Newly observed, deep slow slip events at the central Hikurangi margin, New Zealand: Implications for downdip variability of slow slip and tremor, and relationship to seismic structure

摘要

We present previously undocumented deep (25-45 km depth), moderate-duration (2-3 months) slow slip events (SSEs) directly downdip of known shallow (<15 km depth), short-term (2-3 weeks) SSEs at the central Hikurangi margin, New Zealand. The moderate-duration SSEs produce 2-6 mm of horizontal displacement at continuous Global Positioning System stations in 2006 and 2008, similar to Cascadia SSEs. They involve 2-5 cm of slip over ～5000 km~2 of the subduction interface. Tremor occurs just downdip of the deep SSE source area. We also present results from a large, shallow (<12 km) SSE in 2013 just updip of the 2006/2008 SSEs. The location of deep SSEs between shallow, short-term SSEs and tremor indicates strong downdip variation of subduction interface slip behavior at central Hikurangi. The deep SSEs occur where Qp and Vp/Vs data suggest an accumulation of fluid-rich underplated sediment at the interface, consistent with the idea that SSEs occur under high fluid pressure. Key Points Slow slip is highly variable in the downdip direction Slow slip occurs over a broad range of depths Slow slip occurs in a region of inferred high fluid pressure