Subduction thermal regime, slab dehydration, and seismicity distribution beneath Hikurangi based on 3-D simulations

The downdip limit of seismogenic interfaces inferred from the subduction
thermal regime by thermal models has suggested relating to the faulting
instability caused by brittle failure regime in various plate convergent
systems. However, the featured three-dimensional (3-D) temperature
structure especially along the horizontal two-dimensional (2-D) dimension
of a subduction zone remains still poorly constrained. To robustly
investigate and further map the horizontal distribution of subduction
regime and subsequently induced slab dewatering in a decent plate beneath
a convergent margin, we construct a regional thermal model that
incorporates an up-to-date 3-D slab topography and the MORVEL plate
velocity to simulate plate subduction history in Hikurangi. The
calculation provides an identified thrust zone featured by remarkable slab
dehydration near the Taupo volcanic arc in North Island distributed along
the Kapiti, Manawatu, and Raukumara (KMR) region. Average
subduction-associated slab dehydration of 0.09 to 0.12 wt%/km is greater
than the dehydration in the other portions of descending slab and possibly
contributes to an along-arc variation of interplate pore fluid pressure. A
large-scale slab dehydration (>0.05 wt%/km) and a high thermal
gradient (>4°C/km) are also identified in KMR associated with
frequent deep slow slip events (SSEs). Intra-slab dehydration that exceeds
0.2 wt%/km beneath Manawatu near the source region of tectonic tremors
suggests an unknown relationship in the genesis of slow earthquakes.