Earthquake-prone Regions Research Articles

Southern California’s Crustal Motion Tells of Earthquake Hazards

Precise measurements of the Earth’s vertical surface motion help to elucidate the hazards of faults in an earthquake-prone region.

Exploring probabilistic seismic risk assessment accounting for seismicity clustering and damage accumulation: Part I. Hazard analysis

Probabilistic seismic hazard analysis (PSHA), as a tool to assess the probability that ground motion of a given intensity or larger is experienced at a given site and time span, has historically comprised the basis of both building design codes in earthquake-prone regions and seismic risk models. The PSHA traditionally refers solely to mainshock events and typically employs a homogeneous Poisson process to model their occurrence. Nevertheless, recent disasters, such as the 2010–2011 Christchurch sequence or the 2016 Central Italy earthquakes, to name a few, have highlighted the potential pitfalls of neglecting the occurrence of foreshocks, aftershocks, and other triggered events, and pinpointed the need to revisit the current practice. Herein, we employ the epidemic-type aftershock sequence (ETAS) model to describe seismicity in Central Italy, investigate the model’s capability to reproduce salient features of observed seismicity, and compare ETAS-derived one-year hazard estimates with ones obtained with a standard mainshock-only Poisson-based hazard model. A companion paper uses the hazard models derived herein to compare and contrast loss estimates for the residential exposure of Umbria in Central Italy.

Damage Probability Assessment of Hospital Buildings in Yogyakarta, Indonesia as Essential Facility due to an Earthquake Scenario

Indonesia is a country located in an earthquake-prone region, and is characterized by significantly increased peak ground acceleration value. The seismic hazard map of Indonesia stated in SNI 1726-2012 and the current statistics published by PUSGEN in 2017 emphasized on the significance of assessing building damage probabilities, especially for essential structures in Yogyakarta. However, immediate action is required to handle response and recovery operations during and after a disaster. The aim of this study, therefore, is to ascertain the vulnerability and damage probability of hospital buildings in Yogyakarta by employing the 2006 earthquake scenario, where reports showed the destruction of over 156,000 houses and other structures. Furthermore, a Hazard-US (HAZUS) method was used for structural analysis, while a ground motion prediction equation was adopted to produce the building response spectra, following the characteristics of the earthquake incidence. The vital step in this assessment involves building type classification and identification of seismic design levels. However, the damage tendency of buildings is determined using the peak building response, which ensures the generation of capacity curves. The most significant findings on building damage probability value were less than 15% in each damage state (slight, moderate, extensive, complete). In addition, the optimum value was achieved at the minimum level of damage (minor), while the least values were recorded at the highest damage level (complete).

Study on the dynamic response correction factor of a coupled high-speed train–track–bridge system under near-fault earthquakes

The extension of high-speed railway construction to earthquake-prone regions has significantly increased the probability of trains encountering an earthquake while running on a bridge. Therefore, it is urgent to explore the applicability of the additional static quality method (ASQM) of train load simulation specified in the Code for seismic design of railway engineering. Based on comprehensively considering the uncertainty of ground motions, this paper builds spatial analysis models for train–track–bridge systems based on ASQM and the moving spring-mass column method (MSMCM), respectively. Next, it calculates the seismic responses of structures under near-fault earthquakes using a large number of samples and evaluates the applicability of ASQM through large-sample analysis. As the analysis results revealed, the statistical characteristics of over-standard ratios tend to stabilize with the increase of sample size. Under near-fault earthquakes, bearing deformation, pier shear strength, and maximum ductility all have high over-standard ratios. The seismic checking computations of bridge structures based on ASQM have failed to meet the applicability requirements, and the calculation results of the seismic responses of track structures are severely distorted. Introducing a reasonable dynamic response correction factor based on ASQM helps to effectively lower over-standard ratios, thus meeting the applicability requirements for the seismic checking computations of bridges.

Optimal Submarine Cable Path Planning and Trunk-and-Branch Tree Network Topology Design

We study the path planning of submarine cable systems with trunk-and-branch tree topology on the surface of the earth. Existing work on path planning represents the earth's surface by triangulated manifolds and takes account of laying cost of the cable including material, labor, alternative protection levels, terrain slope and survivability of the cable. Survivability issues include the risk of future cable break associated with laying the cable through sensitive and risky areas, such as, in particular, earthquake-prone regions. The key novelty of this paper is an examination and solution of the path planning of submarine cable systems with trunk-and-branch tree topology. We formulate the problem as a Steiner minimal tree problem on irregular 2D manifolds in R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . For a given Steiner topology, we propose a polynomial time computational complexity numerical method based on the dynamic programming principle. If the topology is unknown, a branch and bound algorithm is adopted. Simulations are performed on real-world three-dimensional geographical data.

Rigorous versus less-demanding fragility relations for RC high-rise buildings

Analytical seismic scenario-based probabilistic fragility relations form the spine of earthquake risk assessment and mitigation of RC high-rise wall buildings. In this study, a framework is proposed to develop both rigorous (refined) and less-demanding (cheaper) fragility relations for such structures. Multi-record incremental dynamic analysis is employed using a new scalar intensity measure and net inter-storey drift as a consistent global damage measure for varying heights of buildings. To illustrate the framework, a 30-storey wall building located in a multiple-scenario earthquake-prone region is analysed. The refined fragility sets are derived using 40 real earthquake records representing two seismic scenarios, while the proposed methodology to develop less-demanding seismic scenario-based fragility relations employs a considerably lower number of earthquake records. In this methodology, a new record selection criterion and a fragility curve tolerance factor are introduced. Finally, the two fragility relation sets for the reference structure are developed, assessed, and compared to provide insights into their features and accuracy. Using the proposed methodology, the study revealed that fairly reliable seismic scenario-based fragility sets can be developed for RC high-rise buildings with a significant reduction in computational time and efforts. The proposed framework is generic and can be implemented to deriving refined and less-demanding fragility relations for RC high-rise buildings of different configurations and structural systems.

Sloshing Motion in a Real-Scale Water Storage Tank under Nonlinear Ground Motion

Water storage tanks in cities are usually large and are occasionally affected by earthquakes. A sudden earthquake can cause pressure pulses that damage water containers severely. In this study, the sloshing motion in a high filling level tank caused by seismic excitation is investigated by the numerical method in a 2D model. Two well-studied strong earthquakes are used to analyze the broadband frequency nonlinear displacement of the tank both in the longitudinal and vertical directions. Based on careful experimental verification, the free surface motion and the elevations at the side wall are captured, and the sloshing pressure response is examined. The results show that the 2D section of the cylindrical tank can be used to estimate the maximum response of the 3D sloshing, and the water motions under the seismic excitations are consistent with the modal characteristics of the sloshing. The time histories response of the water motion reflected that the sloshing response is hysteretic compared with the seismic excitation. The anti-seismic ability of the damping baffle shows that its effect on sloshing pressure suppression is limited, and further study on the seismic design of water tanks in earthquake-prone regions is needed.

Ductile steel plate external end diaphragms for steel tub girder straight highway bridges

The end diaphragm of bridges are normally designed to resist lateral seismic forces imposed on the superstructure in earthquake prone regions. Using ductile diaphragms with high deformation capacity could reduce the seismic demands on the substructure and prevent costly damage under strong ground motions. The end diaphragms of steel tub girder bridges with high lateral stiffness and dominant shear behavior have a potential to be used as ductile fuse elements. In this study, a steel plate shear diaphragm (SPSD) is introduced as an external end diaphragm of tub girder steel bridges to reduce the seismic demands imposed on the substructure. Quasi static nonlinear analyses were conducted to evaluate responses of sixteen SPSDs with different boundary conditions, aspect ratios and diaphragm plate thicknesses. Moreover, nonlinear time history analyses were performed using three different ground motions corresponding to DBE and MCE level spectrums. Cyclic and time history analyses proved the proper behavior of SPSD and its efficiency to reduce seismic demands by more than 25%.

A Proposal of Seismic Index for Existing Buildings in Indonesia using Pushover Analysis

Indonesia has often suffered major earthquake damage over the past 50 years. There are thousands of buildings in earthquake-prone regions that still need seismic evaluation and rehabilitation. One method of evaluating the seismic performance of an existing building is by assessing it using the Japanese seismic index for structures. A basic seismic index can be calculated based on the strength and ductility criteria. The strength and ductility performance of a structure can be obtained by pushing a building until it reaches its maximum deformation capacity. This paper describes a proposal to obtain a basic seismic index using pushover analysis. Its adjustment to determine a seismic demand index by considering seismic hazard in Indonesia was carried out using the capacity spectrum method. Two existing buildings in Indonesia were evaluated. The evaluation result indicated that both buildings were in safe condition. The proposal of the seismic index method can be useful in determining the performance index of existing structures. The ductility index can also be used to estimate the response modification factor of a structure.

Seismic performance evaluation of deficient steel moment-resisting frames retrofitted by vertical link elements

In many earthquake prone regions in developing countries, substandard steel moment resisting frame (SMRF) systems pose a profound danger to people and economy in the case of a strong seismic event. Eccentric bracing systems with replaceable vertical links can be utilized as an efficient and practical seismic retrofitting technique to reduce future earthquake damages to such structures. This paper aims, for the first time, to demonstrate the efficiency of eccentric bracing systems with vertical links as a seismic retrofitting technique for the SMRF structures with WCSB and to develop fragility curves for such structures. To achieve this aim, first, the effect of the vertical links on the behaviour of 3, 5 and 7-storey frames are studied through conducting the Nonlinear Static Analyses (NSA) as well as Nonlinear Time History Analyses (NTHA) using the artificial accelerograms compatible with the target design spectrum. The analysis results indicate that, as aimed in the design stage, the seismic damage is only concentrated at the replaceable vertical links and remaining structural members work mainly in the elastic range. In addition, the proposed retrofitting technique considerably improves the performance of the deficient SMRF systems by effectively restricting the displacement response and damage distribution in such structures. Following the NTHA, Incremental Dynamic Analyses (IDA) are performed to develop the seismic fragility curves for the retrofitted SMRF systems. The results indicate that the proposed retrofitting technique significantly reduces the fragility of such systems, and therefore, can provide a simple and efficient method to improve the seismic performance of deficient steel moment resisting frames in seismic regions.

Seismic behaviour of stiffness irregular steel frames under mainshock–aftershock

Generally, the buildings located in earthquake-prone regions are subjected to a sequence of earthquakes. The sequence of earthquakes is termed as mainshock–aftershock (MS–AS). Most of the time the rehabilitation of structure before the occurrence of aftershock cannot be carried out due to a short interval of time between mainshock and aftershock results in additional damage to the structure. The irregular distribution of mass, stiffness and strength along the height of the building may exhibit the poor seismic performance of the structures. The present study examined the influence of stiffness irregularity on seismic demands of 3-, 6- and 9-storey steel moment-resisting frames by comparing the mean seismic demands on reference regular frames under mainshocks and MS–AS seismic sequences. Stiffness irregular frames are obtained by modifying the stiffness at three different locations (bottom, middle and top storey) along with the height of reference regular frame. MS–AS seismic sequences are generated by using a randomized approach. The comparison between reference and stiffness irregular frames shows that the effect of stiffness irregularity on the height-wise variation of interstorey drift ratio is significant. Results of the effect of MS–AS seismic sequence show that aftershock increases the structural responses of both reference regular and stiffness irregular frames.

Seismic vulnerability comparison between rural Weinan and other rural areas in Western China

Generally, the anti-seismic capacity of rural buildings in China is poor due to their irregular design and construction. On the basis of historical destructive earthquake records, corresponding earthquake loss evaluation compilations (1993–2016), field investigations, and remote sensing interpretation, building structures in rural Weinan are classified into two types and analyzed to acquire the seismic vulnerability matrices by employing the fitting method of beta probability density function (BPDF). Results show that BPDF can well reveal the probability density distribution of seismic damage index, and also the damage ratio obtained agrees well with the description of damage degrees in Chinese macroseismic intensity scale.The vulnerability indexes in rural areas of Yunnan, Sichuan, Qinghai provinces and in Weinan City (Shaanxi province) were calculated and a comparison of aseismic ability was made. Results show that, among the rural areas in Western China, the aseismic abilities of traditional buildings in rural Weinan are the lowest while those of masonry buildings are highest. Moreover, potential losses in rural Weinan are estimated on the assumption that a scenario earthquake with a magnitude Ms 6¾ hit Weinan City, proposed by the UK-China Collaboration programme ‘‘Increasing Resilience to Natural Hazards in Earthquake-Prone regions in China”. It was found that the damage ratios obtained captured the distribution of the aseismic abilities of the rural buildings and therefore improved the accuracy of the loss assessment, which provides scientific basis for the scenario narratives. What we discovered in this paper is also helpful in future earthquake damage prediction and enhancement of public awareness on earthquake resistance.

Earthquake early warning-enabled smart base isolation system

Recent deployments of Earthquake Early Warning (EEW) system in Japan and some other earthquake-prone regions provide the vital warning signals prior to the arrival of destructive ground motions. The EEW system uses the different traveling speed of seismic P- and S-waves to achieve the goal of earthquake warning. This technology is primarily used to produce warning signals to alert the public to avoid potential risks, such as to evacuate from buildings. It is also used to mitigate other risks such as reducing train speed of Shinkansen trains. The present study suggests a new seismic-risk mitigation technique by connecting a base isolation system with the EEW. Base isolation is a mature technology which decouples structure from its base and lengthens its natural period of vibration. However, existing base isolation devices must possess certain lateral resistance to withstand service lateral forces such as wind, and such stiffness hinders the effectiveness of vibration isolation. In addition, supplementary damping devices are sometimes added to control excessive displacements in isolation level. This paper proposes a smart system which changes the property of a base isolation system upon EEW signal. In normal times when earthquake risk is not present, the base isolation system is locked by shear keys. When an earthquake is signalled by the EEW system, a mechanical system releases the base isolation system. When the earthquake ceases, the system resets and base isolation is locked again. On-board vibration sensors are added to activate the system in case of EEW fails to detect incoming waves. A crucial benefit of the system is that supplementary damper is no longer required to control excessive isolator displacements, and elastic stiffness of base isolation is no longer required to re-enter the base isolation system. The result is that it maximizes the vibration isolation effectiveness. A conceptual framework of proposed system is described and demonstrated by laboratory-scaled experiments. A 6-storey test frame is excited on a shake table subjected to historical earthquakes. Results indicates that the proposed system is effective in reducing earthquake responses on the building. It is an IoT-enabled earthquake-risk mitigation system.

Numerical Study of Panel Zone in a Moment Connection without Continuity Plates

ABSTRACT Built-up box columns are more frequently used in earthquake-prone regions such as Japan and Iran. As the installation process of continuity plates and welding inspection are difficult, expensive, and time-consuming, this study was aimed at experimentally and numerically investigating continuity plate elimination from built-up box columns with regard to the seismic design specifications of special and intermediate moment resisting frames. Results of an experimental study of three full-scale rigid connections between I-beam and box-column subjected to cyclic loading were used for comparison and verification of numerical results. Experimental study showed that samples reached story drift angle of 0.06 radians before experiencing the permissible strength degradation. Therefore, the tested connections satisfied the criterion for special moment resisting frame (SMRF) in AISC. Based on observations of crack initiation and propagation in the experimental study, a rupture index (RI) was employed to investigate the effects of different complete joint penetration (CJP) groove welding methods used in the experimental study on connection ductility as well as to identify the regions prone to crack initiation and propagation. Both the numerical and experimental results showed the superiority of using back plate in CJP welding.

Simplified design of bridges for multiple-support earthquake excitation

This paper presents a novel, bridge-dependent approach for quantifying the increase of design quantities due to spatially variable earthquake ground motion (SVEGM). Contrary to the existing methods for multiple support bridge excitation analysis that are either too complicated to be applied by most practitioners or oversimplied (e.g. Eurocode 8, Annex D provisions), this method aims to strike a balance between simplicity, accuracy and computational efficiency. The method deliberately avoids generating support-dependent, acceleration or displacement, asynchronous inputs for the prediction of bridge response. The reasons behind this decision are twofold: (a) first, the uncertainty associated with the generation of asynchronous motion scenarios, as well as the exact soil properties, stratification and topography is high while, (b) the response of a bridge is particularly sensitive to the above due to the large number of natural modes involved. It is therefore prohibitive to address SVEGM effects deterministically in the framework of a design code. Instead, this new method is based on two important and well-documented observations: (a) that SVEGM is typically globally beneficial but locally detrimental [1], and (b) that the local seismic demand increase is very closely correlated with the excitation of higher modes, which are not normally activated in the case of uniform ground motion [2,3]. Along these lines, a set of static analyses are specified herein to complement the standard, code-based response spectrum analysis. These static analyses apply spatially distributed lateral forces, whose patterns match the shape of potentially excited anti-symmetric modes. The amplitude of those forces is derived as a function of the expected amplification of these modes according to the process initially proposed by Price et al. [4]. Two real bridges with different structural configurations are used as a test-bed to demonstrate the effectiveness of the new method. Comparison of the results with those obtained through rigorous response history analysis using partially correlated, spatially variable, spectrum-compatible input motions [5] shows that, the simplified method presented herein provides a reasonably accurate estimation of the SVEGM impact on the response of the bridges examined at a highly reduced computational cost. This is essentially an elastic method that is found to be simple, yet precise enough to consist an attractive alternative for the design and assessment of long and/or important bridge structures in earthquake-prone regions.

Aftershock probabilistic seismic hazard analysis for Bushehr province in Iran using ETAS model

Aftershock probabilistic seismic hazard analysis (APSHA) has a key role in risk management after a major earthquake. The main goal of the current study is to assess aftershock hazard in a strategic and earthquake-prone region of Iran (Bushehr province). Bushehr province is a strategic region in the Middle East due to its major petroleum export facilities, industrial corridors and the Bushehr nuclear power plant. To prepare APSHA for Bushehr province, a seismic source is selected which surrounds the active faults in the study area. A uniform earthquake catalog is collected which contains information on a total of 1143 earthquakes (Mw > 4) occurred in the study area from 1900 to 2018. Aftershock parameters are calculated using the epidemic-type aftershock sequence model. Aftershock sequences follow a non-homogenous Poisson’s process, and their magnitude and location depend on the size and location of the mainshock. In this study, APSHA is performed for the intervals of 1, 7 and 30 days after the mainshock, by assuming occurrence of mainshocks with return periods of 475 and 2475 years. The results show that the aftershock hazard curve is greater than that of the mainshock hazard curve.

Verifying the periods of vibration for different structural systems using earthquake data and simulation

Large fundamental period data from two sources are collected and compared with expressions from building codes and previous studies. The first data set is collected from 147 instrumented buildings with various lateral force resisting systems (LFRSs). The second set is obtained from the inelastic dynamic response simulation of 26 multi-story structures. Seven LFRSs are considered, including steel moment-resisting frames (SMRFs), reinforced concrete moment-resisting frames (RCMRFs), concentrically braced frames (CBFs), eccentrically braced frames (EBFs), RC shear walls (RCSWs), masonry buildings and pre-cast structures. It is concluded that the design provisions are conservative enough for SMRFs, RCMRFs, and CBFs. For low-to-medium rise RCSWs and EBFs along with low-rise masonry and pre-cast structures, recently proposed expressions in previous studies provide conservative estimates for the fundamental periods. More data is highly needed to arrive at a reliable formula for the design of high-rise RCSW structures in earthquake-prone regions.

Risk analysis of seismic bridge damage: case study after Lombok and Palu earthquake

Indonesia is known as an earthquake-prone region, lies in the ring of fire zone. This potential hazard can impact several infrastructures, including bridges. Seismic bridge damages could possibly disrupt traffic flow furthermore cut off the regional connectivity. In this study, risk analysis is carried out on several bridges after Lombok and Palu earthquake. Visual inspection has been undertaken on 38 bridges on-site, and several damages identification are reported. Risk analysis was then carried out according to the severity of element damages and the frequency of occurrence. From the analysis, it is concluded that embankment settlement in the approach road is found to be the most potential element with the highest risk of damage due to earthquakes. Besides, the superstructure displacement and crack in the wing wall are at moderate risk. This finding makes the substructure become the most vulnerable element which needs more attention. Therefore, it is recommended to specify a higher design specification for substructure to mitigate seismic bridge damages, especially for bridges located in the high seismic zone area.

Effects of steel fibres and prestress levels on behaviour of newly proposed exterior dry joints using SFRC and CFRP bolts

This study proposes a new type of dry exterior beam-column joints for precast moment-resisting concrete frames. This dry joint type uses steel fibre reinforced concrete (SFRC) and carbon fibre reinforced polymer (CFRP) bolts to improve the joint capacities. In addition, an analytical model to predict the load-carrying capacity of this precast joint type is also proposed. Five exterior beam-column joints were cast and tested under quasi-static cyclic loads until failure. The experimental results revealed that the use of SFRC significantly improved all the indices, including the load-carrying capacity, drift ratio, ductility, energy dissipation and stiffness. Also, the proposed joints outperformed the monolithic specimen in terms of load-carrying capacities, energy dissipation, and stiffness by 27–61%, 45–75%, and 27–55%, respectively. Particularly, the drift ratio of the proposed joints reached 3.5%, which satisfies the requirements for ductile joints to be used in earthquake-prone regions according to various standards. Finally, the proposed model yielded good predictions as compared to the experimental results with minor errors of approximately 0.9–2%. These exciting results indicate that the use of SFRC and CFRP bolts could help to avoid the challenging issue of corrosion in the conventional dry exterior joints and still ensure the sufficient requirements for reinforced concrete structures in non-seismic and seismic-prone areas.

The MyShake Platform: A Global Vision for Earthquake Early Warning

The MyShake Platform is an operational framework to provide earthquake early warning (EEW) to people in earthquake-prone regions. It is unique among approaches to EEW as it is built on existing smartphone technology to both detect earthquakes and issue warnings. It therefore has the potential to provide EEW wherever there are smartphones, and there are now smartphones wherever there are people. The MyShake framework can also integrate other sources of alerts and deliver them to users, as well and delivering its alerts through other channels as needed. The MyShake Platform builds on experience from the first 3 years of MyShake operation. Over 300,000 people around the globe have downloaded the MyShake app and participated in this citizen science project to detect earthquakes and provide seismic waveforms for research. These operations have shown that earthquakes can be detected, located, and the magnitude estimated ~ 5 to 7 s after the origin time, and alerts can be delivered to smartphones in ~ 1 to 5 s. A human-centered design process produced key insights to the needs of users that have been incorporated into MyShake2.0 which is being release for Android and iOS devices in June 2019. MyShake2.0 will also deliver EEW alerts, initially in California and hopes to expand service to other regions.