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

Abstract

Slow slip events (SSEs) with a moment magnitude of 6.6–6.7 occur at intervals of 5–9 months along the southern Ryukyu subduction zone in southwestern Japan. To obtain detailed image of these SSEs, this study applies a modified Network Inversion Filter to the Global Navigation Satellite System time series from March 2010 to February 2013 and estimates the spatiotemporal evolution of slow slip on the plate interface. Five SSEs are detected during this period. These events have similar cumulative slip distributions and are located near the northwestern coast of Iriomote Island at depths of 30–60 km, indicating that the SSEs recur in the same fault area. The analysis reveals that the spatiotemporal evolution of slip during the five SSEs varies from event to event. The notable feature is that three of the five SSEs nucleate rapidly and reach the maximum slip rate within several days, while the other two SSEs show much slower nucleation, lasting for 25–45 days prior to rapid acceleration of slip. Such variations in spatiotemporal evolution suggest temporal changes of fault properties such as fluid distribution and fault friction. Very low frequency earthquakes and low‐frequency earthquakes are activated during one of the five SSEs. The source area of the SSEs is complimentarily located in a deeper part of the very low frequency earthquakes and low‐frequency earthquake source areas, and a possible tsunami source region is located near the trench, indicating the depth dependence of the physical properties along the plate interface.

Slip-rate-dependent friction as a universal mechanism for slow slip events

“…We considered case examples of well-characterized repeating SSEs in Cascadia 33 , Hikurangi 6 (New Zealand), Ryukyu 34 (Japan) and the Guerrero gap 35 (Mexico) (Fig. 4).…”

“…In the other examples we selected representative time series at particular GPS stations. We rescaled each time series for slip on the megathrust on the basis of published fault slip inversions 6,33,34,35 (second y-axis), assuming that repeated SSEs result from slip on the same segment and that GPS displacement varies linearly with fault slip.…”

Spatiotemporal Evolution of Long‐ and Short‐Term Slow Slip Events in the Tokai Region, Central Japan, Estimated From a Very Dense GNSS Network During 2013–2016

“…To overcome these difficulties, we use a modified version of the NIF (Fukuda et al, 2008) to examine the spatiotemporal evolution of slow slip. The modified NIF enables us to recover the slip evolution accurately, including initiation and propagation of slip (Fukuda et al, 2004(Fukuda et al, , 2008Fukuda, 2018;Kano et al, 2018). Furthermore, the modified NIF is capable of extracting small slow slip signals from noisy GNSS time series (Fukuda et al, 2004(Fukuda et al, , 2014.…”

Potential of Megathrust Earthquakes Along the Southern Ryukyu Trench Inferred from GNSS Data

“…The large slip areas of SSEs exhibit an average slip rate of ~ 13 cm/yr. These are comparable to the relative plate motion, indicating that the main slip area is entirely coupled during the inter-SSE period and the SSEs release most of the accumulated strain (Kano et al 2018b). On the shallower side of the SSE region at depths of ~ 10 to 20 km, the seismic signatures of slow fault slips with dominant frequencies of a few Hz and a few tens of seconds, known as lowfrequency earthquakes (LFEs) and very low-frequency earthquakes (VLFEs), have often been identi ed (Ando et al 2012; Nakamura and Sunagawa 2015; Arai et al 2016;Nakamura 2017).…”

“…1a) (Heki and Kataoka 2008;Nishimura 2014;Tu and Heki 2017). These SSEs occur approximately every six months with a moment magnitude (Mw) of 6.6-6.7 (Kano et al 2018b). The large slip areas of SSEs exhibit an average slip rate of ~ 13 cm/yr.…”