Research on the February 18, 1996 earthquake in the caves of Saint-Paul-de-Fenouillet area, (eastern Pyrenees, France)

Eight caves have been investigated near Saint-Paul-de-Fenouillet after the magnitude 5.2 earthquake of February 1996 which occurred in the Eastern Pyrenees (France) and caused moderate damage at the ground surface. The earthquake has been associated with the movement of a E-W fault. The caves were not visited since the earthquake. Some damage, mainly collapses of soda straws and small rocks, could be attributed to this earthquake. The most interesting cave in the epicentral area is the Paradet cave which is situated on a recently activated fault plane. In this cave, soda straw falls could be assigned to the earthquake, but other more ancient damage were observed also. Analysis of the azimuth of fallen speleothems which are natural pendulums, may indicate the directions and an estimation of their mechanical properties gives the threshold of the seismic ground motion amplitude responsible for their collapse and thus supply information to calibrate damage due to past earthquakes. A statistical study indicates that the main direction of the collapsed soda straws is E-W. Numerical simulations confirm that soda straws are relatively strong objects that may break under certain conditions during earthquakes.