Multiply scattered waves are a new tool for monitoring changes in the earth's subsurface. In this study we use the air pressure and displacement recorded at the Arenal Volcano to detect temporal changes. The pressure pulses emitted by the volcano are associated with a complex displacement signal of overlapping coda waves. By deconvolving the ground motion with the air pressure for different time intervals we obtain a highly repeatable displacement signal that has the character of diffusive wave propagation. This deconvolved displacement signal changes with the time interval analyzed in the employed data. This change can be explained by a shift in the point of excitation of the elastic waves over a distance of about 15 meters.