Laboratory investigation of borehole breakouts and Multi-step failure model

Based on our experiment of borehole breakouts with a group of sandstone samples described in this paper, a multi-step failure model of borehole breakouts are proposed to quantitatively explain the relationship between the section shape of borehole breakouts and the state of crustal stress. In this model the borehole spalling is not only related to the state of stress at a single point but also the state of stress on its neighboring area. The comparison between the experimental results of borehole breakouts and the calculation results shows a good agreement. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, 493–499, 1992. This research is sponsored by the Chinese Joint Seismological Science Foundation under Contract No. 9000025.     

In situ stress state in Mainland China

In situ stress measurements are one of the important methods for studying the recent tectonic stress field and stress state. In this paper, the stress state and variation of stresses with depth in Mainland China are presented and analyzed on the basis ofin situ stress data measured by both hydrofracturing and overcoring techniques.     

Determination of Porosity and Permeability out of Dispersion Analyses of Borehole Wall Displacements

Waves carried in the borehole can be measured by the use of controlled sources inside the borehole and receivers located in the same borehole as well. This article gives the theoretical background and develops a new method to determine rock-physical parameters out of such controlled measurements of waves carried inside the borehole. Theoretical dispersion curves of the group velocities are matched to dispersion analyses of registrations obtained in the borehole. This inversion process intends to determine the in situ porosity and permeability of the rock.     

The effect of stress on pore pressure in rocks and the mechanism of water table anomaly before earthquakes

Triaxial compressive experiments of porous rock samples were carried out under various confining pressures and initial pore pressures without drainage; axial strain and pore pressure were observed versus differential stress. The results of such experiments show that pore pressure increases with increase of differential stress at low differential stress; pore pressure decreases with increase of differential stress at medium and high differential stress. Pore pressure also increases with large amplitude decrease of differential stress at high differential stress. Based on such experiments, it is suggested that water table anomaly before an earthquake reflects the change of differential stress in crustal rocks. The anomalous behavior of water tables in the epicentral and peripheral areas before the great Tangshan earthquake of July 28, 1976 are explained by such suggestion. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 88–95, 1991. This study is supported by the Chinese Joint Seismological Science Foundation. Professor Yongtai Che gave us much help in applying fund support and supplying earthquake case histories.     

Comprehensive study on stability of deep crust and unstable behavior of earthquake source by both failure mechanism and frictional sliding mechanism

In this paper the relation between fault movement and stress state in deep crust is discussed, based on synthetic analysis of the crustal stresses measured over the world and the concerned data of focal mechanism. Using Coulomb criterion for shear failure and frictional slip, analytical expressions for estimating stabilities of intact rock and existing fault in the crust and for identifying the type of faulting (normal, strike-slip or thrust fault) are derived. By defining the Failure FunctionF _m and the Fraction FunctionF _f, which may describe steadiness of crustal rock and existing fault, respectively, a synthetic model is set up to consider both fracturing mechanism and the sliding mechanism. By this model, a method to study stability and unstable behavior of crustal rock and fault at different depths is given. According to the above model, quantitative study on the crustal stability in the North China plain is made in terms of the measured data of hydraulic fracturing stress, pore-fluid pressure, terrestrical heat flow in this region. The functionsF _m andF _f and the shear stresses on faults with different strike angle and dip angle at various depths in this region are calculated. In the calculation the constraint condition of fault movement obeys Byerlee’s Law, and the depth-dependent nonlinear change in the vertical stress due to inhomogeneity of crustal density and the high anomalous pore-fluid pressure in deep crust of this region are considered. The conclusions are: the unstable behavior of the crust in the North China plain is not failure of crustal rock but slip on existing fault; the depth range where stick-slip of fault may happen is about from 8 to 20 km or more; stability of steep fault is lower than that of gentle sloping fault; the shear stresses in the range where may occur stick-slip are nearly horizontal; the steep faults trending from NNE to NE in this region are liable to produce strong earthquakes, whose co-seismic faultings are, for the most part, right lateral slip; the change in pore-fluid pressure in depth remarkably affects the stability of the crust and the increase in pore-fluid pressure, therefore, would be an important factor exciting strong earthquake in this region. The above theoretical inferences are consistent with the data measured in this region. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologia Sinica,13, 450–461, 1991. This work is supported by Chinese Joint Seismological Science Foundation.     

Clarification of regional and local in situ stresses using the compact conical-ended borehole overcoring technique and numerical analysis

Abstract Stress measurement is performed to estimate the states of in situ rock stress at the Torigata open‐pit limestone mine in Japan using the compact conical‐ended borehole overcoring (CCBO) technique. A set of back and forward analyses are then carried out to evaluate the states of regional and local in situ rock stresses and the mine‐induced rock slope stability using a 3‐D finite element model. The maximum horizontal local in situ rock stress measured by the CCBO technique acts in the northeast–southwest direction. The horizontal regional tectonic stresses obtained by the back analysis are in good agreement with those of the horizontal local in situ rock stress measured by the CCBO technique. However, the horizontal regional tectonic stress is more compressive than the horizontal local in situ rock stress. This is because the horizontal regional stress due to gravity is not considered in the back‐analyzed horizontal regional tectonic stress, but it is included in the local in situ rock stress measured by the CCBO technique. The local stress obtained by the forward analysis, especially its horizontal components, is in good agreement with the horizontal local in situ rock stress measured by the CCBO technique, and the magnitude of the vertical normal stress increases more rapidly than those of the horizontal normal stresses with depth. As a result, the ratio of the horizontal normal stress to the vertical normal stress is largest at the nearest excavation level and decreases with depth. This means that the stress field within the mine‐induced rock slope is affected by the horizontal components of the local in situ rock stress.     

Shear wave splitting and polarization anomaly with deep seismic sounding data

In this paper we study the S wave basement velocity structure and S wave splitting and polarization anomalies using the three component records of deep seismic sounding in the Three Groges Dam area, and further discuss the methods to study the anisotropy of crustal medium, the direction of regional tectonic stress field, and the physical indicator of potential earthquake sources using shear wave splitting and polarization anomalies. It has been demonstrated by analyzing the DSS data in the Three Gorges Dam area that S wave splitting and polarization anomalies are reliable means for studying seismic anisotropy of crustal medium and the direction of regional tectonic stress field. At the same time, it has been shown that DSS data are very useful for widening S wave observing window and distinguishing anomalous body, because DSS data have the advantage that the source position is known prior and S wave ray path can be traced exactly. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 1–3, 1993.     

Deep mantle flow, global tectonic pattern and the background of seismic stress field in China

In this paper we investigate the sources of two kinds of forces to form the stress field in the lithosphere. These are the drag force caused by mantle flow and the force system along plate boundaries. The results show that both forces control the basic stress pattern in China and compressive stresses can fit with the stress patterns constructed by focal mechanisms,in-situ stress measurements in boreholes and that deduced from other geophysical and geological observation. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 295–306, 1991. This research is sponsored by the Chinese Joint Seismological Science Fundation.     

Characteristics of present-day active strain field of Chinese mainland

On the basis of the GPS data obtained from repeated measurements carried out in 2004 and 2007,the horizontal principal strain of the Chinese mainland is calculated,which shows that the direction of principal compressive strain axis of each subplate is basically consistent with the P-axis of focal mechanism solution and the principal compressive stress axis acquired by geological method.It indicates that the crustal tectonic stress field is relatively stable in regions in a long time.The principal compressive stress axes of Qinghai-Tibet and Xinjiang subplates in the western part of Chinese mainland direct to NS and NNE-SSW,which are controlled by the force from the col-lision of the Eurasia Plate and India Plate.The principal compressive strain axes of Heilongjiang and North China subplates in the eastern part direct to ENE-WSW,which shows that they are subject to the force from the collision and underthrust of the Eurasia Plate to the North America and Pacific plates.At the same time,they are also af-fected by the lateral force from Qinghai-Tibet and Xinjiang subplates.The principal compressive strain axis of South China plate is WNW-ESE,which reflects that it is affected by the force from the collision of Philippine Sea Plate and Eurasia Plate and it is also subject to the lateral force from Qinghai-Tibet subplate.It is apparent from the comparison between the principal compressive strain axes in the periods of 2004～2007 and 2001～2004 that the acting directions of principal compressive stress of subplates in both periods are basically consistent.However,there is certain difference between their directional concentrations of principal compressive stress axes.The sur-face strain rates of different tectonic units in both periods indicate that the events predominating by compressive variation decrease,while the events predominating by tensile change increase.     

Horizontal crustal movement in Chinese mainland from 1999 to 2001

The paper introduces the horizontal crustal movement obtained from GPS observations in the regional networks (including the basic network and the fiducial network) of the Crustal Movement Observation Network of China (CMONOC) carried out in 1999 and 2001. This paper is characterized by the acquisition of the horizontal displacement velocities during the period from 1999 to 2001 at the observation stations in the regional networks with datum definition of a group of stable stations with small mutual displacements in east China. Based on the most detailed map of horizontal crustal movement in Chinese mainland, the division of blocks, their displacements and deformations are studied. An approach to analysis of the intensity of the horizontal crustal deformation is proposed. The general characteristics of the recent horizontal crustal movement in Chinese mainland and that before the Kunlunshan earthquake of M=8.1 on November 14, 2001 are analyzed. Foundation item: The National Development and Programming Project for Key Basic Research (95-13-03-07).     

Calculation of elastic properties in lower part of the Kola borehole from bulk chemical compositions of core samples

In-situ elastic properties in deep boreholes are controlled by several factors, mainly by lithology, petrofabric, fluid-filled cracks and pores. In order to separate the effects of different factors it is useful to extract lithology-controlled part from observedin-situ velocities. For that purpose we calculated mineralogical composition and isotropic crack-free elastic properties in the lower part of the Kola borehole from bulk chemical compositions of core samples. We use a new technique of petrophysical modeling based on thermodynamic approach. The reasonable accuracy of the modeling is confirmed by comparison with the observations of mineralogical composition and laboratory measurements of density and elastic wave velocities in upper crustal crystalline rocks at high confining pressure. Calculations were carried out for 896 core samples from the depth segment of 6840–10535m. Using these results we estimate density and crack-free isotropic elastic properties of 554 lithology-defined layers composing this depth segment. Average synthetic P- wave velocity appears to be 2.7% higher than the velocity from Vertical Seismic Profiling (VSP), and 5% higher than sonic log velocity. Average synthetic S-wave velocity is 1.4 % higher than that from VSP. These differences can be explained by superposition of effects of fabric-related anisotropy, cracks aligned parallel to the foliation plain, and randomly oriented cracks, with the effect of cracks being the predominant control. Low sonic log velocities are likely caused by drilling-induced cracking (hydrofractures) in the borehole walls. The calculated synthetic density and velocity cross-sections can be used for much more detailed interpretations, for which, however, new, more detailed and reliable seismic data are required.     

Study on in-situ stress measurement around coastal marginal land in Fujian

Introduction The southeast coastal margin of Chinese mainland is important to understand the mutual movement, matter exchange and energy transfer between ocean and land lithospheres, as well as their effects. The coastal area in Fujian Province is advanced in economy development but it has frequent earthquakes, or even strong earthquakes. Therefore, the current study on in-situ stress state measurement is of great significance for studying continental dynamics, marginal sea dy- namics, seismo…     

青藏高原拉萨块体地应力测量及其意义

受印度板块向欧亚板块持续北东向挤压作用,青藏高原腹地拉萨块体内新构造活动强烈,其地应力特征一直是工程规划建设、地球动力学和地壳稳定性研究的重要内容.2014至2015年,沿雅鲁藏布江断裂带,分别在西藏林芝县(LZ)、朗县(LX)和乃东县(ND)开展了水压致裂原地应力测量工作.本文通过测试结果分析,获得了拉萨块体现今地壳浅表层的应力状态及分布特征.LX及ND测点应力强度均高于LZ测点,且应力结构均为逆断型,表现为S_HS_hS_v,水平应力作用占主导.LZ测点在测试深度内揭穿了断裂,且应力结构不够明确.三个测点的应力状态显示出拉萨块体现今地壳强度处于破裂临界状态,结合各测点所处构造环境,应力的持续累积可能会打破这种平衡导致断裂活动.主应力比值K_(Hv)=S_H/S_v,K_(av)=(S_H+S_h)/2S_v和K_f=(S_H—S_h)/2也显示出该区强烈的水平构造运动.三测点揭示的最大水平主应力方向集中于近SN(LX)-NNE(LZ及ND)向,与该区背景应力场特征相一致,且与地壳运动场相耦合,反映出该区应力状态主要受控于印度板块北向欧亚大陆持续挤压碰撞的构造背景,同时各测点之间应力状态的差异性也体现了区域构造作用的差异影响.     

北京地区地应力测量与主要断裂稳定性分析

2008年汶川地震后,为查明北京地区现今地应力状态、评价断裂稳定性,相继在北京地区开展了5个深孔（600~1000 m）的水压致裂法地应力测量,并在适宜深度安装了地应力相对变化监测探头,建立了地应力变化监测台站.本文首先利用实测地应力数据分析了北京地区地壳浅表层应力状态,结果表明：（1）北京地区千米深度内,最大、最小水平主应力随深度增加梯度系数分别为0.0328和0.0221,侧压系数K_av和K_Hv值,最大、最小水平主应力之比K_Hh值与国内外已有认识基本一致,而水平向剪应力相对强度参数μ_m值较低;（2）北京地区最大水平主应力优势方向为近EW向,与华北地区构造应力场方向基本一致,同时受区内断裂活动等影响,存在与区域主应力方向偏差的局部应力场;（3）实测数据揭示的应力结构显示,北京地区地壳浅表层最大主应力（σ₁）总体为最大水平主应力（σ_H）,受区域构造演化以及测点附近断裂的影响,中间主应力（σ₂）与最小主应力（σ₃）所对应的实测地应力存在变化,但总体来讲,实测地应力数据揭示的应力结构与北京地区主要断裂性质基本相吻合.其次,基于实测应力数据,采用库仑摩擦滑动准则,结合拜尔定律,并取摩擦系数为0.2~1.0,初步评价了北京地区主要断裂稳定性,结果显示：（1）在摩擦系数取0.6~1.0条件下,北京地区现今应力状态尚未达到导致断裂失稳滑动水平,断裂不会出现失稳滑动现象;（2）摩擦系数弱化到0.4时,西峰寺钻孔应力状态满足断裂失稳滑动条件,揭示出八宝山断裂存在失稳滑动可能性,而夏垫-马坊断裂和黄庄-高丽营断裂附近测点应力状态将趋近满足断裂失稳滑动条件,表明这两条断裂有趋向失稳滑动可能性;（3）只有当摩擦系数弱化到0.2时,北京地区主要断裂才可能在现今应力状态出现断裂失稳滑动.本文的认识对北京地区乃至华北地区构造应力场、地震地质研究有重要参考意义.     

Comparison of SMOS,modelled and in situ long-term soil moisture series in the northwest of Spain

ABSTRACT

This work aimed to evaluate the capability of modelled vs in situ soil moisture observations in the northwest of Spain for a period of four years (2010–2013) in order to validate the SMOS L2 product. Comparisons were performed for a set of representative stations of the Soil Moisture Measurement Stations network of the University of Salamanca (REMEDHUS) at both point and area scales. The SMOS series showed good correlation with the modelled series, better than that obtained with the in situ observations (0.77 vs 0.68 average correlation coefficients). However, some underestimation or overestimation of the SMOS series, related to the soil characteristics, was observed with respect to both the in situ and the modelled series. The SMOS data normalization produced a notable improvement in the results, highlighting the capability of the modelled data to validate the SMOS soil moisture series. This research provides a solid foundation for the future validation of SMOS at large scales, overcoming the spatial representativeness issues arising from the use of in situ point measurements.

Editor M.C. Acreman; Associate editor N. Verhoest     

Coupling two radar backscattering models to assess soil roughness and surface water content at farm scale

Abstract

Remote sensing techniques are useful for agro-hydrological monitoring at the farm scale because the availability of spatially and temporally distributed data improves agricultural models for irrigation and crop yield optimization under water scarcity conditions. This research focuses on the surface water content retrieval using active microwave data. Two semi-empirical models were chosen as these showed the best performances in simulating cross and co-polarized backscatter. Thus, these models were coupled to obtain reliable assessments of both soil water content and soil roughness. The use of the coupled model enables one to avoid using roughness measured in situ. Remote sensing images and in situ data were collected between April and July 2006 within the European Space Agency-funded project AgriSAR 2006. The images data set includes L-band in HH, VV and VH polarizations acquired from the airborne E-SAR sensor, operated by the German Aerospace Centre. Results were validated using in situ soil water content and roughness measurements. The results show that reliable assessment of both soil roughness (r ² up to ?0.8) and soil water content (r ² ? 0.9) can be retrieved in fields characterized by low fractional coverage.

Editor D. Koutsoyiannis; Associate editor C. Onof

Citation Capodici, F., Maltese, A., Ciraolo, G., La Loggia, G., and D’Urso, G., 2013. Coupling two radar backscattering models to assess soil roughness and surface water content at the farm scale. Hydrological Sciences Journal, 58 (8), 1677–1689.     

Shear-wave splitting in the crust: Regional compressive stress from polarizations of fast shear-waves

When propagating through anisotropic rocks in the crust, shear-waves split into faster and slower components with almost orthogonal polarizations. For nearly vertical propagation the polarization of fast shearwave (PFS) is parallel to both the strike of the cracks and the direction of maximum horizontal stress, therefore it is possible to use PFS to study stress in the crust. This study discusses several examples in which PFS is applied to deduce the compressive stress in North China, Longmenshan fault zone of east edge of Tibetan plateau and Yunnan zone of southeast edge of Tibetan plateau, also discusses temporal variations of PFS orientations of 1999 Xiuyan earthquake sequences of northeastern China. The results are consistent to those of other independent traditional stress measurements. There is a bridge between crustal PFS and the crustal principal compressive stress although there are many unclear disturbance sources. This study suggests the PFS results could be used to deduce regional and in situ principal compressive stress in the crust only if there are enough seismic stations and enough data. At least, PFS is a useful choice in the zone where there are a large number of dense seismic stations.     

Comparison between Time-domain and Frequency-domain Measurement Techniques for Mantle Shear-wave Attenuation

—We study the frequency- and time-domain techniques which have been used to measure shear attenuation in the mantle using long-period body waveforms. In the time-domain technique, waveform modeling is carried out and the attenuation model that best fits the data is chosen. In the frequency-domain technique, we solve for the attenuation model that best fits the spectra of the seismic waveforms. Though theoretically both these techniques are equivalent, modeling assumptions and measurement biases associated with each technique can give rise to different results. In this study, we compare these two techniques in terms of their accuracy in obtaining mantle shear attenuation. Specifically, we estimate the biases in constraining attenuation from differential SS?S and absolute S waveforms. We carry out these tests using realistic synthetic seismograms and we follow this with an analysis of recorded data to verify the results from the synthetic tests. For the SS?S waveforms, the primary biasing factors are interference with seismic phases due to mantle discontinuities and due to crustal reverberation under the SS bounce point. These factors can affect the t* measurements by up to 0.5 s in the frequency domain and more than 1.5 s in the time domain. For the S waveforms, the frequency-domain measurements are accurate to 0.3 s while the time-domain measurements can vary by more than 2.0 s from the predicted values. These errors are also manifested in the t* measurements made using teleseismically recorded waveforms and lead to comparatively larger noise levels in the time-domain measurements. Based on these results, we propose that in long-period body-wave attenuation studies, frequency-domain techniques should be the method of choice.     

Characteristics of recent tectonic stress field in Jiashi, Xinjiang and adjacent regions

Introduction The Pamirs region where Jiashi is located is one of the most active regions of continental plate dynamics in China. Frequent earthquakes here, especially several strong earthquakes oc- curred in 1997 and 2003, have provided excellent conditions for studying the tectonic stress field in this region and a large number of results (GAO and WEN, 2000; GAO et al, 2004; XU, 2001; ZHOU et al, 2001) have been obtained. Although different methods and data were used, under- standings …     

Role of mantle-derived magma in genesis of early Yanshanian granites in the Nanling Range,South China: <Emphasis Type="Italic">in situ</Emphasis> zircon Hf-O isotopic constraints

Although a number of petrographic observations and isotopic data suggest that magma mixing is common in genesis of many granite plutons, it is still controversial whether the mantle-derived magmas were involved in granites. We carried out in this study a systematic analysis of in situ zircon Hf-O isotopes for three early Yanshanian intrusions dated at ca. 160 Ma from the Nanling Range of Southeast China. The Qinghu monzonite has very homogeneous zircon Hf-O isotopic compositions, εHf(t) =11.6±0.3 and δ18O=5...