Seismic Velocity Structure and Composition of the Continental Crust of Eastern China

On the basis of a one-by-one latitude-longitude grid three-dimensional seismic velocity model, the crustal P-wave velocity structure in eastern China (105-125°E and 18-41°N) is obtained, and a set of geotherms for each grid is established for P-T correction on P-wave velocities. The average depths of sub-crustal layers and their average P-wave velocities of 18 tectonic units in eastern China are exhibited. Our result presents a 32-34 km thick crust beneath eastern China, which is thinner than previous studies, with an average velocity of 6.54 km/s, corresponding to a 5 kg/m3 variation in crustal mean density. The thicker upper but thinner middle and lower crust results in a lower average seismic velocity of eastern China. An intermediate crustal composition with a SiO2 content of 59.7 wt% has been estimated. However, there exists a significant lateral variation in the crustal structures among the tectonic units of eastern China. The structure and composition features of some regions in eastern China indicate that extension has played an important role in the continental crust evolution of eastern China.

The Crustal Structure and Seismic Activity in North China

A layered crustal block model of North China has been constructed based on large amount of data from seismic sounding carried out in recent two decades. Some deep fault zones, such as the Zhangjiakou.Penglai and Tancheng-Lujiang fault zones, divide the upper crust of North China into three upper crustal terranes and nine bolcks. There are distinct differences in velocity and depth distributions, which reflects Cenozoic block faulting in North China in the process of formation of the deep structure. The upper crust shows the features of transition in isostatic adjustment. The existence of a low-velocity layer in the middle crust is characteristic of the crustal structure in North China. There seems to be an increase of rheology of the rocks in the lower crust and a persistence of stable regional stress field. The patterns of the Moho on two sides of the Yanshan-Taihang Mountains are different. The relief of the Moho around Beijing, Shijiazhuang and Guangrao where the deep faults join together shows a quadrantal distribution in some degree. The dynamic sources for seismic activity are the NE-SW horizontal compression and the diapirism of the upper mantle. The middle and upper crust, especially the layered block structure has the most significant effects on seismicity, and the occurrence of earthquakes is more closely related to them than to the Moho.

Complex Seismic Focus Structure and Earthquake-Triggered Landslide Distribution:Analysis of the 2014 Ludian M_w6.1 Earthquake in Yunnan

Objective The 2014 Ludian Mw6.1 earthquake in Yunnan occurred in a mountainous area with complex tectonics and topography, which caused serious damage as well as co-seismic landslides of an unusual large scale. Because the suspected seismogenic faults on the surface, distribution of aftershocks and focal mechanism solutions are not consistent, it remains difficult to determine what is the real causal fault or seismogenic structure for this event. Actually, it may imply the complicity of the seismic source at depth. In addition, the distribution of the co- seismic landslides also exhibits some diffusion that is different from general eases, likely associated with the seismic focus structure.

Seismic protection of frame structures via semi-active control:modeling and implementation issues

Theoretical and practical issues concerning the multi-faceted task of mitigating the latero-torsional seismic response of a prototypal frame structure with asymmetric mass distribution are approached, Chevron braces with embedded magnetorheological dampers acting on the interstory drift are used to ensure additional energy dissipation. The semi-active control strategy employed to govern the modification of the damper characteristics via feedback is based on the selection of optimal forces according to a H2/LQG criterion, with respect to which the actual forces are regulated by a clipped-optimal logic. A dynamic observer is used to estimate the state through a non-collocated placement of the acceleration sensors. Several aspects to be addressed throughout the complex process including the design, modelization, and implementation phases of semi-active protection systems are discussed. Finally, experimental results obtained to mitigate the motion induced by ground excitation in a large-scale laboratory prototype, simulating the seismic response of a two-story building, are summarized.

SEISMIC RANDOM VIBRATION ANALYSIS OF STOCHASTIC STRUCTURES USING RANDOM FACTOR METHOD

Seismic random vibration analysis of stochastic truss structures is presented. A new method called random factor method is used for dynamic analysis of structures with uncertain parameters, due to variability in their material properties and geometry. Using the random factor method, the natural frequencies and modeshapes of a stochastic structure can be respectively described by the product of two parts, corresponding to the random factors of the structural parameters with uncertainty, and deterministic values of the natural frequencies and modeshapes obtained by conventional finite element analysis. The stochastic truss structure is subjected to stationary or non-stationary random earthquake excitation. Computational expressions for the mean and standard deviation of the mean square displacement and mean square stress are developed by means of the random variable＇s functional moment method and the algebra synthesis method. An antenna and a truss bridge are used as practical engineering examples to illustrate the application of the random factor method in the seismic response analysis of random structures under stationary or non-stationary random earthquake excitation.

Crustal velocity structure of central Gansu Province from regional seismic waveform inversion using firework algorithm

The firework algorithm（FWA） is a novel swarm intelligence-based method recently proposed for the optimization of multi-parameter, nonlinear functions. Numerical waveform inversion experiments using a synthetic model show that the FWA performs well in both solution quality and efficiency. We apply the FWA in this study to crustal velocity structure inversion using regional seismic waveform data of central Gansu on the northeastern margin of the Qinghai-Tibet plateau. Seismograms recorded from the moment magnitude（MW） 5.4 Minxian earthquake enable obtaining an average crustal velocity model for this region. We initially carried out a series of FWA robustness tests in regional waveform inversion at the same earthquake and station positions across the study region,inverting two velocity structure models, with and without a low-velocity crustal layer; the accuracy of our average inversion results and their standard deviations reveal the advantages of the FWA for the inversion of regional seismic waveforms. We applied the FWA across our study area using three component waveform data recorded by nine broadband permanent seismic stations with epicentral distances ranging between 146 and 437 km. These inversion results show that the average thickness of the crust in this region is 46.75 km, while thicknesses of the sedimentary layer, and the upper, middle, and lower crust are 3.15,15.69, 13.08, and 14.83 km, respectively. Results also show that the P-wave velocities of these layers and the upper mantle are 4.47, 6.07, 6.12, 6.87, and 8.18 km/s,respectively.

Crust-mantle structure feature and the seismic activity of the main tectonic units in the North Tanlu fault zone

Using recent data of geoscience transaction in Northeast China, the author analyses and studies the crust-upper mantle structure feature of the North Tanlu fault zone. The result shows the crust-mantle structure are obvious difference at both sides of the North Tanlu fault zone. The fault activity and segmentation are closely related with abruptly change zone of the crust-upper mantle structure. There is a clear mirror image relationship between the big geomorphic shape and asthenosphere undulate, the former restricts tectonic stability and tectonic style of dif- ferent crustal units. The significantly strengthening seismicity of north set and south set in the North Tanlu fault zone just correspond to the low-velocity and high conductivity layer of crust-upper mantle. In the North Tanlu fault zone, the main controlling structure of the mid-strong seismic generally consists of the active fault sectors, whose crust-mantle structure is more complicated in rigidity massif.

A novel simple procedure to consider seismic soil structure interaction effects in 2D models

A method is proposed to estimate the seismic soil-structure-interaction （SSI） effects for use in engineering practice. It is applicable to 2D structures subjected to vertically incident shear waves supported by homogenous half-spaces. The method is attractive since it keeps the simplicity of the spectral approach, overcomes some of the difficulties and inaccuracies of existing classical techniques and yet it considers a physically consistent excitation. This level of simplicity is achieved through a response spectra modification factor that can be applied to the free-field 5%-damped response spectra to yield design spectral ordinates that take into account the scattered motions introduced by the interaction effects. The modification factor is representative of the Transfer Function （TF） between the structural relative displacements and the free- field motion, which is described in terms of its maximum amplitude and associated frequency. Expressions to compute the modification factor by practicing engineers are proposed based upon a parametric study using 576 cases representative of actual structures. The method is tested in 10 cases spanning a wide range of common fundamental vibration periods.

基于物理信息引导深度学习的建筑响应实时预测方法

High-precision and efficient structural response prediction is essential for intelligent disaster prevention and mitigation in building structures,including post-earthquake damage assessment,structural health monitoring,and seismic resilience assessment of buildings.To improve the accuracy and efficiency of structural response prediction,this study proposes a novel physics-informed deep-learning-based realtime structural response prediction method that can predict a large number of nodes in a structure through a data-driven training method and an autoregressive training strategy.The proposed method includes a Phy-Seisformer model that incorporates the physical information of the structure into the model,thereby enabling higher-precision predictions.Experiments were conducted on a four-story masonry structure,an eleven-story reinforced concrete irregular structure,and a twenty-one-story reinforced concrete frame structure to verify the accuracy and efficiency of the proposed method.In addition,the effectiveness of the structure in the Phy-Seisformer model was verified using an ablation study.Furthermore,by conducting a comparative experiment,the impact of the range of seismic wave amplitudes on the prediction accuracy was studied.The experimental results show that the method proposed in this paper can achieve very high accuracy and at least 5000 times faster calculation speed than finite element calculations for different types of building structures.

S-wave velocity structure beneath Changbaishan volcano inferred from receiver function

The S wave velocity structure in Changbaishan volcanic region was obtained from teleseismic receiver function modeling. The results show that there exist distinct low velocity layers in crust in volcano area. Beneath WQD station near to the Tianchi caldera the low velocity layer at 8 km depth is 20 km thick with the lowest S-wave velocity about 2.2 km/s At EDO station located 50 km north of Tianchi caldera, no obvious crustal low velocity layer is detected. In the volcanic region, the thickness of crustal low velocity layer is greater and the lowest velocity is more obvious with the distance shorter to the caldera. It indicates the existence of the high temperature material or magma reservoir in crust near the Tianchi caldera. The receiver functions and inversion result from different back azimuths at CBS permanent seismic station show that the thickness of near surface low velocity layer and Moho depth change with directions. The near surface low velocity layer is obviously thicker in south direction. The Moho depth shows slight uplifting in the direction of the caldera located. We con- sider that the special near surface velocity structure is the main cause of relatively lower prominent frequency of volcanic earthquake waveforms recorded by CBS station. The slight uplifting of Moho beneath Tianchi caldera indicates there is a material exchanging channel between upper mantle and magma reservoir in crust.

Seismic structural control using semi-active tuned mass dampers

This paper focuses on how to determine the instantaneous damping of the semi-active tuned mass damper (SATMD) with continuously variable damping.An off-and-towards-equilibrium (OTE) algorithm is employed to examine the control performance of the structure/SATMD system by considering the damping as an assumptive control action.The damping modification of the SATMD is carried out according to the proposed OTE algorithm,which is formulated based on analysis of the structural movement under external excitations,and the measured responses of the structure at every time instant. As examples two numerical simulations of a five-storey and a ten-storey shear structures with a SATMD on the roof are conducted.The effectiveness on vibration reduction of MDOF systems subjected to seismic excitations is discussed.Analysis results show that the behavior of the structure with a SATMD is significantly improved and the feasibility of applying the OTE algorithm to the structural control design of SATMD is also verified.

F-structure model of overlying strata for dynamic disaster prevention in coal mine

The rupture and movement scope of overlying strata upon the longwall mining face increased sharply as the exploitation scale and degree growing recently,and the spatial structure formed by fractured strata became much more complex.The overlying strata above the working face and adjacent gobs would affect each other and move cooperatively because small pillar can hardly separate the connection of overlying strata between two workfaces,which leads to mining seismicity in the gob and induces rockburst disaster that named spatial structure instability rockburst in this paper.Based on the key stratum theory,the F-structure model was established to describe the overlying strata characteristic and rockburst mechanism of workface with one side of gob and the other side un-mined solid coal seam.The results show that F-structure in the gob will re-active and loss stability under the influence of neighboring mining,and fracture and shear slipping in the process of instability is the mechanism of the seismicity in the gob.The F-structure was divided into two categories that short-arm F and long-arm F structure based on the state of strata above the gob.We studied the underground pressure rules of different F-structure and instability mechanism,thus provide the guide for prevention and control of the F-structure spatial instability rockburst.The micro-seismic system is used for on-site monitoring and researching the distribution rules of seismic events,the results confrmed the existence and correct of F-spatial structure.At last specialized methods for prevention seismicity and rockburst induced by F-structure instability are proposed and applied in Huating Coal Mine.

Compositional change of seismic event sequences in focal zones during preparation of strong earthquakes

The change of the structure of seismic event sequences in focal area in preparation period of strong earthquakes has been studied. Findings show that weak earthquake clustering in time increases in earlier stage of forming of focal area. However,spatial clustering of seismic events rises at the latest stage.

Lithospheric structure in NW of Africa:Case of the Moroccan Atlas Mountains

This study presents the outcomes of the local earthquake tomography applied in the Moroccan Atlas domains. A seismic data collected by 36 seismic and a linearized inversion technics are used for determination of local velocity structure.The interpretation of tomography images results emphasizes a new and detailed lithosphere structure： a remaining subducted zone beneath the Souss Basin located from 20-to 45-km depth dipping to the North is detected and interpreted as a body that marks the border between the Moroccan Anti-Atlas and the Meseta-Atlas domains.A subduction zones is detected in the SW of the High Atlas, beneath the Hercynian Tichka massif from 10 to 50-km inclined away from Anti Atlas and in the eastern part of Anti Atlas, dipping northward from Jbel Ougnat at 15e40 km.The junction of the western and middle High Atlas is depicted by two high velocity blocks subducting from 10 to 50 km depth. The first is dipping SW beneath the High Atlas and the second is dipping SE beneath the Ouarzazate Basin.In the northern part of the southwestern High Atlas, a high velocity body dipping towards the north beneath the Essaouira Basin from 15 to 45 km depth.In northeastern part of the High Atlas in the Mougeur zone, a high velocity body is detected from 10 to 45 km depth, dipping to the Se E beneath the eastern High Atlas.The negative lithospheric anomalies found in the upper and in the lower crust are interpreted as a hot asthenospheric material upwelling from deep and gradually replacing the part of crust detached in the High Atlas. The occurrence magmatic activities in these regions testify the existence of a remaining subduction process. This paper argues the implication of these deep structures in the evolution of the Moroccan Atlas Mountain.

Within plate seismicity analysis in the segment between the high Cordillera and the Precordillera of northern Mendoza(Southern Central Andes)

Crustal seismicity in northwestern Mendoza Province in Argentina, corresponding to the transition zone between the Chilean-Pampean flat subduction zone（26.5-33.5°S） and the Southern Central Andes normal subduction zone to the south, is studied in order to i） identify its relationship with the mapped structure, ii）determine deformational mechanisms and iii） constrain the geometry of the fold and thrust belt in the lower crust. Through this, we aim to determine which are the structures that contribute to Andean construction, east of the Frontal Cordillera in Argentina and at the western Principal Cordillera in Chile. Data from a temporary local seismic network are reprocessed in order to achieve a precise location of hypocenters and, whenever possible, to build focal mechanisms. Results are interpreted and compared with previous seismic studies and structural models. Analyzed seismicity is grouped around the eastern front of Frontal Cordillera, with hypocenters mainly at depths of 25-40 km. Contrastingly, earthquakes in the Principal Cordillera to the west are located at the axial Andean sector and Chilean slope, with depths shallower than 15 km. Obtained focal mechanisms indicate mainly strike-slip displacements, left lateral at Frontal Cordillera and right lateral at Principal Cordillera. Based on these observations, new possible structural models are proposed, where seismogenic sources could be either associated with inherited basement structures from the Cuyania-Chilenia suture; or correspond to deep-blind thrusts linked with a deeper-than-previously-assumed decollement that could be shared between Frontal Cordillera and western Precordillera. This deeper decollement would coincide in turn with the one determined from receiver function analysis for the eastern Sierras Pampeanas in previous works, potentially implying a common decollement all through the fold and thrust belt configuration. Apart from this, a new interpretation of seismogenic structures in Principal Cordillera near the Argentina-Chile boundary is provided.

Constraints on the crustal structure beneath the Sinai subplate,SE Mediterranean,from analysis of local and regional travel times

The Sinai Peninsula has been recognized as a subplate of the African Plate located at the triple junction of the Gulf of Suez rift,the Dead Sea Transform fault,and the Red Sea rift.The upper and lower crustal structures of this tectonically active,rapidly developing region are yet poorly understood because of many limitations.For this reason,a set of P- and S-wave travel times recorded at 14 seismic stations belonging to the Egyptian National Seismographic Network（ENSN） from 111 local and regional events are analyzed to investigate the crustal structures and the locations of the seismogenic zones beneath central and southern Sinai.Because the velocity model used for routine earthquake location by ENSN is one-dimensional,the travel-time residuals will show lateral heterogeneity of the velocity structures and unmodeled vertical structures.Seismic activity is strong along the eastern and southern borders of the study area but low to moderate along the northern boundary and the Gulf of Suez to the west.The crustal V_P/V_S ratio is 1.74 from shallow（depth≤10 km） earthquakes and 1.76 from deeper（depth 〉 10 km） crustal events.The majority of the regional and local travel-time residuals are positive relative to the Preliminary Reference Earth Model（PREM）,implying that the seismic stations are located above widely distributed,tectonically-induced low-velocity zones.These low-velocity zones are mostly related to the local crustal faults affecting the sedimentary section and the basement complex as well as the rifting processes prevailing in the northern Red Sea region and the ascending of hot mantle materials along crustal fractures.The delineation of these low-velocity zones and the locations of big crustal earthquakes enable the identification of areas prone to intense seismotectonic activities,which should be excluded from major future development projects and large constructions in central and southern Sinai.

The China Seismological Reference Model project

The importance of developing high-resolution seismic models to improve understanding of tectonic processes and enhance seismic hazard mitigation programs,along with the rapid expansion of seismic coverage in China,called for a seismological reference model to be established in China.The China Seismological Reference Model(CSRM)project was initiated by the National Natural Science Foundation of China with two primary goals:(1)the CSRM would serve as a primary source for the current state of seismological research in China,and(2)the seismic data and constraints used to construct the CSRM would be used as a backbone open-access cyberinfrastructure for future research in seismology.The CSRM project was also intended to promote data exchange and scientific collaboration in seismology in China.Accordingly,two parallel efforts of the project are being pursued:(1)construction of the CSRM,and(2)development of a CSRM product center.The CSRM is jointly constrained by various types of seismic constraints extracted from the seismic data recorded at 4511 seismic stations in continental China following a top-down approach,with the seismic structures in the shallower part of the Earth constrained first.Construction of the CSRM involves three preparation steps:(1)building datasets of various seismic constraints from the seismic data,(2)developing a method to incorporate the constraints of surface wave observations from regional earthquakes into the inversion of the seismic structure,and(3)constructing high-resolution pre-CSRM seismic models of the velocity structure in the shallow crust and the Pn-velocity structure in the uppermost mantle.In the final process,the CSRM will be constructed by jointly inverting all the seismic constraints using the pre-CSRM models as starting models or a priori structures.The CSRM product center(http://chinageorefmodel.org)archives and distributes three types of products:CSRM models,the Level 1 original seismic data used to extract seismic constraints in the construction of the CSRM,and Level 2 data on the seismic constraints derived from the Level 1 data and the inferred earthquake parameters in the construction of the CSRM.The CSRM product center has archived 141 TB of Level 1 data from 1120 permanent broadband stations in the China Seismic Network Center and 3391 temporary stations from various institutions and data centers around the world,as well as 140 GB of Level 2 data on various seismic constraints and inferred event parameters from the construction of the CSRM.The CSRM is expected to provide significant insights into the composition and tectonic dynamics in continental China and to enhance the capability of various seismic hazard mitigation programs in China from near real-time rapid determination of earthquake parameters to an earthquake early warning system.The CSRM could also provide guidance for focuses in future seismological research and the design of future active and passive seismic experiments in China.Several focuses are suggested for future seismological research in China,along with the building of a national cyberinfrastructure to sustain and expand the operations of the CSRM project.

Morphology and possible origins of the Perm anomaly in the lowermost mantle of Earth

We have constrained a small-scale,dome-shaped low-velocity structure near the core-mantle boundary(CMB)of Earth beneath Perm(the Perm anomaly)using travel-time analysis and three-dimensional(3-D)forward waveform modeling of seismic data sampling of the mantle.The best-fitting dome-shaped model centers at 60.0°E,50.5°N,and has a height of 400 km and a radius that increases from 200 km at the top to 450 km at the CMB.Its velocity reduction varies from 0%at the top to–3.0%at 240km above the CMB to–3.5%at the CMB.A surrounding 240-km-thick high-velocity D''structure has also been detected.The Perm anomaly may represent a stable smallscale chemical pile in the lowermost mantle,although the hypothesis of a developing mantle plume cannot be ruled out.

Anomalies of geophysical field in deep crustand earthquakes in Central-South Shanxi

Comprehensive studies on the crustal structures, the anomalies of geophysical field and the seismicity in Central-South Shanxi are conducted. The research results show that there are deep tectonic background for occurring moderate earthquakes in Lingshi-Jiexiu region between Linfen and Taiyuan. From now on, the region should be attached closely.

1-D P- and S-wave velocity models for the collision zone between the northern Tianshan mountain and the Junggar basin based on local earthquake data

We have developed crustal minimum I-D P- and S-wave velocity models of the collision zone between the northern Tianshan mountain and the Junggar basin （86°E-89°E, 43°N-44.5°N）. These two models were created through inversion of 1 370 P- and 1 396 S-wave travel times from 173 well-constrained local earthquakes recorded by the Uriimqi sparse local seismic network and temporary seismic arrays. In contrast to previous models, our results indicate relatively low velocity at both shallow （〈10 km） and deep （30-45 km） depths. The shallow zone is interpreted to be the result of thick surficial sedimentary deposits, whereas the deeper anomaly is interpreted to result from ductile shearing and lower crustal fow. Additionally, we detected several transition layers under the lower crust, which may imply structural complexity of the uppermost mantle in this region. The improved models reduce the RMS residual of earthquake locations by 41.7% from 1.2 to 0.5 seconds. The more accurately located hypocenters appear to correlate with prominent local over-thrusts, which underlie an anticlinal fold belt and several blind faults. Positive station corrections are observed near the Junggar basin, which likely reflects low wave velocity; negative corrections near the Tianshan mountain and Bogda mountain suggest high wave velocity.