GT0 Explosion Sources for IMS Infrasound Calibration: Charge Design and Yield Estimation from Near-source Observations

Three large-scale on-surface explosions were conducted by the Geophysical Institute of Israel (GII) at the Sayarim Military Range, Negev desert, Israel: about 82 tons of strong high explosives in August 2009, and two explosions of about 10 and 100 tons of ANFO explosives in January 2011. It was a collaborative effort between Israel, CTBTO, USA and several European countries, with the main goal to provide fully controlled ground truth (GT0) infrasound sources, monitored by extensive observations, for calibration of International Monitoring System (IMS) infrasound stations in Europe, Middle East and Asia. In all shots, the explosives were assembled like a pyramid/hemisphere on dry desert alluvium, with a complicated explosion design, different from the ideal homogenous hemisphere used in similar experiments in the past. Strong boosters and an upward charge detonation scheme were applied to provide more energy radiated to the atmosphere. Under these conditions the evaluation of the actual explosion yield, an important source parameter, is crucial for the GT0 calibration experiment. Audio-visual, air-shock and acoustic records were utilized for interpretation of observed unique blast effects, and for determination of blast wave parameters suited for yield estimation and the associated relationships. High-pressure gauges were deployed at 100–600 m to record air-blast properties, evaluate the efficiency of the charge design and energy generation, and provide a reliable estimation of the charge yield. The yield estimators, based on empirical scaled relations for well-known basic air-blast parameters—the peak pressure, impulse and positive phase duration, as well as on the crater dimensions and seismic magnitudes, were analyzed. A novel empirical scaled relationship for the little-known secondary shock delay was developed, consistent for broad ranges of ANFO charges and distances, which facilitates using this stable and reliable air-blast parameter as a new potential yield estimator. The delay data of the 2009 shot with IMI explosives, characterized by much higher detonation velocity, are clearly separated from ANFO data, thus indicating a dependence on explosive type. This unique dual Sayarim explosion experiment (August 2009/January 2011), with the strongest GT0 sources since the establishment of the IMS network, clearly demonstrated the most favorable westward/eastward infrasound propagation up to 3,400/6,250 km according to appropriate summer/winter weather pattern and stratospheric wind directions, respectively, and thus verified empirically common models of infrasound propagation in the atmosphere.     

Constraints on Glacial Isostatic Adjustment from GOCE and Sea Level Data

Current constraints on the glacial isostatic adjustment (GIA) process are mainly provided by relative sea-level data and GPS measurements. Due to a lack of resolving power in the shallow earth (down to about 200 km), these data sets only provide weak constraints on the shallow viscosity structure and the thickness of the lithosphere. Future high-resolution gravity data, as expected from ESA’s Gravity field and steady-state Ocean Circulation Explorer (GOCE) launched on March 17, 2009, are predicted to provide additional information on the shallow earth, more specifically the viscosity structure. Here we present an overview of recent developments in extracting information on rheology and stratification of the shallow earth from high-resolution quasi-steady gravity and geoid data to be obtained from GOCE.     

Seismic Attenuation Computed from GLIMPCE Reflection Data and Comparison with Refraction Results

—Instantaneous frequency matching has been used to compute differential t* values for seismic reflection data from the Great Lakes International Multidisciplinary Program on Crustal Evolution (GLIMPCE) experiment. The differential attenuation values were converted to apparent Q ^?1 models by a fitting procedure that simultaneously solves for the interval Q ^?1 values using non-negative least squares. The bootstrap method was then used to estimate the variance in the interval Q ^?1 models. The shallow Q ^?1 structure obtained from the seismic reflection data corresponds closely with an attenuation model derived using instantaneous frequency matching on seismic refraction data along the same transect. This suggests that the effects of wave propagation and scattering on the apparent attenuation are similar for the two data sets. The Q ^?1 model from the reflection data was then compared with the structural interpretation of the reflectivity data. The highest interval Q ^?1 values (>0.01) were found near the surface, corresponding to the sedimentary rock sequence of the upper Keweenawan. Low Q ^?1 values (<0.0006) are found beneath the Midcontinent rift’s central basin. In addition to structural interpretation, seismic attenuation models derived in this way can be used to correct reflection data for dispersion, frequency and amplitude effects, and allow for improved imaging of the subsurface.     

基于NGA数据的震源模型全局参数定标律的统计

依据美国NGA两个版本的数据库,修正、补充了文献[3]的震源全局参数基础数据,形成分别包含189个地震的数据1和204个地震的数据2,分别在三种破裂类型、五(三)个震级段,统计得出矩震级与破裂面的面积、宽度、长度以及破裂面上平均错动量四个震源全局参数之间的经验关系和半经验关系。与文献[3]的结果比较表明,数据量增加后系数值的差异不明显,最大相对差分别为12.4%和8.4%,且统计结果离散减小,稳定性增加。采用本文结果建立震源模型,对一个7.0级走滑地震合成的近场4个地表点的高频地震动,得到的平均反应谱幅值、峰值总体上略大于用文献[3]参数合成的,平均值的相对差在4.6%~23.0%间,随距离增加差别有所减小。     

Travel-times and Attenuation Relations for Regional Phases in the Barents Sea Region

A database containing 45 events in the Barents Sea region has been compiled and analyzed with the aim of evaluating crustal models, travel-times and attenuation relations in the context of performing regional detection threshold monitoring of this region. The 45 events are mostly located around the circumference of the study area due to the virtually aseismic nature of the Barents Sea itself. Regional P _n and S _n phases were observable for most events in the database, while P _g and L _g phases were only observable for events with raypaths that do not cross the tectonic structures in the Barents Sea. This corroborates a number of previous observations of L _g -wave blockage within the Barents Sea. Three existing velocity models were evaluated, with a model having slightly lower S velocities than earlier assumed in the upper mantle giving the overall best fit to the observed arrivals. In order to estimate magnitudes, short-term average (STA) and spectral amplitude values were calculated in several frequency bands for all phase arrivals in the database. There were no significant differences between spectral and STA amplitudes, so the latter were used as this parameter is more efficient to calculate in real-time processing. An inversion was performed in order to determine an attenuation relation specific for this region. The resulting magnitudes based on P _n , P _g , S _n and L _g phases gave an internally consistent, reasonably stable set of values, which can be calibrated towards any existing global or regional scale.     

地震安全性评价中地震动衰减关系的类型及其选取

通过阐述地震安全性评价工作中地震动衰减关系的演变介绍了衰减关系的三种类型,其差别在于是否含有高频地震动震级饱和因子C3M2项和加速度近场饱和因子C5eC6M项;分析了这两个因子的由来和作用,并举实例说明,当场地所处的地震环境受高频地震动影响较小时,可忽略C3M2项的影响;而加速度近场饱和因子因包含了震源体尺度的影响,并与实际观测记录相符,是衰减关系必须包含的内容。     

Source Parameters and Scaling Relations for Reservoir Induced Seismicity in the Longtan Reservoir Area

We investigate the relationship between the impoundment and seismicity in the Longtan reservoir, southwestern China and find evidence that the seismicity was reservoir induced. After the reservoir impoundment, a pronounced increase in seismicity was observed in five clusters mainly concentrated in the areas where few earthquakes had occurred before the first filling. The observed induced seismicity shows a strong correlation with the filling cycles. The activity levels in the five clusters are different due to differences in the structures and permeabilities of the faults. Source parameters for 1,616 earthquakes with M _L 0.1–4.2 recorded by 24 fixed and temporary stations deployed around the reservoir were calculated after applying corrections for geometrical spreading, frequency-dependent Q, and site effects. The static stress drop and apparent stress in this area both appear to increase with increasing seismic moment over the entire magnitude range. Our results show that reservoir induced earthquakes have ten times lower average stress drop than natural tectonic earthquakes. These results may indicate that the reservoir induced seismicity can occur with a lower tectonic stress due to the high pore pressures of the underground medium, and that the effect of the water decreases the coefficient of friction.     

福建及邻区水平基岩加速度反应谱衰减关系

收集福建及邻区内既有仪器测定震级又有宏观烈度调查资料的28次破坏性地震资料,并对上述资料进行烈度等效处理、近远场补点、数据加权处理,加强对大震近场与远场的控制,建立了适合本区的地震烈度衰减关系;利用最新得出的美国西部基岩水平向地震加速度反应谱衰减关系,采用转换方法建立了本区的基岩水平向地震加速度反应谱衰减关系;并与华南地区的地震动参数衰减关系进行了对比,其结果更加符合该区近代地震震害分布的地域性特征.所得结果可应用于该区的地震安全性评价、震害预测、损失快速评估等防震减灾领域.     

中国东部和西部地区水平向基岩加速度反应谱衰减关系

根据核安全法规和导则,对核电厂选址地震安全评价中发震构造与能动断层的关系,以及发震构造与能动断层鉴定的时代问题进行了分析,并结合近年来核电厂选址评价中存在的问题,对发震构造与能动断层的评价方法进行了探讨。     

地震资料叠前去噪技术的现状与未来

地震资料叠前去噪是勘探地震资料处理的关键问题之一，但这个问题长期以来一直没有得到很好的解决，是提高地震资料分辨率的一个主要障碍，其中，如何有效地消除产生与地层间的多次反射波又是地震资料叠前去噪的核心问题。为此，人们进行了长期不懈的努力，以更好地消除多次波。本文着重概述现今实生常中常用的几种比较有效的消除多次波方法，包括拉冬变换，F－K方法和聚束滤波方法；同时也概述了预测反积消除水层混响和用K－L变换方法消除随机噪音提高信噪比等方法；最后，还讨论了近年发展的地震资料叠前去噪新方法及其发展趋势。     

广西龙滩库区地震震源参数定标关系

利用广西龙滩数字地震台网记录的2006年9月—2013年7月1284次ML1.0级以上地震波形资料,采用Brune（1970）模型,通过几何扩散校正,介质衰减校正,仪器校正等将速度记录谱归算为震源位移谱,使用遗传算法计算拐角频率及零频极限,然后计算地震矩、应力降等小震震源参数,给出各种参数之间的定标关系。研究表明：地震矩、近震震级、破裂半径、矩震级和拐角频率等之间可以拟合为对数或半对数线性关系。而应力降、视应力降分布都比较零散,与地震矩、震源半径的关系并不明显,随地震矩、震源半径的变化关系比较弱。     

Constraints on velocity-depth trends from rock physics models

Estimates of depth, overpressure and amount of exhumation based on sonic data for a sedimentary formation rely on identification of a normal velocity–depth trend for the formation. Such trends describe how sonic velocity increases with depth in relatively homogeneous, brine‐saturated sedimentary formations as porosity is reduced during normal compaction (mechanical and chemical). Compaction is ‘normal’ when the fluid pressure is hydrostatic and the thickness of the overburden has not been reduced by exhumation. We suggest that normal porosity at the surface for a given lithology should be constrained by its critical porosity, i.e. the porosity limit above which a particular sediment exists only as a suspension. Consequently, normal velocity at the surface of unconsolidated sediments saturated with brine approaches the velocity of the sediment in suspension. Furthermore, porosity must approach zero at infinite depth, so the velocity approaches the matrix velocity of the rock and the velocity–depth gradient approaches zero. For sediments with initially good grain contact (when porosity is just below the critical porosity), the velocity gradient decreases with depth. By contrast, initially compliant sediments may have a maximum velocity gradient at some depth if we assume that porosity decreases exponentially with depth. We have used published velocity–porosity–depth relationships to formulate normal velocity–depth trends for consolidated sandstone with varying clay content and for marine shale dominated by smectite/illite. The first relationship is based on a modified Voigt trend (porosity scaled by critical porosity) and the second is based on a modified time‐average equation. Baselines for sandstone and shale in the North Sea agree with the established constraints and the shale trend can be applied to predict overpressure. A normal velocity–depth trend for a formation cannot be expressed from an arbitrary choice of mathematical functions and regression parameters, but should be considered as a physical model linked to the velocity–porosity transforms developed in rock physics.     

New Palaeomagnetic Data from the Betic Cordillera: Constraints on the Timing and the Geographical Distribution of Tectonic Rotations in Southern Spain

—A palaeomagnetic investigation has been carried out at 14 sites on Jurassic red nodular limestones from the central and eastern part of the External Zones of the Betic Cordillera (Subbetic and Prebetic Zones). Progressive thermal demagnetisation of samples from the Subbetic Zone reveals the presence of two stable magnetic components of the natural remanent magnetisation: 1) a secondary Neogene syn-folding component and 2) the original Jurassic magnetisation. As similar characteristics have been reported in Jurassic limestones from the western Subbetic Zone, a widespread remagnetisation event took place within <10⁶ years in the entire Subbetic region during Neogene times. In contrast, in the Prebetic region, no evidence for a secondary overprint has been detected. Palaeomagnetic Jurassic declinations indicate variable and locally very large clockwise rotations (35°–140°), but the two sites in the north-westernmost part of the investigated region are not rotated. The use of both components of magnetisation and the incremental fold-test results allowed the timing of block rotations in the Subbetic Zone to be constrained. Rotations in the western Subbetic occurred after the acquisition of the secondary overprint, whereas in the central part of the Subbetic Zone they were completed by the time of the remagnetisation event.     

Attenuation Tomography Based on Strong Motion Data: Case Study of Central Honshu Region, Japan

Three-dimensional frequency dependent S-wave quality factor (Q_β(f)) value for the central Honshu region of Japan has been determined in this paper using an algorithm based on inversion of strong motion data. The method of inversion for determination of three-dimensional attenuation coefficients is proposed by Hashida and Shimazaki (J Phys Earth. 32, 299–316, 1984) and has been used and modified by Joshi (Curr Sci. 90, 581–585, 2006; Nat Hazards. 43, 129–146, 2007) and Joshi et al. (J. Seismol. 14, 247–272, 2010). Twenty-one earthquakes digitally recorded on strong motion stations of Kik-net network have been used in this work. The magnitude of these earthquake ranges from 3.1 to 4.2 and depth ranging from 5 to 20 km, respectively. The borehole data having high signal to noise ratio and minimum site effect is used in the present work. The attenuation structure is determined by dividing the entire area into twenty-five three-dimensional blocks of uniform thickness having different frequency-dependent shear wave quality factor. Shear wave quality factor values have been determined at frequencies of 2.5, 7.0 and 10 Hz from record in a rectangular grid defined by 35.4°N to 36.4°N and 137.2°E to 138.2°E. The obtained attenuation structure is compared with the available geological features in the region and comparison shows that the obtained structure is capable of resolving important tectonic features present in the area. The proposed attenuation structure is compared with the probabilistic seismic hazard map of the region and shows that it bears some remarkable similarity in the patterns seen in seismic hazard map.     

建筑物下爆破地震效应的研究——"爆破安全规程"的应用与修正

叙述了大姚铜矿的大药量爆破振动效应观测,研究了在建筑物下的爆破施工中,如何确保建筑物安保证安全生产最大用药量的问题,结合“爆破安全规程”药量指数m的应用与修正,从而得出正在对爆破上方的建筑物地面爆破振动动加速度a,速度v随爆心距地面投影r与爆心深度h之比值（r/h)的衰减变化规律;发现临近正对爆心的地面振动有强心现象,并定义它为“极震”效应;定义“极震”效应系数N为正对爆心实测加速度a或速度v与用振动衰减普适式求得值a'或v'之比（N＝a/a',或N=v/v'）。经多年的安全生产证明,采用振动衰减普适式（药量指娄m=1/3)和“极震”效应系数修正法,效果良好,获得生产最佳用药量,民房安全率达98％左右。     

Analysis of Soil Vapor Extraction Data to Evaluate Mass-Transfer Constraints and Estimate Source-Zone Mass Flux

Methods are developed to use data collected during cyclic operation of soil vapor extraction (SVE) systems to help characterize the magnitudes and time scales of mass flux associated with vadose zone contaminant sources. Operational data collected at the Department of Energy’s Hanford site are used to illustrate the use of such data. An analysis was conducted of carbon tetrachloride vapor concentrations collected during and between SVE operations. The objective of the analysis was to evaluate changes in concentrations measured during periods of operation and nonoperation of SVE, with a focus on quantifying temporal dynamics of the vadose zone contaminant mass flux, and associated source strength. Three mass flux terms, representing mass flux during the initial period of an SVE cycle, during the asymptotic period of a cycle, and during the rebound period, were calculated and compared. It was shown that it is possible to use the data to estimate time frames for effective operation of an SVE system if a sufficient set of historical cyclic operational data exists. This information could then be used to help evaluate changes in SVE operations, including system closure. The mass flux data would also be useful for risk assessments of the impact of vadose zone sources on groundwater contamination or vapor intrusion.     

用临界点理论讨论应变能加速释放现象和孕震区尺度

20世纪 80年代后期 ,地震的临界现象研究成为地震学界的热点之一。Hirata等 ( 1 987)通过大量实验和观测结果得出结论 :接近破裂的岩石与铁磁模型的二阶相变具有本质上的联系。岩石中的应力参数类似于铁磁相变中的温度参数 ,即低应力状态时 ,微裂纹随机产生且微裂纹之间关联程度较低 ;当应力达到岩石的破裂强度时 ,裂纹相互关联 ,裂纹大小呈幂率 (分形 )分布。根据临界点理论 ,地震孕育过程是一种临界现象 (Vere Jones ,1 977;Sornette ,etal.,1 990 ;1 995;Rundle ,etal.,1 999;Jaume ,etal.,1 999) ,但地壳并不总是处于临界状态。随着…