Subduction zone coupling and tectonic block rotations in the North Island, New Zealand

Abstract

The GPS velocity field in the North Island of New Zealand is dominated by the long‐term tectonic rotation of the eastern North Island and elastic strain from stress buildup on the subduction zone thrust fault. We simultaneously invert GPS velocities, earthquake slip vectors, and geological fault slip rates in the North Island for the angular velocities of elastic crustal blocks and the spatially variable degree of coupling on faults separating the blocks. This approach allows us to estimate the distribution of interseismic coupling on the subduction zone interface beneath the North Island and the kinematics of the tectonic block rotations. In agreement with previous studies we find that the subduction zone interface beneath the southern North Island has a high slip rate deficit during the interseismic period, and the slip rate deficit decreases northward along the margin. Much of the North Island is rotating as several, distinct tectonic blocks (clockwise at 0.5–3.8 deg Myr−1) about nearby axes relative to the Australian Plate. This rotation accommodates much of the margin‐parallel component of motion between the Pacific and Australian plates. On the basis of our estimation of the block kinematics we suggest that rotation of the eastern North Island occurs because of the southward increasing thickness of the subducting Hikurangi Plateau. These results have implications for our understanding of convergent margin plate boundary zones around the world, particularly with regard to our knowledge of mechanisms for rapid tectonic block rotations at convergent margins and the role of block rotations in the slip partitioning process.

Tectonics of the Taranaki region, New Zealand: Earthquake focal mechanisms and stress axes

“…1) as a means of elucidating the current tectonics. It complements previous work on active faulting (Nodder 1993;Hull 1994;Nicol et al 2005), and geodetic modelling (Wallace et al 2004), and expands significantly on the previously limited use of focal mechanisms to study Taranaki tectonics (Reyners 1980;Cavill et al 1997;Webb & Anderson 1998). It forms part of a multi-faceted study of Taranaki (Sherburn & White 2005;Sherburn et al in press) with the overall aim of understanding the structure and seismicity of the region and using that information to understand better earthquake monitoring data from Mt Taranaki volcano.…”

“…Earthquakes 5-25 km deep exhibit a normal mechanism with a north-south T axis, and earthquakes 25-42 km deep also had a normal mechanism, with a lesser strike-slip component and a southeast-oriented T axis. Modelling by Wallace et al (2004) suggests there is 1.5 mm/yr of left-lateral transtensional motion across the TRL, which in their model forms the northern boundary of their Taranaki block, as a consequence of clockwise rotation of Taranaki about a pole c. 100 km southwest of Cape Egmont.…”

“…This mechanism has a significant number of polarity violations and therefore may not be very reliable. Wallace et al (2004) divided the North Island into several rigid tectonic blocks, with the block including Taranaki bounded on the west by the CEFZ, and used the GPS velocity field, earthquake slip vectors, and geological fault slip rates to show that there is c. 1 mm/yr of east-west extension along the CEFZ at the latitude of New Plymouth. This is produced by a clockwise rotation of the block at a rate of 0.4°/m.y.…”

Teleseismic constraints on the geological environment of deep episodic slow earthquakes in subduction zone forearcs: A review

“…10a). Spatial variations in plate coupling at the Hikurangi subduction zone are well constrained by a dense network of geodetic stations, where full plate interface coupling based on GPS data occurs at shallow levels to the northeast, and extends to further depth to the southwest (Wallace et al, 2004). Slow slip events with a period of approximately two years have been detected downdip of the locked portion in both areas and follow a similar spatial pattern, with slow slip being much shallower to the northeast (Wallace and Beavan, 2010).…”

Investigating subduction earthquake geology along the southern Hikurangi margin using palaeoenvironmental histories of intertidal inlets

“…GPS data shows the plate interface is presently strongly interseismically coupled ( Fig. 1B; Wallace et al 2004) and seismicity delineates a c. 70 km wide locked zone on the plate interface across the southern North Island (Reyners 1998). Long-term geologic data indicate permanent shortening in the upper plate over the past 5 Ma accounting for only 20% of the margin-normal plate convergence; the remaining 80% is assumed to be accommodated by slip on the subduction interface (Nicol & Beavan 2003).…”