← Back to Sessions

Role of Foreshock Sequences in Triggering the 2016 Mw 6.9 Fukushima Mainshock

Description: 

Large earthquakes are sometimes preceded by foreshocks, which are regarded as precursory activity of the fault that can potentially inform us of the forthcoming mainshock. However, the physical mechanism behind the seismic triggering process remians elusive. Two end-member triggering mechanisms have been hypothesized, namely the cascade triggering and the aseismic slip triggering model. Here, we perform a comprehensive analysis to investigate the nucleation process of the foreshock sequence before the 2016 Mw 6.9 Fukushima earthquake (22/11/2016 05:59:46 JST) with the goal of determining the possible underlying triggering mechanisms of the mainshock. We first used the Hypoinverse algorithm to relocate earthquakes using the JMA arrival-time catalog and visually picked arrival times of S-net ocean bottom seismometers. Then we applied the Match & Locate method on continuous waveform for small events detection using 7 template events, all occurring within 6 hours before the mainshock. With an improved earthquake catalog, we characterized the spatiotemporal evolution of seismicity patterns. Preliminary results show that the foreshock sequence began with 90 minutes of seismic activity including the largest foreshock of Mw 4.6 (03:25:49 JST), followed by a quiescence period of 40 minutes, and a second burst of seismicity before the mainshock. It does not exhibit an expansion pattern and is concentrated within 10 km SW of the mainshock location, but we observed a weak migration pattern towards the mainshock epicenter just before the mainshock occurred. Based on waveform correlations and rupture diameter, we did not observe repeating earthquakes. The lack of repeating earthquakes and spatial expansion, and the overall spatiotemporal migration patterns towards the mainshock suggest that cascade triggering is responsible for the triggering of the foreshock-mainshock sequence. Our ongoing work focuses on analyzing static Coulomb failure stress changes (ΔCFS) induced by the foreshock sequence to assess the potential of cascade triggering, as ΔCFS larger than 0.01 MPa has been identified as a threshold for this mechanism.

Session: Predictability of Seismic and Aseismic Slip: From Basic Science to Operational Forecasts [Poster]

Type: Poster

Date: 4/16/2025

Presentation Time: 08:00 AM (local time)

Presenting Author: Hoi Leung

Student Presenter: Yes

Invited Presentation: 

Poster Number: 45

Authors