Interplate Quasi-Static Slip off Miyagi and Fukushima Prefectures Estimated from Small Repeating Earthquake Data

Abstract

Spatio-temporal distribution of quasi-static slip on the plate boundary east off Miyagi and Fukushima prefectures, NE Honshu, Japan is estimated by using small repeating earthquake data. The analysis of small repeating earthquakes has advantages of relatively high spatial resolution, especially near the trench, and the availability of long-term data (22 years) compared to GPS data. The results show that the repeating earthquakes are distributed outside the coseismic slip areas (asperities) of large earthquakes, showing that fault creep is dominant outside the asperities. The cumulative slip (slip histories) of small repeating earthquake groups reveal the existence of many non-steady aseismic slip events. Most of the episodic quasi-static slip events are associated with M≥ 6 earthquakes and they are frequently seen in the areas near the Japan trench in particular. Minor afterslip (∼15cm) of the 2005 Miyagi-oki earthquake (M7.2) is also estimated in the area which encompasses the coseismic slip area of the 2005 earthquake.