Testing the Influence of Static and Dynamic Stress Perturbations On the Occurrence of a Shallow, Slow Slip Event in Eastern Taiwan

Abstract

We report the first evidence for the detection of a slow slip event in the Longitudinal Valley, in eastern Taiwan. The slow event, which lasted about 3.5 days, has been detected by borehole strainmeters. It occurred at shallow depths (about 2 to 4 km), either on the Longitudinal Valley Fault or on the Central Range Fault. Here we investigate whether the event occurrence was influenced by transient and periodic stress perturbations, in particular by the June 2013 Mw 6.2 Nantou earthquake, which occurred about 60 km away and 6 days prior to the event. Modeled changes in Coulomb stress in the direction parallel to the geologic slip vector on the fault planes show negative static stress changes (approximately −1.5 to −1 kPa), while maximum dynamic stress changes generated by the surface waves are ranging from 5.5 to 14.5 kPa. We also observe that the slow event initiated during a maximum of Earth and ocean tidal Coulomb stress changes (about 0.8 to 1.5 kPa). Dynamic and static stress perturbations represent a few percents to tens of percents of the stress buildup through the slow rupture cycle. However, the absence of recurrent events during the 12 years of strain monitoring (2006 to 2018) prevents to estimate the recurrence interval of the slow event, which limits our ability to further interpret the link between the rupture and the perturbations. Finally, there is no large and unique load transient at the time of the initiation, therefore this single event may have likely occurred spontaneously.

Inherited State of Stress as a Key Factor Controlling Slip and Slip Mode: Inference From the Study of a Slow Slip Event in the Longitudinal Valley, Taiwan

“…To conclude, while a SSE was detected at the transition between the creeping section of the LVF and the locked zone (Canitano et al., 2019), we now show that the fault can also host larger events at seismogenic depths. A limited fraction (about 15%–35%) of ∼0.15–0.35 m of the slip deficit accumulated in 2011 (Figure 4e) has been accommodated by the SSE, additional and/or recurrent aseismic transient slip should likely help to release the remaining slip deficit.…”

“…It rather suggests a triggering cascade of ruptures (e.g., Lengliné & Marsan, 2009), in which event 1, likely triggered by aseismic slip, has then ruptured close-by, but distinct, asperities (as events 2 and 3), together partially rupturing the main asperity (event 54). Overall, burst-type REs are likely caused by local, transient stress concentration from nearby earthquakes and/or aseismic slip events (Templeton et al, 2008) and they are also observed during postseismic slip on the LVF (Canitano et al, 2018a) To conclude, while a SSE was detected at the transition between the creeping section of the LVF and the locked zone (Canitano et al, 2019), we now show that the fault can also host larger events at seismogenic depths. A limited fraction (about 15%-35%) of ∼0.15-0.35 m of the slip deficit accumulated in 2011 (Figure 4e) has been accommodated by the SSE, additional and/or recurrent aseismic transient slip should likely help to release the remaining slip deficit.…”

“…They are unrelated to environmental changes and represent unambiguous evidence for a slow slip episode. Signals follow a logarithmic time‐dependence, a pattern observed on borehole strainmeters during a previous SSE (Canitano et al., 2019). Additionally, following day 41.8, ZANB records a moderate expansion (+20 n ϵ ) during 3 days (Figure 2a), while a contraction of approximately −5 n ϵ is expected due to 10 mm of cumulative rainfall (Figure , station C0T9M0).…”

Earthquake triggering model based on normal-stress-dependent Nagata law: application to the 2016 Mie offshore earthquake

“…There have been many reports of earthquake triggering (e.g., Hill et al 1993;Brodsky et al 2000;Kilb et al 2000;Miyazawa et al 2008;van der Elst and Brodsky 2010;Richards-Dinger et al 2010;Miyazawa 2011;Parsons and Velasco 2011;Lin 2012;Pollitz et al 2012;van der Elst et al 2013;Yukutake et al 2013;Johnson and Bürgmann 2016;Miyazawa 2016;Uchida et al 2016;Yoshida 2016). Besides the seismic event triggering, triggering of very low-frequency earthquakes, tremors, slow slip events (SSEs), and creep events has been observed (e.g., Allen et al 1972;Obara 2009;Itaba and Ando 2011;To et al 2015;Araki et al 2017;Miyazawa 2019;Canitano et al 2019;Katakami et al 2020). A likely mechanism behind earthquake triggering has been based on the rate-and state-dependent friction (RSF) law (Dieterich 1979;Ruina 1983).…”

Stress Sensitivity of Instantaneous Dynamic Triggering of Shallow Slow Slip Events

“…It has been shown that distant earthquakes can trigger tectonic tremors (e.g., Chao et al, 2013; Miyazawa & Mori, 2005; Miyazawa & Brodsky, 2008; Peng & Gomberg, 2010; Rubinstein et al, 2007; Shelly et al, 2011) and VLFEs (e.g., Miyazawa, 2019; To et al, 2015). However, the dynamic triggering of both shallow and deep, detectable ( M w > 5.5) SSEs is relatively rare (Araki et al, 2017; Canitano et al, 2019; Itaba & Ando, 2011; Wallace et al, 2017; Zigone et al, 2012). Among them, Wallace et al (2017) reported the large‐scale dynamic triggering of shallow (<15‐km depth) SSEs in New Zealand during the passage of Kaikoura earthquake waves.…”