Episodic Tremor and Slip (ETS), involving transient deformations accompanied by emergent, low‐frequency tremor occurs in subduction zones around the world. ETS events increase the shear stress on locked megathrusts and may potentially trigger damaging earthquakes. Despite the clear association of tremor and slip the physical relationship between them is unresolved. Tremor appears to result from slip on small asperities on the plate interface due to either creep on the surrounding fault, or stress increases ahead of the propagating slow‐slip front. Previous studies of migrating slow slip events have not had sufficient spatial and temporal resolution to differentiate between these two models. To address this, we invert GPS data from the August 2009 ETS event in central Cascadia for the space‐time evolution of fault slip‐rate. We find a correlation in both space and time between tremor epicenters and the independently determined position of high fault slip‐rate. This supports the first hypothesis that tremor asperities are loaded directly by slow slip, rather than by stress increases ahead of the slip front, and provides new insights into the mechanics of ETS.

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At many plate boundaries, conditions in the transition zone between seismogenic and stable slip produce slow earthquakes. In the Cascadia subduction zone, these events are consistently observed as slow, aseismic slip on the plate interface accompanied by persistent tectonic tremor. However, not all slow slip at other plate boundaries coincides spatially and temporally with tremor, leaving the physics of tremor genesis poorly understood. Here we analyze seismic, geodetic, and strainmeter data in Cascadia to observe for the first time a large, tremor-generating slow earthquake change from tremor-genic to silent and back again. The tremor falls silent at reduced slip speeds when the migrating slip front pauses as it loads the stronger adjacent fault segment to failure. The finding suggests that rheology and slip-speed-regulated stressing rate control tremor genesis, and the same section of fault can slip both with and without detectable tremor, limiting tremor's use as a proxy for slip.

We present a time‐dependent slip model of 12 slow slip events (SSEs) occurring in the Hikurangi margin of New Zealand during 2010 and 2011. This model is obtained by inverting daily GPS solutions from GeoNet's continuous GPS network on the North Island and northern South Island. We compare the properties of these SSEs to observations in Japan, Cascadia, and Mexico and find that Hikurangi SSEs have comparatively large amounts of slip (up to 27 cm), high slip rates (up to 1.4 cm/d), and a large range of depths (10–40 km), durations (7–270 days), and sizes (Mw 5.9–6.9). We further investigate the relationship between the Cape Turnagain SSE and an associated seismic swarm and find that observations are consistent with stress triggering outside the slowly slipping region; however, other explanations cannot be ruled out. We also compare slip during the long‐term Manawatu SSE with the tremor epicenters found by Ide (2012) and note that tremor locations are offset in the downdip direction relative to the slipping region, similar to observations in the Bungo Channel of Japan and Guerrero, Mexico.