  Understanding the penetration dynamics of intruders in granular beds is
relevant not only for fundamental physics, but also for geophysical processes
and construction on sediments or granular soils in areas potentially affected
by earthquakes. In this work, we use Lock-in accelerometry to study the
penetration of intruders into quasi-2D granular matter fluidized by lateral
shaking. We observed that there are two well-defined stages in the penetration
dynamics as the intruder sinks into the granular material.
