Crosshole seismic tomography with cross-firing geometry

Abstract

We have developed a case study of crosshole seismic tomography with a cross-firing geometry in which seismic sources were placed in two vertical boreholes alternatingly and receiver arrays were placed in another vertical borehole. There are two crosshole seismic data sets in a conventional sense. These two data sets are used jointly in seismic tomography. Because the local sediment is dominated by periodic, flat, thin layers, there is seismic anisotropy with different velocities in the vertical and horizontal directions. The vertical transverse isotropy anisotropic effect is taken into account in inversion processing, which consists of three stages in sequence. First, isotropic traveltime tomography is used for estimating the maximum horizontal velocity. Then, anisotropic traveltime tomography is used to invert for the anisotropic parameter, which is the normalized difference between the maximum horizontal velocity and the maximum vertical velocity. Finally, anisotropic waveform tomography is implemented to refine the maximum horizontal velocity. The cross-firing acquisition geometry significantly improves the ray coverage and results in a relatively even distribution of the ray density in the study area between two boreholes. Consequently, joint inversion of two crosshole seismic data sets improves the resolution and increases the reliability of the velocity model reconstructed by tomography.

Characteristics of Karst Cave Development in Urban Karst Area and Its Effect on the Stability of Subway Tunnel Construction

“…With regard to the detection technology of karst caves, a great deal of researches have been done to accurately predict the hazardous geological conditions during tunnel construction in karst terrains. Nowadays, the commonly used detection technologies mainly include two categories: destructive methods such as the Core Drilling and Percussion Drilling [4] and nondestructive methods including the Ground Penetrating Radar (GPR) [5][6][7], Electrical Resistance Topography (ERT) [8,9], Tunnel Seismic Prediction (TSP) [10][11][12], crosshole seismic Computed Tomography (CT) [13,14], and Transient Electromagnetic Method (TEM) [8,9,15]. For example, Gómez-Ortiz and Martín-Crespo had applied shallow and noninvasive geophysical techniques, that is, GPR and ERT, to ascertain the existence and characteristics of cavities and galleries.…”

Dispersion and Stability Condition of Seismic Wave Simulation in TTI Media

“…This acoustic wave equation is defined by two anisotropic parameters e and d measuring the difference between two axes of the elliptic wavefront and the deviation from a perfect elliptical shape, respectively (Thomsen 1986). In the context of seismic waveform inversion, Pratt and Shipp (1999) and Rao and Wang (2011) use an acoustic wave equation defined by a single anisotropic parameter e. Rao et al (2016) provide the derivation of this wave equation with a single anisotropic parameter. In this paper, we adopt the acoustic wave equation with two anisotropic parameters.…”