地震台站空隙角对地震定位精度的影响

利用四川测震台网记录的芦山余震资料,选取20个M≥2.5地震,以Loc3D(川滇)定位方法定位结果为标准。采用MSDP中常用定位方法(HypoSAT、HYP2000、LocSAT、单纯型),在人为增减台站情况下,使得台站空隙角在25°—320°范围内任意变化,采用相同震相和相同台站对选定的地震事件进行定位,并对定位结果与标准结果对比,结果表明:震中位置在台站空隙角25°—130°任意变化时,4种定位方法效果较好,差别不大;在空隙角达到130°时,震中位移具有随着空隙角增大而逐步变大趋势;在空隙角达到190°时,单纯型法震中位移明显加大,出现随机突跳现象。总体而言,LocSAT法定位效果较好,平均震中位移2.6 km,HYP2000法平均震中位移2.8 km,HypoSAT平均震中位移4.1 km,单纯型定位效果较差,平均震中位移10.3 km。     

The influence of tectonic subsidence on volcaniclastic sedimentation: The Cretaceous upper Daeri Member,Wido Island,Korea

The Daeri Member, a Cretaceous volcanic–sedimentary succession, can be divided into lower, middle, and upper parts based on vertical changes in its lithologic characters. The lower Daeri Member is composed of siliciclastic deposits formed in a semi‐arid floodplain environment, which is overlain by the middle Daeri Member consisting mainly of andesite lava flow. After the emplacement of the andesite, activities of intrabasinal normal faults created accommodation on hanging wall blocks together with the development of intrabasinal topographic relief. The upper Daeri Member occurs only in hanging wall blocks and is composed of rhyolitic volcaniclastic sediments formed during an explosive volcanic eruption. Following the eruption, owing to semi‐arid climatic conditions and the destruction of vegetation, the eruptive materials were easily remobilized and deposited by episodic sediment gravity flows, resulting in deposition of the resedimented volcaniclastic deposits with sheet‐like geometry. Away from the intrabasinal normal faults, the resedimented volcaniclastic deposits show a decrease in grain size together with changes in inferred depositional processes from debris flows to hyperconcentrated flows and supercritical sheetfloods. This suggests that the resedimented volcaniclastic deposits were stacked on alluvial fan environments induced by intrabasinal topographic relief associated with normal fault activities. In addition, episodic movement of the faults gave rise to periodic fluctuation of the accommodation and an increase in gradient of the alluvial fan surface, resulting in the development of coarsening‐upward trends in the resedimented volcaniclastic deposits. The development of the alluvial fan and the coarsening‐upward trends indicate that dynamic tectonic subsidence and concomitant changes in the intrabasinal physiographic relief influenced the depositional processes and sizes of the transported volcaniclastic sediments of the upper Daeri Member. Thus, it is necessary to carefully observe tectonic signatures in volcaniclastic successions, particularly the syneruptive lithofacies, in order to reconstruct the tectonic and volcanic histories of receiving basins.     

基于移动平台的测震应急流动台现场监控系统的设计与实现

流动测震观测是在大地震发生以后开展的一项重要的地震应急响应工作,能够获得震区高质量的地震数据,而野外环境的复杂性对测震应急流动台的架设提出了较高的要求。本文通过对地震应急流动现场工作进行需求分析,设计并实现了一种基于IOS系统的测震应急流动台现场监控系统,能够让现场工作队员快速获取流动台数据和状态信息,有利于流动台的快速架设,提高了应急流动观测现场工作的效能。     

Stagnant low-energy ions in the near cusp region observed by Cluster

Measuring the low-energy ions in the Earth's magnetotail lobes is difficult, because a spacecraft becomes positively charged in a sunlit and tenuous plasma environment. Recent studies have introduced a new method, making use of the positive electric potential on the Cluster spacecraft, to measure the low-energy ions(less than a few tens of electronvolts) in the polar caps/magnetotail lobes in the years 2001–2010. With the measured velocities, we are able to study the trajectories of these low-energy ions. Particle tracing has been used in previous studies, confirming that ions of ionospheric origin are the dominant contributor to the ion population in the Earth's magnetotail lobes. In this work, we continue to study the source of low-energy ions measured in the lobes. We found that not all of the low-energy ions in the lobes come directly from the ionosphere. Particle tracing infers that some of the low-energy ions start to move tailward from the cusp/near-cusp region with a zero parallel velocity. In the following, we refer to these low-energy ions as stagnant low-energy ions. On the other hand, the in situ measurements by Cluster show a population of low-energy ions in the cusp/near-cusp region with pitch angles near 90°(i.e., no significant parallel velocity).The locations of stagnant low-energy ions are determined by particle tracing and in situ measurements. Similar ion energies and spatial distributions determined by these two methods confirm the presence of the stagnant low-energy ion population.     

巴颜喀拉块体地壳结构多样性探测

青藏高原内部地壳岩性的改造、岩性随深度变化及形变构造是探索研究地壳增厚、物质运动问题的关键.巴颜喀拉块体位于青藏高原中北部,地域广袤,通过对块体内中、东部不同区域的深地震广角反射/折射震相的综合分析,利用反射率理论地震图方法对不同性质震相走时及振幅特征进行细致的模拟计算,进一步研究巴颜喀拉块体内部不同区域地壳精细结构.结果显示:巴颜喀拉块体地壳厚度50~60 km、整体向西逐渐增厚,结晶地壳平均速度6.07~6.18 km·s~(-1)、岩层速度大幅降低,壳内多强反射界面结构、但不同区域差异明显;东部若尔盖盆地地壳介质速度整体低速、壳幔边界较为清晰;中部玉树一玛多段下部地壳发现约6.8 km·s~(-1)的"高速度"介质结构,壳幔边界不清、被改造为2~4 km厚的高速度梯度层,显示了巴颜喀拉块体内部地壳增厚、介质岩性结构被改造的差异性.地壳内部多组强反射、低视速度走时震相揭示了介质岩性的低速破碎、弱化蠕变以及可能的壳内解耦构造.局部地区下地壳的高视速度震相特征显示了青藏高原地壳改造增厚大背景下可能存在稳定的"原始地壳"结构残留或是与上地幔物质的浸入交流.巴颜喀拉块体内不同区域地壳增厚、岩性结构、结晶基底及壳幔边界性质被改造的多样性为深入认识青藏高原地壳形变及动力学过程带来新的启迪.     

一种数字三分量地震微测井仪器设计

针对当前地震微测井仪器在施工和数据采集方面的难题,从提高数据采集质量及仪器功能性方面提出了几种改进方法.主要利用MEMS加速度传感器结合多路并行处理采集方法设计了数字检波器,并集成姿态检测技术直接实现水平分量数据的校正功能,保证系统采集的质量;提出了Ethernet-RS485分布式总线自动控制技术,实现各级联探管的随机组合,同时采用电动方式控制探管操作,提高系统的集成化程度.文中详细分析了利用姿态检测技术实现水平分量数据校正的方法,解决了级联探管随机组合控制和震源激发方位的判定问题.仪器单节探管支持三分量并行采集,有效分辨率达18位,参数可远程配置,同时具备快速显示探管姿态的功能,且支持远程控制,非常适于复杂环境下的工程勘探,整个系统实现全数字化操作且仅需四芯电缆互连,从而缩小了设备的体积和重量,降低施工布线的复杂性.     

Nonlinear FE model updating and reconstruction of the response of an instrumented seismic isolated bridge to the 2010 Maule Chile earthquake

Nonlinear finite element (FE) modeling has been widely used to investigate the effects of seismic isolation on the response of bridges to earthquakes. However, most FE models of seismic isolated bridges (SIB) have used seismic isolator models calibrated from component test data, while the prediction accuracy of nonlinear FE models of SIB is rarely addressed by using data recorded from instrumented bridges. In this paper, the accuracy of a state‐of‐the‐art FE model is studied through nonlinear FE model updating (FEMU) of an existing instrumented SIB, the Marga‐Marga Bridge located in Viña del Mar, Chile. The seismic isolator models are updated in 2 phases: component‐wise and system‐wise FEMU. The isolator model parameters obtained from 23 isolator component tests show large scatter, and poor goodness of fit of the FE‐predicted bridge response to the 2010 Mw 8.8 Maule, Chile Earthquake is obtained when most of those parameter sets are used for the isolator elements of the bridge model. In contrast, good agreement is obtained between the FE‐predicted and measured bridge response when the isolator model parameters are calibrated using the bridge response data recorded during the mega‐earthquake. Nonlinear FEMU is conducted by solving single‐ and multiobjective optimization problems using high‐throughput cloud computing. The updated FE model is then used to reconstruct response quantities not recorded during the earthquake, gaining more insight into the effects of seismic isolation on the response of the bridge during the strong earthquake.     

Numerical Analysis of Groundwater Ridging Processes Considering Water‐Air Flow in a Hillslope

In this study, a water‐air two‐phase flow model was employed to investigate the formation, extension, and dissipation of groundwater ridging induced by recharge events in a hypothetical hillslope‐riparian zone, considering interactions between the liquid and gas phases in soil voids. The simulation results show that, after a rain begins, the groundwater table near the stream is elevated instantaneously and significantly, thereby generating a pressure gradient driving water toward both the stream (the discharge of groundwater to the stream) and upslope (the extension of groundwater ridging into upslope). Meanwhile, the airflow upslope triggered by the advancing wetting front moves downward gradually. Therefore, the extension of groundwater ridging into upslope and the downward airflow interact within a certain region. After the rain stops, groundwater ridging near the stream declines quickly while the airflow in the lower part of upslope is still moving into the hillslope. Thus, the airflow upslope mitigates the dissipation of groundwater ridging. Additionally, the development of groundwater ridging under different conditions, including rain intensity, intrinsic permeability, capillary fringe height, and initial groundwater table, was analyzed. Changes in intrinsic permeability affect the magnitude of groundwater ridging near the stream, as well as the downward speed of airflow, thereby generating highly complex responses. The capillary fringe is not a controlling factor but an influence factor on the formation of groundwater ridging, which is mainly related to the antecedent moisture. It was demonstrated that groundwater ridging also occurs where an unsaturated zone occurs above the capillary fringe with a subsurface lateral flow.     

Analysis of the Characteristics of the D.P.R. Korean Seismic Event on September 23, 2017

A M3. 4 seismic event occurred in the Punggye-ri nuclear test site,D. P. R Korea at 16∶29 p.m. on September 23,2017. We analyzed the waveforms of this event recorded by the China Earthquake Networks Center. In conclusion,this event is complex,including an explosion with a successive earthquake. Although the beginning of the event is an explosion,fault dislocation plays the main role in the event.     

关于地震科学实验场的一些思考——地下云图

由中国地震局和美国国家科学基金委、地质调查局合作建立的地震预报研究实验场为中国早期地震工作的发展起到了良好的推动作用。由于种种客观原因,地震预报实验场的多数预想目标未能达成,发展受到了阻碍。最近几年,实验场重新受到重视,并更名为"地震科学实验场"。结合目前地震学发展的前沿和防震减灾事业的实际需求,本文提出增加"地下云图"作为实验场的新方向。利用高重复性、环境友好、安全性高的气枪震源,持续激发地震信号,实现对地下介质速度变化的连续监测;结合背景噪声成像获得的高分辨率3维地壳结构,构建4维(三维空间+一维时间)地下结构成像。"地下云图"可以反映地下速度和应力变化,为全国范围的地震监测预测提供新的业务手段,推动地震预测从经验预测到物理预测的转换。