  In this paper, we perform a detailed investigation on the various geometrical
properties of trapped surfaces and the boundaries of trapped region in general
relativity. This treatment extends earlier work on LRS II spacetimes to a
general 4 dimensional spacetime manifold. Using a semi-tetrad covariant
formalism, that provides a set of geometrical and matter variables, we
transparently demonstrate the evolution of the trapped region and also extend
Hawking's topology theorem to a wider class of spacetimes. In addition, we
perform a stability analysis for the apparent horizons in this formalism,
encompassing earlier works on this subject. As examples, we consider the
stability of MOTS of the Schwarzschild geometry and Oppenheimer-Snyder
collapse.
