Crustal and uppermost mantle structure of the northeastern Qinghai-Xizang Plateau from joint inversion of surface wave dispersions and receiver functions with P velocity constraints

Lithospheric structure beneath the northeastern Qinghai-Xizang Plateau is of vital significance for studying the geodynamic processes of crustal thickening and expansion of the Qinghai-Xizang Plateau. We conducted a joint inversion of receiver functions and surface wave dispersions with P-wave velocity constraints using data from the Chin Array Ⅱ temporary stations deployed across the Qinghai-Xizang Plateau. Prior to joint inversion, we applied the H-κ-c method(Li JT et al., 2019) to the receiver function data in order to correct for the back-azimuthal variations in the arrival times of Ps phases and crustal multiples caused by crustal anisotropy and dipping interfaces. High-resolution images of vS, crustal thickness, and vP/vSstructures in the Qinghai-Xizang Plateau were simultaneously derived from the joint inversion. The seismic images reveal that crustal thickness decreases outward from the Qinghai-Xizang Plateau. The stable interiors of the Ordos and Alxa blocks exhibited higher velocities and lower crustal vP/vSratios. While, lower velocities and higher vP/vSratios were observed beneath the Qilian Orogen and Songpan-Ganzi terrane(SPGZ), which are geologically active and mechanically weak, especially in the mid-lower crust.Delamination or thermal erosion of the lithosphere triggered by hot asthenospheric flow contributes to the observed uppermost mantle low-velocity zones(LVZs) in the SPGZ. The crustal thickness, vS, and vP/vSratios suggest that whole lithospheric shortening is a plausible mechanism for crustal thickening in the Qinghai-Xizang Plateau, supporting the idea of coupled lithospheric-scale deformation in this region.

Surface wave inversion with unknown number of soil layers based on a hybrid learning procedure of deep learning and genetic algorithm

Surface wave inversion is a key step in the application of surface waves to soil velocity profiling.Currently,a common practice for the process of inversion is that the number of soil layers is assumed to be known before using heuristic search algorithms to compute the shear wave velocity profile or the number of soil layers is considered as an optimization variable.However,an improper selection of the number of layers may lead to an incorrect shear wave velocity profile.In this study,a deep learning and genetic algorithm hybrid learning procedure is proposed to perform the surface wave inversion without the need to assume the number of soil layers.First,a deep neural network is adapted to learn from a large number of synthetic dispersion curves for inferring the layer number.Then,the shear-wave velocity profile is determined by a genetic algorithm with the known layer number.By applying this procedure to both simulated and real-world cases,the results indicate that the proposed method is reliable and efficient for surface wave inversion.

Three dimensional shear wave velocity structure of crust and upper mantle in South China Sea and its adjacent regions by surface waveform inversion

We assembled approximately 328 seismic records. The data set was from 4 digitally recording long-period and broadband stations of CDSN. We carried out the inversion based on the partitioned waveform inversion (PWI). It partitions the large-scale optimization problem into a number of independent small-scale problems. We adopted surface waveform inversion with an equal block (2((2() discretization in order to acquire the images of shear velocity structure at different depths (from surface to 430 km) in the crust and upper-mantle. The resolution of all these anomalies has been established with (check-board( resolution tests. These results show significant difference in velocity, lithosphere and asthenosphere structure between South China Sea and its adjacent regions.

S-wave velocity structure in Tangshan earthquake region and its adjacent areas from joint inversion of receiver functions and surface wave dispersion

Using the seismic records of 83 temporary and 17 permanent broadband seismic stations deployed in Tangshan earthquake region and its adjacent areas(39°N–41.5°N,115.5°E–119.5°E),we conducted a nonlinear joint inversion of receiver functions and surface wave dispersion.We obtained some detailed information about the Tangshan earthquake region and its adjacent areas,including sedimentary thickness,Moho depth,and crustal and upper mantle S-wave velocity.Meanwhile,we also obtained the vP/vS structure along two sections across the Tangshan region.The results show that:(1)the Moho depth ranges from 30 km to 38 km,and it becomes shallower from Yanshan uplift area to North China basin;(2)the thickness of sedimentary layer ranges from 0 km to 3 km,and it thickens from Yanshan uplift region to North China basin;(3)the S-wave velocity structure shows that the velocity distribution of the upper crust has obvious correlation with the surface geological structure,while the velocity characteristics of the middle and lower crust are opposite to that of the upper crust.Compared with the upper crust,the heterogeneity of the middle and lower crust is more obvious;(4)the discontinuity of Moho on the two sides of Tangshan fault suggests that Tangshan fault cut the whole crust,and the low vS and high vP/vS beneath the Tangshan earthquake region may reflect the invasion of mantle thermal material through Tangshan fault.

Frequency Time Analysis (FTAN) and Moment Tensor Inversion Solutions from Short Period Surface Waves in Cameroon (Central Africa)

Short period surface waves generated by a local earthquake recorded by broadband seismometers at distances of about 186 to 778 km from the earthquake’s epicenter located in Cameroon (Central Africa) were processed for group velocity maps and dispersion waveforms using the frequency time analysis (FTAN) method. The resulting group velocity fundamental modes of the extracted Rayleigh and Love waves were used for a joint amplitude spectral and P polarity inversion using moment tensor inversion. The corresponding group velocity dispersion curves, the residual as a function of depth, the amplitude spectra and the moment tensor solutions of the regions from the epicenter to the different stations up to a depth of about 10 km were obtained.

Influence of Both Magnetic Field and Temperature on Silicon Solar Cell Base Optimum Thickness Determination

The minority carrier’s recombination velocity at the junction and at the back surface is used for the modeling and determination of the optimum thickness of the base of a silicon solar cell in the static regime, under magnetic field and temperature influence. This study takes into account the Umklapp process and the Lorentz effect on the minority carriers photogenerated in the base.

Crustal thickness,V_(P)/V_(S) ratio,and shear wave velocity structures beneath Myanmar and their tectonic implications

The crustal structure in Myanmar can provide valuable information for the eastern margin of the ongoing IndoEurasian collision system.We successively performed H-k stacking of the receiver function and joint inversion of the receiver function and surface wave dispersion to invert the crustal thickness(H),shear wave velocity(V_(S)),and the V_(P)/V_(S) ratio(k)beneath nine permanent seismic stations in Myanmar.H was found to increase from 26 km in the south and east of the study area to 51 km in the north and west,and the V_(P)/V_(S) ratio was complex and high.Striking differences in the crust were observed for different tectonic areas.In the Indo-Burma Range,the thick crust(H~51 km)and lower velocities may be related to the accretionary wedge from the Indian Plate.In the Central Myanmar Basin,the thin crust(H=26.9-35.5 km)and complex V_(P)/V_(S) ratio and V_(S) suggest extensional tectonics.In the Eastern Shan Plateau,the relatively thick crust and normal V_(P)/V_(S) ratio are consistent with its location along the western edge of the rigid Sunda Block.

Back Surface Recombination Velocity Modeling in White Biased Silicon Solar Cell under Steady State

In this paper, we extend the concept of back surface recombination through a study of a silicon mono facial solar cell in static regime and under polychromatic illumination. Back surface recombination velocities noted Sbe, Sbj and Sbr are determined for which respectively we derived, the power, the fill factor and the conversion efficiency, that become constant whatever the thickness of the solar cell. We have then obtained the expression of the minority carrier’s density in the base from the continuity equation. We then have determined the photocurrent density, the photo voltage, the power, the fill factor and finally the conversion efficiency.

Surface Recombination Concept as Applied to Determinate Silicon Solar Cell Base Optimum Thickness with Doping Level Effect

New expressions of back surface recombination of excess minority carriers in the base of silicon solar are expressed dependent on both, the thickness and the diffusion coefficient which is in relationship with the doping rate. The optimum thickness thus obtained from the base of the solar cell allows the saving of the amount of material needed in its manufacture without reducing its efficiency.

Estimating Circulation Patterns by Combining Velocity and Tracer Observations

A method is suggested for estimating unknown velocities by combining their sparse measurements with observations of a tracer on a fine grid advected by the underlined velocity field. The dependence of the estimation error on a coarseness parameter and parameters of the flow in question is investigated numerically using synthetic velocity fields typical for real oceanic circulation. In an advanced version of the estimation procedure uncertainty in the transport equation forcing is modeled via a fuzzy sets approach. We also compare the method with a traditional interpolation which is in contrast to the developed procedure unable to capture the flow details.

厚松散层薄基岩煤层开采地表沉降速度及其影响因素研究

为研究厚松散层薄基岩煤层开采引起的地表沉降速度变化规律,以淮南矿区某矿110801首采工作面为工程背景,采用有限差分软件FLAC3D分别对不同开采速度、采高、采宽、松散层厚度和基岩层厚度条件下煤层开采地表沉降速度进行模拟研究,分析地表沉降速度变化规律及各影响参数对地表沉降速度的敏感性大小。结果表明:地表沉降速度随开采速度、采高、采宽的增大而增大,但随基岩层厚度、松散层厚度的增大而减小;地表最大沉降速度随开采速度、采高、采宽的增大而线性增大,随松散层厚度的增大而线性减小,与基岩层厚度呈幂函数减小关系;各影响因素对地表最大沉降速度的敏感性从大到小依次为采宽、基岩层厚度、松散层厚度、开采速度、采高。

2000—2018年西昆仑山冰川表面运动特征研究——基于ITS_LIVE数据

近年来,西昆仑山冰川物质平衡异常现象受到广泛关注,然而该地区冰川末端却同时存在前进(常态)、后退、稳定及跃动多种状态。冰川末端进退不仅与气候变化引起的物质平衡变化有关,还与冰川的运动速度变化密切相关。以往研究多集中在前者,而对后者研究较少。因此,本文基于ITS_LIVE v01速度产品,结合西昆仑山冰川表面高程变化及冰川厚度资料,分析西昆仑山地区具有不同变化状态的冰川在2000—2018年的表面运动速度变化特征。结果表明,西昆仑山冰川在研究时段内的多年平均运动速度为6.35 m·a^(-1),年均速度波动上升,这主要是由该区域冰川表面高程整体上呈增加趋势[(0.15±0.02)m·a^(-1)]即冰川物质增加所造成;末端前进冰川的多年平均运动速度为4.07 m·a^(-1),年平均运动速度在研究时段内呈增加趋势,这主要与该类冰川在研究时段内物质略微增加有关;末端后退冰川多年平均速度约为4.86 m·a^(-1),年平均运动速度在研究时段内呈减小趋势,这主要与该类冰川物质亏损、减薄有关;末端稳定冰川多年平均速度约为3.04 m·a^(-1),年平均运动速度在研究时段内保持稳定,该类冰川在研究时段物质平衡也基本处于零平衡状态。研究区内末端前进冰川的多年平均运动速度较末端后退冰川的偏小,主要是因为末端前进冰川的平均厚度较末端后退冰川的偏小。2000—2018年西昆仑山有7条冰川发生跃动,多年平均运动速度为13.21 m·a^(-1),物质积累[(0.35±0.02)m·a^(-1)]引起速度增加。长度规模较大的后退冰川在2000年之前发生过跃动,由于目前处于平静期,冰川上部积累的物质未能及时输送到下部导致冰舌厚度减薄并后退。

当阳复向斜页岩气探测区地壳结构及其构造暗示

本文采用接收函数H-κ叠加、多频接收函数和面波联合反演方法,获得了扬子克拉通当阳复向斜区21个密集流动地震台下方的地壳厚度、V_(p)/V_(s)比和S波速度.结果表明,该区平均地壳厚度和V_(p)/V_(s)比值分别为33.8 km和1.75,推测当阳复向斜经历过下地壳减薄但地壳整体尚保持典型克拉通结构特征.研究区绝大部分台站都在3~4 km深度存在1~2 km厚的低S波速度层,推测可能与该深度范围内富集高孔隙度和低密度的页岩气层有关.本研究表明,基于密集流动地震台阵被动源数据资料,可为油气资源勘探提供有价值的参考.

n⁺-p-p⁺Silicon Solar Cell Base Optimum Thickness Determination under Magnetic Field

Base optimum thickness is determined for a front illuminated bifacial silicon solar cell n+-p-p+ under magnetic field. From the magneto transport equation relative to excess minority carriers in the base, with specific boundary conditions, the photocurrent is obtained. From this result the expressions of the carrier’s recombination velocity at the back surface are deducted. These new expressions of recombination velocity are plotted according to the depth of the base, to deduce the optimum thickness, which will allow the production, of a high short-circuit photocurrent. Calibration relationships of optimum thickness versus magnetic field were presented according to study ranges. It is found that, applied magnetic field imposes a weak thickness material for solar cell manufacturing leading to high short-circuit current.

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.

联合多源数据反演郯庐断裂带南段地壳三维速度结构

郯庐断裂带南段位于不同块体交汇区,高分辨率的地壳速度结构有助于理解该地区的构造特征及成因.本文基于多源数据,利用2015年安徽实验中气枪的体波和高频面波,2008—2018年区域地震体波信号以及背景噪声面波频散等资料,将不同来源、不同周期的面波频散数据和体波走时进行联合反演,获取了郯庐断裂带南段的高精度地壳速度结构.研究结果表明:(1)加入面波信息进行联合反演后,获取的P波和S波速度模型的分辨能力较单一体波数据反演在中下地壳均有显著提升.(2)郯庐断裂带是控制区域异常的主要因素,两侧具有明显的速度差异.地震主要发生在断层附近,集中分布于高低速交界区.(3)秦岭—大别造山带下方5~10 km深度存在明显的高速异常体,对应于超高压变质岩,是大陆深俯冲经历超高压变质作用后折返上升到中上地壳形成的.(4)长江中下游成矿带的矿集区呈现高的P波和S波速度值,可能是陆内俯冲、岩石圈拆沉、幔源岩浆底侵和一系列成矿作用共同造就的.

基于震源机制解析的巨厚覆岩矿震破裂机制

鄂尔多斯矿区侏罗系煤层覆岩中常见巨厚层状砂岩组,为了解释和量化巨厚覆岩下煤层开采矿震破裂机制与顶板破断特征,基于震动波P波辐射位移场与相对矩张量反演方法,提出了以震源群为单位、微震台站为对象构建反演矩阵进行煤矿矿震震源机制反演,提高了反演效率与准确性,求解了巨厚覆岩下实体煤段与临空段工作面回采诱发大能量矿震事件的震源机制,定量分析了顶板破裂演化特征与震动波辐射影响方位。结果表明:巨厚覆岩下临空段工作面回采白垩系巨厚砂岩层开始产生破断,地表沉降量快速上升,开始出现100 kJ以上的矿震事件,矿震分布较实体煤阶段更为密集;大部分大能量矿震事件位于采空区后方,与煤层上方厚层顶板破断、滑移密切相关;巨厚覆岩下煤层开采诱发的震源顶板张拉破裂占比85%以上,临空段回采期间震源有向上扩展的趋势,剪切滑移破裂相对实体煤回采阶段有所增加;破裂面走向方向大致与工作面推进方向一致或与工作面推进方向成“X”夹角,但临空回采阶段相较实体煤阶段走向“X”夹角由30°增加至45°;震源破裂面倾角0°~30°,占比50%左右,顶板以水平离层张拉、顶板回转压缩失稳为主,产生的P波大多向下方采空区传播,对工作面回采影响较小;仅部分顶板断裂张拉与剪切滑移失稳产生的P波向周围采场传递,可能对工作面影响较大。巨厚覆岩型矿震的防治思路可从弱化巨厚覆岩的整体性、使巨厚覆岩结构分层破断的角度出发,降低巨厚覆岩整体破断诱发矿震对工作面冲击危险性的影响。

面波反演苏北—南黄海盆地地壳三维S波速度结构

区域地壳速度结构对于地震定位和地球动力学特征认识十分重要,一直是地震反演研究的主要内容。利用收集到的基于背景噪声面波成像方法的瑞利面波相速度数据,我们对苏北—南黄海地区地下三维S波速度结构开展了深度反演,进而探讨苏北—南黄海盆地地质结构与地震构造的关系。面波层析成像结果表明区域速度结构模型与地质特征基本一致,速度结构清晰刻画出了苏北—南黄海沉积盆地的主要沉积构造范围和基底起伏。反演结果还揭示了南黄海盆地中地壳内存在一显著的低速层,与历史强震集中分布区高度一致,表明浅源强震活动与壳内的低速层密切相关。

基于噪声面波直接反演法研究天山中段地壳S波速度结构

天山造山带是新生代以来复活隆升的陆内造山带,强烈的地震活动性使得理解和认识天山造山带深部结构及盆山耦合关系尤为重要。文章中使用天山造山带及邻区(40°~49°N,79°~93°E)85个台站2017—2019年的背景噪声资料,结合背景噪声互相关方法获得了6~52 s瑞利波相速度频散曲线,利用基于射线追踪的面波直接反演法对天山中段地壳三维S波速度结构及盆山耦合关系进行研究。结果显示:地壳浅层S波速度分布与构造单元中沉积层厚度相关,塔里木盆地北缘、准噶尔盆地南缘表现为低速,天山造山带表现为高速;到了中下地壳,天山造山带下方存在被高速异常包裹的低速体;莫霍面附近,天山造山带表现出相对低速;准噶尔盆地南缘和天山造山带的地壳厚度分别在45~50 km、50~62 km之间,沿南北向,天山造山带莫霍面呈现较为宽缓的形态;在82°~86.5°E之间,塔里木盆地和准噶尔盆地向天山下方双向俯冲,86.5°~88°E之间,准噶尔盆地向天山南向俯冲,由西向东,不同盆山耦合关系揭示了新生代以来天山中段不同区域构造运动差异,为进一步探讨造山动力过程提供参考。