Highly Systematic Response of Seismic Rupture Patterns to Background Loading Rate: Insights From Repeating Earthquakes

Abstract

Although earthquakes are known to recur in approximately the same areas, their recurrence patterns and final sizes can vary considerably. To understand this variability, we analyzed a prominent sequence of repeating earthquakes from the latest catalog in Japan, activated following the 2011 earthquake (M_w 9.0). Waveform analysis of 53 events (2003–2023) revealed variations in magnitude from M_w 3.2 to 4.0. Their moment-rate functions suggest they were not mere repetitions, but rather represented a more generalized form of recurrence. Their ruptures were consistently initiated in the same patch, and most events exhibited double ruptures after the Tohoku earthquake, transitioning to single ruptures over time, in a surprisingly systematic manner. A comparison with 40 smaller events (M_w 2–2.5) showed no obvious relationship between initial momentum and final magnitude. Our results suggest earthquake rupture patterns respond remarkably systematically to changes in the background loading rate, reflecting in situ frictional characteristics.