Normalized rupture potential for small and large earthquakes along the Pacific Plate off Japan

Abstract

We combine temporal variability in local seismic activity rates and size distributions to estimate the evolution of a Gutenberg-Richter-based metric, the normalized rupture potential (NRP), comparing differences between smaller and larger earthquakes. For the Pacific Plate off Japan, we study both complex spatial patterns and how they evolve over the last 18 years, and more detailed temporal characteristics in a simplified spatial selection, i.e., inside and outside the high-slip zone of the 2011 M9 Tohoku earthquake. We resolve significant changes, in particular an immediate NRP increase for large events prior to the Tohoku event in the subsequent high-slip patch, a very rapid decrease inside this high-stress-release area coupled with a lasting increase of NRP in the immediate surroundings. Even in the center of the Tohoku rupture, the NRP for large magnitudes has not dropped below the 12 year average and is not significantly different from conditions a decade before the M9 event.