Forecast experiment on the Kamaishi repeating earthquakes based on numerical simulations using friction law

Shingo Yoshida,Naoyuki Kato,Jun’Ichi Fukuda

doi:10.1186/s40623-016-0448-7

Abstract

Repeating M5-class earthquakes occurred with a regular recurrence interval on the plate boundary offshore Kamaishi before the 2011 M9 Tohoku-oki earthquake. Since this event, 11 repeating events of M5–M6 have occurred with shorter recurrence intervals than before the M9 event. We performed a forecast experiment on the Kamaishi repeaters after the Tohoku-oki earthquake based on numerical simulations assuming a large patch containing a small patch on a fault model that undergoes continuous afterslip. Simulations were conducted for various parameter values to produce time history of repeated ruptures. To forecast the Ith event, we selected several modeled sequences that are able to accurately reproduce the observed event sequence up to the (I − 1)th event. The averages of the occurrence times and magnitudes over the selected sequences were used as ensemble forecasts. We attempted to predict the 7th event to the 11th event and discussed the obtained forecast spreads and errors.

Highlights

Repeating M5-class earthquakes on the plate boundary offshore Kamaishi occurred with a regular recurrence intervals before the 2011 M9 Tohoku-oki earthquake (Matsuzawa et al 2001, 2002; Uchida et al 2005) as denoted by circle in Fig. 1. Uchida et al (2014) reported that an M6-class event occurred immediately after this M9 event and was followed by M5-class events at shorter intervals than before the M9 event
Before the M9 event, the conditionally stable regions are characterized by aseismic slip, whereas seismic slip occurs only in the unstable region, resulting in regular occurrence of the repeating earthquakes
After the M9 event, aseismic-to-seismic transition in the surrounding region was caused by the afterslip, and the seismic slip occurred in the whole area, resulting in an M 6-class

Summary

Introduction

Repeating M5-class earthquakes on the plate boundary offshore Kamaishi occurred with a regular recurrence intervals before the 2011 M9 Tohoku-oki earthquake (Matsuzawa et al 2001, 2002; Uchida et al 2005) as denoted by circle in Fig. 1. Uchida et al (2014) reported that an M6-class event occurred immediately after this M9 event and was followed by M5-class events at shorter intervals than before the M9 event. To explain the expansion of the seismic slip area under the high loading rates after the M9 event, they proposed a conceptual fault model as that contains conditionally stable regions. Before the M9 event, the conditionally stable regions are characterized by aseismic slip, whereas seismic slip occurs only in the unstable region, resulting in regular occurrence of the repeating earthquakes. After the M9 event, aseismic-to-seismic transition in the surrounding region was caused by the afterslip, and the seismic slip occurred in the whole area, resulting in an M 6-class. Numerous studies have been conducted on the statistical forecasting of earthquakes. Kano et al (2013) developed an adjoint data assimilation method to estimate the frictional parameters on a fault with the objective of predicting earthquakes triggered by afterslip propagation. Using synthetic data generated by simulations, they tested the feasibility of such prediction. Kano et al (2015) estimated the frictional parameters for the afterslip of the Yoshida et al Earth, Planets and Space (2016) 68:71

Objectives

Results

Conclusion