Variability of the Space‐Time Evolution of Slow Slip Events Off the Boso Peninsula, Central Japan, From 1996 to 2014

Abstract

Global Navigation Satellite System data are inverted to investigate the space‐time evolution of five Mw 6.6–6.7 slow slip events (SSEs) off the Boso Peninsula, central Japan, in 1996, 2002, 2007, 2011, and 2013–2014. Our analyses reveal that the nucleation style and space‐time evolution of slip vary among the five SSEs. The 2002, 2007, and 2011 SSEs nucleated more rapidly, with moment accelerations higher than those of the 1996 SSE by a factor of ∼2–6, and higher than those of the 2013–2014 SSE by an order of magnitude. Furthermore, the 2002, 2007, and 2011 SSEs exhibited more rapid temporal variations in their slip and moment rates and showed larger seismic moments and higher maximum slip rates than the 1996 and 2013–2014 SSEs, suggesting that the overall evolution of the SSEs is correlated with the nucleation style. The along‐strike expansion/propagation of slip is identified for the five SSEs, revealing that the expansion/propagation patterns vary from event to event. The earthquake swarms accompanying the SSEs occurred near the downdip edge of high‐slip‐rate areas, and the seismicity migrated during slow slip with directions and speeds similar to those of the slip expansion/propagation. These space‐time correlations between seismicity and slow slip suggest that the earthquake swarms were triggered by stress changes due to slow slip. The relative timing between the onsets of the SSEs and their associated seismicity varies from event to event and appears to be correlated with the nucleation style of the SSEs.

Spatiotemporal Evolution of Recurrent Slow Slip Events Along the Southern Ryukyu Subduction Zone, Japan, From 2010 to 2013

“…Similar variations in nucleation style within a single series of SSEs are also found in the SSEs off the Boso Peninsula in central Japan (Fukuda, 2018). Another similarity for the SSEs in both regions is that the maximum slip rate durations are comparable.…”

“…Another similarity for the SSEs in both regions is that the maximum slip rate durations are comparable. SSEs in the Boso area exhibit a correlation between nucleation style and the maximum slip rate/seismic moment; events with rapid nucleation have a faster maximum slip rate and larger seismic moment than events with slower nucleation (Fukuda, ). The maximum slip rate for Event 3 in the Ryukyu area, which exhibits slower nucleation, is smaller than those for Events 1, 2, and 4, suggesting a correlation between nucleation style and maximum slip rate similar to that for the Boso SSEs.…”

“…The temporal evolution of fault slip is formulated in the following discretized equations, assuming that slip rate follows a random walk process: where t k represents the k th observation epoch and Δ t is the time interval of observations defined as t k − t k− 1 , which is equal to 1 day in the present study (Fukuda, ). Equation shows that temporal roughness of slip rate is controlled by the hyperparameter .…”

“…where t k represents the kth observation epoch and Δt is the time interval of observations defined as t k À t kÀ1 , which is equal to 1 day in the present study (Fukuda, 2018). Equation (3) shows that temporal roughness of slip rate is controlled by the hyperparameter α 2…”

Magmatic or Not Magmatic? The 2015–2016 Seismic Swarm at the Long-Dormant Jailolo Volcano, West Halmahera, Indonesia

“…They are thought to originate in response to stress histories more complex than a sudden stress change, e.g., due to a large earthquake, producing typical aftershock sequences (Mogi, 1967). High pore-pressure diffusion (Talwani and Acree, 1984), pressurization of fluid-filled reservoirs (Simpson et al, 1988), man-made or natural hydrofractures (including magmatic diking) Passarelli et al, 2015b), and slow-slip events (Lohman and McGuire, 2007;Peng and Gomberg, 2010;Fukuda, 2018) have all been identified as trigger mechanisms of seismic swarms.…”