Forward modelling receiver functions for crustal structure beneath station TBZ (Trabzon, Turkey)

We use teleseismic three-component digital data from the Trabzon, Turkey broadband seismic station TBZ to model the crustal structure by the receiver function method. The station is located at a structural transition from continental northeastern Anatolia to the oceanic Black Sea basin. Rocks in the region are of volcanic origin covered by young sediments. By forward modelling the radial receiver functions, we construct 1-D crustal shear velocity models that include a lower crustal low-velocity zone, indicating a partial melt mechanism which may be the source of surfacing magmatic rocks and regional volcanism. Within the top 5 km, velocities increase sharply from about 1.5 to 3.5 km s⁻¹. Such near-surface low velocities are caused by sedimentation, extending from the Black Sea basin. Velocities at around 20 km depth have mantle-like values (about 4.25 km s⁻¹ ), which easily correlate to magmatic rocks cropping out on the surface. At 25 km depth there is a thin low-velocity layer of about 4.0 km s⁻¹. The average Moho velocity is about 4.6 km s⁻¹, and its depth changes from 32 to 40 km. Arrivals on the tangential components indicate that the Moho discontinuity dips approximately southwards, in agreement with the crustal thickening to the south. We searched for the solution of receiver functions around the regional surface wave group velocity inversion results, which helped alleviate the multiple solution problem frequently encountered in receiver function modelling.
Station TBZ is a recently deployed broadband seismic station, and the aim of this study is to report on the analysis of new receiver function data. The analysis of new data in such a structurally complex region provides constraining starting models for future structural studies in the region.     

Mantle transition zone thickness beneath Afar: implications for the origin of the Afar hotspot

The velocity spectrum stacking method is applied to receiver functions from stations ATD and AAE to image P -to- S converted phases originating at the 410 and 660 km discontinuities beneath Afar. A transition zone thickness of 244 ± 19 km is obtained, similar to the global average transition zone thickness. This result suggests that any broad thermal anomaly beneath Afar probably does not extend as far down as the transition zone. However, because of the 19 km uncertainty in the thickness estimate, a small thermal anomaly of ~100–150 K at mantle transition zone depths cannot be ruled out.     

The Moho Structure in The Western Eger Rift: A Receiver Function Experiment

We used teleseismic recordings of a temporary deployment of seismic stations and of permanent short period stations in the western Eger Rift system to study the lithosphere with the help of Receiver Functions. The crust-mantle boundary (Moho) is observed at almost all stations by strong P-to-S converted phases. The Moho is basically flat between about 26 – 30 km depth in the entire region. At one station in the Eger Rift (BOH-1, Loket castle) no Moho is observed. We interpret this with the existence of a broad gradient zone there, instead of a sharp discontinuity. This observation, however, needs to be confirmed by more data.     

Constraining the crustal structure under the central and western Tian Shan based on teleseismic receiver functions and gravity anomalies

The Tian Shan is a vast range that spans several countries in Asia. Understanding its evolutionary history may provide valuable insights into intracontinental orogenic dynamics. In this study, we explored the crustal characteristics of the Tian Shan and their relationships to the tectonic evolution of the region. A new H-stacking method that combines the P receiver function and gravity anomalies was used to estimate the thickness and ratio of P- to S-wave velocities (v_P/v_S) for 91 broadband seismic stations in the central and western Tian Shan. Our results revealed significant lateral variations in crustal thickness and v_P/v_S. A ~45-km-thick crust and an intermediate-high v_P/v_S (~1.74–1.84) were found in the Kazakh Shield and Tarim Basin, which we interpreted to indicate a mafic crystalline basement and lower crust. The central Tian Shan varied greatly in crustal thickness (40–64 km) and v_P/v_S ratio (1.65–2.00), which may be due to crustal shortening, mafic underplating, and crustal melting. In contrast, we observed a relatively thin crust (42–50 km) with an intermediate v_P/v_S ratio (~1.78) in the western Tian Shan. The differences in the crustal structures between the western and central Tian Shan imply that the Talas-Fergana Fault may be trans-lithospheric.     

青藏高原东北缘甘东南地区地壳各向异性特征及构造意义

本文利用径向和切向接收函数确定地壳各向异性的方法,处理了布设在青藏高原东北缘甘东南地区、横跨西秦岭北缘等断裂的24个密集宽频带流动台站远震资料,得到了研究区地壳各向异性特征.结果显示,平均快波方向呈现NW-SE、NWW-SEE及NNW-SSE,平均分裂时间0.56 s.甘东南中部及北部地区快波方向与GPS速度方向、前人利用XKS波分裂获取的快波方向及该地区断层展布方向基本一致,说明该地区壳幔运动可能是耦合的.同时研究区南部少数台站快波方向呈现NNW-SSE,与断裂方向及GPS速度方向有一定夹角,表明台站下方壳幔运动可能是解耦的.全区快波方向自北向南由近E-W逐渐转变为NW-SE,最后变为NNW-SSE.据此推测地壳在该区的变形挤压有顺时针方向旋转的趋势,这与该区块体挤压应力方向一致.     

坑(井)-地多参数电磁接收系统

坑（井）-地多参数电磁接收系统在地面、坑道、井中三维空间观测天然场源及人工源电磁信号,观测装置接近或穿过矿体,借助动源、大功率发射可获得更加明显的异常值,旨在加大探测深度的基础上提高深部分辨率,同时获取电阻率、极化率、复阻抗等参数.为坑（井）-地电磁成像方法现场数据采集提供硬件设备支持,针对坑道、井中电磁观测的特殊需求,开发了由不极化电极、非接触电极、小型感应式线圈、微型三分量音频磁传感器、地面-坑道电磁接收机、井中电磁接收机等组成的坑（井）-地多参数电磁接收系统,解决了传统不极化电极坑道硬岩表面接地困难和传统感应式磁传感器难以适应坑道狭窄空间的问题;通过多层次的室内、弱干扰条件下野外测试验证了接收系统的各项技术指标,接收机通道全频段噪声水平接近10 nV/rt（Hz）,微型三分量音频磁传感器体积压缩至32 cm×32 cm×32 cm;强干扰条件下的矿山试验验证了接收系统的可靠性、适用性及先进性.     

多波束测深系统在航道测量中的关键问题探讨

介绍了多波束测深系统与GPS RTK技术集成的工作原理及优势,并以秦皇岛港航道疏浚前后多波束扫海测量为例,论述该作业模式中的几个关键问题,即在声速改正和参数校准的前提下,RTK三维水深测量省去传统水深测量中繁琐的水位测量,能够自动消除波浪起伏和动态吃水变化的误差影响。航道疏浚结果表明,在近海海域该方法可以取代有验潮的常规水深测量,既能指导疏浚施工,又能方便检查疏浚结果,为今后的相关工作提供参考。     

Crustal structure beneath the Hi-CLIMB seismic array in the central-western Tibetan Plateau from the improved H-κ-c method

The Hi-CLIMB seismic array is located in the central-western Tibetan Plateau. The H-κ-c method (Li JT et al., 2019) was applied to receiver function data on the HiCLIMB, which corrects the back-azimuthal variations in the arrival times of Ps and crustal multiples caused by crustal anisotropy and dipping interfaces before performing H-κstacking. Compared to the traditional H-κ method, the H-κstacking results after harmonic corrections showed considerable improvements, including greatly reduced errors, significantly less scattered H (crustal thickness) and κ (crustal vP/vS ratio) values, and clearer patterns of H and κ in different Tibetan blocks. This demonstrates that the H-κ-c method works well even for regions with complex crustal structures, such as the Tibetan Plateau, when there are helpful references from nearby stations or other constraints. The variation in crustal thickness agrees with previous studies but tends to be relatively shallower beneath most of the plateau. Two regions with particularly high crustal vP/vS were observed, namely, one in the northern Himalaya block and beneath the YarlungZangbo suture, and the other in the Qiangtang block. Their correlation with mid-crust low S velocities from previous studies suggests the possible presence of fluid or partial melt in the two regions, which may have implications for the crustal flow model. In contrast, the Lhasa block had relatively lower crustal vP/vS and relatively higher crustal S velocity within the plateau, which is interpreted to be mechanically stronger than the Himalaya and Qiangtang blocks, and without mid-crust partial melt.     

多波束与侧扫声纳海底目标探测的比较分析

侧扫声纳是目前常用的海底目标(如沉船、水雷、管线等)探测工具,在测深领域,多波束以全覆盖和高效率证明了它的优越性。由于多波束具有很高的分辨率,目前在工程上已经开始应用多波束进行海底目标物的探测。对多波束和侧扫声纳进行了比较分析,并着重探讨了影响多波束分辨率的各种因素。结果表明:多波束的最大优点在于定位精度高,但其适用范围不如侧扫声纳广泛,尤其受到水深和波束角的限制,多波束和侧扫声纳在探测海底目标时具有很好的互补性,同时应用可以提高目标解译的准确性。