Here we propose a local earthquake tomography method that applies a structured regularization technique to determine sharp changes in the Earth's seismic velocity structure with travel time data of direct waves. Our approach focuses on the ability to better image two common features that are observed the Earth's seismic velocity structure: velocity jumps that correspond to material boundaries, such as the Conrad and Moho discontinuities, and gradual velocity changes that are associated with the pressure and temperature distributions in the crust and mantle. We employ different penalty terms in the vertical and horizontal directions to refine the imaging process. We utilize a vertical-direction (depth) penalty term that takes the form of the l1-sum of the l2-norm of the second-order differences of the horizontal units in the vertical direction. This penalty is intended to represent sharp velocity jumps due to discontinuities by creating a piecewise linear depth profile of the average velocity structure. We set a horizontal-direction penalty term on the basis of the l2-norm to express gradual velocity tendencies in the horizontal direction. We use a synthetic dataset to demonstrate that our method provides significant improvements over the estimated velocity structures from conventional methods by obtaining stable estimates of both the velocity jumps and gradual velocity changes. We also demonstrate that our proposed method is relatively robust against variations in the amplitude of the velocity jump, initial velocity model, and the number of observed travel times. Furthermore, we present a considerable potential for detecting a velocity discontinuity using the observed travel times from only a small number of direct-wave observations.

翻译：此处我们提出一个局部地震地形学方法,采用结构化的正规化技术,确定地球地震速度结构的急剧变化,同时提供直接波浪的旅行时间数据。我们的方法侧重于更好地映射地球地震速度结构所观察到的两个共同特征的能力:与物质界限相对应的快速跳跃,如康拉德和莫霍不连贯,以及与地壳和地壳的压力和温度分布相关的渐进速度变化。我们在垂直和水平方向上采用不同的惩罚条件来改进图像过程。我们使用垂直方向(深度)惩罚术语,其形式为垂直方向地震速度结构中水平波浪的二阶点差异的l1和l2-诺姆。这一处罚旨在代表与物质界限相对的快速跳动,通过对平均速度结构进行一个小角度的线性线性深度描述。我们使用一个合成数据来显示我们所使用的方法在水平速度结构上相对于水平单位的l1和l2-诺姆差异的l++++++。我们所观察到的快速速度结构中,我们使用一个稳定的移动方法来展示我们所观察到的快速速度结构的深度变化。