Combining GPS and repeating earthquakes for a high resolution analysis of subduction zone coupling

Abstract

Increasingly complex spatiotemporal patterns of subduction zone coupling are being revealed by geodetic and seismic observations. Understanding the mechanisms which control it is useful for improving seismic hazard assessments. GPS and characteristically repeating earthquakes (CREs) are complementary datasets for monitoring aseismic slip. Here, both of them are combined to estimate the rate and distribution of creep on the northeast Japan subduction zone between 21 March 1996 and 24 September 2003. We find that the majority of the upper part at 0–30km depth remains locked. There are three regions creeping at 7–8cm/yr distributed along-strike at 40–70km depth. We observe that these creeping regions occur in areas of low effective pressure and reduced porosity, which are inferred from Vp and Vs velocities. Moreover, an area of high clay content and high effective pressure coincides with the rupture area of the Tohoku-oki earthquake. We discuss these results in the context of potential mechanisms governing creep in northeast Japan. Our results highlight the benefits of combining GPS and CREs for advancing our understanding of the seismic cycle in subduction zones.