共查询到20条相似文献，搜索用时 140 毫秒
1.
《世界地震译丛》2016,(1)
建筑规范中,地表到地下30m深度的走时平均剪切波速度[VS(30)]是场地分类的重要参数。利用在两个不同深度[VS(z1)和VS(z2),且z1z230m]下得到的走时平均剪切波速度,提出了用井孔中测量的浅层剪切波速度剖面估计VS(30)的新方法。选用剪切波速度剖面达30m的日本KiK-net台网594个井孔和美国加利福尼亚州的135个井孔的数据,通过VS(30)实测值与VS(30)估计值之间的相关性和用VS(30)估算值给出场地分类的准确性验证了该新方法的可靠性。结果显示,该方法可以提高VS(30)的准确度,且VS(30)的实测值与估算值之间的皮尔逊相关系数等于0.999,VS(30)的估算值给出的场地分类准确率大于96%,而z1≥10m,z2=25m。利用来自日本的数据研究了VS(z)的实测值与估算值在6个不同深度(50,100,150,200,400,600m)时的相关性,结果表明当所选的两个深度(z1,z2)接近某个深度z时,利用该假设方法估算的VS(z)(z≥50m)的准确度有所提高。相比Boore(2004)和Boore等(2011)的方法,新方法不需要对大量场地做回归分析以获得经验关系,没有区域性依赖,准确度有显著提高,且在世界的许多地方均有潜在的用途。 相似文献
2.
重力数据的密度界面反演是位场数据解释中的一项主要工作,在区域构造演化、深部莫霍面确定等领域的研究中发挥重要作用.近年来,数据驱动的深度学习方法广泛地应用在地球物理数据处理与反演中,本文提出一种基于深度学习U-net网络的重力数据密度界面反演方法.首先,对半椭球体界面模型进行随机抽取和组合进而形成地下起伏界面数据集,并基于Parker正演理论对界面数据集进行重力异常正演计算,为深度学习网络模型的训练提供特征完备的数据源;其次,设计了基于U-net网络模型的深度学习界面反演算法,在传统的损失函数基础上增加光滑损失项和过拟合抑制项,提高重力界面反演结果的光滑性和收敛效率;最后通过测试样本集进行反演预测,验证建立深度学习网络模型的泛化性.本文通过理论模型和实际数据试验分析了本文方法在密度界面反演中的有效性和实用性,基于改进损失函数约束的深度学习界面反演方法有效地提高了密度界面反演的收敛效率和计算稳定性. 相似文献
3.
断层识别是地震解释的一项重要任务.相对传统的基于人工或半人工的断层检测方法,基于深度学习的断层检测方法具有自动化程度高等特点,近年来已经吸引了业界广泛兴趣.目前,大多数利用深度学习的断层识别方法都是基于语义分割或图像分类,但基于语义分割或图像分类的方法预测出的断层噪声较多.而边缘检测网络可以通过学习断层在地震剖面中不连续的特征,从而提高网络的抗噪能力.为了利用边缘检测网络的抗噪优点并提升其性能,本文采用基于像素差分的卷积运算构建出像素差分网络模型(Pixel Difference Networks, Pidinet).相较于传统的边缘检测网络,Pidinet将传统的边缘检测算子与深度学习网络结合,有效地提升了边缘检测的效果.为了使Pidinet网络更好地预测断层,本文对原始Pidinet网络进行了优化,去掉了相对断层识别任务而言多余的分支结构和卷积层.相对于传统的卷积运算,基于像素差分的卷积运算可以让神经网络更好地学习断层信息.为了让网络充分学习数据中的断层特征,本文将真实地震样本与合成地震样本混合得到训练所用数据集.实验证明Pidinet在交并比(Intersection over ... 相似文献
4.
《地球物理学进展》2020,(2)
在本文中,我们基于模型试验讨论了利用等效源实现剖面重力异常转换的可靠性,并针对发现的问题提出了一套场源设置优化策略:(1)沿剖面两侧对等效源层和观测数据扩边;(2)通过局部异常单调变化区间个数的整倍数控制等效源层中线质量的数量;(3)利用Tikhonov正则化确保反演的稳定性,并在迭代计算过程中维持条件数不变.合成模型试验表明:(1)单独对等效源层扩边可以消除异常导数在剖面边界附近的振荡,同时对等效源和数据扩边则可以进一步抑制垂向一阶导数和向上延拓计算值与理论值之间的剪刀差;(2)以深度偏移量、倍数、单侧扩边距离以及条件数为控制参数的等效源设置方式具有良好的可操作性.最后,我们将这些优化措施应用在了一条实测重力剖面上,并取得了与模型试验类似的结果. 相似文献
5.
重力异常:过去断层运动的化石证据 总被引：1，自引：0，他引：1
《地球物理学进展》1991,(4)
地球表面上的不同地区的重力值是不相同的,油储上方的重力值比较低就是一个好例子。于是,地球物理学家推测:地下物质的非均匀分布是引起重力异常的主要原因(重力异常是局部重力值归算到大地水准上与理论重力值之差)。但意想不到的是,在日本的北伊豆断层系(简称NIFS),我们发现了一个完全不同类型的重力异常(图1),它的象限图型强有力地说明断层运动在重力异常的形成中起着主要作用(图2(a))。因此,重力异常很可能保留了过去地震断层活动的信息。 相似文献
6.
《地球物理学进展》2016,(4)
2014年8月跨越六盘山东麓断裂带,在长度约为200公里的剖面上展开了流动重力/GPS联合剖面观测.观测结果表明,测线东端的布格重力异常约为-190 m Gal(10~(-5)ms~(-2)),西端则为-250 m Gal左右.在假设地壳均一的前提下,基于Airy均衡模型,利用布格重力异常和GPS观测数据,分别计算了测线所在剖面的莫霍面深度与均衡面深度,发现六盘山地区处于正均衡异常状态.使用布格重力异常数据反演六盘山地区的地壳密度结构,并据此地壳分层结构,计算了六盘山地区均衡面与莫霍面深度,对比显示该区域亦处于均衡正异常状态.为了确定青藏高原东北缘岩石圈有效弹性厚度和六盘山隆升机制,我们利用EMG2008自由空气异常和SRTM V18.1 DEM数据,使用自由空气重力异常导纳方法,研究了以六盘山地区为中心的青藏高原东北缘岩石圈有效弹性厚度(Te)和加载机制,发现六盘山地区的Te为5 km,岩石圈加载主要来自于地表,占总加载的95%.最后,对比六盘山地区Airy均衡异常与弹性板均衡异常,发现六盘山东麓断层处地壳承载梯度值最大,表明该断裂带吸收了较多的应变能. 相似文献
7.
《地球物理学进展》2015,(4)
直升机航空瞬变电磁法一次作业覆盖面积广,数据采集量巨大,信息丰富,对于剖面成像解释有很大的优势.本文利用航空电磁数据量大的优势,采用微分电导参数与相关叠加相结合的技术,实现航空瞬变电磁快速成像解释.首先,利用等效导电平面法求取视纵向电导与视深度.然后,将纵向电导对视深度求二次导数获得微分电导参数.最后,利用相关叠加算法对微分电导数据进行合成,形成合成后的微分电导剖面,实现航空瞬变电磁相关叠加快速成像.利用文中所述的成像算法对模型数据和航空瞬变电磁实测数据进行解释分析,结果表明基于微分电导的相关叠加成像算法不仅具有很好的抗噪性,而且计算速度快可以进行实时成像,对于地下介质的电性分层具有较好的分辨,有效提高了航空瞬变电磁法的解释精度. 相似文献
8.
《地球物理学进展》1986,(1)
作为日本地热资源的综合的、全国性评价的一部分,做出了覆盖九州岛的第一份居里点深度图。该图是根据反演区域航空磁测网格数据做出的,这里提出了根据点偶极子分布反演网格数据的两种令人满意的算法。第一种算法通过计算傅里叶变换径向频谱的最小二乘拟合,估算这种分布的质心坐标x_0、y_0和z_0,第二种算法通过计算频谱振幅平方的最小二乘拟合,只估算质心深度,至于点偶极子集合的顶部平均深度z_t,由第二种算法的改变来估算,作为居里点深度的偶极子底部度深为zb=2z_0-z_t。由深度估计量用手画等值线得到最后的图,用居里点深度图与区域地质和热流数据,以及有限的重力数据作比较,居里点深度和热流以及区域地质之间有很好的相关,在重力和居里点深度之间观察到的空间相关被认为是次级的构造效应。目前正在运转着的地热发电站的位置与最浅的居里点深度相对应,根据这些比较,我们得出结论,这些方法提供了地质上合理的结果,而在全国性的地热评价计划中是合用的。 相似文献
9.
东北地区上地幔顶部深度及其深部构造特征 总被引：3，自引：0，他引：3
利用1/100万布格重力异常图,进行了东北地区上地幔顶部深度及其深部构造特征的研究.依据东北地学大断面深地震测深剖面的成果资料,参考本区及其邻区有关物探成果,结合东北地区复杂的地质构造背景,在东经115°～133°,北纬36°～50°范围内,切割了71条重力计算剖面,取得了10185个重力值。采用多边形线性积分与sinx/x计算方法,求得了东北地区上地幔顶部深度及其深部构造分布特征并对其进行了初步的分析与研究。 相似文献
10.
地质体的重力建模是正确解释和应用重力资料的关键问题之一.针对非规则形状变密度的三度体,本文提出了基于3D Delaunay剖分算法的重力建模方法.采用3D Delaunay剖分算法将三维目标地质体分解为若干变密度四面体体元,推导了基于四面体体元的重力正演公式,建立了剩余密度值与重力异常值的线性方程组;以变密度的长方体和倾斜台阶组合体为例,比较分析了常规块体算法和3D Delaunay剖分算法应用于重力正演的有效性,并采用共轭梯度法加密度约束条件对非规则形状变密度的倾斜台阶组合体进行了密度反演.计算结果验证了本文方法的正确性和有效性.基于3D Delaunay剖分算法的重力建模可应用于存在褶皱、断层、裂缝等复杂地质体的重力正反演计算. 相似文献
11.
Mohammad E. Hekmatian Vahid E. Ardestani Mohammad A. Riahi Ayyub M. K. Bagh Jalal Amini 《Acta Geophysica》2015,63(4):1000-1024
In gravity interpretation methods, an initial guess for the approximate shape of the gravity source is necessary. In this paper, the support vector classifier (SVC) is applied for this duty by using gravity data. It is shown that using SVC leads us to estimate the approximate shapes of gravity sources more objectively. The procedure of selecting correct features is called feature selection (FS).In this research, the proper features are selected using inter/intra class distance algorithm and also FS is optimized by increasing and decreasing the number of dimensions of features space. Then, by using the proper features, SVC is used to estimate approximate shapes of sources from the six possible shapes, including: sphere, horizontal cylinder, vertical cylinder, rectangular prism, syncline, and anticline. SVC is trained using 300 synthetic gravity profiles and tested by 60 other synthetic and some real gravity profiles (related to a well and two ore bodies), and shapes of their sources estimated properly. 相似文献
12.
An automatic inversion using ridge regression algorithm is developed in the space domain to analyze the gravity anomalies of sedimentary basins, among which the density contrast decreases with depth following a prescribed exponential function. A stack of vertical prisms having equal widths, whose depths become the unknown parameters to be estimated, describes the geometry of a sedimentary basin above the basement complex. Because no closed form analytical equation can be derivable in the space domain using the exponential density-depth function, a combination of analytical and numerical approaches is used to realize forward gravity modeling. The depth estimates of sediment-basement interface are initiated and subsequently improved iteratively by minimizing the objective function between the observed and modeled gravity anomalies within the specified convergence criteria. Two gravity anomaly profiles, one synthetic and a real, are interpreted using the proposed technique to demonstrate its applicability. 相似文献
13.
Depth Estimation from the Scaling Power Spectral Density of Nonstationary Gravity Profile 总被引：1，自引：0，他引：1
-- A technique to estimate the depth to anomalous sources from the scaling power spectra of long nonstationary gravity profiles is presented. The nonstationary profile is divided into piecewise stationary segments based on the criterion of optimum gate length in which the time-varying and time-invariant autocorrelation functions are similar. The division of a nonstationary into piecewise stationary allows identification of the portion of the crust with different geological histories, and using the stationary portion of the gravity profiles, more consistent depths to the anomalous sources have been obtained. The technique is tested with the synthetic gravity profile and applied along the Jaipur-Raipur geotransect in western and central India. The geotransect has been divided into four stationary parts: Vindhyan low, Bundelkhand low, Narmada rift and Chhattisgarh basin; each section corresponding to a different geological formation. Forward modeling of gravity data using results of each stationary section is carried out to propose the subsurface structure along the Jaipur-Raipur transect. 相似文献
14.
密度界面反演作为了解地球内部结构的一种重要方法,长期以来都是重力学研究的主要内容.本文结合抛物线密度模型及频率域算法的优点,将抛物线密度函数应用于Parker-Oldenburg算法,经过理论推导得到了抛物线密度模型的频率域公式,从而建立了基于抛物线密度模型的三维密度界面重力异常正反演的算法和流程.理论模型数据试验表明本方法快速、有效,适用于大多数浅部比深部增加更快的实际地壳密度.研究中还利用该方法对川滇地区重力异常进行了反演,获得了该区的莫霍面深度分布,并与接收函数研究结果进行对比分析,进一步验证了本文方法的正确性和有效性. 相似文献
15.
The Buyuk Menderes Graben is a depression in the Menderes core complex of western Turkey. The region is one of the most rapidly
deforming regions of continental crust in the world and has exceptionally high seismic activity. In this study, shallow and
deep seismic studies were conducted at the Buyuk Menderes graben. These studies included surface geological mapping and two
seismic reflection sections. Detailed modelling was performed with the seismic study. In addition to these, a moving windows
power spectrum was applied to the Bouguer gravity profile data of the study area. Since no deep well is available in this
area, the geological interpretation of the seismic stratigraphy is based on the correlation with the surface geology, this
was combined with the major reflections and the seismic facies observed along the profiles, and, thus, four main seismic units
can be distinguished in the basin fill. Structural features of the basin is driven by a complex extensional faults system,
consisting of a low-angle, S-dipping Buyuk Menderes detachment and by its synthetic and antithetic splays, bordering the opposite
flanks of the basin. As a result of conventional deep seismic reflection sections and gravity data, three layers were defined
in the study area. The first layer occurs at a thickness of 6 km, and the second layer is between 13 and 18 km. The third
layer is at ~33 km and may also emphasize Moho depth. The Buyuk Menderes graben has three clear reflectors which are base
sediments, brittle-ductile transition, Moho and faults that show a half-graben floored by a detachment. The Moho depth is
comparable with previous estimates. According to the results obtained, Bouguer gravity and seismic results are very much consistent
with each other. It was observed that at the depths determined from seismic and gravity data, the distribution percentage
of earthquake focal depths also rises. 相似文献
16.
We have developed a least-squares approach to determine simultaneously the depth to both the top and base of a buried finite
vertical cylinder (vertical line element approximation) and a 2-D vertical thin sheet from moving average residual anomaly
profiles obtained from gravity data using filters of successive window lengths. The method involves using a relationship between
the depth to the top, and base of the source and a combination of windowed observations. The method is based on computing
the standard deviation of the depths to the top, determined from all moving average residual anomalies for each value of the
depth to the base. The standard deviation may generally be considered a criterion for determining the correct depth to the
top and base of the buried structure. When the correct depth to the base value is used, the standard deviation of the depths
to the top is less than the standard deviation using incorrect values of the depth to the base. This method can be applied
to residuals as well as to the observed gravity data. The method is applied to synthetic examples with and without random
errors and tested on two field examples from the USA and Canada. 相似文献
17.
We develop an inversion procedure using the total variation (TV) regularization method as a stabilizing function to invert surface gravity data to retrieve 3-D density models of geologic structures with sharp boundaries. The developed inversion procedure combines several effective algorithms to solve the TV regularized problem. First, a matrix form of the gradient vector is designed using the Kronecker product to numerically approximate the 3-D TV function. The piecewise polynomial truncated singular value decomposition (PP-TSVD) algorithm is then used to solve the TV regularized inverse problem. To obtain a density model with depth resolution, we use a sensitivity-based depth weighting function. Finally, we apply the Genetic Algorithm (GA) to select the best combination of the PP-TSVD algorithm and the depth weighting function parameters. 3-D simulations conducted with synthetic data show that this approach produces sub-surface images in which the structures are well separated in terms of sharp boundaries, without the need of a priori detailed density model. The method applied to a real dataset from a micro-gravimetry survey of Gotvand Dam, southwestern Iran, clearly delineates subsurface cavities starting from a depth of 40 m within the area of the dam reservoir. 相似文献
18.
重力数据包含较多的低频信息,重力梯度数据包含较多的高频信息,将重力数据和重力梯度数据进行联合反演得到的结果更加可信.本文基于聚焦反演方法,实现了这一过程.因为联合反演中分量种类增加,所以计算灵敏度矩阵所需要的时间增加,为此,本文提出了一种快速计算灵敏度矩阵的方法.因为联合反演对内存的要求增大,本文选择有限内存BFGS拟牛顿法求解反演问题.本文通过再加权的方法实现深度加权.文中利用单一分量的反演结果来预测异常体的埋深信息,随后将埋深信息结合到深度加权函数中,将其用于多分量组合反演计算.给出了模型试验,发现预测得到的异常体的埋深信息与其实际埋深存在偏差,但是将这一信息应用到反演计算,能够得到与真实模型一致的结果.之后,本文通过模型试验来探究重力和重力梯度联合反演的优势,发现将重力和重力梯度数据联合,能够识别出额外的噪声,反演得到的模型更加合理.但是,对于不同分量组合得到的反演结果是相近的,反演模型的提高很小.最后,将联合反演方法应用到美国路易斯安那州Vinton岩丘的实际数据中,结果显示,将重力和重力梯度数据联合反演,反演模型得到了提高,反演得到的结果与地质资料吻合. 相似文献
19.
Accurate and Efficient Regularized Inversion Approach for the Interpretation of Isolated Gravity Anomalies 总被引：1，自引：0，他引：1
Salah A. Mehanee 《Pure and Applied Geophysics》2014,171(8):1897-1937
A very fast and efficient approach for gravity data inversion based on the regularized conjugate gradient method has been developed. This approach simultaneously inverts for the depth (z), and the amplitude coefficient (A) of a buried anomalous body from the gravity data measured along a profile. The developed algorithm fits the observed data by a class of some geometrically simple anomalous bodies, including the semi-infinite vertical cylinder, infinitely long horizontal cylinder, and sphere models using the logarithms of the model parameters [log(z) and log(|A|)] rather than the parameters themselves in its iterative minimization scheme. The presented numerical experiments have shown that the original (non-logarithmed) minimization scheme, which uses the parameters themselves (z and |A|) instead of their logarithms, encountered a variety of convergence problems. The aforementioned transformation of the objective functional subjected to minimization into the space of logarithms of z and |A| overcomes these convergence problems. The reliability and the applicability of the developed algorithm have been demonstrated on several synthetic data sets with and without noise. It is then successfully and carefully applied to seven real data examples with bodies buried in different complex geologic settings and at various depths inside the earth. The method is shown to be highly applicable for mineral exploration, and for both shallow and deep earth imaging, and is of particular value in cases where the observed gravity data is due to an isolated body embedded in the subsurface. 相似文献
20.
In hydraulic fracturing treatments, locating not only hydraulic fractures but also any pre‐existing natural fractures and faults in a subsurface reservoir is very important. Hydraulic fractures can be tracked by locating microseismic events, but to identify the locations of natural fractures, an additional technique is required. In this paper, we present a method to image pre‐existing fractures and faults near a borehole with virtual reverse vertical seismic profiling data or virtual single‐well profiling data (limited to seismic reflection data) created from microseismic monitoring using seismic interferometry. The virtual source data contain reflections from natural fractures and faults, and these features can be imaged by applying migration to the virtual source data. However, the imaging zone of fractures in the proposed method is strongly dependent on the geographic extent of the microseismic events and the location and direction of the fracture. To verify our method, we produced virtual reverse vertical seismic profiling and single‐well profiling data from synthetic microseismic data and compared them with data from real sources in the same relative position as the virtual sources. The results show that the reflection travel times from the fractures in the virtual source data agree well with travel times in the real‐source data. By applying pre‐stack depth migration to the virtual source data, images of the natural fractures were obtained with accurate locations. However, the migrated section of the single‐well profiling data with both real and virtual sources contained spurious fracture images on the opposite side of the borehole. In the case of virtual single‐well profiling data, we could produce correct migration images of fractures by adopting directional redatuming for which the occurrence region of microseismic events is divided into several subdivisions, and fractures located only on the opposite side of the borehole are imaged for each subdivision. 相似文献