Along‐strike variability of rupture duration in subduction zone earthquakes

Abstract

Subduction zone earthquakes exhibit a wide spectrum of rupture times that reflect conditions on the megathrust fault. Tsunami earthquakes are examples of slower than expected ruptures that produce anomalously large tsunamis relative to the surface‐wave magnitude. One model explaining tsunami earthquakes suggests slip within patches of low rigidity material at shallow depths. Heterogeneous fault conditions, such as having patches of low rigidity material surrounded by higher strength material, should produce heterogeneous earthquake rupture parameters. Here we investigate along‐strike variation in rupture duration for 427 shallow thrust earthquakes (Mw = 5.0–7.0) in the Peru, Chile, Alaska, Tonga, Kuril, Izu, and Java‐Sumatra subduction zones to explore how heterogeneous seismic and tectonic characteristics, such as differences in sediment type, thickness, and roughness of subducting bathymetry, affect earthquake properties. Earthquake source parameters, including rupture durations, are estimated using multi‐station deconvolution of teleseismic P and SH waves to solve for earthquake source time functions, and all events are relocated using additional depth phase information. We classify events into shallow (≤26 km) and deep (>26 km and ≤61 km) groups based on the overall mean depth and focus on the longest duration events with moment normalized rupture durations of >1 standard deviation above the mean duration for each group. We find long‐duration events at all depths within the study regions except Peru and Chile. We find no correlation with incoming sediment thickness or type, and limited spatial correlation with regions of past tsunami earthquakes, regions of observed afterslip, and subducting bathymetric features.