  The main goal of this paper is to analyse the influence of cracks on the
azimuthal variations of amplitude. We restrict our investigation to a single
set of vertical, circular, and flat cavities aligned along a horizontal axis.
Such cracks are embedded in either isotropic surroundings or transversely
isotropic background with a vertical symmetry axis. We employ the effective
medium theory to obtain either transversely-isotropic material with a
horizontal symmetry axis or an orthotropic medium, respectively. To consider
the amplitudes, we focus on a Vavrycuk-Psencik approximation of the PP-wave
reflection coefficient. We assume that cracks are situated in one of the
halfspaces being in welded contact. Azimuthal variations depend on the
background stiffnesses, incidence angle, and crack density parameter. Upon
analytical analysis, we indicate which factors (such as background's
saturation) cause the reflection coefficient to have maximum absolute value in
the direction parallel or perpendicular to cracks. We discuss the irregular
cases, where such extreme values appear in the other than the aforementioned
directions. Due to the support of numerical simulations, we propose graphic
patterns of two-dimensional amplitude variations with azimuth. The patterns
consist of a series of shapes that change with the increasing value of the
crack density parameter. Schemes appear to differ depending on the incidence
angle and the saturation. Finally, we extract these shapes that are
characteristic of gas-bearing rocks. They may be treated as gas indicators. We
support the findings and verify our patterns using real values of stiffnesses
extracted from the sedimentary rocks' samples.
