Segmentation of Slow Slip Events in South Central Alaska Controlled by the Yakutat Plateau

Abstract:

Slow slip events (SSEs) have been observed in many subduction zones and are believed to affect the timing and size of future large earthquakes. However, the underlying mechanism that controls the segmentation of SSEs is still unclear. Segmentation of SSEs behavior at subduction zones has been observed in Cascadia [Brudzinski and Allen, 2007], southwest Japan [Obara 2010], Mexico [Brudzinski et al., 2010] and New Zealand [Wallace et al., 2012]. The possible causes include along-strike variations of pore-pressure related to silica enrichment [Audet and Burgmann, 2014], strength variation due to composition change of upper geological terraces [Brudzinski and Allen, 2007], variation of interseismic coupling depth [Wallace and Beavan, 2010], and variations of effective normal stress [Liu et al., 2013; Watkins et al., 2015] and slab geometry [Li et al., 2014]. Here we build a comprehensive 3D model in rate-and-state friction to investigate the factors that control the SSE segmentation in South Central Alaska, where the 1964 M9.2 earthquake occurred. Our results show that the segmentation of the SSEs in this region are likely controlled by the different effective normal stress in the fault zone. Seismic data constrained Vp/Vs ratio in the fault zone show little along-strike variation, indicating the different effective normal stress is not likely from variation of pore-pressure condition. As the boundary of the SSEs segments alined with the subducted Yakutat Plateau, the extra effective normal stress is likely caused by the extra buoyancy of the subducted plateau. In conclusion, the segmentation of SSEs in south central Alaska is likely controlled by the Yakutat Plateau. Our work implies that structure anomaly will have a long-lived effect on the slip behavior of the subduction zone.