The earthquake of 1980 November 23 in Campania--Basilicata (southern Italy)

Abstract

Teleseismic waveforms, local ground acceleration, elevation changes, surface faulting and aftershocks are used to investigate the three-dimensional geometry of fault movement in the destructive earthquake (Ms= 6.9) of 1980 November 23 in Campania—Basilicata (southern Italy). Twelve kilometres of surface faulting has been identified following this earthquake. The re-determined epicentre and focal mechanism, and the focal depth of 10 km, determined by modelling long-period teleseismic body waves, show that the hypocentre was on a downward projection of the surface faulting, and that the seismogenic normal fault was approximately planar, with a dip of 60°, from the hypocentre to the surface. Further analysis of the long-period body-waves indicates that, within 10s of the origin time of the earthquake, motion occurred on three discrete fault-segments extending for 30 km along strike. Fault rupture in the earthquake propagated predominantly towards the NW. An overall moment tensor for the earthquake is obtained from the inversion of long-period GDSN and WWSSN data, and shows that the total scalar moment of 26 × 1018 Nm is approximately double that accounted for by the fault motion in these first three subevents. We use teleseismic body-waves, locally recorded ground acceleration and aftershocks to investigate the position, timing and orientation of the additional seismic sources responsible for the remaining seismic moment. These data suggest that a fourth subevent occurred about 13 s after the first motion, approximately 20 km SE of the hypocentre of the first subevent. Two later fault ruptures also occurred, beneath the hanging wall of the earlier ruptures, about 20 and 40 s after the first motion. Long-period body waves and elevation changes are consistent with these occurring on normal faults, dipping at about 20°NE, at the base of the upper-crustal seismogenic zone. The total of six subevents that we identify for this earthquake account for almost all of the scalar moment in the overall moment tensor.