Earthquake Shaking Research Articles

Detailed space–time variations of the seismic response of the shallow crust to small earthquakes from analysis of dense array data

SUMMARYWe compute high-resolution space–time variations of subsurface seismic properties from autocorrelation functions (ACF’s) of noise and local earthquakes, recorded by the Sage Brush Flat dense array deployed around the Clark branch of the San Jacinto fault. The resolved temporal changes are referred to as apparent velocity changes because they reflect both nonlinear response and variations of material properties such as cracking and damage. Apparent velocity changes are estimated at four frequency bands (10–15, 10–20, 15–30 and 20–40 Hz) for two local earthquake data sets. In one analysis, ACF’s from P- and S-wave windows of 31 small events with magnitudes below 3.1 are used to compute the apparent velocity variations with respect to the mean ACF of each phase, and we also use the mean ACF of noise data as reference to estimate the changes. In a further analysis, the temporal evolution of properties is computed using moving time windows in continuous waveform over one-hour long data with noise and earthquake signals. The apparent velocity changes and recovery times are frequency dependent and present a strong spatial variability across the array. The resolved changes are larger and recovery time shorter with data associated with higher frequencies. At frequencies larger than 15 Hz, and using the mean ACF of noise data as a reference, the apparent average velocity changes across the array during the passage of the P and S waves from the small local events are 2.5 per cent and 6 per cent, respectively. The apparent velocity changes decrease by one order of magnitude when the earthquake data are used as a reference. The relatively large changes in response to very low ground motion have important implications on nonlinear processes involving degradation and healing of the subsurface material during common earthquake shaking.

Integration of 3D large‐scale earthquake simulations into the assessment of the seismic risk of Bogota, Colombia

AbstractBogotá, the capital city of Colombia, is mostly located on a lacustrine soil deposit surrounded by hills in a central plateau of the eastern cordillera of the Colombian Andes. This highly populated urban area is exposed to a significant seismic hazard from local and regional fault systems. In addition, the potential ground motion amplification during earthquakes due to the presence of soft soil deposits, along with the effects of the surface and subsurface topography, can strongly influence the seismic hazard and consequently the seismic risk to the city. This study aims to develop a physics‐based framework to generate synthetic ground records that can help better understand the seismic response of the basin and other amplification effects during strong earthquake shaking in the region, and to incorporate these effects into the estimation of seismic risk. To this end, a set of simulations were first conducted on Hercules, the wave propagation octree‐based finite element simulator developed by the Quake Group at Carnegie Mellon University, to identify the impacts of hypothetical strong earthquakes scenarios. Then, the results from these simulations were integrated with the exposure and vulnerability information previously developed for the main building constructions in the city to assess the seismic risk in the region under different conditions of analysis. Results from this more detailed model are compared with previously published results from simplified models. Sensitivity analyses help identify critical aspects that should be considered in the future to improve the seismic risk assessment of infrastructure.

Performance evaluation of curved damper truss moment frames designed using equivalent energy design procedure

Curved damper truss moment frame (CDTMF) system is a novel seismic force-resisting structural system which utilizes the curved dampers integrated into a semi-rigid moment frame to dissipate the earthquake input energy. To ensure the CDTMF has high performance, the state-of the art equivalent energy design procedure (EEDP) is applied to its design. EEDP allows engineers to design CDTMF to achieve different performance objectives at different levels of earthquake shaking intensities. In this study, two different prototype buildings (three and nine-story) were designed using EEDP. The seismic performance of the buildings was assessed using nonlinear time history analysis (NTHA) and incremental dynamic analysis (IDA). The results of the nonlinear dynamic analyses demonstrate that the CDTMFs can achieve the predefined performance targets (selected by the designer) at different earthquake intensity levels. The results of the IDA also show that the EEDP designed CDTMF has a sufficient margin against collapse. The results of this study in general confirm that CDTMF can be used as an effective seismic force-resisting system.

Factors influencing casualty risk in the 14th November 2016 MW7.8 Kaikōura, New Zealand earthquake

The November 14, 2016 MW7.8 Kaikōura Earthquake was one of the largest earthquakes to occur in New Zealand in the past 100 years and resulted in two deaths and 618 injuries. Understanding the context and cause of casualties from earthquakes is important for informing risk reduction activities such as building codes, education of protective actions, and casualty modelling. Data on casualties (deaths and injuries) from the Kaikōura earthquake were sourced from New Zealand's publicly funded accidental injury insurance scheme. Casualties were compared to a control group of uninjured people using a case-control design. Odds ratios were calculated through multivariate logistic regression to quantify the influence of individual, seismological and contextual factors on casualty risk. Females were twice as likely to be injured than males, and injury risk increased 30% with every 10 year increase in age. People were 2.9 times more likely to be injured if they were in non-residential buildings, and injury risk increased 2.2 times for every unit increase in MMI shaking intensity. Thirty-seven percent of casualties were from falls, 44% were from actions of people during shaking and 8% were due to being hit by contents. Nine percent of people were injured after shaking stopped during evacuations, or clean-up. The results indicate that in regions with a well-regulated building industry with modern building codes such as New Zealand, casualties are dominated by non-fatal injuries, and the number of these injuries are determined by the behaviour of individuals during and immediately following earthquake shaking.

Dynamic Stability Analysis of Slope Subjected to Surcharge Load considering Tensile Strength Cut-Off

Surcharge slopes are more vulnerable to instability under the effects of earthquake ground shaking, especially considering the tensile stress. In order to account for the adverse factors of seismic forces and tensile stress, the theory of soil with tensile strength cut-off is deduced and analyzed using the upper bound limit analysis method in this paper. Combined with the quasistatic analysis, the equation of critical acceleration expression for surcharge slope subjected to the dynamic conditions has been evaluated. By using the improved Newmark method, permanent displacements have been analyzed in the case of the classical earthquake ground motions. In addition, optimization algorithm has been undertaken, in which several influencing factors such as slope inclination, internal friction angle, surcharge factor, seismic load, and tension cut-off coefficient have been taken into account, and some results are verified with the classical solutions and FEM results. The results concluded the following: (1) The outcomes of verification results are accurate. (2) The critical acceleration of the slope is significantly affected by tension cut-off with the increasing of surcharge factor and seismic effects. (3) The permanent displacements of surcharge slope considering the tensile strength cut-off can be even 2 times of the traditional analysis; meanwhile, with more reduction of tensile strength, the cumulative displacements increase rapidly. Therefore, considering the influence of tensile strength cut-off is fundamental to the dynamic stability design of surcharge conditions.

ANALISIS POTENSI LIKUIFAKSI PADA PASIR VULKANIK DI PANTAI GLAGAH KULONPROGO BERDASARKAN DATA N-SPT

One of the most causes of damage to structures during earthquake is a liquefaction. Liquefaction happened in a loose sand which saturated under earthquake shaking. Earthquake shaking will cause cyclic loading to the surface of the ground which potential for occurrence of liquefaction. The liquefaction phenomenon is a soil behavior under cyclic loads that occurs in just a few moments. Due to the short cyclic load, the soil mass suddenly changes from a solid limit to a liquid limit or has a main consistency such as liquid. Liquefaction events during an earthquake can be characterized by the presence of ground movement in the horizontal direction, seepage water out from fracture of the ground, movement of sloping or descending buildings, displacement of ground advance, and landslides. This study took a case study in Glagah Beach at Kulonprogo Regency. That is beach areas which is a landform alongside a body water which consist of loose particles such as sand where Yogyakarta International Airport (YIA) is located. Analysis was carried out to determine the potential of liquefaction based N-SPT data using the Seed, Martin & Lysmer (1975). Based on these data, The Cyclic Stress Ratio (CSR) value is calculated, which is the ratio between the average shear stress caused by the earthquake with the effective vertical stress in each layer and the value of the Cyclic Resistance Ratio (CRR), which is the amount of soil resistance to liquefaction. The analysis in the Kulonprogo Regency area is an area that is considered to require liquefaction. Analysis of liquefaction potential based on on N-SPT data with the Seed, Martin & Lysmer (1975) method on a 6,3 magnitude earthquake. The Result indicate the potential for liquefaction occurs up to a depth of 8,5 meters.

Identification of surface-basement layer distribution of Wangi-Wangi Island based on HVSR method of microtremor data

<span class="jlqj4b"><span>To find out the distribution of the surface-basement layer of Wangi-Wangi Island, it can be done by calculating the surface layer thickness of each measurement point using microtremor data. The surface layer thickness (<em>h</em>) also indicates the position of the basement to the surface. The microtremor recording data used in this study were 47 data. Furthermore, the data were processed using the HVSR method to obtained the soil predominant frequencies which together with the <em>V</em><sub>s30</sub> values were used to calculated the <em>h </em>values. The results showed that the thickness of the surface layer or sediment layer of Wangi-Wangi Island was in the range of 5.7339 to 241.2557 meters. Based on its distribution, the areas with a thick surface layer are in the areas of Sombu, North Wandoka, Wandoka, South Wandoka, Pada Raya Makmur and Wanci. In the case of a disaster, these areas are thought to have the most potential to experience damage if an earthquake shakes.</span></span>

Expanded Byrne model for evaluating seismic compression

Seismic compression is the accrual of contractive volumetric strain in unsaturated or partially saturated sandy soils during earthquake shaking and has caused significant distress to overlying and nearby structures. The phenomenon can be well characterized by load-dependent, interaction macro-level fatigue theories. Toward this end, the Byrne cyclic shear-volumetric strain coupling model is expanded and calibrated for evaluating seismic compression for several soil types. In addition, the model was transformed to allow it to be implemented in a “simplified” manner, in addition to the original “non-simplified” formulation. Both implementation approaches are used to analyze a site in Japan impacted by the 2007, Mw6.6 Niigata-ken Chuetsu-oki earthquake. The results from the analyses are in general accord with the post-earthquake field observations and highlight the sensitivity of predicted magnitude of the seismic compression to the input variables used and modeling assumptions (e.g. relative density of the soil, magnitude of the volumetric threshold strain, orientation of the ground motions, settlement of soils below the ground water table, and accounting for multidirectional shaking). Although additional studies are needed to further validate the findings presented herein, estimation of relative density and threshold shear strain of the soil and ground motion orientation individually have moderate-to-significant influence on the computed magnitude of seismic compression, but they have a significant influence when taken in combination. Also, the seismic compression models can seemingly be used to predict the settlement in fully saturated sand when the excess pore water pressures are limited. Finally, accounting for multidirectional shaking has a significant influence on the computed magnitude of seismic compression.

Seismic performance of eccentrically braced frames designed by the conventional and equivalent energy procedures

Eccentrically braced frame (EBF) is a robust structural system designed for seismic application. The design philosophy for EBF is to utilize the link beams to dissipate the earthquake energy. While such system has been proven to provide sufficient stiffness and strength to prevent the structure from collapse, the structural performance in terms of damage and resilience after strong earthquakes is not explicitly considered. In this paper, a novel design method, named the Equivalent Energy Design Procedure (EEDP), is adopted to design the EBF. EEDP is an alternative design procedure for fused structural systems, where engineers can design the structure to achieve the intended performance objectives at different earthquake hazard levels. To evaluate the performance of the EBF, a 5 storey EBF located in Vancouver, British Columbia, Canada is designed using both the EEDP and the Equivalent Static Force Procedure (ESFP) outlined in the 2015 National Building Code of Canada. Detailed nonlinear dynamic analyses were conducted. The results show that the EEDP designed EBF has better performance with lower initial and repair costs at different levels of earthquake shaking intensities.

Data Mining Applied for Liquefaction Mapping and Prediction Learn from Palu Earthquakes

The 2018 Palu-Sigi-Donggala earthquakes in Center Celebes have caused significant damage to many residential houses due to varying degrees of soil liquefaction over a vast extent of urban areas unseen in past destructive earthquakes. Soil liquefaction occurred in Palu and Sigi, thus providing researchers with a wide range of characterizing soil and site response to large-scale earthquake shaking. One of the essential learning issues is the prediction of liquefaction. Prediction of liquefaction is also a complex problem as it depends on many different physical factors, and the relations between these factors are highly non-linear and complex. Most of these approaches are based on classical statistical criteria and neural networks. In this paper, a new method which is based on classification data mining (DM) is proposed. The proposed approach is based on historical data from the field and sciences portal. The proposed algorithm is also compared with several other DM algorithms based on the miner. It is shown that the proposed algorithm is very useful and accurate in the prediction of liquefaction.

Analytical Solutions for Seismic Fluid-Structure Interaction of Head-Supported Cylindrical Tanks

AbstractFluid-structure interaction (FSI) of earthquake shaking is a design consideration in the civil, nuclear, chemical, and mechanical industries. Preliminary sizing of structures and components...

Evaluating the ShakeOut drill in Aotearoa/New Zealand: Effects on knowledge, attitudes, and behaviour

Earthquakes pose a significant risk to Aotearoa/New Zealand (NZ), where many injuries occur during shaking. These negative outcomes can be reduced by teaching the protective action, ‘Drop, cover, and hold’. The ShakeOut earthquake drill, developed in the United States to encourage practice of these protective actions, has been run nationwide in NZ in 2012, 2015, 2018, and 2019. Here we report an evaluation of the 2012 and 2015 ShakeOut drills. Previous research focuses on logistics of the drill, such as participation rates. In contrast, this study demonstrates that ShakeOut drill participants have better knowledge of correct protective actions, use of those actions during actual earthquake shaking, and additional preparedness actions, as well as weaker biases such as fatalism. In line with calls for more thorough evaluation of the behavioural and cognitive impacts of the drill, this research represents important preliminary evidence for meaningful benefits of employing ShakeOut.

Earthquake response of monopiles and caissons for Offshore Wind Turbines founded in liquefiable soil

Monopile has been the most widespread foundation type for Offshore Wind Turbines (OWTs) in shallow waters. Caisson (skirted) foundations have also been evaluated in some projects as an economical alternative. While the main concern in design of offshore foundations has been the environmental loads, the recent growth in construction of OWTs in seismic regions with the possibility of soil liquefaction has necessitated evaluation of the impact of earthquake and liquefaction from strong shakings on these structures. Several studies have reported the consequences of soil liquefaction for buildings and onshore structures; However, the effects of liquefaction on offshore foundations have not been sufficiently studied. This paper investigates the use of advanced liquefaction modeling in assessment of the response of monopiles and caissons for offshore wind turbines. The software FLAC3D and the SANISAND constitutive model are used to conduct the nonlinear dynamic analyses for OWTs. Excess pore water pressure during earthquake shaking and earthquake-induced displacements are computed at various points in the soil medium around the considered monopile and caisson foundations. The analyses reveal that SANISAND model is capable of simulating the pore pressure generation in the free-field as observed in a recent centrifuge test. The numerical results also indicate that both monopile and caissons in liquefiable soil deposits experience considerable rotations under the combined action of wind loads and earthquake shaking when liquefaction occurs.

Seismic active earth pressure of unsaturated soils with a crack using pseudo-dynamic approach

Abstract The analyses of active earth pressure subjected to earthquake shaking are routinely explored concerning dry or saturated soils. However, the fact often neglected in previous literature is that soils are mostly unsaturated in nature. This work puts forward a kinematical approach for the assessment of active resistance of a rigid retaining structure against unsaturated backfills with pseudo-dynamic approach, and the effect of a crack presented in backfills is also considered. A layer-wise summation method is employed to compute the non-uniformly distributed seismic forces due to earthquake accelerations considering time and spatial effects and corresponding work rates. Several nonlinear formulae as well as different soil-water characteristic curve models are employed to determine the additional cohesion caused by matric suction. To verify the validity of the proposed approach, a comparison is conducted with its simplified modality and conventional pseudo-static approach based on identical input conditions. The comparison results show good agreement. The lateral earth pressure can be derived from the principle of work rate balance using a numerical optimization technique. A parametric analysis is implemented to investigate the influences of crack depth, water level, dynamic factors of seismic effects and nonlinear evaluation models on the critical seismic active earth pressure.

Analysis of a novel subway station structure to mitigate damages induced by normal faulting

Underground structures are more vulnerable to faulting than earthquake shaking. However, there are no effective mitigation measures for the damages of underground structures subjected to normal faulting. This study proposes a novel structure for new subway stations to mitigate the normal fault induced damages. The novel subway station consists of a rectangular cross-section and two rigid diaphragm walls. The diaphragm walls are made of reinforced concrete, connecting with the bottom corners of the structure. A series of analyses was conducted by finite elements, which had thoroughly validated in previous studies. The results show that the responses of the novel structure depend on fault throw, its location relative to the rupture, soil depth, burial depth, and the length of diaphragm walls. The presence of diaphragm walls substantially reduces the structure rotation in two ways: (1) obtaining skin friction from surrounding soil to conquer the rigid body rotation, and (2) restraining differential soil displacements underneath the bottom slab.

Probabilistic Seismic Demand Assessment of Steel Moment-Resisting Frame Buildings with Ordinary and Essential Occupancy Uses

In the perspective of disaster-resilient communities, the essential buildings should be able to play an important role with limited damage for civil protection during and after natural hazards. However, this type of buildings may exhibit extensive damage of their structural and non-structural components. In this regard, there has been an increasing need for the accurate quantification of the earthquake performance of essential buildings in order to minimize societal and economic losses due to injuries, casualties, business disruption, etc. This paper aims to quantify the expected earthquake performance of higher risk steel frame buildings through collapse risk over their lifetime and seismic demand hazard. These buildings are designed for high-seismic regions on the West Coast of the United States following current seismic provisions. The expected earthquake performance is computed using the second-generation performance-based seismic risk evaluation. The collapse risk varies significantly, according to the employed design procedure; the collapse risks over a lifetime of essential buildings designed as per enhanced seismic design requirements are decreased by a factor of about 3, relative to counterparts of the same risk category buildings. The effect of employed seismic design procedure on the nonlinear demands of the buildings under severe earthquake shakings is significant.

Seismic settlement of a strip foundation resting on a dry sand

Seismic settlement of shallow foundations constructed in seismic active areas should be considered for a reasonable estimation of the total settlement. However, the trend of the seismic settlement of shallow foundation constructed on a sandy soil is not clearly understood and it is estimated by designer using simple analytical methods. These methods do not consider the effect of the soil–structure interaction. This research, therefore, reports the results of 105 robust finite element models developed to investigate the seismic settlement of a shallow foundation constructed on a dry sand. The influence of the load applied on the foundation, relative density of sand, foundation embedment, peak ground acceleration of the earthquake shake, thickness of the sandy soil, and the dominant frequency of the earthquake shake have been examined to provide a comprehensive understanding of the parameters influencing the seismic settlement. The results of the analyses showed that increasing the load applied on the foundation or the peak ground acceleration remarkably increases the seismic settlement, while increasing the embedment depth remarkably reduces the seismic settlement. In addition, the relationship between the thickness of the sandy layer and the seismic settlement is found to be very complex and noticeably influenced by the relative density of the sand. More importantly, it was found that the seismic settlement dramatically increases when the dominant frequency of the earthquake approaches the natural frequency of the system. Thus, all these parameters are important and should be considered by designers for a reasonable estimation of the seismic settlement. The conclusions drawn from this paper will aid the development of a good analytical method in future, and the results reported in this paper also provide useful and novel database to designers and practitioners.

Rapid prediction of earthquake ground shaking intensity using raw waveform data and a convolutional neural network

SUMMARY This study describes a deep convolutional neural network (CNN) based technique to predict intensity measurements (IMs) of earthquake ground shaking. The input data to the CNN model consists of multistation, 3C acceleration waveforms recorded during the 2016 Central Italy earthquake sequence for M ≥ 3.0 events. Using a 10 s window starting at the earthquake origin time, we find that the CNN is capable of accurately predicting IMs at stations far from the epicentre which have not yet recorded the maximum ground shaking. The CNN IM predictions do not require previous knowledge of the earthquake source (location and magnitude). Comparison between the CNN model predictions and those obtained with the Bindi et al. GMPE (which requires location and magnitude) shows that the CNN model features similar error variance but smaller bias. Although the technique is not strictly designed for earthquake early warning, we find that it can provide useful estimates of ground motions within 15–20 s after earthquake origin time depending on various setup elements (e.g. times for data transmission, computation, latencies). The technique has been tested on raw data without any initial data pre-selection in order to closely replicate real-time data streaming. When noise examples were included with the earthquake data the CNN was found to be stable, accurately predicting the ground shaking intensity corresponding to the noise amplitude.

Contrasting seismic risk for Santiago, Chile, from near-field and distant earthquake sources

Abstract. More than half of all the people in the world now live in dense urban centres. The rapid expansion of cities, particularly in low-income nations, has enabled the economic and social development of millions of people. However, many of these cities are located near active tectonic faults that have not produced an earthquake in recent memory, raising the risk of losing hard-earned progress through a devastating earthquake. In this paper we explore the possible impact that earthquakes can have on the city of Santiago in Chile from various potential near-field and distant earthquake sources. We use high-resolution stereo satellite imagery and imagery-derived digital elevation models to accurately map the trace of the San Ramón Fault, a recently recognised active fault located along the eastern margins of the city. We use scenario-based seismic-risk analysis to compare and contrast the estimated damage and losses to the city from several potential earthquake sources and one past event, comprising (i) rupture of the San Ramón Fault, (ii) a hypothesised buried shallow fault beneath the centre of the city, (iii) a deep intra-slab fault, and (iv) the 2010 Mw 8.8 Maule earthquake. We find that there is a strong magnitude–distance trade-off in terms of damage and losses to the city, with smaller magnitude earthquakes in the magnitude range of 6–7.5 on more local faults producing 9 to 17 times more damage to the city and estimated fatalities compared to the great magnitude 8+ earthquakes located offshore in the subduction zone. Our calculations for this part of Chile show that unreinforced-masonry structures are the most vulnerable to these types of earthquake shaking. We identify particularly vulnerable districts, such as Ñuñoa, Santiago, and Providencia, where targeted retrofitting campaigns would be most effective at reducing potential economic and human losses. Due to the potency of near-field earthquake sources demonstrated here, our work highlights the importance of also identifying and considering proximal minor active faults for cities in seismic zones globally in addition to the more major and distant large fault zones that are typically focussed on in the assessment of hazard.

A Probabilistic Model of Aquifer Susceptibility to Earthquake-Induced Groundwater-Level Changes

ABSTRACTA probabilistic model for earthquake-induced persistent groundwater-level response as a function of peak ground velocity (PGV) has been constructed using a catalog of monitoring well observations spanning multiple earthquakes. The regional-scale, multi-site, multi-earthquake investigation addresses the occurrence and absence of hydraulic responses to large earthquakes spanning almost a decade of seismic shaking. Persistent groundwater-level changes, or absences of change, have been quantified in 495 monitoring wells in response to one or more of 11 recent New Zealand earthquakes larger than Mw 5.4 that occurred between 2008 and 2017. A binary logistic regression model with random effects has been applied to the dataset using three predictors: earthquake shaking (PGV), degree of hydrogeological confinement (monitoring well depth), and rock strength (site-average shear-wave velocity). Random effects were included as a partial proxy for variations in monitoring wells’ susceptibilities to earthquake-induced persistent water-level changes. Marginal probabilities have been calculated as a function of PGV and related to modified Mercalli intensity (MMI) levels using a New Zealand-specific MMI–PGV relationship that enables the likelihood of persistent water-level changes to be expressed for MMIs of II–VIII. This study capitalizes on one of the largest catalogs of earthquake hydrological observations compiled worldwide and is the first attempt at incorporating seismic and hydrogeological factors in a common probabilistic description of earthquake-induced groundwater-level changes. This modeling framework provides a more generalizable approach to quantifying responses than alternative metrics based on epicentral distance, magnitude, and seismic energy density. It has potential to enable better comparison of international studies and to inform practitioners making engineering or investment decisions to mitigate risk and increase the resilience of water-supply infrastructure.