MODELING LOCAL SEISMOGRAMS OF FRENCH NUCLEAR TESTS IN TAOURIRT TAN AFELLA MASSIF, HOGGAR, ALGERIA

The influence of topography on the shape and amplitude of seismograms recorded at short distances is investigated for a set of nuclear explo sions detonated in the Taourirt tan Afella mountain, Hoggar, Algeria, which was the French nuclear test site during the 1960s. The wavefield observed on one side of the mountain compared to that on the other sh ows a large-amplitude phase generated by reflection of the direct fiel d inside the mountain. This phase is back-diffracted and can be seen i n one azimuth and not in the opposite. The existence of such a phase d epends on the source location inside the mountain. The amplitudes of s tandard phases are also modified with a factor of 2.5 by the topograph y between observations made in one azimuth compared to the others.