  In this study, we consider the use of seismic sensors for footstep
localization in indoor environments. A popular strategy of localization is to
use the measured differences in arrival times of source signals at multiple
pairs of receivers. In the literature, most algorithms that are based on time
differences of arrival (TDOA) assume that the propagation velocity is a
constant as a function of the source position, which is valid for air
propagation or even for narrow band signals. However a bounded medium such as a
concrete slab (encountered in indoor environement) is usually dispersive and
damped. In this study, we demonstrate that under such conditions, the concrete
slab can be assimilated to a thin plate; considering a Kelvin-Voigt damping
model, we introduce the notion of {\em perceived propagation velocity}, which
decreases when the source-sensor distance increases. This peculiar behaviour
precludes any possibility to rely on existing localization methods in indoor
environment. Therefore, a new localization algorithm that is adapted to a
damped and dispersive medium is proposed, using only on the sign of the
measured TDOA (SO-TDOA). A simulation and some experimental results are
included, to define the performance of this SO-TDOA algorithm.
