(a) A multi-irregular layer model—a ‘sine wave’ shaped interface followed by a basin structure below a top flat layer. (b) τ-p-p′ seismogram for the multilayer model showing different branches corresponding to successive interfaces. (c) Corresponding τ-p−x′ seismogram for the multilayer model. (d) Shot records at points L, M, R along the shot profile (see text) show varied natures of ‘triplication’ in the arrival times corresponding to the ‘sine wave’ and basin shapes of the lower interfaces. (e) The multilayer zero offset section shows small ‘triplication’ (just below the top flat reflector) due to the trough part of the upper ‘sine wave’ structure and a bow-tie due to the basin shape below but modulated by the sinusoidal interface above it.