Near-source Region Research Articles

Ground-Motion Modeling of the 2016 Mw 6.2 Amatrice, Italy, Earthquake, by a Broadband Hybrid Kinematic Approach, Including Empirical Site Effects

Abstract The region of Central Italy is well known for its moderate to large earthquakes. Events such as the 2016 Mw 6.2 Amatrice earthquake generated in the shallow extensional tectonic regime motivate numerical simulations to gain insights into source-related ground-motion complexities in the near-source region. We utilize a hybrid integral-composite kinematic rupture model by Gallovič and Brokešová (2007) to simulate the Amatrice earthquake in a broadband frequency range (up to 10 Hz). In the first step, we optimize the input source parameters using a grid-search method by minimizing the spectral acceleration bias between synthetic and recorded strong-motion data at reference rock stations within 50 km of the source. To verify the robustness of the optimal model, we simulate the ground motions at 400 virtual stations and compare their spectral accelerations with the predictions of an empirical nonergodic ground-motion model (GMM) for rock sites in Central Italy (Sgobba et al., 2021). The synthetics show a good agreement with the empirical model regarding both median and variability. Finally, we account for local site effects at nonreference stations by combining the simulations on rock with empirical site terms derived by the nonergodic GMM. The site-corrected spectral responses generally improve the match with the observations, demonstrating a successful fusion of numerical simulations with empirical estimates toward reproducing near-source ground motions.

A Study on Estimating Earthquake Magnitudes Based on the Observed S-Wave Seismograms at the Near-Source Region

A Study on Estimating Earthquake Magnitudes Based on the Observed S-Wave Seismograms at the Near-Source Region

On the effects of walking speed, crowd density and human-to-source distance on pollutant dispersion in indoor spaces

The effects of walking speed, crowd density and human-to-source distance on pollutant dispersion in two scaled room models are investigated using simultaneous planar laser-induced fluorescence and particle-image velocimetry techniques. For a small 3 m high room, where the length-scales of the people and room are comparable, the walking motions significantly influenced the macro room mean flow patterns. This has a strong effect on the scalar dispersion properties as the magnitudes of the advective scalar fluxes are often comparable or larger than the turbulent scalar fluxes. As such, the scalar dispersion properties are case specific. For a large 9 m high room, the walking motion influenced only the local mean flow field. The increase in walking speed and crowd density improves the efficiency in which the scalar is transported and mixed with fresh ambient fluid out of the measurement plane (i.e. along the direction of the motion), leading to scalar-free zones observed on the opposite side of the room from the ventilation outlet. The area of the scalar-free zone increases with an increase in the walking speed and crowd density. The advective scalar fluxes are more sensitive to the human motion than the turbulent components, and as the mixing efficiency improves, the advective fluxes show a greater weakening with increased distance from source. The concentration PDFs in the near-source region can be described by the exponential function where the expected value at the 99% percentile can be derived as C99/crms′=4.61, which agreed well with the experimental measurements of 4.1 to 5.9.

Adjusting an active shallow crustal ground motion model to regions with scarce data: application to France

The objective of this work is to test whether an empirical Ground Motion Model (GMM) developed for high-seismicity regions can be effectively adapted to a neighbouring region with lower seismic activity. We select the ITA18 suite of GMMs (Lanzano et al. in Bull Seismol Soc Am 109(2): 525-540, 2019a), developed for Italy, which is a region dominated by moderate-to-strong shallow crustal earthquakes, and assess their applicability to Continental France, where the seismic activity is less frequent and characterised by lower magnitudes. Based on a dataset of more than 2300 records of events with 3.0 ≤ MW ≤ 5.2, occurred in France in the time interval 1996–2019 (named FR20), we perform a residual analysis and calibrate an adjustment factor for both horizontal and vertical-to-horizontal (VH) components of Peak Ground Acceleration, Peak Ground Velocity, and 5% damped Spectral Acceleration (SA). Apart from the median correction, no modification of the scaling with magnitude, focal mechanism, and VS,30 is introduced, while the distance scaling is adjusted to capture the lower anelastic attenuation of the French data. In addition, to overcome the underestimation of the ITA18 model for the short period VH spectral amplitudes in the near-source region (Repi < 15 km), an additional empirical corrective factor is introduced. In spite of the good agreement of the adjusted model with respect to the median trends of the FR20 dataset, a regionalization of the source effects is introduced to reduce the relatively high between-event variability of the proposed model. The proposed model provides predictions similar to ITA18 in the most seismically active regions (Alps or Pyrenees), while, in the other zones, the predicted amplitudes are richer at high frequencies. Given the paucity of seismic records in these zones, this behavior should be confirmed on the basis of additional data (e.g. physics-based simulations, geologic and tectonic features). The use of the proposed model for hazard applications is recommended within the validity limits of the data (3.0 ≤ MW ≤ 5.2). However, the similarity of the ground motion in the Alps and Pyrenees with the predictions of ITA18 suggests that the adjusted model could be also employed for higher magnitudes, upon suitable checks.

Experimental investigation of scalar dispersion in indoor spaces

The scalar dispersion from point sources in indoor spaces is experimentally investigated using simultaneous particle–image velocimetry and planar laser-induced fluorescence techniques in a 20:1 and a 60:1 full-to-model scale room model. The ventilation inlets dominate turbulence production, with magnitudes of the velocities and Reynolds stresses observed to increase with air changes per hour (ACH). Mean concentration maps show a dependence on the ACH and source location which is attributed to the flow field at the near-source region. The peak-to-mean concentration shows a weak dependence on the mean concentration and concentration variance maps, indicating risk for toxic chemicals may be underpredicted if based only on these information. The concentration PDFs are generally well-described by exponential distributions with C99/crms′ values never exceeding 5.0. The magnitudes of the advective and turbulent scalar fluxes are strongly dependent on the ACH and source location, neither of which are able to dominate the other by more than an order of magnitude. The eddy diffusivity tensor was measured and a conditional-averaging based method is proposed to approximate it to an isotropic eddy diffusion coefficient, K. For real applications where K is used to estimate magnitudes of the turbulent scalar flux using the gradient transport model, the assumption of isotropic turbulence can introduce an uncertainty of around 17.8%.

Subduction Interface Earthquake Rise-Time Scaling Relations

ABSTRACT The slip duration in a fault plane, also known as the rise time (Tr), is determined in finite-fault rupture models (FFRMs) through the analysis of seismic source inversions using strong ground-motion (SGM) records and teleseismic data. For subduction interface earthquakes (megathrust), models exist that provide estimates for Tr values. The finite-source rupture model database and National Earthquake Information Center databases include FFRMs that allow for the extension of source-scaling relations. Currently, Tr versus seismic moment (M0) scaling relations specifically derived for large megathrust earthquakes in the near-source region are scarce. The relationship between stress drop and M0 is not straightforward; therefore, the logarithmic distribution of stress drop among earthquakes of different magnitudes (Mw) appears to be constant or self-similar. This self-similarity refers to a symmetry of the time-dependent fields, which remain unchanged under certain scale transformations in space and time characterized by similarity exponents and a function of the scaled variable, called the scaling function. In this study, Tr scaling has been conducted using 45 FFRMs derived from large megathrust earthquakes (Mw≥7.3) obtained from the previously mentioned databases. The scaling relation derived from the FFRMs based on SGM records closely approximates log(Tr)=const+1/3log(M0), which agrees with the self-similarity assumption for earthquake ruptures. On the other hand, the scaling relation obtained from the teleseismic dataset exhibits a smaller slope, indicating that the teleseismic data may overestimate source time characteristics compared with SGM data from seismic stations located close to the source.

Bayesian analysis of ground motion models using chimney fragility curves: 2021, 5.9-Mw Woods Point intraplate earthquake, Victoria, Australia

The 22 September 2021 (AEST) MW 5.9 Woods Point earthquake occurred in an intraplate setting (southeast Australia) approximately 130 km East Northeast of the central business district of Melbourne (pop. ∼5.15 million). A lack of seismic instrumentation and a low population density in the epicentral region resulted in a dearth of near-source instrumental and “felt” report intensity data, limiting evaluation of the near-source performance of ground motion models (GMMs). To address this challenge, we first surveyed unreinforced masonry chimneys following the earthquake to establish damage states and develop fragility curves. Using Bayesian inference, and including pre-earthquake GMM weightings as Bayesian priors, we evaluate the relative performance of GMMs in predicting chimney observations for different fragility functions and seismic velocity profiles. At the most likely VS30 (760 m/s), the best performing models are AB06, A12, and CY08SWISS. GMMs that were preferentially selected for utility in the Australian National Seismic Hazard Model (NSHA18) prior to the Woods Point earthquake outperform other GMMs. The recently developed NGA-East GMM performs relatively well in the more distal region (e.g. &gt;50 km) but is among the poorest performing GMMs in the near-source region across the range of VS30. Our new method of combining analysis of engineered features (chimneys) with Bayesian inference to evaluate the near-source performance of GMMs may have applicability in diverse settings worldwide, particularly in areas of sparse seismic instrumentation.

Engineering validation of BB-SPEEDset, a data set of near-source physics-based simulated accelerograms

Physics-based numerical simulations (PBS) have progressed to the level of providing a realistic description of earthquake ground motion and of its variability, both in time and space, thus enabling to fill the knowledge gaps due to the sparsity of recordings (especially in the near-source region of strong earthquakes). Nevertheless, to build confidence in the utilization of the PBS by the engineering community, simulated accelerograms need to be validated against recorded data from both seismological and engineering perspectives. This article aims at extending the validation of BB-SPEEDset, a data set of near-source broadband simulated accelerograms from multiple regions and faulting styles, obtained by the spectral element computer code SPEED. In addition to seismological checks of BB-SPEEDset proving the absence of systematic biases with respect to a near-source records data set, in this work, the validation is addressed in terms of engineering demand parameters (EDPs) of elastoplastic single-degree-of-freedom systems, taking advantage of a ground motion selection tool including simulated accelerograms. It is found that, when simulated and recorded accelerograms are selected according to the same spectral compatibility criteria, consistent statistical distributions of EDPs are obtained from the two sets. To highlight the potentialities of BB-SPEEDset for near-source analyses, an example of utilization of spectrum-compatible pulse-like motions for structural inelastic analyses is also given, resulting in a good agreement with literature solutions in terms of inelastic displacement demands.

Turbulent dispersion of a passive scalar in a smooth-wall turbulent boundary layer

The scalar dispersion of a ground-level point-source plume in a smooth-wall turbulent boundary layer is experimentally investigated using simultaneous particle image velocimetry and planar laser-induced fluorescence techniques. In the near-source region, the viscous sublayer is observed to trap dye, while in the far field, the half-width, vertical profiles and peak decay of the mean concentration and concentration variance exhibit self-similar behaviour and collapse with empirical relations. Full two-dimensional maps of the turbulent scalar fluxes show a net transport direction of upward and towards the incoming flow, with the vertical profiles collapsing well with Weibull-type exponential functions and the decay of peaks following power laws. Using the first-order gradient transport to model the turbulent scalar fluxes, maps of the anisotropic turbulent diffusivity tensor and an effective turbulent diffusivity coefficient are calculated. The streamwise and wall-normal turbulent scalar fluxes are driven dominantly by the wall-normal concentration gradient. The turbulent Schmidt number, relating the turbulent diffusivity and the turbulent (eddy) viscosity calculated using the Boussinesq hypothesis, varies with wall-normal position with values of the order of unity in the logarithmic layer.

Fault Damage Zone Effects on Ground Motions during the 2019 Mw 7.1 Ridgecrest, California, Earthquake

ABSTRACT We have simulated 0–3 Hz deterministic wave propagation in the Southern California Earthquake Center Community Velocity Model (CVM) version CVM-S4.26-M01 for the 2019 Mw 7.1 Ridgecrest earthquake. A data-constrained high-resolution fault zone model (Zhou et al., 2022) is incorporated into the CVM to investigate the effects of the near-fault low-velocity zone (LVZ) on the resulting ground motions, constrained by strong-motion data recorded at 161 stations. The finite-fault source used for the simulation of the Ridgecrest event was obtained from the Liu et al. (2019) kinematic inversion, enriched by noise following a von Karman correlation function above ∼1 Hz with a f−2 high-frequency decay. Our results show that the heterogeneous near-fault LVZ inherent to the fault zone structure significantly perturbs the predicted wave field in the near-source region, in particular by more accurately generating Love waves at its boundaries. The fault zone decreases the 0.1–0.5 Hz mean absolute Fourier amplitude spectrum bias to seismic recordings for all sites in the model and in the Los Angeles basin area (∼200 km from the source) by 16% and 26%, respectively. The fault zone structure generally improves modeling of the long-period features in the data and lengthens the coda-wave trains, in better agreement with observations. The favorable fit to data was obtained with a model including high-resolution surface topography, a 700-m-thick geotechnical layer and frequency-dependent anelastic attenuation in the model domain, with QS=0.1VS and QS(f)=0.1VSf0.5 (VS in m/s) for frequencies lower and higher than 1 Hz, respectively. We recommend that a data-constrained fault zone velocity structure, where available, be included in ground-motion modeling to obtain the least-biased fit to observed seismic data.

Numerical modeling of a potential landslide-generated tsunami in the southern Strait of Georgia

We report results of numerical simulations of a potential subaerial landslide on the coast of Orcas Island and the resultant tsunami waves in the southern Strait of Georgia near the US/Canada border. A likely trigger is strong ground shaking during large earthquakes on the nearby Holocene active Skipjack Island fault zone. For a worst-case scenario, we assume a 0.17 {textrm{km}}^3 rigid subaerial failure on the steep northeast coast of the island, spanning the sim 5 km between previous landslide deposits on the adjacent seafloor. The landslide motion and resulting tsunami generation are modeled using the three-dimensional (3D) non-hydrostatics physics-based NHWAVE model. The simulated failure moves downslope with a peak velocity of 13.64ṁ/s and travels 732 m before coming to rest after 85 s in 75-m water depth. Tsunami propagation is then continued using the 2D fully nonlinear and dispersive Boussinesq wave model FUNWAVE-TVD in a succession of layered and nested grids. The modeling reveals susceptible locations, particularly as waves will arrive with little or no warning. In the near-source region, modeled waves have peak amplitudes of 15–20 m, current speeds of up to 10 m/s, and runup of up to 30 m. Smaller, but significant, wave amplitudes and runup occur throughout the region surrounding Orcas Island. In the tsunami propagation direction, runup reaches 7.5 m at Neptune Beach near Lummi Bay. Both initial and reflected waves cause significant runup (> 1.5 m) along much of the shoreline between Point Roberts and Lummi Bay.

Shadow effect and source overprint effect of short-offset transient electromagnetic method

AbstractIn artificial-source electromagnetic explorations, the shadow effects and source overprint effects are two of the key factors to affect the detection reliability. Compared with frequency-domain electromagnetic methods, the transient electromagnetic (TEM) shadow effect and source overprint effect are more complex, especially for the short-offset TEM (SOTEM) observed in the near-source region. However, there is less relevant research. Therefore, in this paper, we first realize 3D SOTEM simulations based on the vector time-domain finite element method, then further analyze the generation of SOTEM shadow effect and source overprint effect from view of the diffused electromagnetic fields, as well as their influence on ground horizontal electric field Ex and vertical induced voltage dBz/dt responses. Results show that the attraction or repulsion of the electrical inhomogeneity would affect the diffusion speed of the electromagnetic fields, which is the essential in the two source effects. Besides, from view of the ground Ex and dBz/dt responses, the relative anomaly of SOTEM shadow effect is almost twice those of the SOTEM source overprint effect, i.e. the SOTEM shadow effect is easier to record, especially for dBz/dt responses. In addition, owing to the shadow effect, SOTEM may fail to identify the real target anomaly, whereas the influence of the source overprint effect for recognizing the target anomaly mainly occurs on all-time dBz/dt responses and early-time Ex responses (before about 10 ms), that is, observing late-time SOTEM Ex responses can effectively avoid such influence. Hence, to fully ensure avoiding the influence of the source overprint effect, we suggest adopting high-power transmission to increase the late-time signal-to-noise ratio in field measurements.

P/SVAmplitude Ratios of Shallow Isotropic Explosions and Earthquakes Could Be Indistinguishable at Local Distances: Insights from Single-Station Waveform Simulations

AbstractShear waves play a key role in seismic discrimination between explosions and earthquakes due to their different source mechanisms. However, shear waves are often observed in field explosions with unexpectedly large amplitude, and their generation mechanism is still a significant unresolved question in seismology. Many explanations have been proposed, including the asymmetry of explosive sources, and heterogeneity and/or anisotropy of the Earth’s subsurface. However, it has not been well understood whether source or velocity structure can independently and sufficiently explain the shear waves generated by explosions. Theoretically, tangential SH waves can be converted and scattered from vertical and radial SV waves due to anisotropy and heterogeneity. Thus, it is essential to understand the generation of SV waves by explosions. In this study, we utilize the frequency–wavenumber algorithm and 1D layered velocity models to simulate waveforms of isotropic explosions and double-couple earthquakes at local distances (&amp;lt;20 km). Our results suggest that explosions and earthquakes may generate comparable SV waves if both occurred within a near-surface velocity gradient zone. The earliest SV waves by explosions appear to originate from the near-source region. It implies that P/SV amplitude ratios of explosions and earthquakes could be indistinguishable under certain circumstances.

3D Time-Lapse Electrical Resistivity Imaging of Rock Damage Patterns and Gas Flow Paths Resulting from Two Underground Chemical Explosions

Rock damage from underground nuclear explosions (UNEs) has a strong influence on sub-surface gas movement and on seismic waveform characteristics, both of which are used to detect UNEs. Although advanced numerical simulation capabilities exist to predict rock damage patterns and corresponding detection signals, those predictions are dependent on (generally) unknown properties of the host rock. For example, the effects of in-situ mechanical heterogeneities on the explosively generated damage/fractures that provide gas flow pathways to the surface are not well understood, due largely to the difficulty in accessing and characterizing the near-source region. In this paper we demonstrate the emerging use of electrical resistivity tomography (ERT) for imaging rock damage and gas flow patterns resulting from two relatively small-scale underground chemical explosions. Pre-explosion ERT and crosshole seismic imaging revealed a natural fracture zone within the test bed. Post-explosion imaging revealed that the damage zone was non-symmetric and was focused primarily within the pre-existing fracture zone, located 10 m above the first explosion and 5 m above the second explosion. Time-lapse ERT imaging of heated air injected into the detonation borehole revealed the primary gas flow paths to be within the upper margin of the same primary damage zone. These results point to the utility of ERT imaging for understanding rock damage and gas flow patterns under experimental conditions, and to the importance of understanding the effects of geologic heterogeneity on UNE detection signals, particularly gas surface breakthrough times.

Site-specific seismic hazard and risk potential of Bengal Basin with emphasis on holistic seismic hazard microzonation and its structural impact assessment in the cities of Dhanbad and Mymensingh

The Bengal Basin located in the eastern part of the Indian subcontinent at the conjunction of the Eurasian, Indian, and Indo-Burma plates with two progressing deformation fronts viz. the Himalayas and the Indo-Burmese orogenic belts is one of the largest fluvio-deltaic to shallow marine sedimentary basin covered by alluvial plains of Holocene deposits extending from the Himalayas to the Bay of Bengal over thick younger alluvium comprising shallow layers of silt, clay, and sand that can have disastrous consequences due to site-specific ground motion amplification and liquefaction effects. The basin surrounded by Shillong and Assam plateaus in the Northeast is in the active tectonofabric of major active faults and lineaments triggering many devastating earthquakes in the past implicating the MM Intensity of VIII–XI in the near-source region causing widespread damage and destruction in the basin, thus bringing in the essence of assessing surface level seismic hazard and the risk imposed on the basin. Consideration of seismicity patterns, fault networks, and similarity in focal mechanisms yielded 49 areal seismogenic sources and additional active tectonic features in the 0–25 km, 25–70 km, and 70–180 km hypocentral depth ranges, which along with 14 ground motion prediction equations that include site-specific next generation spectral attenuation models pertaining to Northeast India, East-Central Himalaya, and Bengal Basin tectonic provinces yielded probabilistic peak ground acceleration (PGA) at engineering bedrock in the range of 0.08–0.58 g. Both the geophysical and geotechnical investigations at 6,000 sites provided effective shear wave velocity distribution in the range of 113–948 m/s on the geographical information system, thus classifying the basin into 11 site classes with “None” to “Severe” liquefaction hazard potential. A systematic non-linear/equivalent linear site response analysis and its spectral convolution with firm rock peak ground acceleration yielded surface-consistent hazard in the range of 0.09–1.17 g, thus opening up the issue of risk assessment and holistic seismic hazard microzonation of all the cities in the basin and their structural impact assessment using the SELENA-based capacity spectrum method on FEMA and BMTPC-regulated 11 model building types in the damage states of “none,” “slight,” “moderate,” “extensive,” and “complete” for all of those, however, in-depth studies carried out for Mymensingh and Dhanbad have been presented.

3D multiscale analysis method for explosion problems based on the substructure of the explosion source

When using the explicit finite element method to solve explosion problems at engineering sites, high-density meshes are usually adopted near the explosion source to calculate the high-frequency components of the explosion response. However, the critical time step in an explicit algorithm is usually controlled by the minimum mesh size. The resulting poor computational efficiency will restrain the application of the overall explosion source-engineering site model in explosion problems for large-scale numerical systems, especially in 3D conditions. In this study, a 3D multiscale analysis method based on the substructure of explosion sources is proposed. This method computationally separates the process of explosion initiation and the propagation of shock waves by dividing the model of engineering sites under explosion loads into a small-scale near-source model and a large-scale site-structure model, and the substructure of explosion source is used as an approach for explosion action transmission and mesh transition between different models, thereby progressively completing the explosion analysis of the entire explosion source-site-structure system from the near-source region to the far-field region. The proposed multiscale method adopts appropriate mesh sizes and numerical techniques in different calculation stages and avoids the use of irregularly shaped elements that are employed in traditional mesh transition methods, thereby reducing the calculation cost and modeling difficulties while ensuring accuracy. In addition, the proposed method provides a convenient approach for calculating standard explosion loads for a given explosion equivalent, which can be further applied in multiload-case explosion response analyses of large-scale complex site-structure systems.

Experimental research and simulation of two-phase plume for R134a release and diffusion

The frequent occurrence of Liquefied natural gas (LNG) leakage accidents has caused serious economic loss and environmental damage. Therefore, it's of great significance to make assessments on the LNG hazards during its accidental release and associated consequences. This paper focuses on the two-phase release process in the liquefied gas release and dispersion accident and makes investigatatation on the two-phase plume with experimental and numerical approaches. A small-scale experimental system is developed with different sizes of release holes. With the experiment results, the mass outflow rate and temperature have been obtained, which provided initial parameters for the simulation. Jet velocities have been measured by PIV, and results reveal that an obvious velocity breach existing near the leakage nozzle due to the Joule-Thomson effect. Besides, given a point in the X-axis, the jet velocity is decreasing with an increasing diameter hole. Subsequently, the experimental data are utilized to verify the liquid-gas phase numerical model using Eulerian-Lagrange approach. Comparing with the results obtained by single gas phase model, the velocities obtained by liquid-gas phase model show good consistency with the experiments. Afterwards, the validated numerical liquid-gas phase model is employed to analyze the temperature distribution, concentration distribution and droplet size distribution in the near-source release region. With the simulation results, it depicts that there is a violent temperature decrease near the leakage nozzle in the liquid-gas phase model, which was caused by the evaporation of droplets. Meanwhile, concentration of R134a simulated by liquid-gas phase model is higher than the value of single-gas phase. These results emphasize that it’s essential to simulate the release accidents with liquid-gas phase model, especially in the near-source region. Both the experiments and numerical models are of great value for providing assessments and theoretical supports for the risk consequences in the process safety.

New findings in vorticity dynamics of turbulent buoyant plumes

The vorticity dynamics of turbulent, buoyant, and pure plumes released into the quiescent ambience has been investigated using large-eddy simulations with plume Reynolds number in the range of 6 × 107 to 108. The plume is generated by a circular heat source and sustained by buoyancy forcings generated by heating. As the starting plume rises vertically, it expands radially, entraining ambient fluid into the plume and two distinct stages of evolution are evident. During stage one (initial stage), in the near-source region the plume is accelerating characterized by developing turbulence. During the next stage (mixing stage), the plume is significantly altered by turbulence resulting in significant entrainment and expansion in the radial direction. As turbulent intensities decay during the mixing stage, the enstrophy decays in an exponential manner with height with an exponent of −7/4. The turbulent kinetic energy budget analysis reveals—baroclinic torque, stretching, and compression—as the three dominant mechanisms for the plume growth. The probability distribution function (PDF) of vorticity shows that vorticity is mainly aligned along the transverse direction near the source and slowly reaches to a quasi-isotropy state downstream. Turbulence spectra demonstrate the presence of a buoyancy-regime with a −3 spectral slope. The PDF of vorticity further shows extreme dominance of the strain rate rather than rotation within the plume. Consistent with studies in the literature, the vorticity fluctuations align with the intermediate eigen-vector of strain-rate tensor.

δ-SPN approximation for numerical modeling of directional sources and scattering.

We propose the δ-SPN approximation for the frequency domain coupled radiative transfer equations modeling fluorescence with collimated incident beams and present its numerical implementation using the finite element method. The performance of the proposed model is investigated with respect to Monte Carlo simulations and the standard SPN approximation over sub-centimeter domains for various optical properties. We find that the δ-SPN approximation is more accurate than the SPN in the near-source region, and provides improved estimates of phase and partial currents, at both excitation and emission wavelengths, over a wider range of optical properties. The accuracy of the δ-SPN model improves with increase in approximation order for normally incident beams.

On the Influence of the Vertical Earthquake Component on Structural Responses of High-Rise Buildings Isolated with Double Friction Pendulum Bearings

The double friction pendulum (DFP) bearing is adapted from the well-known single friction pendulum (SFP) bearing. This type of bearings has been widely used for structural vibration controls. The main advantage of the DFP is its capacity to accommodate larger displacements as compared with the SFP one. This paper aims to assess the effect of the vertical earthquake component on the seismic behaviour of a base-isolated high-rise building. In this respect, the mathematical model of the building subjected to earthquake excitations with an implementation of a DFP bearing system is established. The model presented herein considers earthquake excitations in horizontal (X and Y) and vertical (Z) directions. A series model of two friction elements is presented for the bearing, where the friction load of the bearing surface is governed by a modified Bouc-Wen model, which is dependent on the sliding velocity and the contact pressure. The numerical results of an example of a base-isolated 9-story steel building subjected to near-source and far-field earthquakes show the high effectiveness of the bearing system in reduction of the seismic response of the building, especially in the near-source region, as well as exhibit considerable effectiveness of the vertical earthquake component on the bearing and structural behaviour.