Vertical (a) and radial (b) displacements at the free surface (in units of 10⁻⁹ m) at various distances from the conduit axis in Model I. Numbers at the left of each trace represent epicentral distances from the conduit axis (in units of m). (c) Particle orbits obtained from bandpass filtered (0.3–0.6 Hz) seismograms at epicentral distances of 500 and 1000 m. The time windows within which the particle orbits are obtained have a duration of 4 s and start about 3 s after the removal of the lid.