An analytical solution to the scattering of cylindrical SH waves by a partially filled semi-circular alluvial valley: near-source site effects

The earth’s surface irregularities can substantially affect seismic waves and induce amplifi cations of ground motions. This study investigates whether and how the source characteristics affect the site amplifi cation effects. An analytical model of a line source of cylindrical waves impinging on an alluvial valley is proposed to link the source and site. The analytical solution to this problem proves one aspect of the strong effect of source on site amplifi cation, i.e., the wave curvature effect. It is found that the site amplifi cation depends on the source location, especially under conditions of a small source-to-site distance. Whether the displacement is amplifi ed or reduced and the size of the amplifi cation or reduction may be determined by the location of the source. It is suggested that traditional studies of site responses, which usually ignore the source effect, should be further improved by combining the source with site effects.

Estimating the site effects in Luoyang basin using horizontal-to-vertical spectral ratio method from a short-period dense array

The influence of local site effects on seismic ground motions is an important issue in seismic hazard assessment and earthquake resistant design. Determining site effects in densely populated cities built on basins can help to reduce the earthquake hazard. Site effects of Luoyang basin are estimated by the horizontal-to-vertical spectral ratio(HVSR) method using ambient noise records from a short-period dense array. The sites in Luoyang basin are sorted into three types according to the pattern of the HVSR curves. There are cases with a single clear peak, two clear peaks, and an unclear low frequency peak or multiple peaks, which correspond to there being one large impedance contrast interface, two large interfaces, and a moderate one beneath the sites, respectively. The site effects characterized by fundamental frequency from HVSR curves are affected by underlying sedimentary layers and depth of sedimentary basement. According to our results, the existence of thick sediment layer obviously lowers the fundamental frequency to the period range from 2 to 4 s in the downtown area of Luoyang city. The ground motion will amplify when through the sites and the buildings with height of 20–50 floors can resonate at the similar frequency domain. Site effects estimation using HVSR method from a short-period dense array is an effective technique in areas of moderate seismic risk where strong motion recordings are lacking, such as the Luoyang basin.

Analysis of the role of diffraction in topographic site effects using boundary element techniques

The role played by the diffraction field on the problem of seismic site effects is studied. For that purpose we solve and analyze simple scattering problems under P and SV in-plane wave assumptions, using two well known direct boundary-element-based numerical methods. After establishing the difference between scattered and diffracted motions, and introducing the concept of artificious and physically based incoming fields, we obtain the amplitude of the Fourier spectra for the diffracted part of the response： this is achieved after establishing the connection between the spatial distribution of the transfer function over the studied simple topographies and the diffracted field. From the numerical simulations it is observed that this diffracted part of the response is responsible for the amplification of the surface ground motions due to the geometric effect. Furthermore, it is also found that the diffraction field sets in a fingerprint of the topographic effect in the total ground motions. These conclusions are further supported by observations in the time-domain in terms of snapshots of the propagation patterns over the complete computational model. In this sense the geometric singularities are clearly identified as sources of diffraction and for the considered range of dimensionless frequencies it is evident that larger amplifications are obtained for the geometries containing a larger number of diffraction sources thus resulting in a stronger topographic effect. The need for closed-form solutions of canonical problems to construct a robust analysis method based on the diffraction field is identified.

Ground Motion and Site Effects on Performance-Based Design

The objective of Performance-Based Earthquake Engineering （PBEE） is the analysis of performance objectives with a specified annual probability of exceedance. Increasingly undesirable performance is caused by increasing levels of strong ground motion having decreasing annual probabilities of exceedance. The development of this methodology includes three steps： （1） evaluation of the distribution of ground motion at a site; （2） evaluation of the distribution of system response; （3） evaluation of the probability of exceeding decision variables within a given time period, given appropriate damage measures. The work has taken a systematic approach to determine the impact of increasing levels of detail in site characterization on the accuracy of ground motion and site effects predictions. Complementary studies have investigated the use of the following models for evaluating site effects： （1） amplification factors defined on the basis of generalized site categories, （2） one-dimensional ground response analysis, and （3） two-dimensional ground response analysis for surface topography on ground motion. The paper provides a brief synthesis of ground motion and site effects analysis procedures within a Performance-Based Design framework. It focuses about the influence on the evaluation of site effects in some active regions by different shear waves velocity measurements Down Hole （D-H）, Cross Hole （C-H）, Seismic Dilatometer Marchetti Test （SDMT） and by different variation of shear modulus and damping ratio with strain level and depth from different laboratory dynamic tests for soil characterization： Resonant Column Test （RCT）, Cyclic Loading Torsional Shear Test （CLTST）.

Estimation of Site Effects on Stations in the Capital Circle Region Using the Generalized Inversion Method

Generalized Inversion Method has been used to estimate the spatial variation of site effects,using the digital data of SH-waves recorded by 63 stations in the Capital Circle Region of China from 2001 to 2006.We gained the site effects of all stations participating in the calculation.We found that the site effect of rock was stabile and about 1.0 from 1.0Hz to 10.0Hz,while the site effect of deposit was high in low frequencies,about 3 ～ 7 from 1.0Hz to 8.0Hz,and the site effect was protuberant at about 5.0Hz,then fell as the frequency increased.The result shows the shape and intensity of station site effects are mainly influenced by the lithology below the station,and possibly also by the local geological structure.

Site effects by generalized inversion technique using strong motion recordings of the 2008 Wenchuan earthquake

The generalized inversion of S-wave amplitude spectra from the free-field strong motion recordings of the China National Strong Motion Observation Network System （NSMONS） are used to evaluate the site effects in the Wenchuan area. In this regard, a total of 602 recordings from 96 aftershocks of the Wenchuan earthquake with magnitudes of M3.7-M6.5 were selected as a dataset. These recordings were obtained from 28 stations at a hypocenter distance ranging from 30 km to 150 km. The inversion results have been verified as reliable by comparing the site response at station 62WUD using the Generalized Inversion Technique （GIT） and the Standard Spectral Ratio method （SSR）. For all 28 stations, the site predominant frequency F and the average site amplification in different frequency bands of 1.0-5.0 Hz, 5.0-10.0 Hz and 1.0-10.0 Hz have been calculated based on the inversion results. Compared with the results from the horizontal-to-vertical spectral ratio （HVSR） method, it shows that the HVSR method can reasonably estimate the site predominant frequency but underestimates the site amplification. The linear fitting between the average site amplification for each frequency band and the V20 （the average uppermost-20 m shear wave velocity） shows good correlation. A distance measurement called the asperity distance DAspt is proposed to reasonably characterize the source-to-site distance for large earthquakes. Finally, the inversed site response is used to identify the soil nonlinearity in the main shock and aftershocks of Wenchuan earthquake. In ten of the 28 stations analyzed in the main shock, the soil behaved nonlinearly, where the ground motion level is apparently beyond a threshold ofPGA 〉 300 cm/s^2 or PGV 〉 20 cm/s, and only one station coded 51SFB has evidence of soil nonlinear behavior in the aftershocks.

Research on the ShakeMap System with Consideration of Site Effects

In accordance with the principle of similarity in geology and topography, the Vs^30 （the average shear-velocity down to a 30m depth below the surface） approximation of sites is acquired by correlation between Vs^30 and slopes after calculating the maximum slope of topography using the 30-sec Chinese Mainland DEM （Digital Elevation Model） data set. Site-amplification factors are then quantified with Vs^30 and applied to the ShakeMap system developed by this study to revise ground-motion amplitudes on bedrock estimated from empirical relationships. Finally, the distribution of ground motion parameters on the surface is obtained. This article also introduces the calculation process, calculation models of the ShakeMap systems and related software systems. In conclusion, certain examples indicate that the ShakeMap system is feasible in the Chinese Mainland.

Simplified seismic scenario analysis of existing masonry buildings accounting for local site effects

This study discusses the effects of local sites and hazard amplification on the seismic vulnerability assessment of existing masonry buildings.In this context,a rapid seismic evaluation procedure was implemented on an old masonry building stock in the historical center Galata,located inİstanbul,to determine the seismic risk priority of the built heritage.Damage scenarios were generated for all soil classes,different moment magnitudes,and source-to-site distances to obtain more accurate results for the seismic vulnerability assessment of the studied building stock.Consequently,damage distributions estimated under nine different scenarios with/without site effects were compared and illustrated in maps to discuss changes in vulnerability owing to amplification effects.In this study,by re-examining the rapid seismic evaluation procedure by including geo-hazard-based assessment,the importance of site effects on the vulnerability and risk assessment of built heritage was underlined.The proposed framework integrating field data and local site effects is believed to advance the current applications for vulnerability assessment of masonry buildings and provide an improvement in the application of rapid seismic assessment procedures with more reliable results.

Effects of site conditions on earthquake ground motion and their applications in seismic design in loess region

The Loess Plateau is an earthquake prone region of China, where the effects of loess deposit on ground motion were discovered during the 2008 Wenchuan earthquake(Ms8.0) and the 2013 Minxian-Zhangxian earthquake(Ms6.6). The field investigations, observations, and analyses indicated that large number of casualties and tremendous economic losses were caused not only by collapse and damage of houses with poor seismic performance, landslides, but also amplification effects of site conditions, topography and thickness of loess deposit, on ground motion. In this paper, we chose Dazhai Village and Majiagou Village as the typical loess site affected by the two earthquakes for intensity evaluation, borehole exploration, temporary strong motion array, micro tremor survey, and numerical analysis. The aim is to explore the relations between amplification factors and site conditions in terms of topography and thickness of loess deposit. We also developed site amplification factors of ground motion for engineering design consideration at loess sites. The results showed that the amplification effects are more predominant with increase in thickness of loess deposit and slope height. The amplification mayincrease seismic intensity by 1 degree, PGA and predominant period by 2 times, respectively.

Numerical Modelling of Seismic Site Effects Incorporating Non-linearity and Groundwater Level Changes

In the past decades, the necessity for detailed earthquake microzonation studies was recognized worldwide. Therefore, different approaches were established and applied. Unfortunately, the majority of these approaches are not based on pre-existing field data but require extensive seismic measurements and investigations. Furthermore, these approaches incorporate non-linearity inadequately and cannot take groundwater level changes into account. For this purpose, notably numerical models are most suitable. These models require a good knowledge of the local geological conditions （especially of the uppermost unconsolidated units）, information about the geotechnical parameters of these units, and a hydrogeological model of the investigated area. Most of this information can be obtained from geotechnical investigations and surveys that have already been carried out in most densely populated areas. In a case study for Bucharest City, non-linear analyses were performed using software that is based on the visco-hypoplastic constitutive law. The results indicate that groundwater level changes have an important influence on duration and amplitude of ground response and thus should be considered for seismic microzonation studies. This approach ean be used to display site effects and to identify different microzones taking different earthquake magnitudes and groundwater levels into account.

Site 0ccupancy of Alloying Elements and Their Effects on the D0_3 Phase Stability in Fe_3Al

The effects of ternary solutes Ti, Co, V, Cr, Ta, W and Mo on the D03 phase 5tability of Fe3Alintermetallics are investigated by tight-binding linear Muffin-tin orbitaI method. The predictedsite preference5 of these elements in Fe3AI are in agreement with the experimental observations.The calculated Iocal magnetic moment of Fe3AI is identical to the experimentaI. ln addition, itis found that the D03 phase stability of Fe3AI doped with Ti, V, Co and Cr depends on 'energygap- of energy band near Fermi level. while the D03 phase stability of Fe3AI doped with Ta, Wand Mo may be affected by Madelung energy.

Influence of site conditions on ground motion at far field loess sites during strong earthquake

Loess is widely distributed in China and the Loess Plateau is one of the major areas where strong earthquakes often take place. The seismic amplification effects were discovered in the Plateau during the Wenchuan Ms8.0 earthquake and some other strong events. Based on earth tremor observation, borehole exploration and site seismic response analysis, the site effects of topography of Loess Yuan on ground motion were investigated in details. The earth tremor investigation shows that predominant frequencies at the bottom sites of Loess Yuan are greater than those at the top obviously. The sites seismic response analysis shows that the Loess Yuan may amplify peak ground acceleration (PGA) by 1.44 2.0 times. Therefore, site effects of mountains and loess topography on ground motion should be taken account into in seismic design in loess regions.

PGA and structural dynamics input motion at a given site

The computation of the representative ground motions,to be used as input for the dynamic analyses of a struc- ture at a particular site,can be approached by several methods.The choice of the approach depends on two factors:the da- ta available and the type of problem to be solved.This paper reports the experience of the authors in approaching a specific case study:the Southern Memnon Colossus,located in Luxor,Egypt.The results are of interest when the hazard analysis estimation in developing countries and the safeguard of cultural heritage are concerned.Monuments have to be treated as important structures,due to their historical and economical value.Hence,standard procedures of probabilistic seismic haz- ard analysis for the seismic classification of common buildings have to be disregarded.On the other hand,the consequences of the collapse of a monument are not comparable to those related to structures such as nuclear power plants and large dams, for which the deterministic seismic hazard analysis provides a straightforward framework for evaluation of the worst case ground motions.An'intermediate'approach,which requites a lower amount of input data with respect to the deterministic one,is adopted.Its stochastic component can eapture significant eharacteristics of earthquakes,primarily the frequency contents which depend on the magnitude(often referred to as the earthquake scaling law).

Estimation on site-amplification from different methods using strong motion data obtained in Tangshan, China

A seismic observation array for strong motions was deployed to estimate seismic source, propagation path and local site effects in Tangshan, China. We compared site response from the S-wave inversion and those from other techniques, such as traditional direct spectral ratios of S waves and receiver-function of S waves. From the inversion, we found that S-wave quality factor, i.e. Qs-value, is approximately satisfied with the relation of Qs=67f1.1 in the range of frequency from 0.5 Hz to 32 Hz and that the source spectra follow the ω-2 model of seismic source for low frequencies less than about 12 Hz. From the comparison of site responses estimated by the different methods for each soil site, we found that all the methods can extract the same predominant peaks from the responses, the amplifications from direct S-wave spectral ratios are well correlated with those from the S-wave inversion within a factor of 2 to 3, while the correlation between the amplifications from S-wave receiver-function and those from the S-wave inversion is not good, especially for high frequencies more than 8 Hz.

Study on Site Preparation and Restoration Techniques for Forest Restoration in Mining Tailings of Mariana,Brazil

Ecological restoration in forest ecosystem is a priority in Mariana,Brazil.Thus,we evaluated the effects of passive and active restoration methods through different site preparation techniques by manipulating physical-chemical properties of substrates on tree community coverage in Mariana,Brazil.A total of 48 plots(12×12 m each)were established in two areas along the flood plains with accumulation of tailings.The following treatments were established:(1)planting of native tree seedlings with fertilization(PSf)and(2)without fertilization(PS);(3)direct seeding of native trees with fertilization(SDf)and(4)without fertilization(SD);(5)natural regeneration with fertilization(NRf)and(6)without fertilization(NR).Differences in substrate properties and tree community coverage were evaluated between treatments,the substrate properties and tree community coverage relationship,and main effects of substrate fertility and texture on tree community coverage.There were marked differences in substrate and plant coverage between treatments.On average,the highest plant coverage was found in treatment with fertilization,such as NRf(59,5%)and SDf(48%).However,the treatment with seedling planting(PSf and PS)and NR did not show differences(~37%),while the lowest values were observed in SD(23%).There is a strong relationship between substrate fertility and plant community coverage,with significant positive effects.We observed that the passive and active restoration methods can be complementary in the soil and plant community coverage recovery.

Introducing an effective coherence function to generate non-uniform ground motion on topographic site using time-domain boundary element method

In this study,a comprehensive parametric analysis was performed on non-uniform excitation of V-shaped topography using the boundary element method in time domain.For this purpose,wave scattering analysis was carried out on a topography subjected to the SV-wave for different predominant frequencies and shape ratios.Based on the numerical results,new coherence and time delay functions are proposed to generate non-uniform ground motion for topographic irregularities.The efficiency and accuracy of the proposed functions for real engineering problems are indicated by comparison with observations reported in previous literature.

Application of the microtremor measurements to a site effect study

Earthquake has left much life and property damages. The occurrence of such events necessitates the execution of plans for combating the earthquakes. One of the most important methods for combating earthquakes includes assessing dynamic characteristics of soil and site effect. One of the methods by which one can state dynamic characteristics of the soil of an area is the measurement of microtremors. Microtremors are small-scale vibrations that occur in the ground and have an amplitude range of about 0.1-1 microns. Microtremor measurement is fast, applica- ble, cost-effective. Microtremor measurements were taken at 15 stations in the Babol, north of Iran. Regarding H/V spectral ratio method, peak frequency and amplifica- tion factor were calculated for all microtremor stations. According to the analysis, the peak frequency varies from 0.67 to 8.10 Hz within the study area. Also, the authors investigated the validity of the results by comparing them with SESAME guidelines and geotechnical conditions of study area. The microtremor analysis results are consistent with SESAME guidelines and geotechnical condition of study area. The results show that the microtremor obser- vations are acceptable methods for assessing dynamic characteristics of soil and site effect in the Babol City.

Incorporating topographic factors in nonlinear mixed-effects models for aboveground biomass of natural Simao pine in Yunnan,China

A total of 128 Simao pine trees （Pinus kesiya var. langbianensis） from three regions of Pu＇er City, Yunnan Province, People＇s Republic of China, were destructively sampled to obtain tree aboveground biomass （AGB）. Tree variables such as diameter at breast height and total height, and topographical factors such as altitude, aspect of slope, and degree of slope were recorded. We considered the region and site quality classes as the ran- dom-effects, and the topographic variables as the fixed- effects. We fitted a total of eight models as follows： least- squares nonlinear models （BM）, least-squares nonlinear models with the topographic factors （BMT）, nonlinear mixed-effects models with region as single random-effects （NLME-RE）, nonlinear mixed-effects models with site as single random-effects （NLME-SE）, nonlinear mixed-ef- fects models with the two-level nested region and site random-effects （TLNLME）, NLME-RE with the fixed-ef- fects of topographic factors （NLMET-RE）, NLME-SE with the fixed-effects of topographic factors （NLMET-SE）, and TLNLME with the fixed-effects of topographic factors （TLNLMET）. The eight models were compared by modelfitting and prediction statistics. The results showed： model fitting was improved by considering random-effects of region or site, or both. The models with the fixed-effects of topographic factors had better model fitting. According to AIC and BIC, the model fitting was ranked as TLNLME 〉 NLMET-RE 〉 NLME-RE.〉 NLMET-SE 〉 TLNLMET 〉 NLME-SE 〉 BMT 〉 BM. The differences among these models for model prediction were small. The model pre- diction was ranked as TLNLME 〉 NLME-RE 〉 NLME- SE 〉 NLMET-RE 〉 NLMET-SE 〉 TLNLMET 〉 BMT 〉 BM. However, all eight models had relatively high prediction precision （〉90 %）. Thus, the best model should be chosen based on the available data when using the model to predict individual tree AGB.

S wave inelastic attenuation and site effect in the northern Tianshan area

In this paper, according to the relationship of observation spectrum with source spectrum, travel-path attenuation factor and site effect, we use the digital seismic data of moderate-small earthquakes to invert the soft rock site effect and S wave inelastic attenuation under the constraint of site effect, and determine the parameters of path and site. The parameters obtained by this method exclude the topographic effect of seismic stations, and truly reflect the seismic effect of free soft rock sites and the S wave inelastic attenuation in the studied region. The average soft rock site effect is about 1.5 times in the frequency domain of 2-4 Hz and the S wave quality factor is obtained as Qs=278f0.346, which can be directly applied to the stochastic modeling of ground motions in the studied region.

Doping Effect of Co at Ag Sites in Antiperovskite Mn3AgN Compounds

Antiperovskite compounds Mn3Ag1-xCoxN （x =0.2, 0.5 and 0.8） are synthesized and the doping effect of the magnetic element Co at the Ag site is investigated. The crystal structure is not changed by the introduction of Co. However, with the increase of the content of Co, the spin reorientation gradually disappears and the antiferromagnetic transition changes to the ferromagnetic transition at the elevated temperature when x = 0.8. In addition, all of the magnetic phase transitions at the elevated temperature are always accompanied by the abnormal thermal expansion behaviors and an entropy change. Moreover, when x = 0.8, the coefficient of linear expansion is -1.89 × 10^-6 K^-1 （290-310K, △T =20 K）, which is generally considered as the low thermal expansion.