共查询到20条相似文献，搜索用时 140 毫秒
1.
Locating microseismic events using borehole data 总被引：1，自引：0，他引：1
Constraining microseismic hypocentres in and around hydrocarbon reservoirs and their overburdens is essential for the monitoring of deformation related to hydraulic fracturing, production and injection and the assessment of reservoir security for CO2 and wastewater storage. Microseismic monitoring in hydrocarbon reservoirs can be achieved via a variety of surface and subsurface acquisition geometries. In this study we use data from a single, subsurface, vertical array of sensors. We test an existing technique that uses a 1D velocity model to constrain locations by minimizing differential S‐to‐P arrival times for individual sensors. We show that small errors in either arrival time picks or the velocity model can lead to large errors in depth, especially near velocity model discontinuities where events tend to cluster. To address this issue we develop two methods that use all available arrival times simultaneously in the inversion, thus maximizing the number of potential constraints from to N, where N is the number of phase picks. The first approach minimizes all available arrival time pairs whilst the second approach, the equal distance time (EDT) method defines the hypocentre as the point where the maximum number of arrival time surfaces intersect. We test and compare the new location procedures with locations using differential S‐to‐P times at each individual sensor on a microseismic data set recorded by a vertical array of sensors at the Ekofisk reservoir in the North Sea. Specifically, we test each procedure's sensitivity to perturbations in measured arrival times and the velocity model using Monte Carlo analysis. In general, location uncertainties increase with increasing raypath length. We show that errors in velocity model estimates are the most significant source of uncertainty in source location with these experiments. Our tests show that hypocentres determined by the new procedures are less sensitive to erroneous measurements and velocity model uncertainties thus reducing the potential for misinterpretation of the results. 相似文献
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—?The verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) requires the determination of accurate location of seismic events from a fixed network of seismic stations across the globe. The requirements of possible on-site inspections mean that the goal is to place the location estimate in a zone smaller than 1000 km2 that includes the true location. Because a defined set of stations will be used, corrections can be refined to represent the influence of departures from the global reference model IASPEI91. The primary stations in the International Monitoring Scheme (IMS) are mostly seismic arrays and therefore the present location scheme is based on minimisation of a misfit function built from arrival time, azimuth and array slowness residuals. The effective network will change markedly with the magnitude of the event and as a result regional information has to be integrated into the location process. 相似文献
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Tobias Friedrich Toni Zieger Thomas Forbriger Joachim R. R. Ritter 《Journal of Seismology》2018,22(6):1469-1483
We present a case study on the detection and quantification of seismic signals induced by operating wind turbines (WTs). We spatially locate the sources of such signals in data which were recorded at 11 seismic stations in 2011 and 2012 during the TIMO project (Deep Structure of the Central Upper Rhine Graben). During this time period, four wind farms with altogether 12 WTs were in operation near the town of Landau, Southwest Germany. We locate WTs as sources of continuous seismic signals by application of seismic interferometry and migration of the energy found in cross-correlograms. A clear increase of emitted seismic energy with rotor speed confirms that the observed signal is induced by WTs. We can clearly distinguish wind farms consisting of different types of WTs (different hub height and rotor diameter) corresponding to different stable frequency bands (1.3–1.6 Hz, 1.75–1.95 Hz and 2.0–2.2 Hz) which do not depend on wind speed. The peak frequency apparently is controlled by the elastic eigenmodes of the structure rather than the passing of blades at the tower. From this we conclude that vibrations are coupled into the ground at the foundation and propagate as Rayleigh waves (and not as infrasound). The migration velocity of 320 m/s corresponds to their group velocity. The applied migration method can contribute to the assessment of local sources of seismic noise. This topic gets growing attention in the seismological community. In particular, the recent boost of newly installed wind farms is a threat to seismological observatories such as the Black Forest Observatory (BFO) and the Gräfenberg array (GRF) or gravitational wave observatories (e.g. LIGO, VIRGO) in terms of a sensitivity degradation of such observatories. 相似文献
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In this paper, we developed a specialized method to locate small aftershocks using a small-aperture temporary seismic array.
The array location technique uses the first P arrival times to determine the horizontal slowness vector of the incoming P wave, then combines it with S–P times to determine the event location. In order to reduce the influence of lateral velocity variation on the location determinations,
we generated slowness corrections using events well-located by the permanent broadband network as calibration events, then
we applied the corrections to the estimated slownesses. Applications of slowness corrections significantly improved event
locations. This method can be a useful tool to locate events recorded by temporary fault-zone arrays in the near field but
unlocated by the regional permanent seismic network. As a test, we first applied this method to 64 well-located aftershocks
of the 1992 Landers, California, earthquake, recorded by both the Caltech/USGS Southern California Seismic Network and a small-aperture,
temporary seismic array. The average horizontal and vertical separations between our locations and the well-determined catalogue
locations are 1.35 and 1.75 km, respectively. We then applied this method to 132 unlocated aftershocks recorded only by the
temporary seismic array. The locations show a clear tendency to follow the surface traces of the mainshock rupture. 相似文献
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Locating an earthquakes focal depth is always a key project in seismology. Precise focal depth is of critical importance for evaluating seismic hazards, deciphering dynamic mechanisms of earthquake generating,estimating aftershock evolutions and risk,as well as monitoring nuclear tests. However,how we determine an accurate focal depth is always a challenge in seismological studies. Aiming to solve these problems, we analyzed and summarized the present status and the future development of earthquake focal depth locating. In this paper we first reviewed the present status of focal depth locating in the world,and summarized the frequently-used relocating methods and ideas at present,and introduced two types of focal depth relocating ideas: arrival time relocating and waveform modeling methods. For these ideas,we systematically described the S-P and the Pn-Pg methods that belong to arrival time method,and polarization focal depth locating and amplitude focal depth locating that belongs to waveform modeling,and further analyzed the advantages and limitations of these methods. Since the depth phase methods are highly sensitive to focal depth,and are relatively free from the uncertainties of crustal models,we mainly reviewed the depth phases of s Pm P,s PL,s Pn,and s Sn,and quantitatively evaluated their availabilities and characteristics. Second,we also discussed the effects of crustal velocity models on the reliability of focal depth locating,and reviewed the advancements of seismic tomography techniques over recent years. Finally,based on the present status of the progress on the focal depth locating,and studies of seismic velocity structures,we proposed an idea of combining multiple datasets and relocating methods,jointly utilizing seismologic and geodetic techniques to relocate focal depth,which should be the major research field in investigating focal depth and source parameters in the near future. 相似文献
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上海数字地震台网监测能力评估 总被引：6，自引：0，他引：6
利用近震震级公式,分别对上海数字地震台网监测能力、上海佘山地震台阵作为一个加强台站与上海数字地震台网联合定位的监测能力进行估算并比较两者的评估结果,同时利用上海台网的地震记录对评估结果进行检验.结果显示,把台阵作为加强台站加入台网进行联合定位时,台网的监测能力明显提高,本次评估结果基本符合实际上海数字地震台网真实地震监测能力. 相似文献
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We use controlled-source seismic interferometry (SI) and inversion in a unique way to estimate the location of near-surface scatterers and a corner diffractor by using non-physical (ghost) scattered surface and body waves. The ghosts are arrivals obtained by SI due to insufficient destructive interference in the summation process of correlated responses from a boundary of enclosing sources. Only one source at the surface is sufficient to obtain the ghost scattered wavefield. We obtain ghost scattered waves for several virtual-source locations. To determine the location of the scatterer, we invert the obtained ghost traveltimes by solving the inverse problem. We demonstrate the method using scattered surface waves. We perform finite-difference numerical simulations of a near-surface scatterer starting with a very simple model and increase the complexity by including lateral inhomogeneity. Especially for the model with lateral variations, we show the effectiveness of the method and demonstrate the estimation of the subsurface location of a corner diffractor using S-waves. In all models we obtain very good estimations of the location of the scatterer. 相似文献
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The matched filter can be used to identify the location of a specific signal embedded in background correlated noise. The
maximum filter output indicates the likely location and, with appropriate statistical assumptions on the noise, it also serves
as a test statistic in the probabilistic evaluation of the filter’s performance. Different setups of the Neyman-Pearson statistical
hypothesis test yield predictions of either the probability of a miss or that of a false alarm. The needed statistics of the
maximum filter output are properly obtained using the distribution of order statistics. Through Monte Carlo simulations, we
analyzed the ability of the matched filter to identify a sub-surface anomaly in typically correlated gravity fields using
observations of elements of the gravity gradient tensor. We also evaluated the reliability of the hypothesis testing and the
associated predicted probabilities of misses and false alarms. Our simulations and statistical analyses confirm that the power
of the tests increases as the signal strength increases and as more gradient tensor components per observation point are included.
We also found that the hypothesis test that is designed to predict the probability of a miss is more robust and powerful than
the one for predicting a false alarm. Moreover, the probability of a miss is somewhat smaller than the probability of a false
alarm under otherwise equal circumstances. 相似文献
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选取了2003年1月~2004年4月河北省及邻省ML≥2.0级地震149个,针对每个地震记录的具体情况,综合考虑最大空隙角、近台距离、远台距离、台数等因素,选取台站分布相对合理的4~12个台站,利用首都圈数字地震台网交互处理系统提供的Hypo81、GELor-p、Genetic3种定位方法分别进行定位处理,将3种定位结果与全国地震月报目录进行对比得到定位偏差量,定量分析了3种定位方法的定位偏差量随空隙角的变化,探讨了Hypo81、GELor-p、Genetic3种定位方法的定位效果、稳定性及适用性。 相似文献
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Locating the zone of saline intrusion in a coastal karst aquifer using springflow data 总被引：2，自引：0，他引：2
Coastal fresh water aquifers are an increasingly desirable resource. In a karstic aquifer, sea water intrusion occurs as a salt water wedge, like in porous media. However, preferential flow conduits may alter the spatial and temporal distribution of the salt water. This is typically the case when the outlet of the aquifer is a brackish spring. This paper shows that salinity and flow rate variations at a spring, where salinity is inversely proportional to discharge, can help to understand the hydrodynamic functioning of the aquifer and to locate the fresh water-sea water mixing zone deep inside the aquifer. The volume of water-filled conduit between the sea water intrusion zone and the spring outlet is calculated by the integral over time of the flow rate during the time lag between the flow rate increase and the salinity decrease as measured at the spring. In the example of the spring at Almyros of Heraklio (Crete, Greece), this time lag is variable, depending on the discharge, but the volume of water-filled conduit appears to be constant, which shows that the processes of salt water intrusion and mixing in the conduit are constant throughout the year. The distance between the spring and the zone where sea water enters the conduit is estimated and provides an indication of the position where only fresh water is present in the conduit. 相似文献
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Tilt梯度及其水平导数提取重磁源边界位置 总被引：7，自引：6，他引：1
探讨了用于探测异常源边界和形状的Tilt梯度及其水平导数的方法及其性质．通过模型试算,论证了Tilt梯度及其水平导数的有效性,并从理论上给予了证明．Tilt梯度及其水平导数的方法及其性质可广泛用于区域重磁异常的构造解释之中。 相似文献
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Groundwater springs are significant landscape features for humans and the biota that occupies their habitat. Many springs become inactive where groundwater exploitation by humans has lowered the water table or artesian pressure. In order to assess this impact, it is important to identify and locate active, and with more difficulty, inactive springs. Using a variety of archival, environmental and field‐based data, this study presents a protocol for the determination of the location and status of springs across the Great Artesian Basin of Australia. This protocol underpins a database of springs, which is not only important for the assessment of spring ecosystems, but also contributes to understand groundwater extraction impacts and hydrogeological processes. The database indicates that 30.0% of discharge (artesian) springs in the Great Artesian Basin are entirely inactive and another 11.8% are partially inactive. For the outcrop (gravity) springs of the Basin, only 1.9% are entirely inactive and 7.4% partially inactive, and for the outcrop springs in the Tertiary sandstone overlying the Basin 30.9% are inactive and 18.2% are partially inactive. 相似文献
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用PTD方法测定巴林左旗5.9级地震震源深度 总被引：8，自引：0，他引：8
震源深度是描述震源的最基本参数之一, 给出了地震发生在地球内部的具体位置, 对了解地震孕育和发生的物理化学条件, 以及地震能量集结、 释放的活动构造背景都有重要的意义。 根据PTD方法, 对2003年8月16日发生的内蒙古自治区巴林左旗5.9级地震的震源深度进行了测定, 测定震源深度为20 km, 与东北地震构造区地震平均深度11±5 km相比偏深。 文中进一步分析讨论了对测定结果产生误差的各种因素, 给出了减小误差的应对措施; 在此基础上结合相关研究成果对地震区周围的地壳P波速度结构进行了探讨, 给出了具体的P波二层均匀速度结构。 相似文献