Simultaneous tomography of all periods in surface wave analysis

Publication date: Available online 7 November 2019Source: Physics of the Earth and Planetary InteriorsAuthor(s): Najmieh Mohammadi, Ali Gholami, Habib Rahimi, Abdelkrim AoudiaAbstractTwo dimensional surface wave travel time tomography is one of the most practical methods to image the lateral variation of phase/group velocity. In practice, local dispersion curves are reconstructed by performing 2-D inversion of travel times for a series of periods separately. Although 2-D inversion is numerically efficient, it does not consider the dependency between periods and thus can lead to a suboptimal phase/group velocity. To address this issue, in this paper, we propose Simultaneous Tomography of all Periods (STP) method. We consider the model parameters as a 3-D volume of dimensions x, y and T, where the first two parameters are related to spatial location of cells and T denotes period. Then a 3-D inversion is performed which inverts all of the travel times for the model parameters simultaneously. To render the solution unique and stable we employ the Tikhonov regularization in which a 3-D regularization functional is used to couple the periods together and force smooth behavior of the parameters in temporal direction as well as spatial direction. Both l2 and l1 norm regularizations are considered. The former is used to generate a flat model by minimizing the squared l2-norm of the model gradient while the latter is used to force the sparsity of the model in the discrete cosine transf...

Source: Physics of the Earth and Planetary Interiors - November 7, 2019 Category: Physics Source Type: research