Reduction In Wave Velocity Research Articles

Detection of an ultralow velocity zone at the core‐mantle boundary using diffracted PKKPab waves

Seismic phases diffracted around Earth's core contain information about lowermost mantle wave speeds. By measuring the slowness of incident diffracted energy from array recordings, seismic velocity along the diffracted path can be estimated. Here we apply this principle to diffraction of the major arc seismic phase PKKPab recorded at the Canadian Yellowknife array to estimate P wave velocity variations along the core‐mantle boundary. We observe PKKPabdiff about 7.5° past the ray theoretical cutoff distance for PKKPab. We utilize 330 western Pacific rim earthquakes that allow us to probe the core‐mantle boundary beneath the North Atlantic and the South Pacific oceans using PKKPabdiff. Slowness and back azimuth are measured by frequency–wave number analysis. Mapping PKKPabdiff slowness variations suggest 4–19% P wave velocity reductions relative to PREM, in good agreement with the magnitude of velocity reductions previously mapped in ultralow velocity zones. The PKKPabdiff slowness and back‐azimuth variations combined with results from previous ULVZ studies using SPdiffKS imply that the lowered velocities occur at the base of the mantle beneath the North Atlantic Ocean, along the receiver side of raypaths. PKKPabdiff array measurements thus hold important potential for mapping ultralow velocity zone structure in so far unprobed regions of the lower mantle as well as for providing additional and independent information about lower mantle structure.

Geographic boundary and shear wave velocity structure of the “Pacific anomaly” near the core–mantle boundary beneath western Pacific

We determine the geographical boundary and shear-velocity structure of a very-low velocity province at the base of the Earth's mantle beneath western Pacific (we term it the “Pacific anomaly”) based on the waveform modeling and travel time analysis of ScSH–SH phases. Our seismic data are from the China National Digital Seismographic Network, the F-net in Japan, the Global Seismographic Network and several PASSCAL arrays. The observed ScS–SH differential travel-time residuals allow the northwestern geographic boundary of the anomaly to be clearly defined. The seismic data also suggest that the average shear-velocity reduction inside the anomaly reaches − 5% in the lowermost 300 km of the mantle. Waveform modeling of the seismic data sampling the edge of the anomaly suggests that the northwestern boundary is best characterized by a shear-velocity model with a velocity jump of about 2% at about 100–145 km above the core–mantle boundary and a thin (30-km thick) basal layer with a shear wave velocity reduction of − 13%. Stacked seismic data sampling the middle of the anomaly, however, show no evidence for any internal discontinuity with a velocity decrease greater than − 2% in the middle of the anomaly. Overall, the seismic data sampling the base of the “Pacific anomaly” can be explained by a negative shear-velocity gradient from 0% to − 1% (top) to − 13% (bottom) in the lowermost 220 km of the mantle, similar to those of a very-low velocity province beneath the South Atlantic Ocean and the Indian Ocean. Such a strong negative shear-velocity gradient can be explained by partial melting of a compositional anomaly produced early in the Earth's history located within a bottom thermal boundary layer. Our travel time data also exhibit small-scale variations inside the anomaly, indicating existence of internal small-scale seismic heterogeneities inside the “Pacific anomaly”.

What do Doppler indices of renal perfusion tell us for the evaluation of renal disease?

What do Doppler indices of renal perfusion tell us for the evaluation of renal disease?

Effects of Ramipril on Arterial Stiffness

To the Editor: The study by Ahimastos et al1 described reduction in aortic pulse wave velocity (PWV) with 10 mg daily ramipril; this was not associated with any fall in mean brachial artery pressure. There is a curious anomaly in this study, which casts doubt on the conclusions. Whereas the authors report no change in mean pressure with 10 mg ramipril compared with placebo, there was a highly significant reduction in brachial systolic (5.4 mm Hg) and diastolic (6.3 mm Hg) pressures. How is it possible for both systolic and diastolic pressures to fall but mean pressure to be maintained? We have never seen such a phenomenon. We do, however, have serious reservations about using the Dinamap Vital Signs Monitor to measure cuff brachial pressure, because this device has been shown to be inaccurate in a number of studies, especially for diastolic blood pressure.2 If related to diastolic pressure at the foot of the waveform (from which PWV is measured), the fall in …

Nondestructive Assessment of Damage in Concrete Bridge Decks

Impact-echo tests were performed on a precast, reinforced concrete bridge slab that was removed from a maintenance bridge built in 1953 in South Carolina. Impact-echo tests were first performed to nondestructively assess the initial condition and the distribution of damage throughout the slab by analyzing the variation in propagation wave velocity. It was found that the velocity varied by as much as 900 m/s throughout the slab. After the in-service condition was assessed, the slab was subjected to a full-scale static load test in the laboratory and impact-echo tests were again performed, this time to evaluate the initiation and progression of damage (stiffness loss and crack development) within the slab. After structural failure of the slab, a reduction in propagation wave velocity up to 6% was observed correlating to a reduction in slab stiffness. Cracks were detected within the concrete slab that were not visible from the surface. Areas with preexisting damage experienced more crack growth when subjected to the load test than those that were initially intact. Locations exhibiting stiffness loss, crack propagation, and localized damage can be differentiated such that the method can be used to make decisions between rehabilitating and replacing concrete bridge decks depending upon the severity of damage.

Seismic heterogeneous structure in the lowermost mantle beneath the southwestern Pacific

The P and S wave velocity structure of the D″ layer beneath the southwestern Pacific was investigated by using short‐period data from 12 deep events in the Tonga‐Fiji region recorded by the J‐Array and the Hi‐net (two large‐aperture seismic arrays) in Japan. Reflected wave beam forming (RWB) and a migration method were used to extract weak signals originating from heterogeneities in the lowermost mantle. In order to acquire high resolution a double‐array method was applied to the data. The results of the RWB method indicate that seismic energy is reflected at discontinuities near the depths of 2520 and 2650 km, which have a negative P wave velocity contrast of 1% at the most. In addition, there is a positive seismic discontinuity at a depth of 2800 km. In the case of the S wave, reflected energy is produced almost at the same depth (2550 km depth). An apparent depth shift (50 km) of the discontinuity at the depth of 2850 km may indicate that the S wave velocity reduction in the lowermost mantle is ∼2–3 times stronger than that of P. A two‐dimensional cross section, constructed with the RWB method, suggests that the observed discontinuities can be characterized as intermittent lateral heterogeneities whose lateral extent is a few hundred kilometers. The migration shows weak evidence of scattering objects which belong to the seismic discontinuities detected by the RWB method. These anomalous structures may represent a part of hot plume generated beneath the southwestern Pacific in the lowermost mantle.

Reflection properties of the core‐mantle boundary from global stacks of PcP and ScP

Seismic phases that reflect off the core‐mantle boundary (CMB) are sensitive to the velocity and density contrasts between the base of the mantle and the core. We measure the amplitudes of CMB reflections to seek effects of large velocity reductions and possible density increases in proposed thin basal layers (ultralow‐velocity zones, or ULVZs). We construct globally averaged envelope stacks of PcP and ScP in 3°‐wide epicentral distance bins, correcting for propagation and source effects. We measure the amplitude ratios PcP/P and ScP/P and compare them with the predicted range dependence for preliminary reference Earth model (PREM) and several proposed ULVZ models. The amplitude ratios are not compatible with ULVZs containing 30% S wave velocity reductions or with a 3‐km‐wide core‐mantle transition zone. The PcP data cannot distinguish between PREM and models with 10% reductions in both P wave velocity (VP) and S wave velocity (VS) and up to a 20% increase in density. The ScP data also match PREM closely but contain greater uncertainty from the correction for mantle attenuation. In well‐sampled regions, lateral variations of reflection amplitudes mapped to bounce point locations are consistent with previous detections and nondetections of ULVZs. These results suggest that extreme velocity reductions near the CMB are not global features and that regions with large velocity reductions do not result from global phenomena such as phase changes in an isochemical mantle but rather from local thermal or compositional anomalies.

Dynamic tensile strength of terrestrial rocks and application to impact cratering

Abstract— Dynamic tensile strengths and fracture strengths of 3 terrestrial rocks, San Marcos gabbro, Coconino sandstone, and Sesia eclogite were determined by carrying out flat‐plate (PMMA and aluminum) impact experiments on disc‐shaped samples in the 5 to 60 m/sec range. Tensile stresses of 125 to 300 MPa and 245 to 580 MPa were induced for gabbro and eclogite, respectively (with duration time of ˜1 μs). For sandstone (porosity 25%), tensile stresses normal to bedding of ˜13 to 55 MPa were induced (with duration times of 2.4 and ˜1.4 μs). Tensile crack failure was detected by the onset of shock‐induced (damage) P and S wave velocity reduction.The dynamic tensile strength of gabbro determined from P and S wave velocity deficits agrees closely with the value of previously determined values by post‐impact microscopic examination (˜150 MPa). Tensile strength of Coconino sandstone is 20 MPa for a 14 μs duration time and 17 MPa for a 2.4 μs duration time. For Sesia eclogite, the dynamic tensile strength is ˜240 MPa. The fracture strength for gabbro is ˜250 MPa, ˜500 MPa for eclogite, and ˜40 MPa for sandstone. Relative crack‐induced reduction of S wave velocities is less than that of post‐impact P wave velocity reductions for both gabbro and eclogite, indicating that the cracks were predominantly spall cracks.Impacts upon planetary surfaces induce tensile failure within shock‐processed rocks beneath the resulting craters. The depth of cracking beneath impact craters can be determined both by seismic refraction methods for rocks of varying water saturation and, for dry conditions (e.g., the Moon), from gravity anomalies. In principle, depth of cracking is related to the equations‐of‐state of projectile and target, projectile dimension, and impact velocity. We constructed a crack‐depth model applicable to Meteor Crater. For the observed 850 m depth of cracking, our preferred strength scaling model yields an impact velocity of 33 km/s and impactor radius of 9 m for an iron projectile.

Experimental studies on elastic and rheological properties of amphibolites at high pressure and high temperature

Laboratory measurements of compressional-wave velocities and rheological properties are carried out on natural amphibolites collected from Chencai, Zhejiang Province at high pressures and high temperatures. The experiments of elastic wave velocity find that the compressional-wave velocities travel faster along the lineation(X-direction) within the foliation plane than those normal to the foliation (Z-direction). The velocity anisotropies are high for the amphibolites at 550℃ and pressure of 800 MPa or 600 MPa. Furthermore, the values of anisotropy and average velocity are respectively 7.83% and 6.77km/s for the samples with fine grain size, 9.77% and 6.64km/s for the samples with medium grain size. With increasing temperature at high static pressure, the wave velocities spreading along three structure directions in the samples all start to drop from 750℃ up. The rheological experiments also find that there is a marked strength reduction from 750℃ to 800℃ although the flow strength gradually decreases with increasing temperature for the fine-grained amphibolite at a confining pressure of 500 MPa and strain rate of 1×10 -4 s -1 .. Based on the results of microcopy observations, electronic probe analyses and infrared spectra analyses for some samples, the reduction of flow strength and wave velocity may be due to partial melting of amphibole above 750℃. In addition, the rock deformations undergo from localized brittle fracture, semi-brittle deformation (cataclastic flow or semi-brittle faulting, semi-brittle flow) to homogeneous crystal-plastic flow from 600℃ to 1000℃, confining pressure of 500 MPa and strain rate of 1×10 -4 s -1 .

Prognostic significance of arterial stiffness measurements in end-stage renal disease patients.

As epidemiological and clinical studies have shown that damage of large arteries is a major contributory factor to the high cardiovascular morbidity of patients with end-stage renal disease, such a population is particularly appropriate for analysis the impact of arterial stiffness on cardiovascular risk assessment and reduction strategies. Aortic pulse wave velocity, a marker of aortic stiffness, has been shown to be a strong independent predictor of cardiovascular and all-cause mortality in patients with end-stage renal disease on hemodialysis. Local arterial stiffness assessment, namely carotid distensibility was also shown to predict cardiovascular risk, both in end-stage renal disease patients and in renal transplant recipients. Furthermore, it was shown in a therapeutic trial that the lack of aortic pulse wave velocity attenuation, despite significant drug-induced reduction in mean blood pressure, was a significant predictor of cardiovascular death in subjects with end-stage renal disease. These results support the hypothesis that measurement of aortic pulse wave velocity could help, not only in risk assessment strategies, but also in risk reduction strategies by monitoring arterial stiffness under different pharmacological regimens. The drug-related reduction of aortic pulse wave velocity could then give prognostic information, in addition to blood pressure reduction. Aortic stiffness measurements could serve as an important tool in identifying end-stage renal disease patients at higher risk of cardiovascular disease. The ability to identify these patients would lead to better risk stratification and earlier and more cost-effective preventive therapy.

Damage Assessment of Concrete Bridge Decks using Impact-Echo Method

This study presents results of a nondestructive evaluation (NDE) testing program performed to assess the damage in concrete bridge decks subjected to full-scale static and dynamic loading using the impact-loading method. The bridge decks were removed from a bridge built in 1953 in South Carolina. While in service, the concrete decks were retrofitted with FRP composite materials to repair extensive damage. Two slabs were tested by NDE in the lab after removal of the reinforcement layer. Impact-echo tests (IETs) were performed concurrently with full-scale static and dynamic load tests. The first slab was statically loaded to failure, and the second was tested dynamically with cyclic loading. IETs were performed before and after the loading sequence for each slab and between each application of cyclic loading for the second slab. Results from tests on the statically loaded slab detected a significant reduction in propagation wave velocity after failure, indicating a reduction in the slab stiffness. IETs on the dynamically loaded slab quantified the degradation of the slab during dynamic testing. Significant damage was detected earlier than by visual observance and before the slab reached service failure.

Use of SASW Measurements to Evaluate the Effect of Lime Slurry Conditioning in Drilled Shafts

Spectral-Analysis-of-Surface-Waves (SASW) testing was conducted in untreated and treated drilled shafts at the NGES “TXHOUSTO” test site as part of a study on lime-slurry conditioning of soil in drilled shafts for pier foundation construction. Results of SASW testing in an untreated shaft revealed a reduction in shear wave velocity ([Formula: see text]; a measure of small-strain shear stiffness) within an annular zone slightly less than one shaft diameter in thickness. This reduction is attributed to stress relief and soil disturbance during excavation. Results of SASW testing in a treated shaft revealed that [Formula: see text] of the soil surrounding the shaft depended upon whether the measurement was performed above or below the water table. Above the water table, a thin (less than [Formula: see text]) annulus of stiffen cemented soil was created due to the reaction between the lime and the carbon dioxide in the pore spaces of the partially saturated soil. Since the clay was saturated below the water table, there was no carbon dioxide in the pore spaces available to react with the lime, so there was no observed increase in stiffness due to cementation. As a result of these observations, an alternative strategy for the application of lime-slurry conditioning of drilled shafts in the construction of pier foundations has been conceived.

Upper mantle seismic wave velocity: Effects of realistic partial melt geometries

We investigate seismic wave velocity reduction resulting from the presence of partial melt in the upper mantle. The amount of shear and bulk modulus reduction produced by the presence of a connected network of realistically shaped and naturally organized melt inclusions is found using finite element calculations. The geometries of the inclusions are taken directly from laboratory experiments of mantle melting, with finite element meshes constructed to conform to these shapes. The shear and bulk moduli of the composite material are found for both the unrelaxed (isolated inclusions) and relaxed (pressure equalized inclusions) cases by assigning appropriate material properties to the fluid. Modulus reduction from deformation simulations of a solid containing realistically shaped and ellipse‐shaped melt inclusions quantify the effect of melt pocket cuspateness and melt pocket organization on seismic velocity reduction. The three‐dimensional response is estimated from two‐dimensional distributions of the melt phase by determining the mode II and mode III components of elastic modulus reduction separately and summing their effects. In general, cuspate and naturally organized melt inclusions cause greater velocity reduction. It is shown that VP and VS reduction per percent partial melt are at least 3.6% and 7.9%, respectively. Even higher values for velocity reduction are possible above 1% melt fraction if melt exists only in tubules below 1% melt fraction. The lower, more conservative values of velocity reduction are ∼70% greater for VP and 84% greater for VS than the analytically determined values for ellipsoidal inclusions. Somewhat greater effects are possible if nonrandom organization of melt occurs on scales greater than our model.

２０９１アルミニウム合金の層状割れ発生基準

The measurement of ultrasonic wave velocity has been used to detect the delamination cracking during tensile tests in an 2091 T–8 Al–Li alloy at both liquid helium and room temperature. The measured stresses for initiation of delamination cracking are 335 and 357 MPa, for the cryogenic and room temperatures, respectively. The density of delamination cracks in the alloy is estimated from the observed reduction in ultrasonic wave velocity and resultant decrease in modulus of elasticity. It is estimated that the interfacial debonding strengths normal to a grain boundary are 116 and 113 MPa, for the cryogenic and room temperature, respectively. Fracture mechanics analysis has been used to estimate the onset of delamination cracking in the case of a cracked tensile specimen. The predicted levels of far field applied stresses are much lower than that for macroscopic crack initiation at both cryogenic and room temperatures, respectively.

Further structural constraints and uncertainties of a thin laterally varying ultralow‐velocity layer at the base of the mantle

Constraints and uncertainties are presented for modeling of an ultralow‐velocity zone layer (ULVZ) at the base of Earth's mantle using an SKS wave with small segments of P wave diffraction at the SKS core entry and exit locations, called SPdKS. Source or receiver effects are ruled out as causes for the SPdKS anomalies used to map ULVZ structure, since systematic SPdKS‐SKS travel time moveout behavior is present in profiles of recordings of a given earthquake at many seismographic stations and also for many events recorded at one station. The southwest Pacific region produces strong variability in observed SPdKS/SKS amplitude ratios (compared to synthetic seismograms), which geographically corresponds to an anomalous ULVZ region. Accurate determination of absolute ULVZ thicknesses requires knowledge of, in addition to magnitude of P wave velocity (Vp) reduction in the layer, the magnitude of S wave velocity (VS) reduction and density (ρ) perturbation (if any). Synthetic seismogram experiments demonstrate several key points regarding uncertainties and constraints in modeling ULVZ structure: (1) thicker layers (up to 300 km thick) with mild reductions (e.g., −2.5 to −5.0%) cannot reproduce the anomalous SPdKS behavior seen in the data; (2) for ULVZ layers less than 10 km thick, strong trade‐offs exist between discontinuous velocity reductions and linear gradient reductions over a thicker zone; (3) uncertainties preclude precise determination of magnitude of δVP and δVS reductions, as well as the δVS:δVP ratio; (4) large density increases within the ULVZ (e.g., up to 60% and more) can efficiently broaden and delay the peak of the energy that we identify as SPdKS for models with strong velocity reductions in the layer; (5) models with extreme Q reductions in the ULVZ can affect SPdKS waveforms, and dampen spurious ringing energy present in Sd waveshapes due to the ULVZ; and (6) the minimum required Vp reduction for the most anomalous data (around −10%) trades off with thinner ULVZ structures containing larger velocity reductions (with possible density increases as well).

Quantitative Assessment of Extrinsic Damage in Rock Materials

Comminution (crushing and grinding) of rock materials is energy-intensive and expensive. Much effort has been directed to improve the efficiency of conventional milling practice, but relatively little attention has been given to the potential benefits of blast-induced (extrinsic) damage on comminution processes. The objective of this research is to investigate the effect of shock-induced “crack-like” damage on rock properties for three petrologically distinct rock materials under laboratory conditions. In order to evaluate the effect of shock-induced damage, a quantitative measure of rock damage is needed. Shock loading of rock material was accomplished with an explosively driven split Hopkinson pressure bar. Laboratory measurements show that the average uniaxial compressive strengths for damaged specimens are slightly lower than those for intact specimens. Based on damage mechanics, the scalar damage variable ( ) was experimentally determined as the relative reduction in ultrasonic wave velocity of damaged versus intact rock. increases as the shock energy dissipated in rock material increases. A crack density was determined by confocal image analysis. Measurements following shock loading indicate that ultrasonic wave velocity in rock partially recovers with time. Ultrasonic wave velocity and confocal image analysis may be useful in quantitatively assessing the internal crack-like damage in rock materials.

Fracture density estimates in glaciogenic deposits from P‐wave velocity reductions

Subsidence‐induced fracturing of glaciogenic deposits over coal mines in the southern Illinois basin alters hydraulic properties of drift aquifers and exposes these aquifers to surface contaminants. In this study, refraction tomography surveys were used in conjunction with a generalized form of a seismic fracture density model to estimate the vertical and lateral extent of fracturing in a 12-m thick overburden of loess, clay, glacial till, and outwash above a longwall coal mine at 90 m depth. This generalized model accurately predicted fracture trends and densities from azimuthal P‐wave velocity variations over unsaturated single‐ and dual‐parallel fractures exposed at the surface. These fractures extended at least 6 m and exhibited 10–15 cm apertures at the surface. The pre‐ and postsubsidence velocity ratios were converted into fracture densities that exhibited qualitative agreement with the observed surface and inferred subsurface fracture distribution. Velocity reductions as large as 25% were imaged over the static tension zone of the mine where fracturing may extend to depths of 10–15 m. Finally, the seismically derived fracture density estimates were plotted as a function of subsidence‐induced drawdown across the panel to estimate the average specific storage of the sand and gravel lower drift aquifer. This value was at least 20 times higher than the presubsidence (unfractured) specific storage for the same aquifer.

The effect of laryngeal irradiation on pharyngoesophageal motility

The upper esophageal sphincter (UES) receives the full radiation dose during external beam radiotherapy to the adjacent larynx. The aim of the study was to assess the effects, if any, of radical laryngeal radiotherapy on motility patterns in the pharyngoesophageal segment. A strain gauge assembly and a digital manometric recorder were used to assess 19 patients 13 to 71 months after irradiation of T 1 to T 3 glottic cancer to a central dosse of 52.5 to 55.7 Gy in 20 daily fractions. Results were compared with those of 23 healthy controls. Tonic lower esophageal sphincter (LES) pressure, distal peristaltic contraction, tonic UES pressure, and eight parameters of pharyngoesophageal dynamics during water and bread swallows were studied. No difference was found between the two groups in tonic LES pressure, peristaltic amplitude, or tonic UES pressure. Water swallow pharyngoesophageal wave velocity was significantly lower in patients than in controls, and the irradiated group also showed a trend toward increased duration of the distal esophageal peristaltic wave. The reduction in upper esophageal wave velocity was associated with the interval following irradiation. The post-treatment interval was also inversely related to the amplitude of UES after-contraction, and associated with an increase in wave duration throughout the pharyngoesophageal segment. A study of 23 laryngectomy specimens, 5 of which had been removed following radiotherapy, failed to identify pathological features in nerves or muscle which characterised previous laryngopharyugeal irradiation. We conclude that laryngeal irradiation has no effect on upper or lower esophageal sphincter tone but causes an increase in wave duration and a reduction in wave velocity in the pharyngoesophageal segment. These changes are independent of age and sex and are not associated with pathological features like the neural degeneration described in the myenteric plexus of irradiated rectum.

Esophageal function in humans

We determined the effect of increased bolus consistency on esophageal motor function in 11 healthy volunteer subjects. Further, we sought to define the esophageal response to boluses with a wide range of temperatures in nine healthy volunteers. Intraluminal pressure events were measured with an infused catheter system, and lower esophageal sphincter pressure was monitored continuously with a Dent sleeve. Boluses (10 swallows each) consisting of 5 ml of a solid suspension (yogurt), 5 cm3 of a soft solid (gelatin), and 5 ml of water were given in a randomized order. In a separate study, boluses with temperatures of 1 degree C, 5 degrees C, 10 degrees C, 15 degrees C, room temperature, 30 degrees C, 40 degrees C, 50 degrees C, and 60 degrees C were given in a randomized fashion. Compared to the water bolus, the solid boluses elicited a significant (P less than 0.05) reduction in peristaltic wave velocity, which was accompanied by significant (P less than 0.05) increments in the durations of wave contraction and lower esophageal sphincter relaxation. The magnitude of the response elicited by the solid boluses was comparable to that noted with boluses of high viscosity suggesting that the esophagus response to increments in bolus viscosity and consistency in a similar fashion. Alterations in bolus temperature did not elicit any significant changes in the parameters of esophageal peristalsis. It is concluded that bolus temperature does not have a significant role in the modulation of human esophageal peristalsis except under conditions that cause a change in esophageal wall temperature.

Analysis for vertical velocity of seismic waves

Abstract Presented here are the results of seismic wave velocities analyzed using the acceleration time‐histories recorded at the downhole strong motion array of the Lotung large scale seismic test site during the May 20, 1986 Hualien earthquake. The spectral ratios between the surface and downhole accelerograms were used to identify the frequencies of maximum amplification of soil layers, and an elastic 1‐D wave propagation model was proposed to estimate the wave velocities of the ground during the earthquake. The results obtained indicate that significant reduction of shear wave velocity as well as soil modulus was induced by earthquake excitation as compared to the values obtained from low strain level soil testings.