Local Shear Wave Research Articles

Energetic effects analysis of shear waves and their second harmonics in a waveguide with non-ideal component contact

In this article the energetic and kinematic effects that occur in the elastic shear wave and its second harmonics propagation are investigated. The waveguide consists of anisotropic elastic crystal layer of cubic system m3m class enclosed between crystal halfspaces of same anisotropy class. A slipping contact is assumed in the contact zone of waveguide parts. The research is based on a model of general geometrical end physical nonlinearity in dynamic deformation processes. It allows to use elastic potential with the quadratic and cubic deformation components and the deformations with nonlinear terms. The approach of nonlinear elastic wave characteristics expansion into rows of a small parameter is used. Due to this approach at the first stage it's necessary to solve the problem of finding the components of the localized shear wave displacement vector (the problem of the first approximation). In the second stage, using the obtained results of the first approximation problem, the representation of the components of the displacement vector for the second harmonics of the localized elastic wave is solved in analytical form (the problem of the second approximation). By using the obtained kinematic results, the energy effects can be evaluated in the form of a vector of the average for the period of power flow. Specific results of the study of the amplitude-frequency and energy characteristics of the localized shear type elastic waves in the considered waveguide structure were obtained using computer algebra methods.The calculations of cinematic and energetic characteristics (that in contrast to linear SH harmonic are P-SV type waves) have been carried out for NaCl layer and germanium halfspaces waveguide.

The development of seismic anisotropy below south-central Alaska: evidence from local earthquake shear wave splitting

SUMMARYThe Transportable Array in south-central Alaska spans several subduction zone features: backarc, forearc and volcanic arc, making it an ideal tool to study subduction zone anisotropy. Shear wave splitting analysis of 157 local earthquakes of mb ≥ 3.0 that occurred between 2014 and 2019 yields 210 high-quality measurements at 23 stations. Splitting delay times (δt) are generally small (δt ≈ 0.3 s), increasing with distance from the trench. Arc-parallel fast directions, ϕ, are only seen in the forearc, but rotate to arc-perpendicular ϕ in the backarc. Observed ϕ values generally do not parallel teleseismic SKS splitting results, implying that the latter is sensitive primarily to subslab mantle flow, not mantle wedge dynamics. The forearc local-earthquake signal likely originates from anisotropic serpentinite in fractures atop the subducting Pacific Plate, with possible additional signal coming from fractures in the North American crust. Mantle wedge corner flow, potentially with additional arc-perpendicular anisotropy in the subducting slab, explains backarc anisotropy.

S-wave velocity structures at Yedang Reservoir Dam inferred from amplification characteristics determined using H/V spectral ratios with background noise

Local shear wave (S-wave) velocity structure and sedimentary cover thickness are essential parameters that control local amplification of ground motion and associated seismic hazard during earthquakes. Recently, analysis of environmental background noise from individual stations has been used to estimate horizontal-to-vertical spectral ratio (H/V) curves. In the present study, we inverted H/V curves using environmental noise immediately prior to earthquake P-wave arrival to retrieve S-wave velocity (or shear velocity, V S) profiles at four temporary seismic monitoring stations (YDF, YDS, YDU, and YDD) near the Yedang Reservoir Dam. In the first step, we used a random search algorithm to constrain the subvolume of the parameter space (S-wave velocity structure) where the minimum of the misfit was located. In the second step, we independently applied two non-linear processes (a Monte Carlo sampling algorithm and a simulated annealing algorithm) to force the inversion towards an optimal solution, using the minimum misfit model determined in the first step as an initial estimate; we then compared the results. The feasibility and effectiveness of this two-step approach were verified by inversion of H/V curves for seismic noise recorded at four seismic monitoring stations near the Yedang Reservoir Dam. Borehole and topographical data from the four stations provided a well-constrained estimation of the local shear wave profile. Comparisons of synthetic and observed H/V curves showed that combining the two inversion algorithms efficiently overcame the extreme non-linearity of the inversion problem and provided a good resolution of S-wave structures at the Yedang Reservoir Dam. The S-wave velocity profile at the YDF station, which is situated on fresh, uniform bedrock, ranged from ∼2300 to 2700 m/s, which was consistent with the borehole data. Both the YDU station (which exhibited fundamental and first-order resonance frequency harmonics) and the YDD station (which exhibited fundamental, first-, and second-order resonance harmonics) showed significant stepwise velocity profiles for the entire depth. Thus, the entire depth can be regarded as three layers, including bedrock. At the YDS station, located near the dam spillway, the uppermost layer showed the lowest V S values among all four stations (∼726–728 m/s), suggesting that the concrete dam body is well weathered or partially infiltrated by water. Because of these low V S values of the concrete dam body, the Yedang Dam may require a full safety diagnosis in the near future. Analysis of the velocity profiles of all four stations near the Yedang Dam indicated that the bedrock, composed of fresh rock (∼V S > 2700 m/s), varies greatly in depth among stations.

Human plantar fascial dimensions and shear wave velocity change in vivo as a function of ankle and metatarsophalangeal joint positions.

The plantar fascia (PF), a primary contributor of the foot arch elasticity, may experience slack, taut, and stretched states depending on the ankle and metatarsophalangeal (MTP) joint positions. Since PF has proximodistal site difference in its dimensions and stiffness, the response to applied tension can also be site specific. Furthermore, PF can contribute to supporting the foot arch while being stretched beyond the slack length, but it has never been quantitatively evaluated in vivo. This study investigated the effects of the ankle and MTP joint positions on PF length and localized thickness and shear wave velocity (SWV) at three different sites from its proximal to distal end using magnetic resonance and supersonic shear imaging techniques. During passive ankle dorsiflexion, rise of SWV, an indication of slack length, was observed at the proximal site when the ankle was positioned by 10°-0° ankle plantar flexion with up to 3 mm (+1.5%) increase in PF length. On the other hand, SWV increased at the distal site when MTP joint dorsiflexed 40° with the ankle 30°-20° plantar flexion, and in this position, PF was lengthened up to 4 mm (+2.3%). Beyond the slack length, SWV curvilinearly increased at all measurement sites toward the maximal dorsiflexion angle whereas PF lengthened up to 9 mm (+7.6%) without measurable changes in its thickness. This study provides evidence that the dimensions and SWV of PF change in a site-specific manner depending on the ankle and MTP joint positions, which can diversify foot arch elasticity during human locomotion.NEW & NOTEWORTHY Joint angle dependence and site specificity of the plantar fascial dimensions and SWV were examined by combining sagittal magnetic resonance and supersonic shear imaging techniques. We revealed that the site-specific changes in PF SWV were related to joint angle positions, i.e., PF slackness and elasticity changed in varying combinations of ankle and MTP angle. Our findings suggest that PF can elastically support the foot arch throughout the stance phase of human bipedal locomotion.

Imaging the rupture process of the 10 January 2018 MW7.5 Swan island, Honduras earthquake*

The 10 January 2018 MW7.5 Swan island, Honduras earthquake occurred on the Swan island fault, which is a transform plate boundary between the North American and Caribbean plates. Here we back-project the rupture process of the earthquake using dense seismic stations in Alaska, and find that the earthquake ruptured at least three faults (three stages) for a duration of ~40 s. The rupture speed for the longest fault (stage 3) is as fast as 5 km/s, which is much faster than the local shear wave velocity of ~4 km/s. Supershear rupture was incidentally observed on long and straight strike-slip faults. This study shows a supershear rupture that occured on a strike-slip fault with moderate length, implying that supershear rupture might commonly occur on large strike-slip earthquakes. The common occurrence of supershear rupture on strike-slip earthquakes will challenge present understanding of crack physics, as well as strong ground motion evaluation in earthquake engineering.

Four-dimensional (4D) phase velocity optical coherence elastography in heterogeneous materials and biological tissue.

The variations of mechanical properties in soft tissues are biomarkers used for clinical diagnosis and disease monitoring. Optical coherence elastography (OCE) has been extensively developed to investigate mechanical properties of various biological tissues. These methods are generally based on time-domain data and measure the time-of-flight of the localized shear wave propagations to estimate the group velocity. However, there is considerable information that can be obtained from examining the mechanical properties such as wave propagation velocities at different frequencies. Here we propose a method to evaluate phase velocity, wave velocity at various frequencies, in four-dimensional space (x, y, z, f), called 4D-OCE phase velocity. The method enables local estimates of the phase velocity of propagating mechanical waves in a medium. We acquired and analyzed data with this method from a homogeneous reference phantom, a heterogeneous phantom material with four different excitation cases, and ex vivo porcine kidney tissue. The 3D-OCE group velocity was also estimated to compare with 4D-OCE phase velocity. Moreover, we performed numerical simulation of wave propagations to illustrate the boundary behavior of the propagating waves. The proposed 4D-OCE phase velocity is capable of providing further information in OCE to better understand the spatial variation of mechanical properties of various biological tissues with respect to frequency.

Local Phase Velocity Based Imaging of Viscoelastic Phantoms and Tissues.

Assessment of soft tissue elasticity and viscosity is of interest in several clinical applications. In this study, we present the feasibility of the local phase velocity based imaging (LPVI) method to create images of phase velocity and viscoelastic parameters in viscoelastic tissue-mimicking materials and soft tissues. In viscoelastic materials, it is necessary to utilize wave-mode isolation using a narrow bandpass filter combined with a directional filter in order to robustly reconstruct phase velocity images with LPVI in viscoelastic media over a wide range of frequencies. A pair of sequential focused acoustic radiation force push beams, focused once on the left-hand side and once on the right-hand side of the probe, was used to produce broadband propagating shear waves. The local shear wave phase velocity is then recovered in the frequency domain for multiple frequencies, for both acquired data sets. Then, a 2-D shear wave velocity map is reconstructed by combining maps from two separate acquisitions. By testing the method on simulated data sets and performing in vitro phantom and in vivo liver tissue experiments, we show the ability of the proposed technique to generate shear wave phase velocity maps at various frequencies in viscoelastic materials. Moreover, a nonlinear least-squares problem is solved in order to locally estimate elasticity and viscosity parameters. The LPVI method with added directional and wavenumber filters can produce phase velocity images, which can be used to characterize the viscoelastic materials.

Physical mechanism for severe seismic hazard in the 2010 Yushu, China, earthquake (Mw= 6.9): insights from FEM simulations

The moderate-size 2010 Yushu earthquake (Mw 6.9) caused severe seismic damage around the source region which is situated on the sparsely populated hinterland of the Tibetan Plateau. But until now the mechanisms have not been well understood. To this end, we constructed the model to simulate the fault spontaneous rupture propagation, in which the realistic fault with a curved bend is imbedded. Our modeling results show that the special fault geometry controlled the rupture behavior, which encouraged rupture propagation speed transition from subshear to supershear with the speed of 5.17 km/s larger than the local shear wave velocity. Moreover, calculation results demonstrated that strong ground motion acceleration was greatly intensified by supershear ruptures, leading to widespread destruction. This may be the main reason why serious earthquake damage happened in the Yushu earthquake. In particular, we can see from numerous numerical experiments that rupture styles will be different if geometries of fault are varied. It is confirmed that it is the special geometry of the seismogenic fault of the Yushu mainshock produced grave seismic hazard. Thus, deeply investigating fault geometry will be helpful to better understand seismic source process and seismic hazard assessment. Key Points Curved bend in the seismogenic fault for the 2010 Yushu earthquake encouraged the supershear rupture transition. Strong ground motion acceleration was greatly intensified by supershear ruptures. Special geometry of the fault of the Yushu mainshock lead to seriouos seismic damage.

Fast Local Phase Velocity-Based Imaging: Shear Wave Particle Velocity and Displacement Motion Study.

Fast and precise noninvasive evaluation of tissue mechanical properties is of high importance in ultrasound shear wave elastography. In this study, we present an updated, faster version of the local phase velocity-based imaging (LPVI) method used to create images of local phase velocity in soft tissues. The updated LPVI implementation uses 1-D Fourier transforms in spatial dimensions separately in comparison to its original implementation. A directional filter is applied upon the shear wave field to extract the left-to-right (LR) and right-to-left (RL) propagating shear waves. A local shear wave phase velocity map is recovered based on both LR and RL waves. Finally, a 2-D shear wave velocity map is reconstructed by combining the LR and RL phase velocity maps. LPVI performance for shear wave displacement and velocity-wave motion data is examined. A study of LPVI used for only one data acquisition with multiple focused ultrasound push beams is presented. The lesion placement with respect to the pushes and whether two sequential pushes provided different results from two simultaneous radiation force pushes was investigated. The addition of white Gaussian noise to the wave motion data was also tested to examine the LPVI method's performance. Robust and accurate shear wave phase velocity maps are reconstructed using the proposed LPVI method using numerical tissue-mimicking phantoms with inclusions. Results from the numerical phantom study showed that the reconstructed, asymmetric inclusions, for various axial locations, are better preserved for shear wave particle velocity signals compared with particle displacement motion data.

Kinematic Rupture Modeling of Ground Motion from the M7 Kumamoto, Japan Earthquake

We analyzed a kinematic earthquake rupture generator that combines the randomized spatial field approach of Graves and Pitarka (Bull Seismol Soc Am 106:2136–2153, 2016) (GP2016) with the multiple asperity characterization approach of Irikura and Miyake (Pure Appl Geophys 168:85–104, 2011) (IM2011, also known as Irikura recipe). The rupture generator uses a multi-scale hybrid approach that incorporates distinct features of both original approaches, such as small-scale stochastic rupture variability and depth-dependent scaling of rupture speed and slip rate, inherited from GP2016, and specification of discrete high slip rupture patches, inherited from IM2011. The performance of the proposed method is examined in simulations of broadband ground motion from the 2016 Kumamoto, Japan earthquake, as well as comparisons with ground motion prediction equations (GMPEs). We generated rupture models with multi-scale heterogeneity, including a hybrid one in which the slip is a combination of high- slip patches and stochastic small scale variations. We find that the ground motions simulated with these rupture models match the general characteristics of the recorded near-fault motion equally well, over a broad frequency range (0–10 Hz). Additionally, the simulated ground motion is in good agreement with the predictions from Ground Motion Prediction Equations (GMPEs). Nonetheless, due to sensitivity of the ground motion to the local fault rupture characteristics, the performance among the models at near-fault sites is slightly different, with the hybrid model producing a somewhat better fit to the recorded ground velocity waveforms. Sensitivity tests of simulated near-fault ground motion to variations in the prescribed kinematic rupture parameters show that average rupture speeds higher than the default value in GP2016 (average rupture speed = 80% of local shear wave speed), as well as slip rate durations shorter than the default value in GP2016 (rise time coefficient = 1.6), generate ground motions that are higher than the recorded ones at periods longer than 1 s. We found that these two parameters also affect the along strike and updip rupture directivity effects, as illustrated in comparisons with the Kumamoto observations.

Локализованные сдвиговые волны в пьезоэлектрическом слое с тонким упругим покрытием

Локализованные сдвиговые волны в пьезоэлектрическом слое с тонким упругим покрытием

Shear wave elastography in MSK

Objectives To describe our experience applying shear wave elastography to the musculoskeletal system, as well as some potential sources of artifact when applying this new technology. Summary Disease states in the musculoskeletal system often manifest as altered tissue morphology evident on conventional gray-scale ultrasound imaging. These states also display other changes, such as altered tissue vascularity and mechanical properties. An example would be the tendon softening associated with tendinosis. US elastography provides a measure of local soft-tissue stiffness by means of mechanical stimulation. Presently, the two most common forms of US elastography measure tissue stiffness and strain by recording (a) how tissues respond to external compression obtained by applying manual pressure (Quasi-static or compression based on response to acoustic radiation force generated by the ultrasound transducer, the latter referred to as Shear-Wave Elastography (SWE). SWE employs a focused acoustic beam generated by the US transducer to compress the underlying tissue, thereby inducing a local shear wave. The speed of that wave, also known as the shear- wave velocity (SWV), is then measured as it propagates through the tissue and displayed as a parametric image or through selective region-of-interest (ROI) analysis, measured in meters per second. SWV provides a quantitative metric of tissue stiffness because it directly relates to the local shear elastic modulus, such that the stiffer the tissue, the greater the SWV. Consequently, some vendors directly display shear wave data as elastic modulus in kilopascals (KPS). In the current discussion, we briefly review some basic principles of shear wave imaging, review some of the common musculoskeletal applications, to date, and describe our experience using SWE in the musculoskeletal system with attention to skeletal muscle and tendons. We review some potential artifacts that the sonographer should be aware of in applying this new technology to tendon and muscle imaging.

Nonlinear Second Harmonics of Localized Shear Waves in an Anisotropic Layer Between Anisotropic Half Spaces Under the Conditions of Imperfect Contact

We construct a numerical-analytic solution of the problem of generation of the nonlinear second harmonics in the course of propagation of elastic symmetric localized shear waves in the crystalline layer of cubic system of the m3m class located between the crystalline half spaces of the same type and the same class of anisotropy under the conditions of imperfect sliding contact of components of the waveguide. We determine the analytic form of the functions of wave motions for nonlinear anharmonic perturbations in the form of longitudinal-shear-type waves. We also perform the numerical investigations of the amplitude-frequency characteristics of the second harmonics for monochromatic localized waves in a layer of a single crystal of germanium between the half spaces from the single crystal of silicon.

Subslab anisotropy in the Andaman subduction zone controlled by slab dip?

The mechanisms that govern anisotropy in subduction zones are debated. In this study, we present evidence of subslab mantle, crustal and mantle wedge anisotropy in the Andaman Nicobar subduction zone using 52 teleseismic and 103 local shear wave splitting (SWS) measurements. The local SWS measurements reveal a dominant trench-parallel anisotropy in the crust that can be attributed to SPO associated with arc-parallel fault planes of normal earthquakes and strike-slip faults parallel to the trench. 3D-flow from the subslab mantle possibly caused by a tear in the subducting slab is a plausible mechanism for anisotropy in the mantle wedge. Synthesis of the present results with the previous ones from the Andaman-Sumatra-Java arc reveals a clear relation between the fast polarization azimuths in a ray coordinate system (ϕ∗) and slab dip. The sub-slab anisotropy is trench-parallel in steeply subducting (>40° in Java) to trench-normal in gently subducting segments in the Andaman and Sumatra regions.

Local Phase Velocity Based Imaging: A New Technique Used for Ultrasound Shear Wave Elastography.

Ultrasound shear wave elastography is an imaging modality for noninvasive evaluation of tissue mechanical properties. However, many current techniques overestimate lesions dimension or shape especially when small inclusions are taken into account. In this paper, we propose a new method called local phase velocity-based imaging (LPVI) as an alternative technique to measure tissue elasticity. Two separate acquisitions with ultrasound push beams focused once on the left side and once on the right side of the inclusion were generated. A local shear wave velocity is then recovered in the frequency domain (for a single frequency or frequency band) for both acquired data sets. Finally, a two-dimensional shear wave velocity map is reconstructed by combining maps from two separate acquisitions. Robust and accurate shear wave velocity maps are reconstructed using the proposed LPVI method in calibrated liver fibrosis tissue mimicking homogeneous phantoms, a calibrated elastography phantom with stepped cylinder inclusions and a homemade gelatin phantom with ex vivo porcine liver inclusion. Results are compared with an existing phase velocity-based imaging approach and a group velocity-based method considered as the state of the art. Results from the phantom study showed that increased frequency improved the shape of the reconstructed inclusions and contrast-to-noise ratio between the target and background.

Fourier-Domain Shift Matching: A Robust Time-of-Flight Approach for Shear Wave Speed Estimation.

Our primary objective of this work was to design and test a new time-of-flight (TOF) method that allows measurements of shear wave speed (SWS) following impulsive excitation in soft tissues. Particularly, under the assumption of the local plane shear wave, this work named the Fourier-domain shift matching (FDSM) method, estimates SWS by aligning a series of shear waveforms either temporally or spatially using a solution space deduced by characteristic curves of the well-known 1-D wave equation. The proposed SWS estimation method was tested using computer-simulated data, and tissue-mimicking phantom and ex vivo tissue experiments. Its performance was then compared with three other known TOF methods: lateral time-to-peak (TTP) method with robust random sampling consensus (RANSAC) fitting method, Radon sum transformation method, and a modified cross correlation method. Hereafter, these three TOF methods are referred to as the TTP-RANSAC, Radon sum, and X-corr methods, respectively. In addition to an adapted form of the 2-D Fourier transform (2-D FT)-based method in which the (group) SWS was approximated by averaging phase SWS values was considered for comparison. Based on data evaluated, we found that the overall performance of the above-mentioned temporal implementation of the proposed FDSM method was most similar to the established Radon sum method (correlation = 0.99, scale factor = 1.03, and mean difference = 0.07 m/s), and the 2-D FT (correlation = 0.98, scale factor = 1.00, and mean difference = 0.10 m/s) at high signal quality. However, results obtained from the 2-D FT method diverged (correlation = 0.201) from these of the proposed temporal implementation in the presence of diminished signal quality, whereas the agreement between the Radon sum approach and the proposed temporal implementation largely remained the same (correlation = 0.98).

Shear wave sonoelastography in infants with congenital muscular torticollis.

Congenital muscular torticollis (CMT) is characterized by shortening or excessive contraction of the sternocleidomastoid muscle (SCM). The main purpose of this study was to evaluate the feasibility of quantifying SCM stiffness using acoustic radiation force impulse (ARFI) sonoelastography in infants with CMT. Twenty infants with an SCM thickness greater than 10 mm with or without involvement of the entire SCM length (limitation of neck rotation passive range of motion [PROM]: group 1S >30°, group 1M = 15°−30°) and 12 infants with an SCM thickness smaller than 10 mm with or without involvement of any part of SCM (group 2) were included. The SCM thickness was measured using real time B-mode ultrasound, and the local SCM shear wave velocity (SWV) and subcutaneous fat layer using ARFI sonoelastography. The neck rotation PROM was significantly greater in group 1S (36.5° ± 5.3°) than in group 1M (18.8° ± 4.9°; P < .01); the SWV of the SCM in the affected side (2.96 ± 0.99 m/s) was significantly higher than that in the unaffected side (1.50 ± 0.30 m/s; P < .01) in group 1. The SWV of the SCM was significantly higher in group 1S than in group 1M. There was significant correlation between the degree of PROM deficit of neck rotation and the SWV of the affected SCM (r = .75; P < .01) in all infants. This study revealed a difference in the SWV of the affected SCM in relationship to the limitation of neck rotation PROM in infants with CMT, if there was no difference in SCM thickness among infants.

Two-dimensional waves in extended square lattice

We consider a two-dimensional square lattice model extended by additional not closed neighboring interactions. We assume the elastic forces between the masses in the lattice to be nonlinearly dependent on the spring elongations. First, we use an analysis of the linearized discrete equations to reveal the influence of additional interactions on the properties of the dispersion relation for longitudinal and shear plane waves. Then we develop an asymptotic procedure to obtain continuum two-dimensional non-linear equations to study the transverse instability of weakly non-linear localized plane longitudinal and shear waves. We find that the additional interactions used in the model may affect the sign of the amplitude of the plane strain waves (existence of compression (minus sign) or tensile (plus sign) plane waves) and their transverse stability.

Viscoelasticity Mapping by Identification of Local Shear Wave Dynamics.

Estimation of soft tissue elasticity is of interest in several clinical applications. For instance, tumors and fibrotic lesions are notoriously stiff compared with benign tissue. A fully quantitative measure of lesion stiffness can be obtained by shear wave (SW) elastography. This method uses an acoustic radiation force to produce laterally propagating SWs that can be tracked to obtain the velocity, which in turn is related to Young's modulus. However, not only elasticity, but also viscosity plays an important role in the propagation process of SWs. In fact, viscosity itself is a parameter of diagnostic value for the detection and characterization of malignant lesions. In this paper, we describe a new method that enables imaging viscosity from SW elastography by local model-based system identification. By testing the method on simulated data sets and performing in vitro experiments, we show that the ability of the proposed technique to generate parametric maps of the viscoelastic material properties from SW measurements, opening up new possibilities for noninvasive tissue characterization.

Attenuation Relation for Near Field Shallow Crustal Earthquakes Using NGA-West Database with Mixed-Effect Model in Comparison with Attenuation Relations for Iran

This article presents a new empirical equation for the estimation of horizontal strong ground motions caused by shallow crustal earthquakes. This model is developed empirically by regression of the database which is used by the NGA-West2 GMPE developers with a fault rupture distance less than 60 kilometers. The data set consisted of corrected and processed accelerograms of 1545 strong-motion records of earthquakes between Mw 5.2 and 7.9. Model is a function of earthquake magnitude, distance from source to site, local average shear wave velocity, nonlinear soil response, sediment depth, rupture dip, faulting mechanism and hanging wall effect. This equation was derived by a stable algorithm for regression analysis called mixed effect model. The algorithm was used to develop PGA and PSA (T1) for periods from 0.01 to 10.0 seconds. Major differences between this model with recent developed attenuation relations for the world and Iran were observed for large-magnitude ground motions which were recorded at small-to-moderate distances from seismic source. The results showed that the near-field affected the predicted values especially in soil sites. Moreover, comparison with the attenuation relations developed by Iranian data set confirmed that the equation in this region is sensitive more to distance than to other parameters.