考虑电流型畸变的大地电磁三维反演          下载免费PDF全文

李鑫  白登海  闫永利  马晓冰  孔祥儒 《地球物理学报》2016,59(6):2302-2315

大地电磁测深(MT)的观测数据易受到由近地表小尺度非均匀体或地形起伏引起的电流型畸变干扰,消除或压制这种干扰对获取可靠的深部电性结构至关重要.当区域结构为二维时,电流型畸变可采用张量分解等方法予以消除或压制.当区域结构为三维时,畸变问题更加复杂和严重,传统张量分解方法往往效果不佳或无效,严重地制约了MT三维反演技术的实用性.对此,本文提出一种考虑电流型畸变的MT三维反演算法,将完整的电流型畸变参数引入到目标函数,并采用非线性共轭梯度法与电阻率参数同时反演,从而达到压制畸变的目的.该算法有两个关键点:一是通过分析实测数据所遭受畸变的分布特征,在目标函数中对其进行有效约束;二是在迭代过程中,通过自适应地调整双正则化因子保障算法的稳定和效率.理论模型测试结果显示,常规三维反演算法不能合理解释数据中的畸变成分,而只能通过引入虚假异常体强制地拟合受畸变数据,从而造成电阻率模型严重失真.与之相比,本文算法能够在反演中自动求解各测点所受到的畸变,获得更接近真实的电阻率模型.  相似文献   

基于频域衰减的时域全波形反演   总被引：1，自引：1，他引：0       下载免费PDF全文

郭雪豹  刘洪  石颖 《地球物理学报》2016,59(10):3777-3787

时域全波形反演由于采用了全频段信息,因此在迭代过程中不同波长的信息不能由低到高的逐步重建,极易陷入局部极小值.本文通过分频段的方式,对地震数据做正反傅里叶变换,利用频域指数衰减的方法逐级分离出地震数据中的高频成分,在时域上实现由低频向高频的波形反演,从而降低了反演的非线性,使不同波长的信息得到稳步恢复.同时,在高频成分衰减的过程中,后至波的能量也被削弱,由此也降低了深层反射在初始反演过程中的干扰.整个反演仅增加对数据做正反傅里叶变换过程,相较于混合域反演,无需提取全部波场的相应频率成分.在计算效率方面,利用GPU进行加速,并采用CUDA自带函数库中cufft来提高计算效率.通过对Marmousi模型测试,验证了所述方法的有效性.  相似文献   

A preliminary empirical model for frequency-dependent attenuation of Fourier amplitude spectra In Serbia from the Vrancea earthquakes     

《Soil Dynamics and Earthquake Engineering》2016

We present the frequency-dependent attenuation model for Fourier amplitude spectra of strong earthquake ground motion in Serbia from intermediate depth earthquakes in the Vrancea source zone in Romania. The development of this type of scaling is the essential first step toward developing the corresponding attenuation and scaling equations for pseudo relative velocity spectra (PSV), which are necessary for seismic macro- and microzoning in the territory of Serbia. Such scaling is necessary because the Vrancea source zone produces large earthquakes with shaking that attenuates differently from the local earthquakes in Serbia. Development of such a scaling model is associated with several difficulties, the principal one being the lack of recorded strong motion accelerograms at epicentral distances exceeding 300 km. To reduce uncertainties with such scaling, we require our preliminary scaling equations to be consistent with independent estimates of seismic moment, stress drop, and radiated wave energy. In the future, when the recorded strong motion data from Vrancea earthquakes increases several-fold of what it is today, it will become possible to perform this analysis again, thus leading to more reliable and permanent scaling estimates.  相似文献   

Seismic response of deep Quaternary sediments in historical center of L’Aquila City (central Italy)     

《Soil Dynamics and Earthquake Engineering》2016

On 6 April 2009 a M_w=6.1 earthquake produced severe destruction and damage over the historic center of L’Aquila City (central Italy), in which the accelerometer stations AQK and AQU recorded a large amount of near-fault ground motion data. This paper analyzes the recorded ground motions and compares the observed peak accelerations and the horizontal to vertical response spectral ratios with those revealed from numerical simulations. The finite element method is considered herein to perform dynamic modeling on the soil profile underlying the seismic station AQU. The subsurface model, which is based on the reviewed surveys that were carried out in previous studies, consists of 200–400 m of Quaternary sediments overlying a Meso-Cenozoic carbonate bedrock. The Martin-Finn-Seed's pore-water pressure model is used in the simulations. The horizontal to vertical response spectral ratio that is observed during the weak seismic events shows three predominant frequencies at about 14 Hz, 3 Hz and 0.6 Hz, which may be related to the computed seismic motion amplification occurring at the shallow colluvium, at the top and base of the fluvial-lacustrine sequence, respectively. During the 2009 L’Aquila main shock the predominant frequency of 14 Hz shifts to lower values probably due to a peculiar wave-field incidence angle. The predominant frequency of 3 Hz shifts to lower values when the earthquake magnitude increases, which may be associated to the progressive softening of soil due to the excess pore-water pressure generation that reaches a maximum value of about 350 kPa in the top of fluvial-lacustrine sequence. The computed vertical peak acceleration underestimates the experimental value and the horizontal to vertical peak acceleration ratio that is observed at station AQU decreases when the earthquake magnitude increases, which reveals amplification of the vertical component of ground motion probably due to near-source effects.  相似文献   

Frequency staircases in narrow-gap spherical Couette flow     

Andrew M. Soward  Andrew P. Bassom 《地球物理与天体物理流体动力学》2016,110(2):166-197

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高频加热中低纬电离层激励不稳定性研究   总被引：6，自引：3，他引：3       下载免费PDF全文

邓峰  赵正予  周晨  黄建 《地球物理学报》2010,53(1):10-21

高频泵波加热电离层实验二维数值模拟结果显示,虽然背景电离层状态能够明显影响模拟加热结果,但是在大部分平静电离层状态下,模拟加热一段时间后,加热区域内电子浓度、电子温度会趋于稳定,这一结论已为实验所证实.然而部分模拟结果显示,当电离层电子浓度、电子温度空间结构满足一定条件后,过密加热中泵波反射区域,电子浓度、电子温度在加热机开关机后将产生不稳定的时空效果.激发该不稳定性的正反馈过程如下：当泵波反射区域内电子温度受到泵波加热上升后,其引起的等离子体膨胀导致该区域内电子浓度减小,受到电子温度、电子浓度变化的共同影响,电子能量方程中由于电子-离子碰撞导致的电子能量损失项减小,电子温度将进一步升高,一种正反馈机制建立.最后得到以下结论,当电离层电子温度剖面呈明显的双峰结构,被加热区域内电子温度较高,且电子-离子碰撞引起能量损失项成为电子主要的能量损失项后,一种不稳定性被激发,加热将产生更明显的电子浓度、电子温度的变化.以上条件在下午电离层更容易被满足.  相似文献   

对金茂大厦“粗指纹”诊断初探          下载免费PDF全文

徐永林  朱元清  周晶矛  范宜瑶  秦浩文  阮镇基  干劲 《地震工程学报》2010,32(2):169-172

金茂大厦是目前中国最高建筑之一,高达420.5m。本文采用自回归移动平均ARMA模型,利用大厦的随机振动得到其某些振型的频率及阻尼比,在地震、台风过后或经一长段时间之后,看其相应振型频率和阻尼比的变化,以达到健康诊断之目的。结果显示此法具有很好的可操作性,可用于大厦、大桥等的"粗指纹"健康诊断和维护。  相似文献   

Regime shifts in the North Pacific simulated by a COADS-driven Isopycnal model   总被引：5，自引：1，他引：4  

WANG Dongxiao  WANG Ji  Lixin WU  Zhengyu LIU 《大气科学进展》2003,20(5):743-754

The Miami Isopycnal Coordinate Ocean Model (MICOM) is adopted to simulate the intevdecadal variability in the Pacific Ocean with most emphasis on regime shifts in the North Pacific. The computational domain covers 60°N to 40°S with an enclosed boundary condition for momentum flux, whereas there are thermohalirie fluxes across the southern end as a restoring term. In addition, sea surface salinity of the model relaxes to the climatological season cycle, which results in climatological fresh water fluxes. Surface forcing functions from January 1945 through December 1998 are derived from the Comprehensive Ocean and Atmospheric Data Set (COADS). Such a numerical experiment reproduces the observed evolution of the interdecadal variability in the heat content over the upper 400-m layer by a two-year lag. Subduction that occurs at the ventilated thermocline in the central North Pacific is also been simulated and the subducted signals propagate from 35°N to 25°N, taking about 8 to 10 years, in agreement wit  相似文献   

DESIGN OF MODULATION AND COMPRESSION CODING IN UNDERWATER ACOUSTIC IMAGE TRANSMISSION     

程恩  余丽敏  林耿超 《中国海洋湖沼学报》2002,20(3):202-207

This paper describes the design of modulation, compression coding and transmission control in underwater acoustic color image transmission system. This design adapts a special system of modulation and transmission control based on a DSP(Digital Signal Processing) chip, to cope with the complex underwater acoustic channel. The hardware block diagram and software flow chart are presented.  相似文献   

广义相对论在时频计量中的应用   总被引：1，自引：0，他引：1  

潘炼德 《时间频率学报》2001,24(2):81-91

介绍了广义相对论在时频计量中的应用的重要性和当前研究现状，评述了该领域的几个主要问题：原（固有，本征）时与坐标时的关系；不同坐标时之间的转换；各种不同方式的时间比对及各种不同方式的频率比对，给出了有关研究的最新结果。最后，简要地讨论了该领域需要关注的几个问题。  相似文献