The 2016 central Italy seismic sequence consists so far of a series of moderate‐to‐large earthquakes activating within a few months along a 60‐km‐long and Apenninic‐trending normal‐fault system. Regrettably, the high vulnerability of the local infrastructure and the shallowness of the largest events (depth around 8 km) resulted in 299 casualties and more than 20,000 homeless, with great difficulties in the disaster management. The sequence evolved around its largest event (M_w 6.5, 30 October) that occurred right in the middle of a fault system already activated two months before with a first M_w 6.0 mainshock (on 24 August) located to the south near the town of Amatrice. Then, another M_w 5.9 mainshock occurred just four days before the largest mainshock (26 October) at the northernmost extent of the sequence, near the town of Visso. We analyze the space–time evolution of the first four months of seismic activity through the relocation of ∼26,000 earthquakes and the kinematic source models of the three mainshocks. All the main events nucleated at the base of a southwest‐dipping normal‐fault system segmented by the presence of crosscutting compressional structures. The presence of these inherited faults, separating diverse geological domains, appears to modulate evolution of the sequence interfering with coseismic slip distribution and fault segments interaction. Several secondary antithetic and synthetic faults are located at a shallow depth (<4 km), both in the hanging wall and footwall. The whole normal fault system, confined within the first 8 km of the upper crust, is bounded below by a shallow east‐dipping and 2–3‐km‐thick layer in which small events plus a series of large extensional aftershocks (≈M_w 4) occur, possibly decoupling the upper and lower crusts.

Whether fast and slow earthquakes nucleate in the same way is unclear. Laboratory simulations of fast and slow slip reveal similar precursor seismic signals for both modes, suggesting the same physical mechanisms may govern both types of slip. Temporal changes in seismic velocity during the earthquake cycle have the potential to illuminate physical processes associated with fault weakening and connections between the range of fault slip behaviours including slow earthquakes, tremor and low-frequency earthquakes1. Laboratory and theoretical studies predict changes in seismic velocity before earthquake failure2; however, tectonic faults fail in a spectrum of modes and little is known about precursors for those modes3. Here we show that precursory changes of wave speed occur in laboratory faults for the complete spectrum of failure modes observed for tectonic faults. We systematically altered the stiffness of the loading system to reproduce the transition from slow to fast stick–slip and monitored ultrasonic wave speed during frictional sliding. We find systematic variations of elastic properties during the seismic cycle for both slow and fast earthquakes indicating similar physical mechanisms during rupture nucleation. Our data show that accelerated fault creep causes reduction of seismic velocity and elastic moduli during the preparatory phase preceding failure, which suggests that real-time monitoring of active faults may be a means to detect earthquake precursors.