Original figure from the paper by Sgrigna and Malvezzi [16]. Fault creep events recorded during the year 1997 at the GRS (plot (a)), AQU (plot (b)), PES (plot (c)), STI (plot (d)) tilt sites, before the Sept 26, 1997 Umbria-Marches earthquakes (; 6.0). Plot (e) shows selected earthquakes (e equal/greater than 10−8). A vertical bar marks a single event M4.4 occurred on May 12; two adjacent shadow and black rectangles of arbitrary amplitude represent two time intervals characterized by the occurrence of a preseismic swarm (lasting a few weeks with a peak event M4.4 on September 3), and of several thousands of aftershocks recorded in the following months, respectively. The two main shocks M5.7; 6.0 of September 26 occurred in the time interval between those marked by shadow and black areas. Plot (f) is the cumulative energy released by earthquakes in 1997.
