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Figure F11. Global Positioning System (GPS) observations (blue circles and fitted saw-tooth function) showing slow eastward displacement above the Cascadia subduction zone and periodic reversals concurrent with increased seismic tremor levels at and above the subduction thrust interface (Fig. F8B). Reversals are caused by slow slip on the subduction plate interface downdip from the currently locked portion of the subduction fault (from Rogers and Dragert, 2003). Slip events like these have been observed to initiate slow rupture that propagates through the seismogenic part of the subduction fault (Heesemann and Davis, submitted).

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