Joint inversion of Rayleigh group and phase velocities for S-wave velocity structure of the 2021 M_(S)6.0 Luxian earthquake source area,China

On September 16,2021,a MS6.0 earthquake struck Luxian County,one of the shale gas blocks in the Southeastern Sichuan Basin,China.To understand the seismogenic environment and its mechanism,we inverted a fine three-dimensional S-wave velocity model from ambient noise tomography using data from a newly deployed dense seismic array around the epicenter,by extracting and jointly inverting the Rayleigh phase and group velocities in the period of 1.6–7.2 s.The results showed that the velocity model varied significantly beneath different geological units.The Yujiasi syncline is characterized by low velocity at depths of~3.0–4.0 km,corresponding to the stable sedimentary layer in the Sichuan Basin.The eastern and western branches of the Huayingshan fault belt generally exhibit high velocities in the NE-SW direction,with a few local low-velocity zones.The Luxian MS6.0 earthquake epicenter is located at the boundary between the high-and low-velocity zones,and the earthquake sequences expand eastward from the epicenter at depths of 3.0–5.0 km.Integrated with the velocity variations around the epicenter,distribution of aftershock sequences,and focal mechanism solution,it is speculated that the seismogenic mechanism of the main shock might be interpreted as the reactivation of pre-existing faults by hydraulic fracturing.

FeatureMatching Combining Variable Velocity Model with Reverse Optical Flow

The ORB-SLAM2 based on the constant velocity model is difficult to determine the search window of the reprojection of map points when the objects are in variable velocity motion,which leads to a false matching,with an inaccurate pose estimation or failed tracking.To address the challenge above,a new method of feature point matching is proposed in this paper,which combines the variable velocity model with the reverse optical flow method.First,the constant velocity model is extended to a new variable velocity model,and the expanded variable velocity model is used to provide the initial pixel shifting for the reverse optical flow method.Then the search range of feature points is accurately determined according to the results of the reverse optical flow method,thereby improving the accuracy and reliability of feature matching,with strengthened interframe tracking effects.Finally,we tested on TUM data set based on the RGB-D camera.Experimental results show that this method can reduce the probability of tracking failure and improve localization accuracy on SLAM(Simultaneous Localization and Mapping)systems.Compared with the traditional ORB-SLAM2,the test error of this method on each sequence in the TUM data set is significantly reduced,and the root mean square error is only 63.8%of the original system under the optimal condition.

A model for predicting bubble rise velocity in a pulsed gas solid fluidized bed

Bed stability, and especially the bed density distribution, is affected by the behavior of bubbles in a gas solid fluidized bed. Bubble rise velocity in a pulsed gas-solid fluidized bed was studied using photographic and computational fluid dynamics methods. The variation in bubble rise velocity was investigated as a function of the periodic pulsed air flow. A predictive model of bubble rise velocity was derived: ub=ψ(Ut+Up-Umf)+kp(gdb)(1/2). The software of Origin was used to fit the empirical coefficients to give ψ = 0.4807 and kp = 0.1305. Experimental verification of the simulations shows that the regular change in bubble rise velocity is accurately described by the model. The correlation coefficient was 0.9905 for the simulations and 0.9706 for the experiments.

CO_(2) emission control in new CM car-following model with feedback control of the optimal estimation of velocity difference under V2X environment

A new coupled map car-following model in this paper is proposed by considering the influence of the difference of the estimated optimal speed based on the coupled map(CM)car-following model under V2X environment.The stability of the new model is analyzed by applying the control theory,and the conditions are obtained for the stability of the traffic system.And the two scenes of vehicle stopping once and four times have been simulated.The simulation results show that the control term considered with optimal estimation of speed difference can effectively improve the stability of vehicle running and reduce CO_(2) emissions in the CM car-following model.

A multi-scale 3-D crust velocity model in the Hefei-Chao Lake area around the southern segment of Tanlu Fault Zone

Regional high-precision velocity models of the crust are an important foundation for examining seismic activity,seismogenic environments,and disaster distribution characteristics.The Hefei-Chao Lake area contains the main geological units of Hefei Basin,with thick sediments and the Chao Lake depression.Several major concealed faults of the southern NNE-trending Tanlu Fault Zone cross this area.To further explore the underground distribution characteristics of the faults and their tectonic evolutionary relationship with adjacent tectonic units,this study used ambient noise data recorded by a seismic array deployed in Hefei City and Chao Lake,constructing a 3-D velocity model at the depth of 1–8 km.Then a multi-scale high-resolution 3-D velocity model of this area was constructed by this new upper crustal velocity model with the previous middle and lower crustal model.The new model reveals that a high-velocity belt is highly consistent with the strike of the Tanlu Fault Zone,and a low-velocity sedimentary characteristic is consistent with the Hefei Basin and Chao Lake depression.The distribution morphology of high and low velocity bodies shows that the sedimentary pattern of Hefei-Chao Lake area is closely related to the tectonic evolution of the Tanlu Fault Zone since the Mesozoic.This study also identifies multiple low-velocity anomalies in the southeastern Hefei City.We speculate that strong ground motion during the 2009 Feidong earthquake(magnitude of 3.5)was related to amplification by the thick sediments in the Hefei Basin.We also discuss further applications of multi-scale high-resolution models of the shallow layer to strong ground motion simulations in cities and for earthquake disaster assessments.

Unusual Behaviour of Dislocation Velocity Exponent in Dislocation Multiplication Model

The chaotic behavior of dislocation multiplication process is investigated. The change of Lya-punov exponent which is used to determine the stability of quasi-periodic and chaotic behavior as well as that of equilibrium points and periodic solution is reported using an iteration model of dislocation multiplication. An unusual behavior of Lyapunov exponent and Feigenbaum ex-ponent which respond to the geometric convergence of orbit from bifurcation to chaos is shown by dislocation velocity exponent m and there is a distinction on the tendency of convergence for the dislocation multipIication model when it is compared with togistic map. lt is reasonable for the difference to be analyzed from the materials viewpoint.

A comparative study of seismic tomography models of Southwest China

The margin of the Tibetan Plateau of Southwest China is one of the most seismically active regions of China and is the location of the China Seismic Experimental Site(CSES).Many studies have developed seismic velocity models of Southwest China,but few have compared and evaluated these models which is important for further model improvement.Thus,we compared six published seismic shear-wave velocity models of Southwest China on absolute velocity and velocity perturbation patterns.The models are derived from different types of data(e.g.,surface waves from ambient noise and earthquakes,body-wave travel times,receiver functions) and inversion methods.We interpolated the models into a uniform horizontal grid(0.5° × 0.5°) and vertically sampled them at 5,10,20,30,40,and 60 km depths.We found significant differences between the six models.Then,we selected three of them that showed greater consistency for further comparison.Our further comparisons revealed systematic biases between models in absolute velocity that may be related to different data types.The perturbation pattern of the model is especially divergent in the shallow part,but more consistent in the deep part.We conducted synthetic and inversion tests to explore possible causes and our results imply that systematic differences between the data,differences in methods,and other factors may directly affect the model.Therefore,the Southwest China velocity model still has considerable room for improvement,and the impact of inconsistency between different data types on the model needs further research.Finally,we proposed a new reference shear-wave velocity model of Southwest China(SwCM-S1.0) based on the three selected models with high consistency.We believe that this model is a better representation of more robust features of the models that are based on different data sets.

A seismic model for crustal structure in North China Craton

We present a digital crustal model in North China Craton(NCC). The construction of crustal model is based on digitization of original seismic sounding profiles, and new results of three-dimensional structure images of receiver functions. The crustal model includes seismic velocity and thickness of crustal layers. The depths to Moho indicate a thinning crust ~30 km in the east areas and a general westward deepening to more than 40 km in the west. The P wave velocity varies from 2.0 to 5.6 km/s in the sedimentary cover,from 5.8 to 6.4 km/s in the upper crust, and from 6.5 to 7.0 km/s in the lower crust. By analyzing regional trends in crustal structure and links to tectonic evolution illustrated by typical profiles, we conclude that:(1) The delimited area by the shallowing Moho in the eastern NCC represents the spatial range of the craton destruction. The present structure of the eastern NCC crust retains the tectonic information about craton destruction by extension and magmatism;(2) The tectonic activities of the craton destruction have modified the crustal structure of the convergence boundaries at the northern and southern margin of the NCC;(3) The Ordos terrene may represent a relatively stable tectonic feature in the NCC, but with the tectonic remnant of the continental collision during the assembly of the NCC in the north-east area and the response to the lateral expansion of the Tibetan Plateau during the Cenozoic in the south-west.

Effect of Methane Gas on Acoustic Characteristics of Hydrate-Bearing Sediment–Model Analysis and Experimental Verification

Gas leakage is an important consideration in natural systems that experience gas hydrate accumulation.A number of velocity models have been created to study hydrate-bearing sediments,including the BGTL theory,the weighted equation,the Wood equation,the K-T equation,and the effective medium theory.In previous work,we regarded water as the pore fluid,which meant its density and bulk modulus values were those of water.This approach ignores the presence of gas,which results in a biased calculation of the pore fluid's bulk modulus and density.To take into account the effect of gas on the elastic wave velocity,it is necessary to recalculate the bulk modulus and density of an equivalent medium.Thus,a high-pressure reactor device for simulating leakage systems was developed to establish the relationship between wave velocity and hydrate saturation in methane-flux mode.A comparison of the values calculated by the velocity model with the experimental data obtained in this study indicates that the effective medium theory(EMT,which considers gas effects)is more applicable than other models.For hydrate saturations of 10%–30%,the result ranges between EMT-B(homogenous gas distribution)and EMT-B(patchy gas distribution).For hydrate saturations of 30%–60%,the results are similar to those of the EMT-B(homogenous gas distribution)mode,whereas hydrate saturations of 60%–70%yield results similar to those of the EMT-A mode.For hydrate saturations greater than 80%,the experimental results are similar to those of the EMT-B mode.These results have significance for hydrate exploitation in the South China Sea.

A comparative study of seismic tomography models of the Chinese continental lithosphere

The Chinese mainland is subject to complicated plate interactions that give rise to its complex structure and tectonics. While several seismic velocity models have been developed for the Chinese mainland, apparent discrepancies exist and, so far, little effort has been made to evaluate their reliability and consistency. Such evaluations are important not only for the application and interpretation of model results but also for future model improvement. To address this problem, here we compare five published shear-wave velocity models with a focus on model consistency. The five models were derived from different datasets and methods (i.e., body waves, surface waves from earthquakes, surface waves from noise interferometry, and full waves) and interpolated into uniform horizontal grids (0.5° × 0.5°) with vertical sampling points at 5 km, 10 km, and then 20 km intervals to a depth of 160 km below the surface, from which we constructed an averaged model (AM) as a common reference for comparative study. We compare both the absolute velocity values and perturbation patterns of these models. Our comparisons show that the models have large (> 4%) differences in absolute values, and these differences are independent of data coverage and model resolution. The perturbation patterns of the models also show large differences, although some of the models show a high degree of consistency within certain depth ranges. The observed inconsistencies may reflect limited model resolution but, more importantly, systematic differences in the datasets and methods employed. Thus, despite several seismic models being published for this region, there is significant room for improvement. In particular, the inconsistencies in both data and methodologies need to be resolved in future research. Finally, we constructed a merged model (ChinaM-S1.0) that incorporates the more robust features of the five published models. As the existing models are constrained by different datasets and methods, the merged model serves as a new type of reference model that incorporates the common features from the joint datasets and methods for the shear-wave velocity structure of the Chinese mainland lithosphere.

Crust and upper mantle structure of East Asia from ambient noise and earthquake surface wave tomography

The complex tectonic background of East Asia makes it an ideal region for investigating the evolution of the continental lithosphere,for which high-resolution lithospheric structural models are essential.In this study,we measured Rayleigh-wave phase-velocity dispersion curves at periods of 10-120 s and group velocity dispersion curves at periods of 10-140 s using event records from more than 1,000 seismic stations in and around China.By jointly inverting new and previously published dispersion data from ambient noise and earthquakes,we developed a high-resolution shear-wave velocity model down to a depth of~300 km beneath East Asia.Our model revealed heterogeneous lithospheric structures beneath East Asia,and allowed us to investigate the velocity structure of the entire lithosphere.We also derived crustal and lithospheric thickness models from the three-dimensional(3D)shear-wave model,revealing strong spatial heterogeneity and a general thinning trend of lithospheric thickness from west to east across the study region.Overall,our models reveal important lithospheric features beneath East Asia and provide a valuable baseline dataset for understanding continental-scale dynamics and evolution.

The high-resolution community velocity model V2.0 of southwest China,constructed by joint body and surface wave tomography of data recorded at temporary dense arrays

The Sichuan-Yunnan area is located at the southeastern margin of the Tibetan Plateau,where tectonic movement is strong with deep and large faults distributed in a staggered manner,which results in strong seismic activities and severe earthquake hazards.Since the 21st century,several earthquakes of magnitude 7.0 or above occurred in this region,which have caused huge casualties and economic losses,especially the 2008 M_(s)8.0 Wenchuan earthquake.At present,earthquake monitoring and source parameter inversion,strong earthquake hazard analysis and disaster assessment are still the focus of seismological researches in the Sichuan-Yunnan region.Regional high-precision 3D community velocity models are fundamental for these studies.In this paper,by assembling seismic observations at permanent seismic stations and several temporary dense seismic arrays in this region,we obtained about 7.06 million body wave travel time data(including absolute and differential travel times)using a newly developed artificial intelligence body wave arrival time picking method and about 100,000 Rayleigh wave phase velocity dispersion data in the period range of 5-50 s from ambient noise cross-correlation technique.Based on this abundant dataset,we obtained the three-dimensional high resolution V_p and V_(s)model in the crust and uppermost mantle of southwest(SW)China by adopting the joint body and surface wave travel time tomography method considering the topography effect starting from the first version of community velocity model in SW China(SWChina CVM-1.0).Compared to SWChina CVM-1.0,this newly determined velocity model has higher resolution and better data fitness.It is accepted by the China Seismic Experimental Site as the second version of the community velocity model in SW China(SWChina CVM-2.0).The new model shows strong lateral heterogeneities in the shallow crust.Two disconnected low velocity zones are observed in the middle to lower crust,which is located in the Songpan-Ganzi block and the northern Chuandian block to the west of the Longmenshan-Lijiang-Xiaojinhe fault,and beneath the Xiaojiang fault zone,respectively.The inner zone of the Emeishan large igneous province(ELIP)exhibits a high velocity anomaly,which separates the two aforementioned low velocity anomalies.Low velocity anomaly is also shown beneath the Tengchong volcano.The velocity structures in the vicinity of the 2008 M_(s)8.0 Wenchuan earthquake,the 2013 M_(s)7.0Lushan earthquake and the 2017 M_(s)7.0 Jiuzhaigou earthquake mainly show high V_(p)and V_(s)anomalies and the mainshocks are basically located at the transition zone between the high and low velocity anomalies.Along with the segmentation characteristics of seismic activity,we suggest that areas with significant changes in velocity structures,especially in active fault zones,might have a greater potential to generate moderate to strong earthquakes.

A new car-following model with driver's anticipation effect of traffic interruption probability

Traffic interruption phenomena frequently occur with the number of vehicles increasing.To investigate the effect of the traffic interruption probability on traffic flow,a new optimal velocity model is constructed by considering the driver anticipation term in the interruption case for car-following theory.Furthermore,the effect of driver anticipation in the interruption case is investigated via linear stability analysis.Also,the MKdV equation is obtained concerning the effect of driver anticipation in the interruption case.Moreover,numerical simulation states that the driver anticipation term in the interruption case contributes to the stability of traffic flow.

Focal mechanism inversion of the 2018 M_(W)7.1 Anchorage earthquake based on high-rate GPS observation

The M_(W)7.1 Anchorage earthquake is the most destructive earthquake since the 1964 M_(W)9.2 great Alaska earthquake in the United States.In this study,high-rate GPS data and near-field broadband seismograms are used in separate and joint inversions by the generalized Cut-and-Paste(gCAP)method to estimate the focal mechanism.In order to investigate the influence of crustal velocity structure on the focal mechanism inversion results,two velocity models(Crustl.0 and Alaska Earthquake Center(AEC))are used for detailed comparison and analysis.The results show that:(1)The two nodal planes of the optimal double-couple solution are nearly north-south striking,with dip angles of about 30°and 60°respectively,and the centroid focal depth is 54-55 km,which is an intraplate normal fault event.(2)The inversion results for the two types of data and the two velocity models are consistent with some previous studies,which indicates that the results are stable and reliable.The more accurate velocity structure model is helpful for focal mechanism inversion of the complex earthquake.(3)The inclusion of high-rate GPS data in joint inversion provides a more effective constraint on centroid depth.

Obstacle avoidance technology of bionic quadruped robot based on multi-sensor information fusion

In order to improve the ability of a bionic quadruped robot to percept the location of obstacles in a complex and dynamic environment,the information fusion between an ultrasonic sensor and a binocular sensor was studied under the condition that the robot moves in the Walk gait on a structured road.Firstly,the distance information of obstacles from these two sensors was separately processed by the Kalman filter algorithm,which largely reduced the noise interference.After that,we obtained two groups of estimated distance values from the robot to the obstacle and a variance of the estimation value.Additionally,a fusion of the estimation values and the variances was achieved based on the STF fusion algorithm.Finally,a simulation was performed to show that the curve of a real value was tracked well by that of the estimation value,which attributes to the effectiveness of the Kalman filter algorithm.In contrast to statistics before fusion,the fusion variance of the estimation value was sharply decreased.The precision of the position information is 4.6cm,which meets the application requirements of the robot.

A drilling technology guided by well-seismic information integration

The predictions by drilling-related mechanical and geological models are in some degree inaccurate due to non-unique solution of seismic velocity model.To address this problem,a new drilling technology guided by well-seismic information integration is proposed which consists of seismic velocity update of drilled formations,seismic velocity prediction of the formation ahead of drilling bit,and the prediction of geological feature and drilling geological environmental factors ahead of bit.In this technology,real information(velocity,formation and depth)behind the drilling bit and local pre-stack seismic data around the wellbore being drilled are used to correct the primitive seismic velocity field for a re-migration of seismic data and to update geological features and drilling geological environmental factors ahead of the drilling bit.Field application shows that this technology can describe and predict the geological features,drilling geological environmental factors and complex drilling problems ahead of the bit timely and improve the prediction efficiency and accuracy greatly.These new updated results are able to provide scientific basis for optimizing drilling decisions.

Ambient Noise Tomography, Green’s Function and Earthquakes

Green’s function is well-known, among others, in the application of ambient noise tomography methodologies that may demonstrate the potential of hydrocarbon entrapment in the study area. Here it is also shown to be of key importance in identifying the fractal dimension in the unified scaling law for earthquakes as well as in studying an explicit relationship of a future strong earthquake epicenter to the average earthquake potential score. Such studies are now in progress.

Comparison Analysis of Longitudinal Electrical Conductivity Distribution and Seismic Tomography Velocity Models for the Central Tien Shan Region

The paper is dedicated to consider the approach of longitudinal electrical conductivity maps construction for Central Tien Shan region and to complete the comparison analysis of these maps with related seismic tomography data.The results of joint analysis of longitudinal electrical conductivity distribution and seismic tomography velocity models with respect to geological and geophysical senses allow to confirm the already known and to establish the new patterns of structure and geodynamics of the Tien Shan segment of Central Asia such as the manifestation of characteristic structural ensembles,reflection of the longitudinal and transverse segmentation of the Tien Shan,the existence within the framework of a“single”orogen of segments with different near-surface and deep structure and morphological expression.As well,the correlation between the velocity characteristics and geoelectric properties was found.This correlation allows to identify signs of reflection of fault structures in geophysical fields and to clarify the territorial and structural position of both visible and hidden faults.Additionally,in the paper,the geological interpretation of geophysical anomalies is considered.

The Effect of Strong Near Surface Scattering on Seismic Imaging: Investigation Based on Resolution Analysis

In land seismic exploration,strong near-surface heterogeneities can cause serious problems in seismic data acquisition and the quality of depth imaging.By introducing random velocity models to simulate velocity fluctuations in the near-surface layer and using the point spread function to characterize image quality,we examine how the scattering generated in near-surface heterogeneities can affect the subsurface image.In addition to the commonly known scattering noises which lower the signal to noise ratio in seismic data,our results also reveal that intermediate scale hetero-geneities generate forward scattering which forms phase or travel time fluctuations.Due to intermediate-scale uncertainty in the shallow part of the migration velocity model,these phase changes are carried to the target by the extrapolated wavefields,breaking the zero phase image condition at the image point.This is a primary reason for deteriorated image quality in regions with strong near-surface scattering.If this intermediate-scale information can be obtained and built into the migration velocity,the subsurface image quality can be largely improved.These results can be the ba-sis for further numerical investigations and field experiments.The proposed analysis method can also be used to evaluate other potential methods for dealing with near-surface scattering.