Seismic Hazard Levels Research Articles

Novel post‐tensioned rocking piles for enhancing the seismic resilience of bridges

AbstractThe rocking pile foundation system is a relatively new design concept that can be implemented in bridges to improve their seismic performance. This type of foundation prevents plastic damage at the bridge piers and the foundation system, which are difficult to repair and can lead to collapse. However, lack of adequate energy dissipation in this type of foundation can result in large deck displacements and subsequent catastrophic failures of the bridge. The present study proposes a novel foundation system that integrates post‐tensioned piles with the rocking foundation to simultaneously prevent plastic hinging at the piers and reduce the deck displacements during severe earthquakes. The effectiveness of the proposed foundation system is investigated and compared against the rocking pile and conventional fixed‐base foundation systems using identical bridge configurations. Three‐dimensional finite element models of these bridges were developed to capture possible nonlinear behavior of the bridge as well as soil‐structure interaction effects. Six strong earthquakes with both horizontal components were selected and scaled to the appropriate seismic hazard level with a return period of 2475 years. Static pushover and nonlinear time‐history analyses were then performed to compare the dynamic response of the bridges, including deck displacements, pier and pile inertial forces, and other nonlinear behavior experienced by the structure. The results reveal that by integrating the post‐tensioned piles with the rocking foundation, the deck displacements were reduced to an acceptable limit without subjecting the bridge to any damage. In contrast, the bridge with the fixed base foundation experienced extensive damage at the piers, and the bridge with the rocking foundation experienced substantial deck displacements that ultimately led to unseating, resulting in the collapse of both bridges. It was therefore concluded that the proposed rocking foundation system with post‐tensioned piles is the superior alternative and can be implemented in practice as an attractive solution due to the seismic protection it offers.

Determination of the level of seismic hazard in Yogyakarta using fuzzy simple additive weighting method

This study aims to obtain a mapping of seismic hazard vulnerability of Special Region of Yogyakarta (DIY) using the Fuzzy Simple Additive Weighting (FSAW) method. This mapping is serves as an act of mitigation for earthquake disasters to reduce the risk of earthquake disasters and minimize fatalities or losses in earthquake-prone areas. The factors used construct the mapping of earthquake-prone areas in Yogyakarta are social, physical, and economic vulnerabilities. Each factor has several variables. The data of this research were taken from the Central Bureau of Statistics (BPS) and the National Disaster Management Agency (BNPB) of the Special Region of Yogyakarta from 2014 to 2017. The FSAW method was used to determine the level of seismic hazard for each sub-district in DIY with a high, medium, or low vulnerability category. The steps taken in the FSAW method are (1) performing fuzzification for each variable, (2) normalizing, (3) determining the weigh of each variable, (4) determining the classification of the result; whether it is categorized under high, medium, or low level. The result from this study is a map that shows areas in each district of Special Region of Yogyakarta with high, medium, and low seismic vulnerability. Based on the social, economic and physical vulnerability factors, it was found that every sub-district in Yogyakarta City were categorized under the high-level vulnerability, while the sub-districts in Bantul, Gunungkidul, Kulonprogo and Sleman Regencies had the average level of medium.

Energy-based seismic retrofit and design of building frames with passive dampers

This paper aims to present retrofit and design methodologies for building frames using target energy as design criteria for passive dampers. Initially, a damper design methodology based on the energy balance concept is discussed and applied to retrofit buildings: under-designed, requiring seismic up-gradation. Furthermore, a methodology is presented for the seismic design of a new building with passive dampers. The proposed methods were applied to reinforced concrete (RC) frames with and without vertical irregularities. The design of these frames with dampers is verified using nonlinear time history analysis considering spectrum compatible near-field and far-field recorded ground accelerograms. The damping constants obtained from the proposed methodology are compared to those calculated using the FEMA 356 method. The response results indicate that the proposed methodologies effectively enhance the RC frame seismic performance for a given seismic hazard level. The proposed methods find their application to the design offices where damper design can be carried out using design spreadsheets developed while avoiding iterations in determining damping constants.

Site-specific seismic hazard levels at the economic zone of Duqm, Oman

AbstractA site-specific probabilistic seismic hazard assessment (PSHA) was achieved in the area of special economic zone authority of Duqm, involving hazard evaluation at the bedrock conditions and assurance of potential site influence on seismic ground motion at the bedrock. Appropriate source and ground-motion prediction models were selected and seismic hazards were identified by means of 5% damped Uniform Hazard Spectra (UHS) for three return periods of 475, 975, and 2475 years. A logic-tree algorithm was used to study the influence of the epistemic uncertainties on the source models, earthquake recurrency and maximum magnitude, along with ground-motion prediction equations (GMPEs). The local geology effects were characterized by fundamental resonance frequency (Fo) using the horizontal-to-vertical spectral ratio technique and the soil amplification factors. The effects of soil were assessed using SHAKE91 for soil parameters defined by 55 geotechnical boreholes in conjunction with surveys of 2D multichannel analysis of surface waves (MASW) at 90 sites. Scaling was performed for selected strong-motion applying spectral matching technique to be used at the soil column bottom. Selection of such records is based on scenarios characterized by deaggregation of the PSHA results on the bedrock tops. The Duqm area mostly features low amplifications, below 1.3 for the considered spectrum. Surface ground-motion maps show low hazard values with Peak Ground Accelerations (PGA) vary between about 2 and 5% g for a 475-year return period. Although several sites are assessed to be susceptible to liquefy, liquefaction analyses indicate that surface ground motions for a 475-year return period are insufficient to produce liquefaction.

Reduction of seismic resiliency of RC structures caused by chloride corrosion for typical school buildings located in hot climates

The performance of Reinforced Concrete (RC) structures, as one of the most widely used structures in civil engineering, during its useful life is always affected by various deterioration factors such as chloride corrosion, and can lead to irreparable financial and human losses. Therefore, in this study, the effects of chloride corrosion on the seismic resilience index of reinforced concrete structures as a criterion for comparing the amount of damage at different levels of seismic hazard have been investigated. In pursuit of this goal, a two-dimensional model of an elementary school located in Iran has been built in OpenSees software. The effects of chloride corrosion have been applied in two time periods of 15 and 30 years after starting its related process. This corrosion would emerge in the form of uniform reduction of the reinforcement bars diameter of the columns and shear walls as well as the reduction of compressive strength of the concrete cover and steel yield stress to the structure. Fragility and vulnerability curves associated with the structural and non-structural elements were traced using the obtained results of Incremental Dynamic Analysis (IDA) under the effect of eight processed strong ground motion records. Finally, the seismic resilience index of the structure is obtained at two hazard levels containing 10% and 2% in 50 years, assuming a linear recovery function for non-corrosion and corrosion conditions. At the end of this research, sensitivity analysis is conducted to explore the effects of damage index on the resiliency of the case study. The results of this study show that the existence of chloride corrosion in all cases has led to an increase in delay and recovery time and a decrease in the seismic resilience index of the structure. The influence of chloride corrosion on the resiliency of vital structures highlights the urgent need for taking corrosion issues into consideration of engineers and stakeholders to enhance the resiliency and reduce the vulnerability of structures during coming natural hazards such as earthquakes and floods.

Development Prototype of Indonesia Seismic Microzonation Information System (Inasmis)

Indonesia has a high level of seismic vulnerability because located in the junction area of four large plates, namely the Eurasian plate, Indo-Australian plate, Pacific plate, and Philippine Plate, and also the number of active faults that stretch throughout its regions. One of the efforts to mitigate earthquake disasters is to conduct seismic hazard microzonation efforts. The Research and Development Center of BMKG has carried out ongoing research in the field of seismic microzonation to obtain information on the level of seismic hazard in some regions based on microtremor parameter values, including in the Sukabumi (2009), Bantul (2010), Padang (2011), Cilacap (2012), Kulonprogo (2014), Tasikmalaya (2017), Garut (2018) and Pangandaran (2019). This study tries to prototype the seismic microzonation information system in a web-based spatial information system called InaSMIS (Indonesia Seismic Microzonation Information System). InaSIMS contains information about the analysis of microtremor survey results, including the value of the dominant period (T0), Ground Shear Strain (GSS), and USGS Vs30, which states the level of seismic hazard in an area. InaSMIS is still being developed in the research stage and is not yet an operational service for BMKG. In the future, InaSMIS expected to be a source of public information to determine seismic hazards in Indonesian regions.

Present‐Day Activity of the Anninghe Fault and Zemuhe Fault, Southeastern Tibetan Plateau, Derived From Soil Gas CO2Emissions and Locking Degree

AbstractThe Anninghe fault (ANHF) and the Zemuhe fault (ZMHF), located in the southeast of the Tibetan Plateau, have a high level of seismic hazard and are among the most active faults in China. This study performed the first measurements of soil gas CO2at three sites across the ANHF and the ZMHF. The fault locking (FL) depth and extent of different segments of the ANHF and the ZMHF were inverted using the negative dislocation model based on global positioning system velocity data acquired during 2009–2015. Results showed that the degassing intensity of CO2in the ZMHF is substantially higher than in the ANHF, which is spatially consistent with the degree of inverted FL. The inversion results revealed that the level of coupling, including the locking depth and extent, along the southern segment of the ANHF is markedly greater than in the northern segment of the ZMHF. Soil gas CO2geochemistry yielded different spatially anomalous features, indicating that the faults have different properties and permeability. The intensive locking of the ANHF and ZMHF segments has reduced permeability through self‐sealing processes, which has restricted the escape of gas from the deep crust. Correspondingly, a creeping fault with a low level of coupling could maintain high permeability, which would be favorable for CO2migration.

Seismic damage mitigation strategy using an FRP column jacketing system in gravity-designed reinforced concrete building frames

Many existing reinforced concrete building structures designed for gravity loads have seismic vulnerabilities owing to their deficiency in column detailing. A column jacketing system with prefabricated fiber-reinforced polymer materials provides additional confinement and stiffness to existing columns and mitigates their seismic vulnerabilities. This paper presents a seismic retrofit strategy for a low-rise gravity-designed reinforced concrete building frame for maximizing the retrofit effect against low, moderate, and high seismic hazard levels. The retrofit parametric models were created by varying the confinement and stiffness-related parameters and then simulated under various seismic loading scenarios. To establish the seismic strengthening strategy, the effectiveness of the retrofit system was examined in terms of its confinement and stiffness-related parameters. This retrofit effect was computed by comparing energy-based seismic demands between retrofitted and non-retrofitted models. Based on the parametric analysis, the critical parameters of the retrofit system were determined depending on the seismic hazard levels. Thus, the certain threshold values of the retrofit parameters for the seismic hazard levels to maximize the effectiveness of the retrofit system were proposed as the retrofit design scheme.

Exploring energy harvesting and vibration mitigation in tall buildings accounting for wind and seismic loads

With the changing climate and the limited supply of fossil fuels available for global energy use, much research has been done to develop innovative methods of producing clean and renewable energy. Out of the various energy sources, wind forces can cause tall buildings to undergo significant vibrations presenting a potential source of clean and renewable energy for buildings and the power grid. To mitigate wind-induced vibrations in tall buildings, viscous dampers have been widely utilized, which, unlike tuned-mass dampers, are also effective in mitigating earthquake-induced vibrations. Contrary to conventional designs, this research explores the use of energy harvesting transducers, in place of viscous dampers, as a means of not only mitigating vibrations under extreme loading conditions (e.g. earthquakes), but also harvesting energy from wind induced vibrations during service conditions and converting it to electricity. This research demonstrates the often conflicting requirements for supplemental damping related to energy harvesting (EH) from wind loads under service conditions vs. vibration mitigation (VM) under extreme events (e.g., earthquakes). Specifically, this research shows that large damping is usually required for VM, whereas small or moderate damping is often required to maximize EH. In doing so, this research develops, and validates using test data, a nonlinear model for an electromagnetic EH transducer, quantifies the EH potential of a selected tall building as a function of the supplemental damping and wind speed showing that EH power generation can reach kWs (as opposed to W), and assesses the seismic performance of the same building as a function of the supplemental damping for two seismic hazard levels. The findings of this research will support future studies pursuing the concept of energy harvesting in structural design.

Seismic reliability implied by behavior‐factor‐based design

AbstractForce‐based seismic design involves the reduction of elastic spectra by introducing a behavior factor, q. This approach is widespread in engineering practice; however, recent studies have shown that structures consistently designed at different sites will not share the same level of seismic risk, which can be defined as the annual rate of the structure failing to meet a seismic performance objective, despite seismic actions having the same exceedance return period at all sites. This paper investigates whether the definition of site‐specific q factors can lead to uniform risk across sites characterized by varying levels of seismic hazard, based on the pushover curves of bare frame reinforced concrete buildings. These pushover curves are used to establish the backbones of equivalent single degree of freedom systems with varying lateral resistance. These systems are fictitiously placed at several Italian sites and their seismic failure risk is computed by integrating their fragility, assessed by means of incremental dynamic analysis, with each site's hazard curve. By assuming an arbitrary risk threshold, the same for all sites, the corresponding lateral strength leading to said threshold is determined and the corresponding behavior factor is back calculated. As expected, risk‐targeted q factors tend to increase with decreasing seismic hazard and are highly sensitive to the shape of the hazard curve beyond the design return period. Coupled with the fact that at low hazard sites lateral strength is determined by detailing for gravity‐load design and minimum code requirements, rather than seismic design actions, the results suggest that q factor‐based design is unsuitable for warranting territorially uniform seismic safety, yet it may be suitable for setting an upper‐bound to the annual failure probability.

Improvements in the direct displacement-based design procedure for mid-rise steel MRFs equipped with viscous dampers

This paper aims to propose straightforward modifications in the direct displacement-based design (DDBD) procedure to reach an optimal design for mid-rise steel moment-resisting frames (MRFs) equipped with linear fluid viscous dampers (FVDs). The modifications include using an alternative equivalent damping as well as applying the ratio of pseudo-spectral velocity to spectral velocity. To compare the proposed method with respect to the conventional DDBD procedure, the seismic performance of a set of low to mid-rise structures consisting of 3-, 6-, 9- and 12-story steel MRFs is investigated. This is carried out via nonlinear time-history analyses by using a set of design spectrum compatible ground motion records at two seismic hazard levels, i.e., the design earthquake (DE) and maximum considered earthquake (MCE). Furthermore, two different patterns, i.e., uniform and non-uniform, for distribution of damping coefficients at the height of the structures are used. Results show that the proposed method can meet the performance targets defined at the DE and MCE hazard levels. Moreover, the peak roof displacement of the structures that is estimated by the proposed method is acceptably the same as captured via the nonlinear analyses. Finally, implementing the proposed method leads to a reduction in the weight of the steel used in the MRFs in comparison with the structures designed by the conventional DDBD procedure and smaller damper forces, i.e., lighter damper constants, can also be achieved.

Compliance-based estimation of seismic collapse risk of an existing reinforced concrete frame building

Seismic evaluation of existing structures is based on determining the damage likely to occur during the lifetime of these structures due to earthquake ground motion excitation. However, there is not a consensus about the acceptable level of seismic damage, the expected lifetime of these structures, and the seismic hazard level(s) to evaluate the structures at. This paper presents a methodology for a parametric calculation of the seismic collapse risk of an existing Reinforced Concrete (RC) frame building based on its seismic code compliance, quantified by a dimensionless metric. This metric, defined as compliance factor, compares the seismic capacity of an existing structure with the seismic demand for a new structure at a predetermined hazard level. The inelastic seismic behavior of four models of the RC frame building of varying compliance was analytically investigated in this study to demonstrate the novel methodology. The four models of the RC building were chosen to represent existing RC frame structures designed and constructed before the introduction of modern seismic code provisions. These four building models were excited by a group of earthquake ground motion excitations using Incremental Dynamic Analysis. The collapse probabilities of the four building models, representing varying values of seismic code compliance, were determined for two different locations corresponding to regions of moderate and high seismic hazard, thus laying the basis for the compliance-based estimation of the seismic collapse risk of existing structures.

Incremental Dynamic Analysis of Concentric X‐Braced Frames Designed to the TBEC 2018

AbstractConcentrically braced frames (CBF) are an efficient lateral force resisting system which provides significant lateral stiffness and lateral strength. One of the commonly used configurations of CBFs are cross braced (X‐braced) frames where braces are placed diagonally between the beam‐column joints of adjacent stories. The current Turkish seismic code, Turkish Building Earthquake Code 2018 (TBEC), was published in 2018 and superseded the former code, Turkish Earthquake Code 2007 (TEC) as of January 2019 with several differences such as introduction of yield mechanisms for CBFs, seismic hazard levels, and calculation of earthquake loads. Due to these differences, CBFs designed to TBEC are expected to yield different member sizes compared to TEC. Although the seismic behaviour of CBFs designed to TEC is well‐understood, that of CBFs designed to TBEC is still unknown and there has been no study on this topic. This study aims to assess the seismic performance of X‐braced frames designed to TBEC. To this end, a two‐story X‐braced frame was considered, and the seismic collapse performance of this frame was evaluated by adopting incremental dynamic analysis (IDA) under a set of twelve ground motions. The results of this preliminary study have provided insight into the collapse performance of CBFs designed to TBEC.

Integrated Seismic and Energy Retrofit Interventions on a URM Masonry Building: The Case Study of the Former Courthouse in Fabriano

Following the 2016 central Italy earthquakes, the high seismic vulnerability of existing buildings is once again at the center of the debate. Indeed, the majority of the Italian building stock (around 60%) was built before adopting the first seismic provisions (1974) and in a territory entirely characterized by medium to high levels of seismic hazard. On the other hand, the first provisions addressing thermal performance criteria were introduced in 1976 but with limited impact. A consistent reduction in energy consumption was further achieved in 1991, when even more buildings were erected. As a consequence, the Italian building stock is characterized by reduced seismic capacity and poor energy efficiency and, to optimize the available resources, combined retrofit interventions approaches are required. In this context, a synergic strategy for the seismic and energy retrofit of a unreinforced masonry (URM) building was proposed. The former Courthouse in Fabriano (Ancona, Marche), a strategic, three-story, unreinforced masonry building in the network of permanent monitoring systems of the Italian Department of Civil Protection, was selected as a case study. The overall effectiveness of various solutions of combined structural refurbishment and energy retrofit interventions, having different levels of invasiveness on the building, was assessed. In addition, a common methodology based on the expected annual losses allowed evaluating the financial feasibility of the proposed integrated interventions and estimating the changes in the return of the retrofitting investment in various seismic and climate zones. The results also show how the payback period could be significantly reduced by incentives and regulatory frameworks that currently favour the execution of integrated interventions.

On the optimal performance-based seismic design objective for steel moment resisting frames based on life cycle cost

The present study attempts to propose an optimum performance objective in the performance-based design method based on life cycle cost. For this purpose, the optimum hazard level which corresponds to the Life Safety performance level is explored in order to minimize the total cost of standard commercial office buildings. Furthermore, the effect of some parameters such as building depreciation over time, building lifetime, and monetary discounting rate on the optimal seismic hazard level is evaluated. The uncertainties involved in seismic loss assessment are considered according to the FEMA-P-58 methodology. To achieve the objectives of this study, three buildings with steel moment frame structures having 5, 10, and 15 stories are investigated. The buildings are optimally designed at different seismic hazard levels with a performance-based approach and then evaluated for the probabilistic life cycle cost. Among the five designs with different design objectives for each building, the design with the minimum total cost is chosen as the optimal design and the corresponding seismic hazard level is presented as the optimal hazard level. The results show that an increase of up to 25.1% in initial structural cost by selecting the optimal hazard level leads to a decrease of up to 57.7% and 16% in life cycle cost and total cost, respectively.

Performance‐based optimum tuning of tuned mass dampers on steel moment frames for seismic applications using the endurance time method

AbstractA performance‐based framework is presented to investigate the optimum tuning of tuned mass dampers (TMDs) for seismic applications in several steel moment‐resisting frames by single and multi‐objective genetic algorithm. The single objective problems have been developed for a set of given mass ratios so as to meet the best performance, while the multi‐objective problems try to attain a set of Pareto optimal designs so as to find the relation between TMD efficiency and TMD mass. In the proposed approach, nonlinear time history analysis via endurance time (ET) method is utilized to estimate the structural responses at two seismic hazard levels in order to assess the performance of structures, while a new criterion for scaling period of TMD‐equipped structures is proposed to be used in scaling process of seismic excitations. A criterion of interstory drift ratios at BSE‐1N seismic hazard level, as the performance index of the studied frames, is considered to be minimized and finally, detuning effects of the optimum TMD designs are checked at BSE‐2N seismic hazard level. In order to illustrate the superiority of the proposed approach, the robustness of optimal TMD parameters is evaluated under near‐ and far‐field ground motion record sets recommended in FEMA‐P695. Also, the optimum results are compared to those from several analytical methods. The proposed framework, taking the advantage of the ET method, is found to be an efficient and feasible approach for practical and cost‐effective optimum seismic design of TMDs on nonlinear structures with a reasonable accuracy and significantly reduced computational effort.

Seismic design and performance of self-centering precast concrete frames with variable friction dampers

This paper presents the numerical investigation of the seismic performance of post-tensioned self-centering precast concrete (SCPC) frames with variable friction dampers (VFDs) and hidden corbels (HCs). The VFDs are characterized by the combination of flat and grooved plates, where the friction forces change as the connection deformation increases, which enables designs to meet target seismic performance objectives at different seismic hazard levels. Theoretical and numerical models for the connection are proposed based on connection geometry, and a performance-based seismic design approach for the SCPC frames is outlined to meet target performance objectives at two common seismic hazard levels, the design basis earthquake (DBE) and the maximum considered earthquake (MCE). SCPC frames for a six-story prototype building located in a high seismic zone in California were designed using this procedure. Three frames with HC-VFD-SPSC connections were designed using various methods to mitigate concentration of drifts in the first story, and one frame was designed with conventional constant friction devices (CFDs) for comparison. Nonlinear time-history analyses were performed for these different designs using two sets of ground motions representing the DBE and MCE seismic hazard levels. The analysis results indicate that the frames with the HC-VFD-SCPC connections achieved the target performance objectives. The proposed approaches of modifying post-tensioning and VFD design parameters or column stiffness in the first story were effective in mitigating the concentration of drifts. Additionally, through comparison with the results of the frame with CFDs, it was found that the VFDs are effective in decreasing overall drift demands at the MCE level, as well as mitigating detrimental higher mode effects observed in SCPC frames with CFDs.

HAZARD SEISMIC ZONATION ANALYSIS OF WEST SUMATRA REGION USING PROBABILISTIC HAZARD SEISMIC ANALYSIS (PHSA) METHOD

Indonesia is one of the countries that is prone to high intensity seismicity, where Indonesia is located between three main plates, namely the Eurasian plate in the north, the Indo-Australian plate in the south and the Pacific plate in the northeast. As a result of the meeting of the three plates, Indonesia has a high level of seismicity both on land and at sea. One of the provinces with a high level of earthquake hazard is West Sumatra. Seismic hazards are useful in designing earthquake-resistant buildings and can describe the effects of earthquakes at a location which will help in anticipating community preparedness and earthquake disaster mitigation efforts. This type of research is descriptive, namely by collecting catalog data for the NEIC / USGS earthquake with the period 1969-2019 with M ≥ 5 S.R. Seismic hazard data processing uses the probabilistic seismic hazard analysis (PSHA) method. PSHA is based on earthquake parameters that produce the greatest ground motion. The magnitude of the intensity at a location due to an earthquake in the earthquake source area with a magnitude M and a distance of R can be used as an attenuation function. The attenuation function used in this study is Joyner-Boore (1997) and Young et al (1997). The results show that the largest seismic hazard occurs in the PGA with a maximum range of 1.28 g - 3.69 g in the Mentawai Islands region. The seismic hazard level is in the Bukit Barisan area with a maximum PGA value of 1.72 g - 2.12 g.

Life-cycle cost analysis of pile-supported wharves under multi-hazard condition: aging and shaking

Investigating the economic consequences of the natural hazards on the infrastructures is a crucial task in any risk-based decision-making process. Life-cycle cost (LCC) analysis is an important tool in both design (to choose the most economic configuration) and analysis (to estimate the future cost of ownership) stages. The pile-supported wharves, as one of the main parts in a marine harbor system, may experience significant deterioration (i.e. strength reduction) and seismic shaking during their life time. In this paper, damage cost in multiple limit states of a deteriorated pile-supported wharf due to chloride corrosion is calculated. A precise finite element model is developed to account for structural aging and the simultaneous seismic shaking. Aging-dependent seismic fragility functions are first developed using incremental dynamic analysis. Next, the LCC analysis is conducted considering the crane damage, as well as, inspection and maintenance costs. The results are calculated for three seismic hazard levels. The findings confirm significance of corrosion on LCC of pile-supported wharf. It is observed that corrosion may increase the LCC of the structure and system (i.e. structure and cranes) by 15% and 8%, respectively. Finally, a set of analytical formulations are proposed for performance index as a function of age, damage state, and seismic hazard level.

Probabilistic seismic hazard analysis for Northern Tanzania Divergence Region and the adjoining areas

This paper presents the seismic hazard levels for the Northern Tanzania Divergence (NTD) and adjoining areas by using area seismic source zones. The 15 source zones were considered based on the major geological and tectonic features, faulting style, and seismicity trends. For each source, earthquake recurrence parameters were computed by using the earthquake catalogue with events compiled from 1956 to 2011. The peak ground accelerations (PGA) and spectral accelerations (SA) at 0.2 and 2.0 second, respectively, were computed for a 10% probability of exceedance in 50 years at sites defined by a 0.1° x 0.1° grid. The recurrence parameters of 15 zones and attenuation relations developed by Akkar et al. (2014) and Chiou and Youngs (2014) were integrated in a logic tree. Obtained results that are presented as hazard maps show strong spatial variations ranging from 60 to 330 cm/s/s for PGA, from 100 to 650 cm/s/s at 0.2 sec and from 6 to 27 cm/s/s at 2 sec for 475 years mean return period and 5% damping. Hazard levels depict the general tectonic setting of the study area with the western (Eyasi-Wembere) and central (Natron-Manyara-Balangida) rift segments having relatively high PGA values compared with the eastern Pangani rift. This work provides indications of seismic hazards to policymakers and planners during planning and guidelines for earthquake-resistant design engineers.
 Keywords: Homogeneous Earthquakes Catalogue; GMPE; PSHA; NTD