Interseismic locking on the Hikurangi subduction zone: Uncertainties from slow‐slip events

Abstract

Interseismic locking on the Hikurangi subduction zone in New Zealand is examined in light of alternative assumed locking distributions and the impact of transients (slow-slip and volcanic sources) on temporal and spatial resolution. The modern pattern of locking in the north is poorly resolved and, based on simulations of possible transient behavior, may be an ephemeral feature of the subduction cycle. While there appears to be some contemporary locking in the northern half of the Hikurangi subduction zone (HSZ), its location is model dependent, and hence, its relationship to structure, slow-slip, or any transition zone there is unclear. Simulations of site velocities using the 14 year history of transient events reveal that in the timescale of the interseismic period the northern half of the HSZ could be either locked or unlocked, and this may not be resolvable for decades. In the southern half, there is strong contemporary locking in the 15 to 40 km depth range, but again, the slow-slip history leads to uncertainty in the long-term pattern. Slow-slip events not only reduce the long-term locking by aseismic slip but also greatly hinder our ability to see it. It is within the range of possible models that the slip deficit rate at the HSZ is more uniform along strike, and the modern appearance is controlled by the particular pattern of transients over the past 10 to 20 years when the GPS data were collected. Similarly, uncertainties in surface velocities will be large at any subduction zone with large transients.

Can the Updip Limit of Frictional Locking on Megathrusts Be Detected Geodetically? Quantifying the Effect of Stress Shadows on Near‐Trench Coupling

“…Many geodetic inversions show low or zero coupling near the trench, where there is limited model resolution (e.g., Chlieh et al, 2008Chlieh et al, , 2014Loveless & Meade, 2010;McCaffrey, 2014;Nocquet et al, 2017). This is consistent with a general view that shallow faults are velocity strengthening (e.g., Byrne et al, 1988;Ikari et al, 2009;Marone & Scholz, 1988;Wu et al, 1975) and therefore must creep under applied stress.…”

“…However, numerous geodetic inversions propose a scenario in which the fault is fully uncoupled (i.e., creeping at the full long-term rate) at the trench (e.g., Chlieh et al, 2008Chlieh et al, , 2014McCaffrey, 2014;Nocquet et al, 2017), a scenario we show in Figure S2 (dashed line). If the shallow fault has variable strength or some small locked patches, the resulting slip rate would be even lower.…”

“…If the shallow fault has variable strength or some small locked patches, the resulting slip rate would be even lower. However, numerous geodetic inversions propose a scenario in which the fault is fully uncoupled (i.e., creeping at the full long-term rate) at the trench (e.g., Chlieh et al, 2008Chlieh et al, , 2014McCaffrey, 2014;Nocquet et al, 2017), a scenario we show in Figure S2 (dashed line). The results shown here demonstrate that in such a case, the resultant stressing rate on the shallow part of the fault is negative, representing a release of stored energy and thus inconsistent with long-term interseismic loading of the fault.…”

Seismicity at the Northern Hikurangi Margin, New Zealand, and Investigation of the Potential Spatial and Temporal Relationships With a Shallow Slow Slip Event

“…The SSEs of the northern Hikurangi margin near Gisborne, New Zealand, occur at very shallow depths (<15 km). Previous studies of these Hikurangi SSEs have investigated slip distribution determined using Global Positioning System (GPS) and modeling (Bartlow et al, ; Douglas et al, ; McCaffrey, ; McCaffrey et al, ; Wallace et al, , , ; Wallace, Beavan, et al, ; Wallace & Beavan, ; Wallace & Eberhart‐Phillips,), detection and location of tectonic tremor (Kim et al, ; Todd et al, ; Todd & Schwartz, ), analysis of the relation of SSEs to slab and interface seismicity (Jacobs et al, ; Warren‐Smith, Fry, Kaneko, et al, ), and detailed seismic imaging (Barker et al, ; Bell et al, ). SSEs have been observed to occur in the northern Hikurangi margin approximately every 18 to 24 months (Wallace & Beavan, ).…”

Slow slip events and the 2016 Te Araroa Mw 7.1 earthquake interaction: Northern Hikurangi subduction, New Zealand

“…The Hikurangi subduction margin has generated more than 30 slow slip events over the last 15 years, with different durations, sizes, and nucleation depths [Douglas et al, 2005;Wallace and Beavan, 2010;Wallace et al, 2012;Bartlow et al, 2014;McCaffrey, 2014;Wallace et al, 2014Wallace et al, , 2016. Here we use continuous Global Positioning System (cGPS) observations to constrain the spatiotemporal evolution of an SSE sequence in 2016, and seismological observations (Figure 1), to investigate the interaction between the SSE sequence and the 2016 M w 7.1 Te Araroa earthquake.…”