A comment on “Hidden dykes detected on ultra long period seismic signals at Piton de la Fournaise volcano?” by N. Houlié and J.-P. Montagner, EPSL 261, (2007)

Based on horizontal displacements extracted from a very broadband seismic station located near the Piton de la Fournaise Volcano, Houlié and Montagner (Houlié, N., Montagner, J.-P., 2007. Hidden dykes detected on ultra long period seismic signals at Piton de la Fournaise volcano. Earth. Planet. Sci. Lett. 261. doi:10.1016/j.epsl.2007.04.018) conclude that there have been intrusions of large volume hidden dykes into the volcano and suggest the presence of two distinct types of eruptions related to the pressure states of a magma chamber. In this comment, we point out that the recordings of horizontal components may be dominated by tilt and that obtaining displacements with proper amplitudes is prone to errors. We also show that the use of an oversimplified model to explain a single datum leads the authors to conclusions that are inconsistent with other data collected on the volcano as well as with previous interpretations.