic model............................. 16 4. List of materials and technologies used for compilation of new seismic zonation map ............................ 17 REFERENCES ................................................................................................................................................................... 20 ANNEX 1.Schematic Seismic Zonation Map ..................................................................................................................... 22 ANNEX 2.Settlements in the Republic of Armenia by Seismic Zones .............................................................................. 23 ANNEX 3.Methodology of Fault Parameter Estimation .................................................................................................... 27 2 PROJECT# 7179350 Introduction The seismic zonation map of the area of the Republic of Armenia (RA) at the scale of 1:500,000 was prepared by the Consortium of AIR Worldwide Corporation (USA), GEM Foundation (Italy) and GEORISK Scientific Research CJSC (Armenia) under the Project # 7179350 “Probabilistic Seismic Hazard Assessment for the Republic of Armenia” supported by the World Bank. The results produced by the probabilistic seismic hazard assessment were used for the preparation of the map covering the area of the RA and 150 km in the radius from the state boundaries. In the course of Project implementation, probabilistic seismic hazard computations were realized for 0.5%, 1%, 2%, 10% and 20% probabilities of peak horizontal ground acceleration (PGA) exceedance in 50 years, and 10% exceedance probability in 10 years. This corresponds to the return periods of 10000, 5000, 2475, 475, 225, and 95 years, respectively. Also, as recommended by the Intergovernmental Working Group, the hazard was computed additionally for the 5% PGA exceedance probability in 50 years, as well as for the PGA exceedance probabilities of 5% and 10% in 75 years, which corresponds to the return periods of 975, 1462, and 712 years, respectively. This range of return periods covers the hazard levels proposed by the majority of seismic building codes applicable to the different type of facilities. The following products are delivered: 1. “Seismic Hazard Map of the Territory of the Republic of Armenia at the scale of 1:500,000” The Seismic Hazard Map of the Territory of the Republic of Armenia at the scale of 1:500,000 was prepared by probabilistic assessment for 500 m/s velocity of shear wave propagation in soils and 475 year return period of given intensity earthquakes, corresponding to a 90% probability of non-exceedance of the given intensity in 50 years. The Seismic Hazard Map of the Territory of the Republic of Armenia at the scale of 1:500,000 was submitted as color printed map in its original scale, separately in Armenian and in English. 2. “Seismic Zonation Map of the Territory of the Republic of Armenia at the scale of 1:500,000”. The Seismic Zonation Map of the Territory of the Republic of Armenia at the scale of 1:500,000 was prepared based on the 1:500,000 probabilistic seismic hazard map for 475 year return period for given intensity earthquakes, corresponding to a 90% probability of intensity (PGA) non-exceedance rate in 50 years. According to the seismic zonation map, the area of the RA is subdivided into 3 zones in the ascending intensity order (I, II and III), which cover, correspondingly, 50%, 40% and 10% of the entire area of the RA. In the limits of Zones I, II and III, expected PGA values are expressed in fractions of g (gravity) and correspond 0.3g, 0.4g, and 0.5g, respectively. In the meantime, some suggestions and recommendations provided by the Intergovernmental Working Group, established by the RA Emergency Situations Minister’s Decree N374-A of April 18, 2016, and by the authors of the currently effective RA 11-6.02-2006 Building Code on “Earthquake Resistant Construction: Design Codes” were also considered when drawing contours of the zones. For large cities, computation results for the 90% of PGA non-exceedance probability in 75 years for the given intensity earthquake return period of 712 years were studied and considered additionally. Based on the analysis of the data, certain adjustments were introduced into the boundaries of the seismic zones (see Annex 1). In particular, considering the results of computational data analysis, the Yerevan city area was fully encompassed within Seismic Zone II The final “Seismic Zonation Map” is submitted as color printed map in its original scale, separately in Armenian and in English. In addition, by the recommendation of the Intergovernmental Working Group and the authors of currently effective RA 11-6.02-2006 Building Code, the Consortium produced a black-and-white version of the seismic zonation map to be incorporated directly in the “RABC-II-6.02-Seismic Engineering Norms ” Building Code of the RA. The map was prepared based on simplified graphics for the A4 format in Armenian and in English (see Annex 1). The map is supplemented by the alphabetically ordered summary list of cities in the RA with an indication of settlements grouped by Marzes along with their assignment to a specific seismic zone (see Annex 2). 3. The digital database in GIS format including all probabilistic seismic hazard computations indicated above. The GIS database of all digital data and all probabilistic seismic hazard computations 3 PROJECT# 7179350 Sources and Methodology 1. Active Fault Analysis Objectives: • Identification of active faults and other structural elements based on the analysis of evidence from remote sensing, geomorphology, topography, publications, and from field geological-structural and geophysical investigations; assessment of fault activity and seismic potential. • Creation of database on fault parameters: length, geometry, dip, kinematics, slip rate, etc. • Estimation of Мmax for the identified faults. Fault Parameters (length, kinematics, slip rates, 3D geometry, and zone width) In order to identify and estimate parameters of the fault source zones, we analyzed the database of active faults, applying the methodological approach of stage-by-stage assessment of the active faults, and paleoseismological properties of the environment and seismic landscape, as proposed in Slemmons and Depolo (1986), Michetti and Hancock (1997), Michetti et al. (1995, 2005) and INQUA Scale 2007, and according to the methodology approach used in the CauSIN project (see Annex3). The main parameters were estimated for all faults shown in Figure 1.1 and Table1.1. Fault lengths and geometries were derived based on the available geological, geophysical, and other maps, and then updated with the remote sensing information and findings of the field studies. At the next stage, fault geometry data were digitized and entered into the GIS database. Potential uncertainties of fault length estimations are listed for all faults in Table 1.2. The size of uncertainty depends on the completeness of our knowledge about a fault, as well as on its length, and varied from ± 2 km for short structures up to ±50 km for faults several hundreds of kilometers long. Fault segmentation was assessed based on the features of geometry, morpho-structure, kinematics and seismic activity. Kinematics (fault mechanism) was assessed for all faults in the database primarily by field observation data and in individual cases supported by the GPS monitoring data, focal plane solutions, and micro-tectonic measurements. Most of the faults within Armenia, Southern Georgia, Eastern Turkey, and North-Western Iran appeared to have a strike-slip mechanism of displacement combined with reverse-fault or normal-fault component. Faults bounding the troughs of the Greater Caucasus, or those that developed within the ridge itself were produced mostly by thrust or reverse faulting with a small strike-slip component observed for the oblique structures. The estimates made for the main faults in Armenia considered long-term vertical (and horizontal) displacement, long-term slip rate, maximum length of surface