基于BELLHOP 模型的宽带信号波形预报

为解决信号级声纳仿真系统的水声传输信道宽带信号波形预报问题,采用射线模型的基本原理,推导了基于射线的宽带水声信道响应函数.并在Pekeris环境条件下,分析比较了基于BELLHOP射线模型的时域宽带模型与基于BDRM模型的频域宽带模型波形预报结果.结果表明,水声信道具有典型的时域数字滤波器特征,其本质是对脉冲信号进行延迟、加权和求和,这种延迟求和会导致系统频域幅度响应函数呈现“梳状滤波器”形状.在一定条件下,射线模型与简正波模型具有同等计算精度,由于射线模型通过一次计算就能得到所有本征声线的幅度和延迟,相对于简正波模型来说,计算效率更高.同时利用射线模型,能够方便地选择接收特定角度出射的本征声线.     

�봨�������б����Ա��ε���Դ�ֲ����������Ѹ������о�

?????HYPODD???????????????о????λ????????????CAP?????????????????????????????5??????????????????????????ε??????????????????????????????????????????????е??????????????????????????????????????????????????????????????????-??????????????????????????????????Σ????????о??и??μ????λ????5.5?????????????????????????????????????λ???λ??7??5.5???????????????4????????????????3?????????????????????????-??????????-????4?????????????????????     

地层错动引起的上覆饱和黏土层变形特性的离心试验研究

地震断层错动会引起上覆土层变形,从而造成断层附近的建筑结构、管线产生附加的变形和内力引起破坏。通过一个土工离心机试验分析上覆饱和黏土层在4步连续断层错动作用下的静力响应行为。着重分析断层错动引起的地层变形的范围、不均匀沉降区的分布特点、剪切裂缝在土层传播路径及地表开裂的位置等工程上重点关注的问题。得到以下几点认识：(1) 基岩断层错动引起的地层变形范围基本上不受基岩错动量大小的影响。(2) 断层错动引起地层的不均匀沉降区基本呈三角形分布,其地表宽度约为1倍左右的土层厚度。(3) 基岩错动引起的主剪切裂缝基本沿竖直方向向上传播,其传播距离取决于基岩错动量及土体的破坏应变。(4) 基岩断层错动在主剪区的下盘一侧边缘会产生张拉裂缝,且产生张拉裂缝所需基岩错动量远小于产生剪切裂缝所需的错动量。     

On crustal corrections in surface wave tomography

Mantle models from surface waves rely on good crustal corrections. We investigated how far ray theoretical and finite frequency approximations can predict crustal corrections for fundamental mode surface waves. Using a spectral element method, we calculated synthetic seismograms in transversely isotropic PREM and in the 3-D crustal model Crust2.0 on top of PREM, and measured the corresponding time-shifts as a function of period. We then applied phase corrections to the PREM seismograms using ray theory and finite frequency theory with exact local phase velocity perturbations from Crust2.0 and looked at the residual time-shifts. After crustal corrections, residuals fall within the uncertainty of measured phase velocities for periods longer than 60 and 80 s for Rayleigh and Love waves, respectively. Rayleigh and Love waves are affected in a highly non-linear way by the crustal type. Oceanic crust affects Love waves stronger, while Rayleigh waves change most in continental crust. As a consequence, we find that the imperfect crustal corrections could have a large impact on our inferences of radial anisotropy. If we want to map anisotropy correctly, we should invert simultaneously for mantle and crust. The latter can only be achieved by using perturbation theory from a good 3-D starting model, or implementing full non-linearity from a 1-D starting model.