Interseismic Strain Localization in the San Jacinto Fault Zone

We investigate interseismic deformation across the San Jacinto fault at Anza, California where previous geodetic observations have indicated an anomalously high shear strain rate. We present an updated set of secular velocities from GPS and InSAR observations that reveal a 2–3 km wide shear zone deforming at a rate that exceeds the background strain rate by more than a factor of two. GPS occupations of an alignment array installed in 1990 across the fault trace at Anza allow us to rule out shallow creep as a possible contributor to the observed strain rate. Using a dislocation model in a heterogeneous elastic half space, we show that a reduction in shear modulus within the fault zone by a factor of 1.2–1.6 as imaged tomographically by Allam and Ben-Zion (Geophys J Int 190:1181–1196, 2012) can explain about 50 % of the observed anomalous strain rate. However, the best-fitting locking depth in this case (10.4 ± 1.3 km) is significantly less than the local depth extent of seismicity (14–18 km). We show that a deep fault zone with a shear modulus reduction of at least a factor of 2.4 would be required to explain fully the geodetic strain rate, assuming the locking depth is 15 km. Two alternative possibilities include fault creep at a substantial fraction of the long-term slip rate within the region of deep microseismicity, or a reduced yield strength within the upper fault zone leading to distributed plastic failure during the interseismic period.     

超声弹性应变率值在鉴别乳腺炎与乳腺癌中的应用分析

目的：探讨超声弹性应变率值在乳腺炎与乳腺癌患者中的鉴别及应用效果。方法：选择2015年6月至2017年10月入院治疗的乳腺癌患者48例和乳腺炎患者50例,分别设乳腺炎组和乳腺癌组。两组入院后均采用日立图腾彩超诊断仪对患者进行诊断,检查时患者先行常规二维超声检查,然后对患者进行弹性图像检查,选择感兴趣区域,采用系统软件计算出弹性应变率比值,绘制ROC曲线,分析超声弹性应变率值在乳腺炎与乳腺癌患者中的诊断、鉴别效能。结果：乳腺癌与乳腺炎患者均经过病理检查得到确诊,乳腺癌类型中排在前两位为浸润性导管癌、导管内癌,分别占68.75%和16.67%;乳腺炎排在前两位为导管壁增厚,周围伴有炎细胞浸润和导管壁结构破坏伴结核样肉芽肿,分别占36.0%和34.0%;乳腺炎组与乳腺癌组均顺利完成弹性图像检查,乳腺癌组超声弹性应变率值,高于乳腺炎组（P<0.05）;ROC曲线结果表明,超声弹性应变率ROC曲线下面积为0.935,诊断乳腺炎、乳腺癌敏感度、特异度及准确度分别为93.1%、90.2%和85.7%。结论：将超声弹性应变率值用于乳腺癌和乳腺炎鉴别中效果理想,能获得较高的诊断效能,能为临床治疗提供依据和参考,值得推广应用。     

Tsunami Wave Analysis and Possibility of Splay Fault Rupture During the 2004 Indian Ocean Earthquake

The 2004 Indian Ocean tsunami was observed by two satellites, close in space and time, that traversed the Indian Ocean 2?h after the Sumatra–Andaman earthquake, but which observed different tsunami lead wave morphologies. The earlier satellite, Jason-1, recorded a lead wave with two peaks of similar amplitude and wavelength, while the later satellite, TOPEX/Poseidon, recorded a lead wave with only one longer wavelength uplift. To resolve this disparity, we examine the travel paths of long wavelength waves over the seafloor bathymetry. Waves traveling from the margin will traverse significantly different paths to arrive at the two satellite transects. The result is that the satellites are sensitive to different parts of the margin; Jason-1 is highly sensitive to the margin in the area of the epicenter, while TOPEX is sensitive to a more northerly section. By developing solutions of the ocean gravity wave equations, accounting for dispersion, we show that the double peak of the Jason-1 satellite observations are consistent with coseismic rupture of a splay fault of limited along-strike extent, located north of Simeulue Island. The doubly peaked morphology can be reproduced with co-activation of the subduction zone interface and the splay fault, which creates a seafloor uplift pattern with two distinct areas of uplift. The Jason-1 satellite is sensitive to a splay fault in this portion of the margin, whereas the TOPEX satellite would not be significantly affected by this uplift pattern. By back-projecting satellite observation points to the margin, we constrain the location of the proposed splay fault and find that it correlates with a bathymetric high. The aftershock locations, uplift of corals on Simeulue Island and a fault scarp on Pulau Salaut Besar are also consistent with the activation of a splay fault in the area delimited by the back-projection. Our work also shows that it is critical to fully capture gravity wave dispersion in order to represent features of the lead wave profile that may not be as well characterized by the shallow water (long-wavelength) model. It is also necessary to account for dispersion so as to precisely assess wavefront travel times; this leads us to conclude that the rupture must have reached very near to the trench and propagated with an updip rupture velocity of order 2.0?km/s or more.     

利用断层活动协调比方法分析云南现今地壳应变积累

断层活动协调比方法在分析云南地区的地壳应变积累上具有适用性.利用区域11处跨断层流动监测场地的三十余年观测资料,首先计算跨断层场地的三维活动量,进而得出场地的断层活动协调比参数,结果显示:(1)丽江、永胜、剑川、石屏、建水场地在对应6～7级地震上,历史映震效果良好;云南地区近期存在异常的跨断层监测场地有剑川、石屏和建水...     

Strain and tilt changes measured during a water injection experiment at the Nojima Fault zone, Japan

Abstract In order to make geophysical and geological investigations of the Nojima Fault on Awaji Island, Japan, three boreholes measuring 1800 m, 800 m and 500 m deep were drilled into the fault zone. The fault is one of the seismic source faults of the 1995 Hyogo-ken Nanbu earthquake of M 7.2. A new multicomponent borehole instrument was installed at the bottom of the 800 m borehole and continuous observations of crustal strain and tilt have been made using this instrument since May 1996. A high-pressure water injection experiment within the 1800 m borehole was done in February and March 1997 to study the geophysical response, behavior, permeability, and other aspects of the fault zone. The injection site was located approximately 140 m horizontally and 800 m vertically from the instrument. Associated with the water injection, contraction of approximately 0.7 × 10⁻⁷ str (almost parallel to the fault) and tilt of approximately 1 × 10^-7 rad in the sense of upheaval toward the injection site were observed. In addition to these controlled experiments, the strainmeter and tiltmeter also recorded daily variations. We interpret strain and tilt changes to be related to groundwater discharge and increased ultra-micro seismicity induced by the injected water.     

On the Generation of ULF Magnetic Variations by Conductivity Fluctuations in a Fault Zone

v--vPrior to the October 18, 1989 Loma Prieta M_s 7.1 earthquake, Fraser-Smith et al. (1990) recorded a 10-100 fold increase in ultra-low frequency (ULF) magnetic fields near the earthquake epicenter. Several mechanisms for generation of these ULF fields by fluid flow in the earth have been advanced, but all appear to require unrealistic fluid velocities or hydraulic permeabilities to match the observations. As an alternative explanation, Merzer and Klemperer (1998) proposed that the increase in ULF magnetic fields could result from induced electric currents flowing in a fault-zone made temporarily much more electrically conductive by stress-induced reorganization of pore geometry. Using a numerical model we show that while this mechanism could produce a significant increase in ULF variations, mutual induction between the fault zone and the surrounding crust would probably limit the amplitude increase to levels well below those observed at Loma Prieta. We consider a variant on this quasi-static conductive fault zone model in which low frequency telluric currents are modulated by small higher frequency variations of bulk fault zone conductivity. We show that because the spectrum of natural EM variations is red, substantially larger relative increases in ULF magnetic fields could be produced by this mechanism with even small conductivity fluctuations at these frequencies. These variations would be easy to detect with a well-designed experiment, if they occurred. In principle this mechanism could explain the Loma Prieta ULF observations, however the magnitude of conductivity fluctuations that would be required to match the very large reported amplification factors still appears to be too large to be physically plausible.     

应变控制下深层黏土动弹性模量与阻尼比试验研究

为研究天津滨海新区深层黏土动力特性,借助GDS动三轴仪器对应变控制条件下天津滨海新区深层黏土的动弹性模量及阻尼比的变化规律进行研究。每组试验中将相应深度土体上覆土层压力作为试验围压,其间只改变控制应变进行循环三轴试验。试验结果表明,土体动弹性模量、阻尼比受围压影响有一个限值,超过这个限值(约3倍参考围压),围压对土体动弹性模量、阻尼比影响很小,但土体动应变对其影响较大。     

基于钻孔应变观测约束的2016年新疆呼图壁M6.2地震的发震断层研究

利用北天山地区的钻孔应变观测资料,分析2016年呼图壁M6.2地震同震应变阶跃的张、压性特征。结合余震精定位方法等给出的震源参数,基于弹性位错理论,模拟不同震源参数下的同震应变阶跃的张、压性特征。通过对钻孔应变张、压性的模拟值与实测值进行对比分析,研究呼图壁M6.2地震的发震断层。结果表明:(1)震中附近4个四分量钻孔应变台站数据自检性能较好,且多记录到明显的同震应变阶跃,其中,呼图壁、石场、巴伦台应变阶跃较为明显,张、压性变化最大值分别达2.5×10^-8和-3.4×10^-8;(2)在地震震源参数为293°/64°/90°(走向/倾角/滑动角)、发震断层面倾向北时,钻孔应变张、压性的模拟值与实测值最为吻合,呼图壁M6.2地震的发震断层极有可能为一条倾向北的高角度逆冲型盲断层。本文结果为认识呼图壁M6.2地震的发震构造提供重要力学依据。     

The Elastic Strain Energy of Damaged Solids with Applications to Non-Linear Deformation of Crystalline Rocks

Laboratory and field data indicate that rocks subjected to sufficiently high loads clearly deviate from linear behavior. Non-linear stress–strain relations can be approximated by including third and higher-order terms of the strain tensor in the elastic energy expression (e.g., the Murnaghan model). Such classical non-linear models are successful for calculating deformation of soft materials, for example graphite, but cannot explain with the same elastic moduli small and large non-linear deformation of stiff rocks, such as granite. The values of the third (higher-order) Murnaghan moduli estimated from acoustic experiments are one to two orders of magnitude above the values estimated from stress–strain relations in quasi-static rock-mechanics experiments. The Murnaghan model also fails to reproduce an abrupt change in the elastic moduli upon stress reversal from compression to tension, observed in laboratory experiments with rocks, concrete, and composite brittle material samples, and it predicts macroscopic failure at stress levels lower than observations associated with granite. An alternative energy function based on second-order dependency on the strain tensor, as in the Hookean framework, but with an additional non-analytical term, can account for the abrupt change in the effective elastic moduli upon stress reversal, and extended pre-yielding deformation regime with one set of elastic moduli. We show that the non-analytical second-order model is a generalization of other non-classical non-linear models, for example “bi-linear”, “clapping non-linearity”, and “unilateral damage” models. These models were designed to explain the abrupt changes of elastic moduli and non-linearity of stiff rocks under small strains. The present model produces dilation under shear loading and other non-linear deformation features of the stiff rocks mentioned above, and extends the results to account for gradual closure of an arbitrary distribution of initial cracks. The results provide a quantitative framework that can be used to model simultaneously, with a small number of coefficients, multiple observed aspects of non-linear deformation of stiff rocks. These include, in addition to the features mentioned above, stress-induced anisotropy and non-linear effects in resonance experiments with damaged materials.     

近年来龙门山断裂GPS剖面变形与应变积累分析

利用1999~2012年4期GPS速度场数据,对龙门山断裂天全—映秀段及安县—广元段的GPS剖面变形与应变积累作了探讨。在剖面应变积累对地震触发成因及程度方面,将芦山MS7.0与汶川MS8.0地震进行了对比分析。结果表明:(1)芦山地震之前,该地区压性速率远高于1999~2007年,它是汶川大震后的应力调整过程;(2)汶川MS8.0、芦山MS7.0两次强震间隔如此之短,不排除是汶川地震之后龙门山断裂西南段应力场高值压应力的调整过程对此次芦山地震起到触发作用的可能性。     

On the Problem of Elastic Anisotropy Estimation in the Rocks with Quasi Orthotropic Symmetry

Izvestiya, Physics of the Solid Earth - Abstract—The principles for estimating the degree of elastic anisotropy of the medium (the rocks) with transverse isotropic and orthorhombic symmetry...     

Localisation of a wave source by point measurements of its field

Summary As a solution of an inverse problem consisting of finding the position of a wave source in a linear medium by measuring its field components at several points we propose a method which would replace the inverse by a direct method. This enables us to perform an effective numerical realization.

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Transient Scattering of Elastic Waves by Dipping Layers of Arbitrary Shape Part 1: Antiplane Strain Model

Scattering of elastic waves by two dimensional multilayered dipping sediments of arbitrary shape embedded in an elastic half-sapce is investigated by using a bondary method. The displancement field is evaluated throughout the elastic media for both steady state and transient incident SH waves. The unknown scattered field is expressed in terms of wave functions which satisfy the equation of motion, traction-free boundary condition and appropariate radiation conditions. The transient response is constructed from the steady state solution by using the fast Fourier transform technique. The numerical results presented demonstrate that scattering of waves by subsurface irregularities may cause locally very large amplification of surface ground motion. The motion can be affected greatly by the scattered surface waves in the sediments. The results clearly indicate that the surface ground motion depends upon a number of parameters present in the problem, such as frequency and the angle of incidence of the incoming wave, impedance contrast between the layers and location of the observation point.     

On the Relationship Between the Crustal Strain Rate and Seismicity:Detect the Source-Field Relation from the Crustal Strain Field

The relationship between the strain cumulative rate (i.e., the crustal strain rate, or CSR in short) and seismic activity is analyzed to develop a new method to determine risky regions for strong shocks within recent years by the recorded crustal strain field. Seismic activity, especially the recurrence period, is different in different areas. Ding Guoyu (1984) pointed out that, for different seismic regions, the difference in the recurrence period of strong earthquakes is mainly controlled by their difference in the rate of the tectonic movement, which is controlled by the seismogenic environment and the tectonic conditions. The method of determining the risky regions for strong shocks from the gradient of vertical strain rates observed in a geodetic survey is preliminarily tested with the earthquakes in recent years; the results show that this method is effective and useful for earthquake prediction. The relationship between CSR and seismicity in a specific region is studied with strain theories, obse     

Elastic wave velocities in a granitic geothermal reservoir

Geothermal resources have potential for providing cost-effective and sustainable energy. Monitoring of production-induced changes in geothermal reservoirs using seismic waves requires understanding of the elastic properties of the rock and how they change due to injection of fluids and opening and closing of natural and hydraulic fractures. P- and S-wave velocities measured in a granitic geothermal reservoir using sonic logging are systematically lower than those predicted using the composition of the rock. Cracks may occur in granitic rocks from tectonic stresses and from the thermal expansion mismatch between differently oriented anisotropic crystals. An isotropic orientation distribution of microcracks causes a significant reduction in both the P- and S-velocities, consistent with the observed sonic P- and S-velocities. Vertical fractures cause a difference in the velocity of vertically propagating shear waves polarized parallel and perpendicular to the fractures. An assumption that the lower measured velocities are caused by the presence of vertical fractures is inconsistent with the sonic data. This is because vertical fractures cause a decrease in slow S-wave velocity that greatly exceeds the decrease in P-wave velocity, in contrast to the observed data. The growth of vertical fractures in the geothermal reservoir may be monitored using the difference in velocity of the fast and slow shear waves, while the change in P-velocity in a crossplot of measured P- and slow S-velocities is useful for estimating the ratio of the normal-to-shear compliance of the fractures.     

Development of Algae in Waters and a Possibility of Spectrometric in-situ Monitoring

A short review is given on the production of algae, their influence on the matter budget, the damage to the biocoenosis of waters and on the purification processes of algae-enriched rawwaters. For the development and construction of an in-situ device to monitor the content of phytoplankton in eutrophicated waters on ships, measurements of the spectral reflectance in shallow inland and bay waters were made from 1983 till 1985. Simultaneously chlorophyll-a and secchi-disk transparency were measured. Especially marked correlations (partly dependent on the season and the type of the water body) exist between the quotient of reflectance at the wavelengths of 710 and 660 nm and the chlorophyll-a concentrations (7… 320 μg/l) and between the reflectance at 710 nm and reciprocal values of secchi-disk transparency (0.3… 3.0 m). On the basis of these results a prototype of a two-channel spectrometer was produced.     

地壳应变速率与地震活动关系的研究——从地壳应变场探索强震活动的场源关系

通过研究应变积累速度（亦即地壳应变速率）与地震活动的关系,籍以探讨从地壳应变场中寻找近期强震危险区的方法。针对不同地区的地震活动水平特别是地震复发期的差异,丁国瑜（１９８４）指出,各地震区大震复发时间的差异主要取决于由大震孕育环境和构造物理条件所决定的构造活动速率（亦即应变累积速率）的差异。从近几年地震实况的初步（阶段性）检验看,应用大地测量中垂直形变速率梯度判定强震危险区,具有较好的效果和可喜的前景。作者从理论分析、实际资料对比及计算机模型研究等方面来讨论地壳应变速率与地震活动水平之间的关系,进而为场源关系研究中的“场中求源”的科学思路探索可能的技术途径,并讨论了从应变速率场中寻找强震危险区的方法。     

Evidence of Strain Partitioning Between the Sierra Madre Fault and the Los Angeles Basin, Southern California from Numerical Models

— Geodetic data indicate that the northern Metropolitan Los Angeles region is shortening at a rate of 4.5–6.0 mm/yr between downtown Los Angeles and the San Gabriel Mountains. If we assume that all of the uplift of the San Gabriel Mountains is due to the major frontal fault system (the Sierra Madre fault) and use reported values for bedrock uplift, slip per event and recurrence intervals to determine the slip rate on the Sierra Madre fault, we obtain slip rates between 0.6–1.27 mm/yr. Using these slip rates, the horizontal shortening attributable to the Sierra Madre fault accounts for only ~33% of the observed shortening across the basin, leaving ~67% of the shortening to be accounted for elsewhere. Herein we present a suite of models that test possible shortening mechanisms to account for this strain deficit. The models incorporate a range of fault geometries and have a layered structure with variable vertical and horizontal rheologies. The models demonstrate how lower-crust rheology and the presence of a low rigidity, anelastically deforming sedimentary basin affects the dissipation of stress imposed on the viscous layers by elastic failure of the faults. We found that viscoelastic models with a single fault, vertically strong crust and a compliant sedimentary basin yield a horizontal velocity profile that best matches the geodetically observed velocity profile across the Los Angeles Basin. Our models also indicate that we are still not accounting for all of the observed deformation. Therefore, more complex models that include both laterally varying rheologies and frictional properties on faults must be considered.     

利用水准测量数据分析芦山M_S7.0地震前龙门山断裂带南段应变积累

利用2010年和2013年两期一等水准测量数据分析了龙门山断裂带南段芦山MS7.0地震前的应变积累。结果表明:(1)汶川地震的发生明显加速了该区域应变积累的过程,龙门山断裂带南段主要断层区域垂直形变速率为6~9 mm/a,表明汶川地震的发生加速了此次芦山地震的孕育过程;靠近鲜水河断裂带区域垂直形变速率为1~5 mm/a,低于汶川地震前的隆升速度。(2)芦山地震并未释放该区域长期积累的应变能,龙门山断裂带南段仍然具有发生破坏性地震的可能。