Scuderi et al. Precursors to the spectrum of fault failure modes p.1 Seismic velocity changes reveal precursors for the spectrum of earthquake 1 failure modes 2 3 Authors: M.M. Scuderi 1,2 *, C. Marone 3 , E. Tinti 2 , G. Di Stefano 2 and C. Collettini 1,2 4 Affiliations: 5 1 Dipartimento di Scienze della Terra, La Sapienza Università di Roma, Piaz. Aldo Moro 5, 00185 Rome Italy 6 2 Istituto Nazionale di Geofisica e Vulcanologia (INGV), Via di Vigna Murata 605, 00143 Rome Italy 7 3 Department of Geoscience, The Pennsylvania State University, University Park, PA 16802 8 *Correspondence to: marco.scuderi@uniroma1.it 9 10 Temporal changes in seismic velocity during the earthquake cycle have the potential to 11 illuminate physical processes associated with fault weakening and connections between the 12 range of fault slip behaviors including slow earthquakes, tremor and low frequency 13 earthquakes 1 . Laboratory and theoretical studies predict changes in seismic velocity prior 14 to earthquake failure 2 , however tectonic faults fail in a spectrum of modes and little is 15 known about precursors for those modes 3 . Here we show that precursory changes of wave 16 speed occur in laboratory faults for the complete spectrum of failure modes observed for 17 tectonic faults. We find systematic variations of elastic properties during the seismic cycle 18 for both slow and fast earthquakes indicating similar physical mechanisms during rupture 19 nucleation. Our data show that accelerated fault creep causes reduction of seismic velocity 20 and elastic moduli during the preparatory phase preceding failure, which suggests that real 21 time monitoring of active faults may be a means to detect earthquake precursors. 22 23