Regional earthquakes followed by delayed ground uplifts at Campi Flegrei Caldera, Italy: Arguments for a causal link

Earthquake-triggered volcanic activity promoted by dynamic and static stresses are considered seldom and difficult-to-capture geological processes. Calderas are ideal natural laboratories to investigate earthquake-volcano interactions due to their sensitivity to incoming seismic energy. The Campi Flegrei caldera, Italy, is one of the most monitored volcanic systems worldwide. We compare ground elevation time series at Campi Flegrei with earthquake catalogues showing that uplift events at Campi Flegrei are triggered by large regional earthquakes. Over a 70 years time window we identify 14 uplift events, 12 of them were preceded by an earthquake, and for 8 of them earthquake-to-uplift time span is within 1.2 yr. To investigate the process that may be responsible for such causative relationship we simulate the propagation of elastic waves and show that passing body waves impose high dynamic strains at the roofof the magmatic reservoir of the Campi Flegrei at about 7 km depth. This may promote a short-lived embrittlement of the magma reservoir’s carapace, which is otherwise impermeable during inter-seismic times. Such failure allows magma and exsolved volatiles to be released from the magmatic reservoir. The fluids, namely exolved volatiles and/or melts, ascent through a nominally plastic zone above the magmatic reservoir. The proposed mechanism and the associated inherent uncertainties require further investigations but the new concept already implies that geological processes triggered by passing seismic waves may become apparent after several months, i.e. far behind the few-days time window normally accepted for dynamic triggering.