Slow slip events are well documented in global subduction
zones at depths of 30-50 km. Tectonic (non-volcanic) tremor is
considered to be the seismic manifestation of slow slip and is
spatiotemporally correlated with slip events in most regions. Along the
northern Hikurangi Margin, New Zealand, where a seamount studded igneous
plateau subducts beneath the North Island, slow slip occurs shallowly at
depths <15 km. Here, slow slip is associated with increases in
microseismicity levels and has previously been weakly linked to tectonic
tremor. Over a six-year period, the spatiotemporal progression of slow
slip events along the northern Hikurangi Margin with respect to tremor,
earthquake occurrence, and Coulomb failure stress changes imparted on
the megathrust is analyzed. In this study, the first comprehensive
tremor catalog is presented for 2010-2015. The catalog demonstrates that
tremor is temporally associated with shallow slow slip events and deep
tremor episodes may indicate the occurrence of previously undetected
long duration slip events. A slow slip event in 2014 was recorded by the
Hikurangi Ocean Bottom Investigation of Tremor and Slow Slip (HOBITSS)
experiment, resulting in a detailed spatiotemporal analysis of various
interplate slip processes with respect to a local subducted seamount.
Coulomb failure stress change analysis of this event suggests that
seamount subduction plays a dominant role in the stress state of the
shallow megathrust, and that the northern Hikurangi Margin is weakly
coupled and largely releases strain through slow slip events. A detailed
analysis of the Coulomb failure stress change imparted on the shallow
megathrust by seven slow slip events along the northern Hikurangi Margin
between 2010-2014 demonstrates that stress changes from these events
influence the along strike migration of slow slip event sequences.
Additionally, the stress changes dictate the spatial relationship
between tectonic tremor and slow slip, with onshore tectonic tremor
occurring almost wholly within regions of stress increase. Over multiple
slow slip events, the shallow-most part of the plate interface
experiences a net stress increase and may promote failure in future
shallow earthquakes, such as tsunami earthquakes, which impact seismic
hazards along the east coast of New Zealand.