Scattering of seismic waves by three-dimensional large-scale hill topography simulated by a fast parallel IBEM

To solve seismic wave scattering by a large-scale three-dimensional(3-D) hill topography, a fast parallel indirect boundary element method(IBEM) is developed by proposing a new construction method for the wave field, modifying the generalized minimum residual(GMRES) algorithm and constructing an Open MP plus MPI parallel model. The validations of accuracy and efficiency show that this method can solve 3-D seismic response of a large-scale hill topography for broadband waves, and overcome the weakness of large storage and low efficiency of the traditional IBEM. Based on this new algorithm architecture, taking the broadband scattering of plane SV waves by a large-scale Gaussian-shaped hill of thousands-meters height as an example, the influence of several important parameters is investigated, including the incident frequency, the incident angle and the height-width and length-width ratio of the hill. The numerical results illustrate that the amplification effect on the ground motion by a near-hemispherical hill is more significant than the narrow hill. For low-frequency waves, the scattering effect of the higher hill is more pronounced, and there is only a single peak near the top of the hill. However, for high-frequency waves, rapid spatial variation of displacement amplitude appears on the hill surface.

Monitoring and Prediction of the Vibration Intensity of Seismic Waves Induced in Underwater Rock by Underwater Drilling and Blasting

All underwater drilling and blasting operations generate seismic waves.However,due to a lack of suitable vibration sensing instruments,most studies on the propagation of seismic waves have been limited to shorelines near construction areas or wharfs,whereas comparatively few studies have beerconducted on the larger seafloor itself.To address this gap,a seafloor vibration sensor system was developed and applied in this study that consists of an autonomous acquisition storage terminal,soft-ware platform,and hole-plugging device that was designed to record the blasting vibration intensities received through submarine rocks at a given measurement point.Additionally,dimensional analyses were used to derive a predictive equation for the strength of blast vibrations that considered the in fluence of the water depth.By combining reliable vibration data obtained using the sensor system in submarine rock and the developed predictive equation,it was determined that the water depth was ar important factor influencing the measured vibration strength.The results using the newly derivedequation were compared to those determined using the Sadowski equation,which is commonly used on land,and it was found that predictions using the derived equation were closer to the experimental values with an average error of less than 10%,representing a significant improvement.Based on these results the developed sensor system and preliminary theoretical basis was deemed suitable for studying the propagation behavior of submarine seismic waves generated by underwater drilling and blasting operations.

A laboratory method to simulate seismic waves induced by underground explosions

The seismic waves induced by underground explosions generate geological hazards affecting deep buried tunnels such as rockbursts and engineering-induced earthquakes. This issue is difficult to study through full-scale testing due to the expense and unpredictable danger. To solve this problem, the authors developed experimental apparatus and presented a laboratory method to simulate seismic waves induced by underground explosions. In this apparatus, a combined structure of a diffusive-shaped water capsule and a special-shaped oil capsule was designed. This structure can provide an applied confining stress and freely transmit the stress wave generated by external impact. Therefore, the coupled loading of in situ stress and seismic waves induced by underground explosions in the deep rock mass was simulated. The positive pressure time and peak value of the stress wave could be adjusted by changing the pulse-shaper and the initial impact energy. The obtained stress waves in the experiments correspond to that generated by 0.15-120 kt of TNT equivalent explosion at a scaled distance of 89.9-207.44 m/kt.

Studies on seismic waves

The development of seismic wave study in China in the past four years is reviewed. The discussion is divided into several aspects, including seismic wave propagation in laterally homogeneous media, laterally heterogeneous media, anisotropic and porous media, surface wave and seismic wave inversion, and seismic wave study in prospecting and logging problems. Important projects in the current studies on seismic wave is suggested as the development of high efficient numerical methods, and applying them to the studies of excitation and propagation of seismic waves in complex media and strong ground motion, which will form a foundation for refined earthquake hazard analysis and prediction.

Reflection and transmission of seismic waves at an interface betwen two saturated soils

Based on the modified Biot model for asturated soils, taking the compressibilities of the grains and the pore fluid as well as the viscous coupling into account, the reflection and transmission of seismic aves at an interface between two saturated soils are studied in this paper. A formula is derived for calculation of the amplitude reflection and transmission coefficients of various waves. A aumerical investigation of the dependence of the coefficients on the angle of incidence and the frequency is performed. This study is of a value for seismological studies and geophysical exploration.

Forward prediction for tunnel geology and classification of surrounding rock based on seismic wave velocity layered tomography

Excavation under complex geological conditions requires effective and accurate geological forward-prospecting to detect the unfavorable geological structure and estimate the classification of surround-ing rock in front of the tunnel face.In this work,a forward-prediction method for tunnel geology and classification of surrounding rock is developed based on seismic wave velocity layered tomography.In particular,for the problem of strong multi-solution of wave velocity inversion caused by few ray paths in the narrow space of the tunnel,a layered inversion based on regularization is proposed.By reducing the inversion area of each iteration step and applying straight-line interface assumption,the convergence and accuracy of wave velocity inversion are effectively improved.Furthermore,a surrounding rock classification network based on autoencoder is constructed.The mapping relationship between wave velocity and classification of surrounding rock is established with density,Poisson’s ratio and elastic modulus as links.Two numerical examples with geological conditions similar to that in the field tunnel and a field case study in an urban subway tunnel verify the potential of the proposed method for practical application.

A comparative analysis of seismic response of shallow buried underground structure under incident P,SV and Rayleigh waves

In this study,A time-domain seismic response analysis method and a calculation model of the underground structure that can realize the input of seismic P,SV and Rayleigh waves are established,based on the viscoelastic artificial boundary elements and the boundary substructure method for seismic wave input.After verifying the calculation accuracy,a comparative study on seismic response of a shallow-buried,double-deck,double-span subway station structure under incident P,SV and Rayleigh waves is conducted.The research results show that there are certain differences in the cross-sectional internal force distribution characteristics of underground structures under different types of seismic waves.The research results show that there are certain differences in the internal force distribution characteristics of underground structures under different types of seismic waves.At the bottom of the side wall,the top and bottom of the center pillar of the underground structure,the section bending moments of the underground structure under the incidences of SV wave and Rayleigh wave are relatively close,and are significantly larger than the calculation result under the incidence of P wave.At the center of the side wall and the top floor of the structure,the peak value of the cross-sectional internal force under the incident Rayleigh wave is larger than the calculation result under SV wave.In addition,the floor of the underground structure under Rayleigh waves vibrates in both the horizontal and vertical directions,and the magnification effect in the vertical direction is more significant.Considering that the current seismic research of underground structures mainly considers the effect of body waves such as the shear waves,sufficient attention should be paid to the incidence of Rayleigh waves in the future seismic design of shallow underground structures.

Influence of long period seismic waves induced by the Taiwan large earthquake on Shanghai area

In this paper a group of long period seismic waves in Shanghai area induced by Taiwan large earthquake is presented by using the method of semi empirical Green function, the period is up to 20 s. Such seismic waves can be used as a reference curve to test the strength of long period structures and their aseismic design. The long period part of seismic influence curve presented in 'Architecture Aseismic Design Code'(GBJ11 89) is less than 3 s, and uncertainties exist in the effects of earthquake safety evaluation. This research will be able to eliminate these shortages.

A real time processing system of seismic waves using personal computers-Function and characteristics

Seismological Bureau of Sichuan Province, Chengdu 610041, China2) Center for Analysis and Prediction, State Seismological Bureau, Beijing 100036, China3) Observation Center for Prediction of Earthquakes and Volcanic Eruptions, Faculty of Sciences, Tohoku University, Sendai 98077, Japan

Rayleigh waves from correlation of seismic noise in Great Island of Tierra del Fuego,Argentina:Constraints on upper crustal structure

In this study, the ambient seismic noise cross-correlation technique is applied to estimate the upper structure of the crust beneath Great Island of Tierra del Fuego（TdF）, Argentina, by the analysis of shortperiod Rayleigh wave group velocities. The island, situated in the southernmost South America, is a key area of investigation among the interaction between the South American and Scotia plates and is considered as a very seismically active one. Through cross-correlating the vertical components of ambient seismic noise registered at four broadband stations in TdF, we were able to extract Rayleigh waves which were used to estimate group velocities in the period band of 2.5-16 s using a timefrequency analysis. Although ambient noise sources are distributed in homogeneously, robust empirical Green＇s functions could be recovered from the cross-correlation of 12 months of ambient noise, The observed group velocities were inverted considering a non-linear iterative damped least-squares inversion procedure and several 1-D shear wave velocity models of the upper crust were obtained.According to the inversion results, the S-wave velocity ranges between 1.75 and 3,7 km/s in the first10 km of crust, depending on the pair of stations considered. These results are in agreement to the major known surface and sub-surface geological and tectonic features known in the area. This study represents the first ambient seismic noise analysis in TdF in order to constraint the upper crust beneath this region.It can also be considered as a successful feasibility study for future analyses with a denser station deployment for a more detailed imaging of structure.

Comparative Analysis of Application of Seismic Wave Reflection Method in Advanced Geological Prediction

Seismic wave reflection method is an advanced geophysical detection method in tunnel geological prediction.It is more sensitive and effective in detecting geological anomalies such as fault fracture zone and karst.In order to verify the prediction efficacy and accuracy of the seismic wave reflection method with different instruments and equipment(tunnel geological prediction[TGP]/tunnel seismic prediction[TSP])and different vibration modes(hammering,explosives),a comparison test was carried out in Jinping Tunnel.The test results showed that the time-consumption of the hammering source was short,which can greatly reduce the impact on the construction site;different vibration sources methods of seismic wave reflection can predict the unfavorable geological sections accurately.

Seismic performance of an existing bridge with scoured caisson foundation

This paper presents in-situ seismic performance tests of a bridge before its demolition due to accumulated scouring problem. The tests were conducted on three single columns and one caisson-type foundation. The three single columns were 1.8 m in diameter,reinforced by 30-D32 longitudinal reinforcements and laterally hooped by D16 reinforcements with spacing of 20 cm. The column height is 9.54 m,10.59 m and 10.37 m for Column P2,P3,and P4,respectively. Column P2 had no exposed foundation and was subjected to pseudo-dynamic tests with peak ground acceleration of 0.32 g first,followed by one cyclic loading test. Column P3 was the benchmark specimen with exposed length of 1.2 m on its foundation. The exposed length for Column P4 was excavated to 4 m,approximately 1/3 of the foundation length,to study the effect of the scouring problem to the column performance. Both Column P3 and Column P4 were subjected to cyclic loading tests. Based on the test results,due to the large dimension of the caisson foundation and the well graded gravel soil type that provided large lateral resistance,the seismic performance among the three columns had only minor differences. Lateral push tests were also conducted on the caisson foundation at Column P5. The caisson was 12 m long and had circular cross-sections whose diameters were 5 m in the upper portion and 4 m in the lower portion. An analytical model to simulate the test results was developed in the OpenSees platform. The analytical model comprised nonlinear flexural elements as well as nonlinear soil springs. The analytical results closely followed the experimental test results. A parametric study to predict the behavior of the bridge column with different ground motions and different levels of scouring on the foundation are also discussed.

Stabilisation of estuarine sediments with an alkali-activated cement for deep soil mixing applications

In this work,an alternative alkali-activated cement(AAC)made of ladle slag precursor mixed with sodium hydroxide and sodium silicate has been developed to enhance the bearing capacity of estuarine soils in coastal conditions via deep soil mixing(DSM).The AAC was optimized to use a low reactivity precursor(ladle slag)and to deal with a contaminated high-water content natural sediment cured under water.The material performance was analysed by comparison to a mixture made with Portland cement and cured in the same conditions.Flexural and unconfined compressive strength tests as well as seismic waves measurements after 3-,7-,14-and 28-d curing were performed to obtain a relationship between elastic stiffness and strength with curing time for both mixtures.Remarkably,the AAC mix demonstrated superior strength results,exhibiting almost double flexural and compressive strengths after 28 d compared to the Portland cement mix.The AAC mix also showed a higher rate of stiffness increase than the Portland cement mix,which has a higher initial stiffness at young ages but lower stiffness evolution.Leachate analysis confirmed that the proposed AAC could effectively immobilise any contaminants from soil or precursors.The effect of curing under stress was analysed in triaxial compression tests and found to be insignificant,indicating that laboratory data obtained without stress curing can represent the material's behaviour in a DSM column,which will cure under the weight of the column.

Amplification effect of near-field ground motion around deep tunnels based on finite fracturing seismic source model

Dynamic failure of rock masses around deep tunnels,such as fault-slip rockburst and seismic-induced collapse,can pose a significant threat to tunnel construction safety.One of the most significant factors that control the accuracy of its risk assessment is the estimation of the ground motion around a tunnel caused by seismicity events.In general,the characteristic parameters of ground motion are estimated in terms of empirical scaling laws.However,these scaling laws make it difficult to accurately estimate the near-field ground motion parameters because the roles of control factors,such as tunnel geometry,damage zone distribution,and seismic source parameters,are not considered.For this,the finite fracturing seismic source model(FFSSM)proposed in this study is used to simulate the near-field ground motion characteristics around deep tunnels.Then,the amplification effects of ground motion caused by the interaction between seismic waves and deep tunnels and corresponding control factors are studied.The control effects of four factors on the near-field ground motion amplification effect are analyzed,including the main seismic source wavelength,tunnel span,tunnel shape,and range of damage zones.An empirical formula for the maximum amplification factor(a_(m))of the near-field ground motion around deep tunnels is proposed,which consists of four control factors,i.e.the wavelength control factor(F_(λ)),tunnel span factor(F_(D)),tunnel shape factor(F_(s))and excavation damage factor(F_(d)).This empirical formula provides an easy approach for accurately estimating the ground motion parameters in seismicityprone regimes and the rock support design of deep tunnels under dynamic loads.

SEISMIC RISK ANALYSIS FOR OCEAN OIL PLATFORMS

The seismic risk analysis method and some special aspects concerning its application to ocean oil platforms are reviewed briefly through an example of analysis for the oil platforms in the Bohai sea. In view of the features of temporal and spatial distribution of earthquakes in China, it is emphasized that the temporal and spatial inhomogeneity of seismicity should be thoroughly studied when dealing with a specific project where a short service life and a high degree of safety are required.

Seismic isolation effect of lined circular tunnels with damping treatments

The Havriliak-Negami model for dynamic viscoelastic material behavior and Biot＇s theory of poroelasticity are employed to develop an exact solution for three-dimensional scattering effect of harmonic plane P-SV waves from a circular cavity lined with a multilayered fluid-filled shell of infinite length containing viscoelastic damping materials and embedded within a fluid-saturated permeable surrounding soil medium. The analytical results are illustrated with numerical examples where the effects of liner/coating structural arrangement, viscoelastic material properties, liner-soil interface bonding condition, seismic excitation frequency, and angle of incidence on the induced dynamic stress concentrations are evaluated and discussed to obtain representative values of the parameters that characterize the system. It is demonstrated that incorporating viscoelastic damping materials with a low shear modulus in the constrained layer configuration is an efficient means of enhancing the overall seismic isolation performance, especially for near-normally incident seismic shear waves where the amplitudes of induced dynamic stresses may be reduced by up to one-third of those without isolation in a relatively wide frequency range. Some additional cases are considered and good agreements with solutions available in the literature are obtained.

Monitoring of velocity changes based on seismic ambient noise: A brief review and perspective

Over the past two decades,the development of the ambient noise cross-correlation technology has spawned the exploration of underground structures.In addition,ambient noise-based monitoring has emerged because of the feasibility of reconstructing the continuous Green’s functions.Investigating the physical properties of a subsurface medium by tracking changes in seismic wave velocity that do not depend on the occurrence of earthquakes or the continuity of artificial sources dramatically increases the possibility of researching the evolution of crustal deformation.In this article,we outline some state-of-the-art techniques for noise-based monitoring,including moving-window cross-spectral analysis,the stretching method,dynamic time wrapping,wavelet cross-spectrum analysis,and a combination of these measurement methods,with either a Bayesian least-squares inversion or the Bayesian Markov chain Monte Carlo method.We briefly state the principles underlying the different methods and their pros and cons.By elaborating on some typical noisebased monitoring applications,we show how this technique can be widely applied in different scenarios and adapted to multiples scales.We list classical applications,such as following earthquake-related co-and postseismic velocity changes,forecasting volcanic eruptions,and tracking external environmental forcing-generated transient changes.By monitoring cases having different targets at different scales,we point out the applicability of this technology for disaster prediction and early warning of small-scale reservoirs,landslides,and so forth.Finally,we conclude with some possible developments of noise-based monitoring at present and summarize some prospective research directions.To improve the temporal and spatial resolution of passive-source noise monitoring,we propose integrating different methods and seismic sources.Further interdisciplinary collaboration is indispensable for comprehensively interpreting the observed changes.

Physics informed machine learning: Seismic wave equation

Similar to many fields of sciences,recent deep learning advances have been applied extensively in geosciences for both small-and large-scale problems.However,the necessity of using large training data and the’black box’nature of learning have limited them in practice and difficult to interpret.Furthermore,including the governing equations and physical facts in such methods is also another challenge,which entails either ignoring the physics or simplifying them using unrealistic data.To address such issues,physics informed machine learning methods have been developed which can integrate the governing physics law into the learning process.In this work,a 1-dimensional(1 D)time-dependent seismic wave equation is considered and solved using two methods,namely Gaussian process(GP)and physics informed neural networks.We show that these meshless methods are trained by smaller amount of data and can predict the solution of the equation with even high accuracy.They are also capable of inverting any parameter involved in the governing equation such as wave velocity in our case.Results show that the GP can predict the solution of the seismic wave equation with a lower level of error,while our developed neural network is more accurate for velocity(P-and S-wave)and density inversion.

The effect of local irregular topography on seismic ground motion

Effects of irregUlar topography on ground motion for incident P, SV and the propagation of Rayleigh waves are studied by combining finite element method with modified transmitting boundary. TheoretiCal models include isolated protrUding topography and similar adjacent Protruding topography. The concluaion drawn from thisstudy is that the effects Of isolated protruding topography are remarkably larger for Rayleigh wave propagation than for P and SV they waves; Considering adjacent irregUlar toography ground motion is amplified, the duration of ground motion becomes longer and the speCtral ratios exhibit narrowband peaks Considering adjacent irregular topography and Rayleigh wave Propagation, the theoretical results wb more approach the results obtained in practice.

Influence of seismic wave type and incident direction on the dynamic response of tall concrete-faced rockfill dams

Owing to the stochastic behavior of earthquakes and complex crustal structure,wave type and incident direction are uncertain when seismic waves arrive at a structure.In addition,because of the different types of the structures and terrains,the traveling wave effects have different influences on the dynamic response of the structures.For the tall concrete-faced rockfill dam(CFRD),it is not only built in the complex terrain such as river valley,but also its height has reached 300 m level,which puts forward higher requirements for the seismic safety of the anti-seepage system mainly comprising concrete face slabs,especially the accurate location of the weak area in seism.Considering the limitations of the traditional uniform vibration analysis method,we implemented an efficient dynamic interaction analysis between a tall CFRD and its foundation using a non-uniform wave input method with a viscous-spring artificial boundary and equivalent nodal loads.This method was then applied to investigate the dynamic stress distribution on the concrete face slabs for different seismic wave types and incident directions.The results indicate that dam-foundation interactions behave differently at different wave incident angles,and that the traveling wave effect becomes more evident in valley topography.Seismic wave type and incident direction dramatically influenced stress in the face slab,and the extreme stress values and distribution law will vary under oblique wave incidence.The influence of the incident direction on slab stress was particularly apparent when SH-waves arrived from the left bank.Specifically,the extreme stress values in the face slab increased with an increasing incident angle.Interestingly,the locations of the extreme stress values changed mainly along the axis of the dam,and did not exhibit large changes in height.The seismic safety of CFRDs is therefore lower at higher incident angles from an anti-seepage perspective.Therefore,it is necessary to consider both the seismic wave type and incident direction during seismic capacity evaluations of tall CFRDs.