Earthquake Shaking Research Articles

Sedimentological records of atastrophic mass movements in the lake bottom-sediments of north-western Kola Peninsula and possible scenarios to explain the seismogenic trigger

Abstract. In this present article, we describe disturbances in the sedimentary records of lakes on the western flank of Lake Imandra (NE Fennoscandia, Kola Peninsula). The research framework comprises sedimentological and textural criteria for a visual description of sedimentary structures, borehole drilling data, chronological (radiocarbon dating) data, and ground-penetrating radar (GPR) data. Synchronicity specific features and fast spontaneous sediment accumulation in lakes, as well as traces of strong prehistoric and historical earthquakes and geomorphic setting in the studied area suggest that the observed mass movements in lake sediments are potentially generated by earthquake shaking.

Performance of URM structures under earthquake shakings: Validation using a template building structure by the 2019 Albanian earthquakes

Performance of URM structures under earthquake shakings: Validation using a template building structure by the 2019 Albanian earthquakes

Experimental Study on Seismic Compression of Chinese Loess under Cyclic Direct Simple Shear Testing

Seismic compression is the accumulation of contractive volumetric strains in unsaturated soil from earthquake shaking. For Chinese loess, the behavior of seismic compression is extremely significant and has been recognized in historical earthquakes. As a main technical mean, dynamic triaxial apparatus has been employed to study the seismic compressibility of loess for a long time. However, dynamic simple shear apparatus is superior to dynamic triaxial apparatus in modeling the real stress condition of soil under earthquake. Meanwhile, dynamic triaxial apparatus could not measure the volumetric strain of unsaturated loess precisely. A series of cyclic compression tests are hereby performed on unsaturated and intact loess by the new cyclic direct simple shear device developed in Xi’an University of Technology. The properties of cyclic compression of loess specimens are analyzed under the combined conditions of four water contents, four vertical stresses, and six shear strains. The test results reveal that the volumetric strain is constantly compacted through the process of cyclic load‐unloading and is much larger during loading half‐cycle than unloading half‐cycle. It has been found that the cyclic compressibility of loess is dependent upon density, water content, confining pressure, shear strain (or stress), and cycles. An empirical formula to estimate the increment of cyclic volumetric strain per cycle is expressed in terms of the amplitude of shear train, dry density, water content, and vertical stress. Moreover, a simplified evaluation procedure is proposed for the probable settlements of loess deposits subjected to earthquake shaking.

Sub‐Kilometer Correlation Between Near‐Surface Structure and Ground Motion Measured With Distributed Acoustic Sensing

AbstractEarthquake ground motion depends strongly on near‐surface structure, which is challenging to image in urban areas at high resolution. Distributed acoustic sensing (DAS) is an emerging technique that provides a scalable solution by converting preexisting fiber‐optic cables into dense seismic arrays. After the July 2019 M7.1 Ridgecrest earthquake, we converted an underground dark fiber across the city of Ridgecrest, CA, into a DAS array. The recorded aftershocks show substantial lateral variability in site amplification over only 8‐km in distance. To understand the cause of such variability, we used three months of continuous data, dominated by traffic‐generated seismic noise, to image near‐surface structure along the fiber path. We find that the lateral variations of earthquake shaking correlate well with the shallow shear velocity model at sub‐kilometer scales, in particular micro‐basins filled with soft sediments. These results highlight the great potential of DAS for high‐resolution seismic hazard mapping in urban areas.

Seismic Ground Response Analysis of Input Earthquake Motion and Site Amplification Factor at KUET

Ground motion is the movement of the earth's surface due to explosions or the propagation of seismic waves. In the seismic design process, ground response analysis evaluates the impact of local soil conditions during earthquake shaking. However, it is difficult to determine the dynamic site response of soil deposits in earthquake hazard-prone areas. Structural damage has a great influence on the selection of input ground motion, and in this study, the importance of bedrock motion upon the response of soil is highlighted. The specific site response analysis is assessed through “DEEPSOIl" software with an equivalent linear analysis method. Furthermore, four input motions including Kobe, LomaGilroy, Northridge, and Chi-Chi were selected to obtain normalized response spectra. This study aims to obtain the site amplification of ground motion, peak spectral acceleration (PSA), and maximum peak ground acceleration (PGA) based on shear wave velocity from the detailed site-specific analysis of Bangabandhu Sheikh Mujibor Rahman hall at Khulna University of Engineering & Technology. The maximum shear wave velocity obtained was 205 m/s while the amplification factor varied from 4.01 (Kobe) to 1.8 (Northridge) for rigid bedrock properties. Furthermore, the Kobe earthquake produced the highest (4.3g) PSA and the Northridge earthquake produced the lowest (1.08g) PSA for bedrock, with Vs=205 m/s. The surface PGA values were acquired in the range of 0.254g (Northridge) to 0.722g (Kobe), and the maximum strain values for Kobe earthquakes were in the range of 0.016 to .303. Therefore, the surface acceleration values were very high (>0.12g) for the Kobe earthquake motion.

Seismic Analysis of 3D Framed Building

Generally RC framed structures are designed without regards to structural action of masonry infill walls present. Masonry infill walls are widely used as partitions. These buildings are generally designed as framed structures without regard to structural action of masonry infill walls. They are considered as non- structural elements. RC frame building with open first storey is known as soft storey, which performs poorly during strong earthquake shaking. Past earthquakes are evident that collapses due to soft storeys are most often in RC buildings. In the soft storey, columns are severely stressed and unable to provide adequate shear resistance during the earthquake. Hence a combination of two structural system components i.e. Rigid frames and RC shear walls or Rigid frames and Bracings leads to a highly efficient system in which shear wall and bracings resist the majority of the lateral loads and the frame supports majority of the gravity loads.

Macroseismic survey of the 6 February 2016 KwaZulu-Natal, South Africa earthquake

AbstractOn the 6th of February 2016 at 11:00 hours local time (0900 UTC), KwaZulu-Natal was struck by an earthquake of local magnitude ML=3.8. The epicentre of the earthquake was located offshore in the Durban Basin. The earthquake shaking was widely felt within the province as well as in East London in the Eastern Cape province and was reported by various national media outlets. Minor structural damage was reported. A macroseismic survey using questionnaires was conducted by the Council for Geoscience (CGS) in collaboration with the University of KwaZulu-Natal (UKZN) which yielded 41 intensity data points. Additional intensity data points were obtained from the United States Geological Survey (USGS) Did You Feel It? programme. An attempt was made to define a local intensity attenuation model. Generally, the earthquake was more strongly felt in low-cost housing neighbourhoods than in more affluent suburbs.

Effects of seismic activity on groundwater level and geothermal systems in İzmir, Western Anatolia, Turkey: the case study from October 30, 2020 Samos Earthquake

The October 30, 2020 Samos earthquake (Mw 6.6) affected the Aegean Sea and environs, caused destruction and loss of life in the city of İzmir located 70 km away from the earthquake epicenter. Before this earthquake, water resources were monitored in the areas of Bayraklı, Gülbahçe, and Seferihisar. For this purpose, 10 groundwater monitoring wells were drilled in the Bayraklı area, where groundwater level, temperature, and electrical conductivity changes were monitored at 1-h intervals in 5 wells. Besides physical parameters such as groundwater levels, temperatures and electrical conductivities, hydrogeochemical cations, and anions measured in the study area. Change in the groundwater levels was observed before, during, and after the Samos earthquake. A trend of rising groundwater level was observed two days before the mainshock, to a height of 10 cm, and the level was maintained till the end of the earthquake. The water levels returned to its original height after about 7 to 10 days of the earthquake. Moreover, electrical conductivity (EC) values were changed because of the interaction with the surrounding rocks and well walls, mixing with different waters during the earthquake shaking. The essential anomalies were observed in the geothermal fields of Gülbahçe and Seferihisar. Due to this earthquake, new geothermal springs emerged along the NE-SW trending Gülbahçe and Tuzla faults, located about 50 to 20 km from the Samos earthquake epicenter, respectively. The new geothermal waters are in Na-Cl composition and similar to other geothermal springs in the region. While the recorded water temperatures in the new geothermal springs vary from 40 to 45 °C in Seferihisar, it was measured between 35 and 40 °C in Gülbahçe. Due to these anomalies, it is found essential to monitor the effect of the earthquake on the physical and chemical characteristics of the groundwater and its usefulness in earthquake predictions.

Influence of the sloping ground conditions and the subsequent shaking events on the pile group response subjected to kinematic interactions for a liquefiable sloping ground

The soil-pile kinematic interaction under large nonlinearity, including soil liquefaction, represents a complex phenomenon that depends on many unforeseen factors. This paper presents the results of dynamic centrifuge tests carried out considering varying sloping inclination angles for a liquefiable ground subjected to four successive earthquake shakings having an increasing amplitude of acceleration. The results indicated the ground surface sloping inclinations to have a significant influence on the kinematic bending moment response of the piles. The significantly larger kinematic moments were generated on the downslope pile compared to the upslope pile highlighting the non-existence of shadowing effects during the lateral spreading for a liquefiable sloping ground. The kinematic moments generated during the first shaking, having predominant lateral spreading were substantially larger than the following three shakings, indicating the complex kinematic interaction to depend not only on the amplitude of base excitation; but mostly on the magnitude of lateral spreading. Moreover, the influences of the generated E.P.W.P on the pile response was studied and it was found that the piles may receive maximum kinematic moments around the occurrence of liquefaction to the time of initiation of dissipation phase of the generated E.P.W.P.

Design and Modelling of Ballscrew Linear Guide Actuator for Earthquake Shaking Table (EST) Based on Neural Network

Earthquake Shaking Table (EST) is a device which can simulate an earthquake motion. This device is used to test the strength of a building structure against an earthquake motions before it’s actually made. EST uses a variety of actuators one of them is ball-screw linear guide actuator. The EST used in this project is a bi-axial type which uses 2 linear actuators to simulate the x-axis and y-axis movement of earthquake, each of them used bipolar stepper motor as the main rotary-actuating device. This project models the linear guide actuator using backpropagation neural-network algorithm. The model is built with empirical method using datas taken from the real behavior of both linear actuators. The datas include acceleration, displacement, and velocity of both actuators and they are used to train the neural network using backpropagation with Levenberg-Marquadt method. Simulation is done using Simulink and the results show that model is able to produces nearly same exact movement with the real hardware with error approximately 0,214 % and 0,685% respectively for both actuators.

Performance evaluation of self-centering rocking shear walls: Part 2 — Determination of performance objectives

With increasing demand to achieve higher performance after strong earthquake shakings, novel high-performance systems have been developed. Self-centering rocking shear wall (SCRSW) is one of the high-performance structural systems which has been developed. To quantify the performance of SCRSWs, a robust performance evaluation model is needed. In this paper, the damage model developed in the companion paper (part 1) is adopted to evaluate the performance of 24 SCRSWs. The results of the performance evaluation are used to quantify the damage indexes (DI) for SCRSWs at different damage states. Design performance objectives, including the maximum and residual deformations corresponding to various performance levels are suggested based on the performance evaluation targeting different damage states. The proposed DI intervals and design performance objectives can be used by other researchers to design SCRSWs to achieve different performance objectives.

Archaeoseismological study of the Cherichira aqueduct bridge, Kairouan, Tunisia

In the past, several destructive earthquakes have occurred in the North African Atlas Mountain ranges located along the Africa–Eurasia plate boundary. Although the region is rich with impressive archaeological sites, including those in modern Tunisia, few comprehensive archaeoseismological studies have been conducted. Historic sources account at least three damaging earthquakes in the Kairouan area in central Tunisia between AD 859 and 1041. Little is known about which faults triggered these earthquakes or the size of these events. The water supply of the city of Kairouan depended on a 32-km-long aqueduct with a large bridge (now partially collapsed) at the confluence of the de Mouta and Cherichira rivers. The original bridge of Roman construction was retrofitted twice during the Aghlabid period (AD 800–903) and probably in AD 995 during the Fatimid period. The ruined section of the bridge shows damage which might be related to the AD 859 earthquake shaking. Here, we present a detailed study of the history, the status and the damage of the Cherichira aqueduct bridge using previous historic accounts and written works, a 3D laser scan model, local geological and seismological characteristics, and include results of radiocarbon dating and a timeline of events. In addition to earthquake ground motions, we consider severe flash floods on the bridge as a potential cause of the damage. We estimate the severity of such flash floods and develop a model with 18 earthquake scenarios on local reverse and strike-slip faults with magnitudes between MW 6.1 and 7.2. While a few damage patterns might be indicative of flooding, most damage can be attributed to earthquakes. It is highly probable that the earthquake in AD 859 caused enough damage to the Aghlabid bridge to render it dysfunctional; however, to resolve the question of whether another earthquake in AD 911 or 1041 caused the complete destruction of the previously retrofitted aqueduct by the Fatimids requires dating of additional sections of the bridge.

Seismic design and evaluation of controlled outriggered rocking wall (CORW) using equivalent energy design procedure (EEDP)

Next-generation earthquake engineering design seeks to develop robust structural systems to limit structural and non-structural damage after strong earthquake shaking. In this study, an innovative high-performance tall building, named Controlled outriggered rocking wall (CORW) system is proposed. The CORW system improves the conventional reinforced concrete (RC) core wall by adding a damped outrigger system and a damped controlled rocking base. The CORW is designed using the novel Equivalent energy design procedure (EEDP) to meet different performance objectives for different shaking intensities. Detailed EEDP for the CORW system is presented in this paper. Three prototype buildings (with 25, 35, and 45 stories) located in Vancouver Canada were designed using the proposed procedure. Robust finite element models of the CORW systems were developed in OpenSees and subjected to a series of nonlinear time history analysis. The results of the nonlinear time history analysis indicate that the CORW system designed using EEDP performs well under different levels of earthquake intensities, where it can be used reliably as an effective seismic force resisting system for high-rise application.

Performance evaluation of self-centering rocking shear walls: Part 1 — Quantification of structural damages

Self-centering rocking shear wall (SCRSW) is an innovative structural system which is designed to achieve low damage after strong earthquake shaking. In this paper, an effective damage quantification method is developed to quantify the damages of SCRSWs. The procedure is applied in the performance evaluation and damage quantification for 24 SCRSWs. An equation of the critical parameter β in the damage model is proposed. The results show that increasing stirrup reinforcement ratio, self-centering parameter and concrete strength can reduce the damage developed in SCRSWs effectively, while higher prestress in post-tensioned (PT) tendons tends to increase the damage. An empirical equation between the critical parameter β and structural features is proposed. The critical parameter is then used to quantify the damage index (DI) of SCRSW. The result shows that the proposed β can be used to evaluate and quantify the damages developed in SCRSWs efficiently and accurately.

Survey of Fragile Geologic Features and Their Quasi-Static Earthquake Ground-Motion Constraints, Southern Oregon

ABSTRACTFragile geologic features (FGFs), which are extant on the landscape but vulnerable to earthquake ground shaking, may provide geological constraints on the intensity of prior shaking. These empirical constraints are particularly important in regions such as the Pacific Northwest that have not experienced a megathrust earthquake in written history. Here, we describe our field survey of FGFs in southern Oregon. We documented 58 features with fragile geometric characteristics, as determined from field measurements of size and strength, historical photographs, and light detection and ranging point clouds. Among the surveyed FGFs, sea stacks have particular advantages for use as ground-motion constraints: (1) they are frequently tall and thin; (2) they are widely distributed parallel to the coast, proximal to the trench and the likely megathrust rupture surface; and (3) they are formed by sea cliff retreat, meaning that their ages may be coarsely estimated as a function of distance from the coast. About 40% of the surveyed sea stacks appear to have survived multiple Cascadia megathrust earthquakes. Using a quasi-static analysis, we estimate the minimum horizontal ground accelerations that could fracture the rock pillars. We provide context for the quasi-static results by comparing them with predictions from kinematic simulations and ground-motion prediction equations. Among the sea stacks old enough to have survived multiple megathrust earthquakes (n = 16), eight yield breaking accelerations lower than the predictions, although they generally overlap within uncertainty. FGFs with the lowest breaking accelerations are distributed uniformly over 130 km of coastline. Results for inland features, such as speleothems, are in close agreement with the predictions. We conclude that FGFs show promise for investigating both past earthquake shaking and its spatial variability along the coasts of Oregon and Washington, where sea stacks are often prevalent. Future work can refine our understanding of FGF age and evolution.

A drift-based design procedure for RC buildings considering the effect of shear wall-floor slabs junction

Reinforced Concrete (RC) structural wall is widely used in the lateral force resisting system for multistoried RC frame buildings located in earthquake-prone regions. In such buildings, the wall is connected to the RC slab at every floor level. The junction region of shear wall and floor slab constitutes an important link in the load path from slab to wall during earthquake shaking, thereby influencing the pattern of lateral load distribution in the shear wall. In case of multistoried building, the maximum elastic drift is estimated by carrying out linear static analysis for different load combinations as recommended by the Indian Earthquake Code IS 1893 (Part 1): 2016. However, during strong earthquake shaking, the inelastic lateral drift needs to be monitored to avoid undesirable levels of damage in structural members. The inelastic drift level of an isolated slender shear wall considering the behaviour of wall-slab junction has not been studied in the past. The present study aims to investigate the possible lateral drift limit of RC wall frame building considering the effect of floor slabs.

A discontinuous cantilever beam analogy for quantifying higher mode demands in stacked rocking cores

SummaryStacked rocking core (SRC) combinations are innovative sustainable structural assemblies that mitigate seismic demands through uplift at the hinge joints and direct damage to replaceable fuses. The stacked segments curtail substantially higher mode effects by the relative motions between multilevel cores. Currently, few research studies have quantified the behavior of SRCs under earthquake shaking. This paper presents a novel closed‐form solution for quantifying the higher mode demands of stacked braced frames subjected to seismic excitation. The mathematical formulae for modal analysis are derived using the analogy of discontinuous cantilever beam and Euler–Bernoulli equation. The proposed equations provide a method for rapid analysis and preliminary design of low‐ to mid‐rise SRCs. A parametric study is carried out to investigate the influences of rotational restraint of segments and the location of the rocking joints. Results verified by time response analysis indicate the validity and accuracy of the suggested formulae.

Bi‐directional ground motions: Stochastic simulation and frequency‐dependent modal combination rule

AbstractFor direct statistical analysis of 3‐D structures against lateral earthquake shaking, stochastic simulation of fully nonstationary bi‐directional ground motions is essential. The recorded bi‐directional ground motions (or their projections) along the two orthogonal axes of a structure are usually correlated and their correlation influences the overall structural response. Further, the correlation is, in general, frequency‐dependent, that is, the correlation coefficients are different for different narrow frequency bands of the (composite) pair of motions. So it is important to have a method for stochastic simulation of bi‐directional motions that can maintain a target frequency‐dependent correlation. This type of simulated ensemble of bi‐directional motions for a recording process provides a sound basis for the statistical analysis of structural response vis‐à‐vis the observed/recorded correlation. In the present paper, a Priestley process based framework is proposed to simulate bi‐directional ground motions that can emulate the frequency‐dependent correlation structure of the parent recording process while maintaining the time–frequency characteristics of the recorded bi‐directional motion. Since principal directions are frequency‐dependent, it is imperative to develop a modal combination rule for multi‐directional ground motions which can address the frequency‐dependence of principal directions. For this purpose, a new ground motion frequency‐dependent modal combination rule is also proposed. It is found that the proposed frequency‐dependent combination rule performs better than the conventional frequency‐independent one, especially when the response is dominated by some frequency bands having different individual principal directions from each other or from those of the composite pair of motions.

Between Necessity and Legal Responsibility: The Development of EEWS in Italy and its International Framework

Earthquake Early Warning Systems (EEWSs) represent a technical-scientific challenge aimed at improving the chance of the population exposed to the earthquake shaking of surviving or being less affected. The ability of an EEWS to affect the risk and, in particular, vulnerability and exposure, may determine serious legal responsibilities for people involved in the system, as scientists and experts. The main question concerns, in fact, the relationship between EEWSs and the predictability and avoidability of earthquake effects-i.e., the ground shaking affecting citizens and infrastructures - and the possibility for people to adopt self-protective behavior and/or for industrial infrastructures to be secured. In Italy, natural disasters, such as the 2009 L’Aquila earthquake, teach us that the relationship between science and law is really difficult. So, before EEW’s become operational in Italy, it is necessary to: 1) examine the legislative and technical solutions adopted by some of the international legal systems in countries where this service is offered to citizens; 2) reconstruct the international and European regulatory framework that promotes the introduction of EW systems as life-saving tools for the protection of the right to life and understand whether and how these regulatory texts can impose an obligation on the Italian legal system to develop EEWS; 3) understand what responsibilities could be ascribed to the scientists and technicians responsible for managing EEWS in Italy, analyzing the different impact of vulnerability and exposure on the predictability and avoidability of the harmful event; 4) reflect on the lessons that our legal system will have to learn from other Countries when implementing EEW systems. In order to find appropriate solutions, it is essential to reflect on the opportunity to provide shared and well-structured protocols and creating detailed disclaimers clearly defining the limits of the service. A central role must be recognized to education, because people should not only expect to receive a correct alarm but must be able to understand the uncertainties involved in rapid estimates, be prepared to face the risk, and react in the right way.

Seismic simulation tools and methods appropriate for developing countries

Understanding the earthquake behavior of structures is the first step towards developing a strategy for earthquake-resilient design and construction of the built environment. The growing number of earthquake simulators (shake tables) globally has allowed researchers to closely study the response of different building types when subjected to simulated earthquake shaking. Typically, such simulators are sophisticated and complex testing apparatus that require high levels of skill and experience for their effective operation and are associated with high costs of installation, operation, maintenance, and repair. In developing countries where there is limited investment in research, the application of such tools to meet the current need for experimental campaigns is generally not feasible, and hence alternative tools and methods are sought. In this context, a detailed review into alternative cost-effective tools and methods such as shock tables, harmonic shake tables, and controlled underground explosions for experimental testing was undertaken and is reported herein. Furthermore, the design, detailing, and construction of a shock table and a harmonic shake table are presented.