Spatial and temporal variations in slip rate over millions of years on an extensional fault system: implications for seismic hazard

Billy Andrews, Zoe K Mildon , Christopher Aiden-Lee Jackson , Constanza Rodriguez Piceda, francesco iezzi, Joanna Faure Walker

Slip rate is a key input for fault-based seismic hazard assessment, with temporal and spatial variations in slip rate along and between faults influencing earthquake size and recurrence. Temporal variations in slip rate have been attributed to earthquake clustering and anti-clustering in tectonically active settings. Here we explore the combined temporal and spatial assessment of slip rate variations of individual faults and the network they form part of. Here we present slip rates derived from a seismically imaged, inactive fault network, offshore NW Australia. We show spatial and temporal slip rate variations across million-year time scales for individual faults within a network of across-strike faults. Slip rate profiles also differed through time, with the location of maximum slip rate on individual faults migrating along-strike by several kilometres between time periods (over 106 to 107 million years). We then calculate the resulting temporal variations in seismic hazard arising from the changes in slip rates. We show that within a fault network, whilst overall the earthquake recurrence rates over the entire fault system remain similar, recurrence rates on individual faults vary on the million-year timescales we study. Spatial and temporal variability of slip rate can introduce uncertainty in earthquake probability calculations, highlighting the need to incorporate this into probabilistic seismic hazard assessments.