Spatial Variability Of Ground Motion Research Articles

Effects of spatial variability of ground motions on collapse behaviour of buildings

The seismic damage simulation of buildings has become a research focus because of the rapid urbanisation and the increase in the building density. However, there is no consensus regarding whether the spatial variability of ground motions at the local sites must be considered in collapse simulations. Thus, in the present study, a numerical model based on the finite element method that can effectively predict the collapse behaviour of reinforced concrete buildings is developed. Then, field ground motion records are selected from the measurement database. Finally, a building neighbourhood comprising four typical three-storey reinforced concrete frame structures is established as a numerical example, and the effects of the spatial variability and intensity of ground motions on the structural response and collapse behaviour of buildings are comprehensively investigated. The results indicate that the spatial variability of the ground motions significantly affects the structural responses and collapse behaviours of the buildings within a certain range of the ground motion intensity. The collapse behaviour of a single building exhibits significant differences with different ground motion intensities. These differences are attributed to the coupling of the nonlinearity of the structures and the randomness of the ground motions. It is concluded that the spatial variability of ground motions should be fully considered in the collapse simulation of buildings.

Network analysis of earthquake ground motion spatial correlation: a case study with the San Jacinto seismic nodal array

SUMMARYThe spatial correlation of earthquake ground motion intensity can be measured from strong motion data; however, the data used in past studies is sparsely sampled in space, and only the interstation distance was considered as a correlation variable. These limitations mean that we have only weak constraints on the true correlation structure of ground motion and that potentially important aspects of spatial correlation are unconstrained. In this study, we combine a large-N seismic array and graph analytics to explore this issue at a local scale using small local and regional earthquakes. Our result suggests site conditions, and how they interact with the incident seismic wavefield, strongly condition the spatial correlation of ground motion. Future progress in characterizing ground motion spatial variability will require dense wavefield measurements, either through nodal deployments, or perhaps distributed acoustic sensing measurements, of seismic wavefields. Aftershock sequences of major earthquakes would provide particularly data-rich targets of opportunity.

Vibration of submerged floating tunnels under asynchronous support excitation

In recent years, submerged floating tunnels (SFT) have received considerable attention due to the growing increase of traffic volume and travel time. SFT provides eligible options for crossing long waterways. The long span of the SFT increases the probability of asynchronous excitation. This study examines the seismic behavior of the SFTs considering a) spatial variation of ground motion along the tunnel length, b) effect of different assumptions regarding this spatial variation, c) effect of of two- and three-dimensional modeling of fluid field. Two approaches including finite element and analytical solutions are used in the assessments. The results show that accounting for spatial variation of ground motion and three dimensionalities of the fluid field are detrimental in obtaining a realistic estimate of response parameters. Also, it is shown that using a linear approximation of spatial variation of ground motion along the tunnel length could give acceptable approximation of actual response.

Coherence and variability of ground motion in New Madrid Seismic Zone using an array of 600 m

The spatial variation of ground motion is determined for high-frequency P- and S-waves in the New Madrid Seismic Zone at a site near Mooring, TN. An L-shaped array consisting of 19 seismometers and having arm lengths of 600 m located on Holocene fluvial sediments of the Mississippi River was used to examine wave coherency appropriate for many sites throughout the Mississippi embayment and other sediment sites associated with large rivers. Data from local and regional earthquakes within a distance range of 300 km show that coherency within the frequency band of 0.5 to 16 Hz degrades with inter-station distance across the array according to an empirical exponential model. Vertical component P-waves are coherent over nearly 2 horizontal wavelengths. However, the coherency for horizontal component S-waves degrades more rapidly than the vertical component P-waves. S-waves become significantly incoherent at distances of only 0.2 horizontal wavelength and become completely incoherent after 0.5 wavelength. The results of this study show clear and quick decay of wave coherence likely to occur in strong ground motions from nearby earthquakes. The observed incoherence can be a significant factor for the response of structures having foundation lengths of even 100 m.

Investigating the Effect of Pseudo-Static Components on Bridge Structures under Multiple Support Excitations Using Conditional Simulated Records

Long-span bridges, as vital structures, play an important role in economic development. Previous studies revealed that the seismic responses of such structures, under non-uniform excitations, are different from the same result due to uniform excitations. Furthermore, the results of several earthquake-damaged bridges showed that their seismic behavior was different from that predicted under uniform excitation and, in some cases; the responses were more than predicted results. Therefore, the damaged bridges under non-uniform excitations were re-analyzed and the obtained results were in good agreement with the recorded outcomes. Considering current bridge designing codes it is clear that almost all of them ignored it and just the Euro Code 2008 prepared some recommendations. It is found that the main reason for the differences in results from the uniform and non-uniform excitations is the spatial variation of earthquake ground motions. Based on the papers three phenomena were introduced for spatial variability of ground motion: the wave-passage, the incoherence, and also the site-response effects. The responses of structures under non-uniform excitations obtained from the superposition of dynamic and pseudo-static components. This paper investigated the seismic behavior of a long-span structure under non-uniform movements to evaluate the most undesirable conditions. So, different soils and load combinations considered and soil-structure effects included. The effect of wave-passage, incoherence, and site-response on the structure was measured and the results were compared with the uniform excitation. The results indicate that the variation in soil condition significantly affects the seismic responses under non-uniform excitations. Also, it is found that the results from uniform excitations with considering soil-structure interactions are remarkably increased. Moreover, the outcomes of analysis under-considered load cases and soil conditions showed that ignoring the spatially varying ground motions may lead to a non-conservative design.

Longitudinal response of buried pipeline under non-uniform seismic excitation from multi-point shaking table tests

The spatial variability of ground motion has a significant influence on the seismic response of long infrastructure and is considered the primary cause of pipeline damage during earthquakes. In this study, a series of three-dimensional shaking table tests were carried out to investigate the influence of non-uniform seismic excitation on the pipeline response using a scaled pipeline model installed in sand. The pipeline-soil model was enclosed in a suspension continuum soil box situated on three shaking tables that can induce uniform and non-uniform seismic excitations. Accelerometers were distributed along the soil profile, and strain gauges and accelerometers were attached to the pipeline to monitor the dynamic response of the pipeline-soil system during the shaking. The pipeline-soil model was subjected to a series of uniform and non-uniform excitations with gradually increasing intensity. The testing results demonstrated that the pipeline experienced tensile and compressive strains due to the longitudinal seismic excitation because the phase and waveform of the seismic waves were almost the same at the strain measuring points around the pipeline profile. The acceleration response of the pipeline under non-uniform seismic excitation was larger than that of the surrounding soil. The pipeline strain response under non-uniform seismic excitation was approximately twice that under uniform seismic excitation. The soil-pipeline interaction exhibited complex behavior; sliding may occur with the increase of loading intensity, and more likely to occur under non-uniform seismic excitation. These results indicate that the dynamic response of the pipeline-soil system is sensitive to non-uniform ground motion, which should be properly considered in the seismic design of pipeline.

Impact of High Energy Mining-Induced Seismic Shocks from Different Mining Activity Regions on a Multiple-Support Road Viaduct

In this paper, the dynamic responses of a large-scale multiple-support road viaduct to mining-induced seismic events registered in two regions of mining activity were compared. The regions differ in geological structure, which results in discrepancies in the dominant frequency content. Spatial variation of ground motion causing the kinematic excitation non-uniformity was accounted for in the dynamic analyses of this large-scale structure. Non-uniform mining-induced kinematic excitation models were proposed, with respect to the specificity of mining origin quakes. The dynamic performance of the viaduct was determined using three different methods of calculation: the time history analysis, the response spectrum analysis, and the multiple support response spectrum analysis. Both the uniform and non-uniform kinematic excitation models were adopted for the dynamic performance assessment. The research revealed that the dynamic response of some members of the structure, determined using the non-uniform excitation model, was significantly greater than that obtained for the uniform one. Hence, in the dynamic analysis of multiple-support structures under mining-induced events, the effect of spatial variation of ground motion should be considered. The study pointed out that the commonly used response spectrum analysis may lead to the underestimation of the dynamic response of large-scale multiple-support structures. Instead, the multiple support response spectrum method, which takes into account the non-uniformity of ground motion, is recommended as a conservative approximation. This method provides a safe upper estimation of the full-dynamic analysis results of large-scale structures under mining-induced tremors. Finally, the research indicated that the dynamic performance of a structure strongly depends on the frequency range attributed to a specific mining region. The dynamic performance of identical engineering structures under tremors of similar maximal amplitudes may differ significantly due to discrepancies in frequency contents of shocks occurring in various mining regions.

A new solution to estimate the time delay on the topographic site using time domain 3D boundary element method

This study focuses on investigating spatial variation of ground motion that has great influence on the dynamic behavior of the large structures located on the surface topography. One of the most effective parameters on the spatial variation of ground motion is the difference between the arrival time of seismic waves in different points located on the abutments. In this research, a three-dimensional model of the Pacoima Dam site is prepared. The time domain 3D boundary element method is used to apply non-uniform excitation at the dam supports. This model is subjected to vertically propagating incident SH and P waves. The time delay can be characterized by calculating the value of the time delay for which the cross-correlation between two records is maximized. Finally, to obtain the time delay in a topographic site, a function considering effective parameters such as the height from the canyon base, wave velocity and predominant frequency, is presented. Furthermore, a code was developed for generating the spatially variation of seismic ground motions. The results show that the proposed functions have an acceptable accuracy in estimating the time delay to generate non-uniform ground motion.

Seismic Analysis of a Curved Bridge Considering Soil-Structure Interactions Based on a Separated Foundation Model

A separated foundation model was proposed in order to reduce the calculation scale of the numerical model for analyzing soil-bridge structure dynamics. The essence of the wave input analysis model considering soil-structure interaction was analyzed. Based on the large mass method, a one-dimensional time-domain algorithm of the free field was derived. This algorithm could simulate the specified ground motion input well. The displacement expansion solution of the free wave field was solved based on the propagation law of waves in a medium. By separating the soil foundations around the pile foundations of the bridge, the ground motion was transformed into an equivalent load applied on an artificial boundary. The separated foundation model could consider the incoherence effect and soil-structure interaction simultaneously; the number of model elements were reduced, and the computational efficiency was improved. In order to investigate the seismic response of a curved bridge considering soil-structure interaction under spatially varied earthquakes, a curved bridge with small radius was adopted in practical engineering. Spatially correlated multi-point ground motion time histories were generated, and the nonuniform ground motion field was simulated based on the wave input method on an artificial viscoelastic boundary. The effects of different apparent wave velocities, coherence values, and site conditions on the seismic response of the bridge were analyzed. The results showed that the spatial variation of seismic ground motion had a considerable effect on the bending moment and the torsion of the girder. The site effect had great influence on the bending moment of the pier bottom. When considering soil-structure interaction, the spatial variation of ground motion should be fully considered to avoid underestimating the structural response.

An inter-disciplinary and multi-scale approach to assess the spatial variability of ground motion for seismic microzonation: the case study of Cavezzo municipality in Northern Italy

Seismic microzonation represents a basic tool for prevention activity planning and land management. An extensive and detailed microzonation study was performed with reference to the territory of the Municipality of Cavezzo, damaged during the seismic sequence hitting Emilia-Romagna Region, Northern Italy, in 2012. In this paper, we discuss the work carried out to characterize the spatial variability of ground motion amplification due to local soil conditions in the municipality area.An inter- and multi-disciplinary approach is presented, involving geotechnical engineers, geophysicists, geologists and seismologists from different institutions, to thoroughly characterize the territory using complementary techniques with different level of resolution and confidence. A considerable amount of geomorphological, geological, hydrogeological, seismological, geotechnical and geophysical investigations was collected and processed for the purpose. A GIS-based (Geographic Information System) platform was initially setup to manage the gathered data, which now includes the results of about 1000 geotechnical and geophysical tests. Such an extended dataset was then used as a primary constraint for the creation of a comprehensive pseudo-3D geotechnical and seismo-stratigraphic model of the territory, consisting of a dense grid of one-dimensional vertical profiles to depict the variability of the soil properties over the area. The model was finally used as input for linear-equivalent ground response analysis. For the calculation of the amplification factors, special emphasis was given to the treatment and propagation of the uncertainties of the model parameters, whose different realizations have been accounted through a logic tree approach.

Effect of spatial variability of earthquake ground motions on the reliability of road system

This paper presents an approach for assessing the failure probability of a road system due to its interaction with landslides induced by the earthquake. The landslide occurrence and failure probability of the road system is estimated by considering the spatial variation of earthquake ground motion. Since significant incoherence in earthquake ground motions is usually observed within the spatial dimensions of large horizontally expanded structures like roads, bridges and dams, it is important to consider the uncertainty due to spatially varying ground motion. The stochastic nature of seismic loading is incorporated in the study by generating a series of earthquake ground motions while the spatial variation of ground motion is accounted for by using cross power spectral density function. Two phase material point method (MPM) is used to simulate the dynamic behaviour of saturated slopes. MPM is able to capture the failure mechanism of slopes under seismic loading and evaluates the travel distance of sliding mass.

Extension of probabilistic seismic hazard analysis to account for the spatial variability of ground motions at a multi-unit nuclear power plant hard-rock site

Nuclear power plant (NPP) sites typically consist of multiple reactors (units). When earthquakes occur in the vicinity of these sites, effects will be experienced at all units. However, a seismic probabilistic risk assessment (PRA) of a multi-unit site typically only considers the possibility of adverse conditions at a single unit or, if multiple unit impacts are considered, typically assumes that all units at the site experience the same ground motion. This assumption of perfect correlation in ground motion is inconsistent with data from dense seismic arrays, which show that there is spatial variability in the ground motion between closely-spaced locations during the same earthquake. Moreover, such an assumption is not inherently conservative as is often assumed. To facilitate more realistic assessments, this paper proposes a method for capturing the effects of spatial variability of ground motion at an NPP site in the seismic PRA. The proposed method uses the results from an existing probabilistic seismic hazard analysis (PSHA) performed for a reference location at the site (e.g., the site seismic hazard curve and magnitude disaggregation) and then estimates the conditional probability distribution of the ground motion at a non-reference location. The proposed method accounts for the spatial variability in ground motion amplitude and includes mathematical formulations for NPP sites classified as “hard-rock.” The proposed method is developed using Bayesian networks because their graphical structure facilitates model transparency and communication. Moreover, Bayesian networks facilitate efficient probabilistic modeling and inference involving dependent random variables. However, the proposed method can be implemented more generally without using Bayesian networks as the calculation framework and commentary is provided regarding these alternative calculation options. This paper concludes with an example application using a PSHA for a hypothetical hard-rock site in the Central United States. Based on the results from the example application, we note that the perfect correlation assumption with respect to the ground motion at multiple locations/units at an NPP site may not necessarily be conservative.

Investigating the spatial variability of ground motions during the 2017 Mw 7.1 Puebla-Mexico City earthquake via idealized simulations of basin effects

We use strong motion records of the Mw 7.1 19 September 2017 mainshock and one- and two-dimensional (1D and 2D) simulations at six stations along a linear array across Mexico City, to shed light to the site amplification and ground motion variability observed during the mainshock. The 2017 Puebla-Mexico City earthquake occurred at the edge of the flat slab segment of the subducted Cocos plate beneath central Mexico, rupturing the top half of the plate. Compared to the 1985 subduction zone event, the intraslab Mw 7.1 mainshock was characterized by a much richer high-frequency content. This characteristic transpired into site amplification of the incoming shaking by the sediments of the transition zone, contrary to the 1985 Mw 8.1 Michoácan earthquake that was amplified by the deeper lake sediments. By means of idealized 1D site and 2D basin models, this paper seeks to disentangle site response from basin resonance and basin edge diffraction effects manifesting in the ground motion records. We specifically compare ground surface observations from the 2017 Mw 7.1 event to 1D and 2D analyses in the time and frequency domain; and empirical transfer functions from several earthquakes to numerical transfer functions computed using 1D and 2D models. Comparison of empirical and simulated amplification spectra shows that, although our 2D model does not capture all the peaks and troughs of the frequency response, theory and observations are nonetheless in good agreement across the entire frequency spectrum. And while frequency peaks of the 1D and 2D models are aligned in the range f>0.2Hz, the long period (f<0.01Hz) match between simulations and observations demonstrates that the 2D model appropriately captures the effects of the largest characteristic lengths of the basin, namely the basin width. In the intermediate frequency range (0.01 Hz <f<0.2Hz), our 2D model captures the scattering of the energy by the concave shape of the basin-rock interface via spectral deamplification, albeit not as strongly as is evidenced by the observations. One-dimensional site response on the other hand cannot capture the larger scale features below 0.2 Hz, which were likely relevant to the performance of lifelines and other infrastructure networks.

Influence of Multiple-Support Excitation on Seismic Response of Reinforced Concrete Arch Bridges

Although post-earthquake observations identified spatial variation of ground motion (i.e., multiple-support excitation) as a frequent cause of the unfavorable response of long-span bridges, this phenomenon is often not taken into account in seismic design to simplify the calculation procedure. This study investigates the influence of multiple-support excitation accounting for coherency loss and wave-passage effects on the seismic response of reinforced concrete deck arch bridges of long spans founded on rock sites. Parametric numerical study was conducted using the time-history method, the response spectrum method, and a simplified procedure according to the European seismic standards. Results showed that multiple-support excitation had a detrimental influence on response of almost all analyzed bridges regardless of considered arch span. Both considered spatial variation effects, acting separately or simultaneously, proved to be very important, with their relative significance depending on the response values and arch locations analyzed and seismic records used. Therefore, it is suggested that all spatially variable ground-motion effects are taken into account in seismic analysis of similar bridges.

Köprü Yapılarının Eş Zamanlı Sistem ve Girdi Tanılaması

Bu makale, deprem kayıtlarını kullanarak köprü yapılarının sistem tanılaması için yeni bir yöntem sunmaktadır. Köprüler, genellikle yapısal elemanlarının geniş mesafelere yayılmasından ötürü, diğer yapılara nispeten yer hareketlerinin uzamsal değişkenliğine daha hassastırlar. Bu nedenle, özellikle temelleri değişik zemin türlerine oturan uzun ve çok kolonlu köprülerin simülasyonlarında kullanılacak nitelikte yer hareketi kayıtlarının ölçümü karmaşık bir süreçtir. Bilhassa hem eylemsizlik hem de kinematik Zemin-Yapı Etkileşimi etkilerinin yaygın olduğu durumlarda, köprü Temel Girdi Hareketlerinin doğrudan ölçümü mümkün olmayabilir. Bu çalışmada, uzamsal olarak seyrek bir şekilde ölçülmüş sismik yapı davranış kayıtlarını kullanarak eş zamanlı sistem ve girdi tanılaması sağlayan yeni bir yöntem önerilmektedir. Önerilen metodun teyidi ve gerçek ölçekte problemlere uygulanabilirliğini doğrulamak adına, yöntem Golden Gate Köprüsü'ne uygulanmış ve elde edilen sonuçlar mevcut veriler ile karşılaştırılmıştır.

Viaduct seismic response under spatial variable ground motion considering site conditions

The evaluation of the seismic hazard for a given site is to estimate the seismic ground motion at the surface. This is the result of the combination of the action of the seismic source, which generates seismic waves, the propagation of these waves between the source and the site, and site local conditions. The aim of this work is to evaluate the sensitivity of dynamic response of extended structures to spatial variable ground motions (SVGM). All factors of spatial variability of ground motion are considered, especially local site effect. In this paper, a method is presented to simulate spatially varying earthquake ground motions. The scheme for generating spatially varying ground motions is established for spatial locations on the ground surface with varying site conditions. In this proposed method, two steps are necessary. Firstly, the base rock motions are assumed to have the same intensity and are modelled with a filtered Tajimi-Kanai power spectral density function. An empirical coherency loss model is used to define spatial variable seismic ground motions at the base rock. In the second step, power spectral density function of ground motion on surface is derived by considering site amplification effect based on the one dimensional seismic wave propagation theory. Several dynamics analysis of a curved viaduct to various cases of spatially varying seismic ground motions are performed. For comparison, responses to uniform ground motion, to spatial ground motions without considering local site effect, to spatial ground motions with considering coherency loss, phase delay and local site effects are also calculated. The results showed that the generated seismic signals are strongly conditioned by the local site effect. In the same sense, the dynamic response of the viaduct is very sensitive of the variation of local geological conditions of the site. The effect of neglecting local site effect in dynamic analysis gives rise to a significant underestimation of the seismic demand of the structure.

Behavior of Self-Supporting Communication Tower under Horizontal Loads

Communication towers have been traditionally designed for wind load. The earthquake load has not been observed in the analysis of the communication tower. Recent earthquakes, there have been indications of collapse to the communication tower. Due to the complex nature of the problem, there is a lack of research work in the area of analysis of the communication tower. The purpose of this research is to test the communication tower's response to earthquake ground movement to determine the current design software methodology. The effect of earthquake ground motion spatial variation on multi-support structures dynamic response may be necessary. The aim of this project is to use the traveling wave assumption to investigate the seismic response of high antenna-supporting guyed towers. The horizontal component of the Bhuj earthquake is considered as excitation. Elements of response analyzed are cable tension, base shear, mast axial force and lateral displacement of the tower tip. Parametric analyses show that the structural response tends to increase as the amplitude of the wave decreases and can become much larger than the reaction from synchronous excitation.

Numerical study on site response considering ground motion spatial variation

Identical support excitation (ISE) of ground motion has been utilized to study the site response, whereas, to a large-scale site, multiple support excitation (MSE) considering the ground motion spatial variation may be more applicable. In this paper, the spatially varying earthquake ground motions (SVEGMs) were simulated first. Then, a large-scale four-layered free-field model was established using ABAQUS. Taking ISE and MSE into account, the significant durations of acceleration responses and shear wave velocities at many observation points were obtained. Comparing the results under MSE with those under ISE, it was shown that: i) the significant durations of acceleration responses under MSE were shorter than those under ISE; ii) even though the input peak ground acceleration (PGA) for MSE is lower, the shear wave velocity under MSE is not necessarily higher. Therefore, the spatial variation of ground motion may have important influence on the seismic response of large-scale site.

Ground motion acceleration and response spectra of Al-Mashair area, Makkah Al-Mukarramah, Saudi Arabia

The residential buildings of Makkah Al-Mukarramah constructed mostly on a soft Quaternary deposits with various thicknesses reaching to more than 30 m in most districts. The spatial variation of ground motion in Al-Mashair area has been assessed by synthetic ground motion acceleration using a point source model coupled by a site response analysis. The bedrock level acceleration time histories have been generated at 27 sites within Al-Mashair area generated by earthquake of 5.0 moment magnitude, using a synthetic ground motion model. While, the ground surface response spectral curves with 5% of the critical damping were assessed using shear-wave velocity profiles of multichannel analysis of surface waves besides the earthquake time histories. Surface ground response spectra were mapped using the ArcGIS platform for 1.5 Hz, 3.0 Hz, 5.0 Hz, 8 Hz, and 10 Hz where this frequency range includes the range of natural frequencies of tall to single story buildings. The surface ground motion maps display that the hazard level ranges from low to moderate, where peak spectral acceleration varies between 13 cm/s2 and 124 cm/s2. The maximum surface ground motion values are calculated with 5% damped horizontal spectral acceleration at 10 Hz, which is equal to the natural frequency of low-rise buildings. These results should be taken into consideration from decision-makers, urban planners, and civil engineers during the design of earthquake-resistant structures in Makkah Al-Mukarramah city in general and Al-Mashair zone in particular.

Influence of 2D heterogeneous elastic soil properties on surface ground motion spatial variability

Spatial variability of earthquake ground motion (SVEGM) refers to the differences in amplitude and phase between recordings of the same earthquake at different locations. In the near-surface, geological processes (sedimentation, erosion) and anthropogenic activities can lead to small scale spatial heterogeneities of soil mechanical properties, which may affect SVEGM. In this paper, the effect of shallow 2D spatial variability of the shear wave velocity (Vs) on the surface ground motion is assessed through a set of numerical experiments, using a simple 2D velocity structure (a sedimentary layer over a half-space). Non-linearity or damping are not considered in the wave propagation calculation in order to solely focus on the effects of soil elastic property variability. Vs is modeled as a random field using the EOLE method (Expansion Optimal Linear Estimation) and considering three statistical parameters: the coefficient of variation, and the horizontal and vertical autocorrelation distances. Seismic ground motions are numerically simulated for a plane wave excitation with SV polarization. Modeling results clearly highlight the scattering of surface waves by ground heterogeneities, leading to large spatial variations in surface ground motion. We computed surface ground motion indicators (resonance frequency, spectral amplification, Arias intensity and duration) and we showed that their spatial variability is mainly controlled by the Vs coefficient of variation. A comparison between 2D and 1D ground motion probabilistic modeling shows that the 1D probabilistic approach may correctly reproduce average fundamental resonance frequencies and corresponding amplification. However, the 1D approach significantly under-predicts both ground motion amplification at higher frequencies and related variabilities, as well as Arias intensities and inferred durations, which are all controlled by the generation of locally diffracted surface waves.