Pendulum-type laser strainmeter

Constructive disposition principles of the basic optical units of Michelson interferometers are used in making one-coordinate laser strainmeters of unequal-arm type.The fundamental advantages of pendulum-type laser strainmeter more than classical-type laser strainmeter are displayed.     

光纤传感技术未来地震监测的发展方向

利用光纤传感器进行地震前兆观测是一种独具优势的地震监测新手段。 光纤传感器具有高精度、 抗电磁干扰、 不存在零漂、 易于组网以及适于长距离传输等一系列独特优势, 可以解决地震前兆观测中电学测量仪器存在的固有问题。 介绍了几类常用光纤传感器的工作原理及特点, 综述了光纤传感器在地壳形变观测和地震波探测两个应用领域国内外的研究进展, 并指出了目前需要解决的问题。 研制了一套基于光纤传感器的钻孔应变、 地震波和地温同时测量的多参量钻孔综合地震观测设备, 现场实验表明, 该光纤综合钻孔地震观测设备适应地震前兆观测中对抗环境干扰能力、 测量精度、 稳定性等方面的性能要求, 具有较好的应用前景。     

钻孔差应变仪观测的苏门答腊大地震激发的地球环型自由振荡

我们率先用钻孔应变仪观测资料研究了地球自由振荡. 泰安地震台有差应变和体应变两种钻孔应变观测仪器,都观测到2004年12月26日苏门答腊大地震激发的地球自由振荡. 体应变仪观测到地球的球型振荡,而差应变仪观测到地球的环型振荡. 两种观测还记录到环型振荡与球型振荡相互的耦合作用. 观测也记录到明显的一些振型的谱线分裂现象. 用直接观测到的高质量的环型振荡资料求解了0T8～0T19等主要振型的Q值. 根据两个方向的剪应变观测数据,求解了环型振荡的最大剪应变方向,发现这个方向是相当稳定的. 这种研究表明,高精度钻孔应变观测仪是一种理想的地壳形变观测仪器,可以为地球自由振荡研究提供更丰富的信息.     

Effect of Near-fault Terrain upon Dislocation Modeling

—Coseismic surface deformation provides important information needed to determine source rupture geometry and slip distribution as well as to estimate seismic moment. In this study, numerical experiments were designed to analyze and classify how free-surface topography affects surface deformation. The investigation was performed by 3-D finite element modeling. Results of this study show that crustal deformation induced by near-fault terrain is significant and can be measured with present geodetic survey techniques. The characteristics of the terrain effects show that a hill structure produces more crustal deformation than a half-space model, and that the crustal deformation of a basin structure is less than that of the half-space model. The topographic correction is in the order of five percent of the fault dislocation. On the basis of the relationship between fault offset and earthquake magnitude, it is suggested that the terrain effects on the coseismic crustal deformation of shallow earthquakes with a magnitude greater than 5.6 should be considered as one of the major errors in coseismic deformation modeling which ignored the surface topography on the order of 300 meters.     

基于InSAR的海原—老虎山—毛毛山断裂带现今地壳形变特征

本文利用107景L波段2007年至2011年的ALOS/PALSAR卫星影像, 采用干涉图堆叠技术, 基于GAMMA软件, 利用影像数据公共区域的均值统计校正, 首次获取海原—老虎山—毛毛山断裂带整体地区的平均地壳形变速度场, 将大范围形变结果进行统一表达。 沿断层方向形变结果表明, 断裂带两侧存在明显差异运动, 断层的运动性质为左旋, 其中毛毛山-老虎山段的差异运动比较显著, 在震情跟踪工作中要给予重视。 另外, 结合研究区域内长期GPS水平速度场, 从多角度研究了区域现今地壳运动的特征。     

Tilt observations from shallow and deep borehole arrays

Measurements of the Earth tide using tilt and strainmeter data can be used to infer crustal structure. However, in almost all measurements of crustal motion using shallow tiltmeters and strainmeters, reference is made to the degradation of the data implied to be caused by influence of meteorological parameters on near surface layers. For example, studies by Wood and King and Goulty et al. indicated that a substantial portion of measured crustal motion by shallow tilt and strain data may be attributed to the weather. These studies were limited to data outside the tidal band. However, it is important to determine the effects of weather on these data, within the tidal band, if shallow tiltmeters are to be used to determine crustal structure.Collocated deep and shallow borehole tiltmeter arrays were operated by The Air Force Geophysics Laboratory in eastern Massachusetts and provided an opportunity to investigate weather effects on shallow tilt. The tiltmeters installed in deep boreholes (100 m) yielded internally consistent M₂ amplitudes (2%) and phases (3%) (Cabaniss and McConnell) but the collocated shallow (4 m) borehole tilt array did not produce the same results. Least squares analyses of the shallow tilt data revealed variations of 20% for M₂ tidal amplitude compared to the deep data. A multichannel Wiener filter technique was used to investigate the hypothesis that this discrepancy was due to meteorological influence. Results indicated that approximately one-half of the anomalous M₂ power was correlated with air and borehole temperatures. It is suggested that the remaining anomalous power may be due to ground deformation caused by the action of groundwater. If this is true, shallow tiltmeters might not be measuring the same deformation as the deep instruments and, therefore, not capable of measuring the Earth tide with the accuracy required to determine crustal structure.     

A 100 m laser strainmeter system installed in a 1 km deep tunnel at Kamioka, Gifu, Japan

We have installed a laser strainmeter system in a deep tunnel about 1,000 m below the ground surface at Kamioka, Gifu, Japan. The system consists of three types of independent interferometers: (1) an EW linear strainmeter of the Michelson type with unequal arms, (2) an NS-EW differential strainmeter of the Michelson type with equal arms and (3) a NS absolute strainmeter of the Fabry–Perot type. These are configured in L-shaped vacuum pipes, each of which has a length of 100 m. (1) and (2) are highly sensitive (order of 10⁻¹³ strain) and have wide dynamical range (10⁻¹³–10⁻⁶). Observations with strainmeters (1) and (2) started on June 11, 2003. (3) is a new device for absolute-length measurements of the order of 10⁻⁹ of a long-baseline (100 m) Fabry–Perot cavity by the use of phase-modulated light. This third strainmeter will be ready for operation before the end of 2004. The laser source of strainmeters (1) and (2) is a frequency-doubled YAG laser with a wavelength of 532 nm. The laser frequency is locked onto an iodine absorption line and a stability of 2 × 10⁻¹³ is attained. The light paths of the laser strainmeter system are enclosed in SUS304 stainless steel pipes. The inside pressure is kept to be 10⁻⁴ Pa. Consequently, quantitative measurement of crustal strains of the order of 10⁻¹³ can be attained by employing the laser strainmeter system of (1) and (2) at Kamioka. This resolving power corresponds to that of a superconducting gravimeter. Using the laser strainmeter system, we expect to determine parameters related to fluid core resonance, core modes and core undertone as well as other geodynamic signals such as slow strain changes caused by silent earthquakes or slow earthquakes.     

3-D Modelling of Plate Interfaces and Numerical Simulation of Long-term Crustal Deformation in and around Japan

— We developed a 3-D simulation model for long-term crustal deformation due to steady plate subduction in and around Japan by incorporating viscoelastic slip-response functions into a realistic 3-D plate interface model, constructed on the basis of the topography of ocean floors and hypocenter distributions of earthquakes. The lithosphere-asthenosphere system is modelled by an elastic surface layer overlying a Maxwellian viscoelastic half-space. Kinematic interaction at plate interfaces is rationally represented by the increase of tangential displacement discontinuity (fault slip) across the interfaces. With this model, giving the steady slip rates at plate interfaces calculated from NUVEL-1A, we simulated long-term crustal deformation due to steady plate subduction in and around Japan. The simulated crustal deformation pattern is characterized by steep uplift at island arcs, sharp subsidence at ocean trenches and gentle uplift at outer rises. The numerical results show the strong dependence of the deformation pattern on the 3-D geometry of plate interfaces.     

天山中段2次6级地震前钻孔应变高频异常分析

2014年以来,天山中段分量钻孔应变仪空前增多,这些高采样率的应变观测资料蕴含着丰富的构造信息。如何从高采样率观测资料中提取有效的前兆异常信息,是分析研究人员亟待解决的问题。文章通过对天山中段分量钻孔应变观测数据进行S变换和超限率分析发现,在天山中段2次6级地震前有5套应变资料出现高频信息异常。这些异常均在震前出现,随后达到峰值,临震前或地震后衰减,其中短周期异常信号主要集中在10～720 min频段,且S变换与超限率分析结果具有很好的同步性。结合精河地震震源区及附近的GPS分析结果,发现高频异常信息的分布与该地区地壳运动场具有很好的一致性,进一步验证了高频信息异常的可信度。     

地震地形变观测系统的组成、发展及应用

简要介绍地震地形变观测系统的组成及地形变观测技术的发展,指出不同观测技术的时空特点,光纤和长基线应变仪等新技术的优点以及不同地形变观测技术进行联合观测的可行性和方法优势。通过对日本岐阜县安装的1500 m臂长应变仪与GNSS地球观测网（GEONET）中的连续观测站获取的应变进行比对的实例分析,得出从连续观测站获取的水平应变去趋势后与应变仪得到的连续应变结果基本一致,地震会引起应变异常,应变仪对环境因素的影响更敏感。实际工作中应注意发展优势观测技术,进行观测技术和研究方法的融合、提高监测密度,增强时空分辨率,提升地震前兆特征识别能力,更好地为科学防震减灾服务。      

集成奇异谱分析和自回归滑动平均预测日本近海海平面变化

本文从日本沿岸选取了28个验潮站及联测的GPS站,利用奇异谱分析（Singular Spectrum Analysis,SSA）和SSA+自回归滑动平均（Auto Regression Moving Average,ARMA）方法预测了2014—2018年的近海海平面变化和地壳垂直变化.并用同时段的验潮及GPS的实际测量值进行验证,结果显示,SSA+ARMA预测的相对海平面精度为0.0357~0.0607 m,地壳垂直运动的精度为0.0049~0.0077 m,绝对海平面的精度为0.0433~0.0683 m,且三者SSA+ARMA的预测结果均优于只用SSA预测的结果.在此基础上本文利用SSA+ARMA预测了日本沿岸2019—2023年的近海绝对海平面变化,结果显示,2019—2023年的平均海面高较往年（2014—2018）升高0.0353 m,2003—2023年绝对海平面的变化率为0.0039 m·a^-1,预测结果较为理想.     

美国PBO计划:钻孔应变仪台网遭遇挑战

PBO(Plate Boundary Observatory)计划专门设计了一批钻孔应变仪台.网,在数百米距离内,安装2～3台仪器,以研究钻孔应变仪如何响应构造活动的信号,以及局部因素会造成何种干扰.本文收集了6个这样的台网的资料,给出了所有仪器数年的记录曲线,并对观测结果显示的地壳应变场做了简要的分析对比,发现6个试...     

Tidal and non-tidal signals in groundwater boreholes in the KTB area,Germany

Tides and barometric pressure variations cause pore pressure changes in the solid earth. In boreholes which are hydraulically connected to confined aquifers these pore pressure changes can be observed as water level variations. In case of confined aquifers boreholes can be regarded as volumetric strainmeters. From June 2004 until May 2005 a large scale injection experiment was realised in the pilot borehole (4000 m) at the German Continental Deep Drilling (KTB) site in Bavaria. During this test the injection induced deformation was observed by a tiltmeter array around KTB consisting of five tiltmeter stations at horizontal distances from 1.6 to 3 km from the injection borehole. At each station the local groundwater level was observed in depths between 30 and 50 m. The pore pressure was recorded in the boreholes. The time series were checked for tidal signals and injection influence. The injection was not verified presumably due to the fact that the penetration of the injected water was controlled by local geology and tectonic faults zones. Although the boreholes extending only to shallow depth tidal signals are clearly observable in at least two of five stations. On December the 26th 2004 the Sumatra–Andaman earthquake occurred which is clearly detectable in the pore pressure variations at all five stations.     

Kinematic model of crustal deformation of Fenwei basin,China based on GPS observations

Using high precision GPS data for the period of 1999–2007 from the China Crustal Movement Observation Network, we have constructed a plate kinematic model of crustal deformation of Fenwei basin, China. We have examined different kinematic models that can fit the horizontal crustal deformation of the Fenwei basin using three steps of testing. The first step is to carry out unbiasedness and efficiency tests of various models. The second step is to conduct significance tests of strain parameters of the models. The third step is to examine whether strain parameters can fully represent the deformation characteristics of the 11 tectonic blocks over the Fenwei basin. Our results show that the degree of rigidity at the Ordos, Hetao, Yinshan and South China blocks is significant at the 95% confidence level, indicating the crustal deformation of these blocks can be represented by a rigid block model without the need to consider differential deformation within blocks. We have demonstrated that homogeneous strain condition is suitable for the Yinchuan basin but not for other 6 blocks. Therefore, inhomogeneous strains within blocks should be considered when establishing the crustal deformation model for these blocks. We have also tested that not all of the quadratic terms of strain parameters are needed for the Yuncheng-Linfen block. Therefore, four kinds of elastic kinematic models that can best represent the detailed deformation characteristics of the 11 blocks of Fenwei basin are finally obtained. Based on the established model, we have shown that the current tectonic strain feature of the Fenwei basin is mainly characterized by tensile strain in the NW–SE direction, and the boundaries betweem the Ganqing and Ordos blocks and the Shanxi graben possess the maximum shear strain. A comparison between our results and past geological and geophysical investigations further confirms that the model established in this paper is reasonable.     

GPS-derived Deformation of the Central Andes Including the 1995 Antofagasta Mw = 8.0 Earthquake

—In order to study both the interplate seismic loading cycle and the distribution of intraplate deformation of the Andes, a 215 site GPS network covering Chile and the western part of Argentina was selected, monumented and observed in 1993 and 1994. A dense part of the network in northern Chile and northwest Argentina, comprising some 70 sites, was re-observed after two years in October/November, 1995. The M _w = 8.0 Antofagasta (North Chile) earthquake of 30th July, 1995 took place between the two observations. The city of Antofagasta shifted 80 cm westwards by this event and the displacement still reached 10 cm at locations 300 km from the trench. Three different deformation processes have been considered for modeling the measured displacements (1) interseismic accumulation of elastic strain due to subduction coupling, (2) coseismic strain release during the Antofagasta earthquake and (3) crustal shortening in the Sub-Andes.¶Eastward displacement of the sites to the north and to the south of the area affected by the earthquake is due to the interseismic accumulation of elastic deformation. Assuming a uniform slip model of interseismic coupling, the observed displacements at the coast require a fully locked subduction interface and a depth of seismic coupling of 50 km. The geodetically derived fault plane parameters of the Antofagasta earthquake are consistent with results derived from wave-form modeling of seismolog ical data. The coseismic slip predicted by the variable slip model reaches values of 3.2 m in the dip-slip and 1.4 m in the strike-slip directions. The derived rake is 66°. Our geodetic results suggest that the oblique Nazca–South American plate convergence is accommodated by oblique earthquake slip with no slip partitioning. The observed displacements in the back-arc indicate a present-day crustal shortening rate of 3–4 mm/year which is significantly slower than the average of 10 mm/year experienced during the evolution of the Andean plateau.     

华北地区地下水开采对地壳应力的影响

近50年来华北地区遭受持续大面积过量开采地下水,已形成区域地下水漏斗、地面沉降、地陷地裂等地质灾害.然而,地下水的抽取减小了地壳的载荷,造成地壳应力场变化,这一点至今尚未被充分认识.为探索华北地区地下水超采对地壳应力场的影响,本文建立了二维有限元模型,定量计算地下水超采引起地壳变形和应力场变化.结果表明:华北地区地下水开采会引起地表抬升达+12.4cm;漏斗区上、中地壳的水平拉应力增量分别达到70kPa和35kPa;而在地下水开采区外围,水平压应力增量达20kPa;而华北地区构造主压应力积累速率约为0.5kPa·a-1.通过对比华北地区1980年前后5级以上地震的分布状况,本文认为地下水开采对区域构造应力场的扰动不可忽略,其卸载过程可能对华北地区大地震孕震过程存在减缓作用.     

远震层析成像中的地壳校正研究及应用

远震层析成像是研究一个地区上地幔三维速度结构的有力手段.但由于远震射线在地壳内的交叉较差,因此无法准确约束地壳内的三维速度结构.为了消除地壳内横向不均匀性对深部速度成像产生的影响,必须进行地壳校正.本文详细描述了地壳校正的基本原理和步骤,主要包括三维地壳模型的选取、地壳内走时差的计算以及校正后的相对走时差的计算.以勘察加地区为例,通过计算各台站的平均相对走时差和远震层析成像结果分析了地壳校正的实际效果,同时验证了该方法的实用性.     

青藏高原东缘地壳运动与深部过程的研究

由于青藏高原东部地区记录了高原约50 Ma演化历史中物质东流的构造史,因此受到地学界的广泛重视. 现代大地测量与地质研究结果给出了该区现代地壳运动的图像,为地球动力学数值模拟提供了重要的边界约束条件. 利用重力异常计算的高原及邻区地幔对流应力场与地表地壳运动格局的明显差异表征了高原东部地壳与地幔物质的运动解耦. 基于随深度变化地壳蠕变率的动力学模拟结果显示,高原东部地壳增厚与高原内部存在很大差异,高原东部地壳增厚主要表现为下地壳的增厚,并且地幔形变过程与地表变化也不一致,同样显示出地壳、地幔运动的解耦. 研究表明,下地壳低强度分布可能是导致这种解耦的重要原因,而了解高原东部地壳及上地幔物理力学性质对我们认识高原物质东流至关重要.     

南北地震带和青藏块体东部近期大地形变与地震特征

通过研究南北地震带及青藏块体东部地区２０多年来大地形变场演化特征及其与地震活动的呼应关系，发现大地形变既具有时空分布的不均匀性，各分区形变场又具有同时段的宏观相似性；继承性运动是现代地壳运动的总趋势，而运动方式为波浪式，涌动式推进。地壳运动过程中存在着区域为能积累阶段和释放调整阶段，这可能是地震活动的相对平静与活跃的动力机制。     

Continuous GPS Array and Present-day Crustal Deformation of Japan

—A GPS array with about 1,000 permanent stations is under operation in Japan. The GPS array revealed coseismic deformations associated with large earthquakes and ongoing secular deformation in the Japanese islands. Based on daily coordinate data of the GPS stations, strain rate distribution is estimated. Most regions with a large strain rate are related to plate boundaries and active volcanoes. In addition, the Niigata-Kobe Tectonic Zone (NKTZ) is recognized as a region of large strain rate along the Japan Sea coast and in the northern Chubu and Kinki districts. This newly found tectonic zone may be related to a hypothetical boundary between the Eurasian (or Amurian) and the Okhotsk (or North America) plates. Precise observation of crustal deformation provides important boundary conditions on numerical modeling of earthquakes and other crustal activities. Appropriate computation methods of continuous deformation field are directly applicable to data assimilation for such numerical simulations.