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Quaternary Geometry, Kinematics and Paleoearthquake History at the Intersection of the Strike-Slip North Island Fault System and Taupo Rift, New Zealand

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The North Island of New Zealand sits astride the Hikurangi margin along which the oceanic Pacific Plate is being obliquely subducted beneath the continental Australian Plate. The North Island Fault System1 (NIFS), in the North Island of New Zealand, is the principal active strike-slip fault system in the overriding Australian Plate accommodating up to 30% of the margin parallel plate motion. This study focuses on the northern termination of the NIFS, near its intersection with the active Taupo Rift, and comprises three complementary components of research: 1) the investigation of the late Quaternary (c. 30 kyr) geometries and kinematics of the northern NIFS as derived from displaced geomorphic landforms and outcrop geology, 2) examination of the spatial and temporal distribution of paleoearthquakes in the NIFS over the last 18 kyr, as derived by fault-trenching and displaced landforms, and consideration of how these distributions may have produced the documented late Quaternary (c. 30 kyr) kinematics of the northern NIFS, and 3) Investigation of the temporal stability of the late Quaternary (c. 30 kyr) geometries and kinematics throughout the Quaternary (1-2 Ma), derived from gravity, seismic-reflection, drillhole, topographic and outcrop data. The late Quaternary (c. 30 kyr) kinematics of the northern NIFS transition northward along strike, from strike-slip to oblique-normal faulting, adjacent to the rift. With increasing proximity to the Taupo Rift the slip vector pitch on each of the faults in the NIFS steepens gradually by up to 60 degrees, while the mean fault-dip decreases from 90 degrees to 60 degrees W. Adjustments in the kinematics of the NIFS reflect the gradual accommodation of the NW-SE extension that is distributed outside the main physiographic boundary of the Taupo Rift. Sub-parallelism of slip vectors in the NIFS with the line of intersection between the two synchronous fault systems reduces potential space problems and facilitates the development of a kinematically coherent fault intersection, which allows the strike-slip component of slip to be transferred into the rift. Transfer of displacement from the NIFS into the rift accounts for a significant amount of the northeastward increase of extension along the rift. Steepening of the pitch of slip vectors towards the northern termination of the NIFS allows the kinematics and geometry of faulting to change efficiently, from strike-lip to normal faulting, providing an alternative mechanism to vertical axis rotations for terminating large strike-lip faults. Analyses of kinematic constraints from worldwide examples of synchronous strike-lip and normal faults that intersect to form two or three plate configurations, within either oceanic or continental crust, suggest that displacement is often transferred between the two fault systems in a similar manner to that documented at the NIFS - Taupo Rift fault intersection. The late Quaternary (c. 30 kyr) change in the kinematics of the NIFS along strike, from dominantly strike-slip to oblique-normal faulting, arises due to a combination of rupture arrest during individual earthquakes and variations in the orientation of the coseismic slip vectors. At least 80 % of all surface rupturing earthquakes appear to have terminated within the kinematic transition zone from strike-slip to oblique-normal slip. Fault segmentation reduces the magnitudes of large surface rupturing earthquakes in the northern NIFS from 7.4-7.6 to c. 7.0. Interdependence of throw rates between the NIFS and Taupo Rift suggests that the intersection of the two fault systems has functioned coherently for much of the last 0.6-1.5 Myr. Oblique-normal slip faults in the NIFS and the Edgecumbe Fault in the rift accommodated higher throw rates since 300 kyr than during the last 0.6-1.5 Myr. Acceleration of these throw rates may have occurred in response to eastward migration of rifting, increasing both the rates of faulting and the pitch of slip vectors. The late Quaternary (e.g. 30 kyr) kinematics, and perhaps also the stability, of the intersection zone has been geologically short lived and applied for the last c. 300 kyr.
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... Regional throw transects (2e7) are indicated by dashed lines (see Fig. 1 for location of transect-1). Seismic-reflection profiles are from Woodward (1988), O'Connor (1988, Davey et al. (1995), Woodward-Clyde (1998), Taylor et al. (2004), Lamarche et al. (2006), Mouslopoulou (2006) and SGN Science unpublished data. The onshore multichannel seismic reflection profiles are migrated with reflectors down to two-way travel times (TWT) of 2 s (Woodward, 1988;O'Connor, 1988;Woodward-Clyde, 1998;Mouslopoulou, 2006). ...
... Seismic-reflection profiles are from Woodward (1988), O'Connor (1988, Davey et al. (1995), Woodward-Clyde (1998), Taylor et al. (2004), Lamarche et al. (2006), Mouslopoulou (2006) and SGN Science unpublished data. The onshore multichannel seismic reflection profiles are migrated with reflectors down to two-way travel times (TWT) of 2 s (Woodward, 1988;O'Connor, 1988;Woodward-Clyde, 1998;Mouslopoulou, 2006). The bulk of the offshore seismic data consist of 3.5 kHz and migrated multi-channel seismic (MCS) reflection profiles that provide data down to 0.04 and 1.5 s, respectively (Davey et al., 1995;Lamarche et al., 2006). ...
... The bulk of the offshore seismic data consist of 3.5 kHz and migrated multi-channel seismic (MCS) reflection profiles that provide data down to 0.04 and 1.5 s, respectively (Davey et al., 1995;Lamarche et al., 2006). Regional gravity profiles are from Mouslopoulou, 2006. For more details about the gravity and seismic data (including the seismic and gravity profiles along transect 3) refer to Mouslopoulou (2006) (an electronic version of Mouslopoulou (2006) can be obtained upon request from the School of Geological Sciences at Victoria University of Wellington, New Zealand). ...
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Intersecting strike-slip and normal fault systems form either two or three plate configurations. In circumstances where they intersect to form a triple junction, internal block deformation produces a quasi-stable 3-D configuration permitting maintenance of both the regional geometry and kinematics of the intersection. This paper examines the temporal stability of such a triple junction in New Zealand over a range of timescales, from individual earthquakes to millions of years, and discusses the factors that impact its stability. Using seismic-reflection, gravity, drill-hole and outcrop data, the accumulation of vertical displacements is examined, both on individual faults and across the intersection zone between the strike-slip North Island Fault System (NIFS) and the Taupo Rift. Fault-throws and throw rates for the NIFS and Taupo Rift suggest that despite a three-fold increase in throw rates in both fault systems at about 0.3Ma, which may have modified the orientation of the slip vectors and therefore the contemporary kinematics of the triple junction, the intersection of the two fault systems has functioned coherently for the last 0.6–1.5Myr accumulating vertical displacements interdependently since the early stages of rifting. The apparent arrest of a large magnitude earthquake on the rift-bounding fault adjacent to the intersection, suggests that the short-term dynamic behaviour of the system is relatively complex compared to the more coherent long-term kinematics.
... Regional throw transects (2e7) are indicated by dashed lines (see Fig. 1 for location of transect-1). Seismic-reflection profiles are from Woodward (1988), O'Connor (1988, Davey et al. (1995), Woodward-Clyde (1998), Taylor et al. (2004), Lamarche et al. (2006), Mouslopoulou (2006) and SGN Science unpublished data. The onshore multichannel seismic reflection profiles are migrated with reflectors down to two-way travel times (TWT) of 2 s (Woodward, 1988;O'Connor, 1988;Woodward-Clyde, 1998;Mouslopoulou, 2006). ...
... Seismic-reflection profiles are from Woodward (1988), O'Connor (1988, Davey et al. (1995), Woodward-Clyde (1998), Taylor et al. (2004), Lamarche et al. (2006), Mouslopoulou (2006) and SGN Science unpublished data. The onshore multichannel seismic reflection profiles are migrated with reflectors down to two-way travel times (TWT) of 2 s (Woodward, 1988;O'Connor, 1988;Woodward-Clyde, 1998;Mouslopoulou, 2006). The bulk of the offshore seismic data consist of 3.5 kHz and migrated multi-channel seismic (MCS) reflection profiles that provide data down to 0.04 and 1.5 s, respectively (Davey et al., 1995;Lamarche et al., 2006). ...
... The bulk of the offshore seismic data consist of 3.5 kHz and migrated multi-channel seismic (MCS) reflection profiles that provide data down to 0.04 and 1.5 s, respectively (Davey et al., 1995;Lamarche et al., 2006). Regional gravity profiles are from Mouslopoulou, 2006. For more details about the gravity and seismic data (including the seismic and gravity profiles along transect 3) refer to Mouslopoulou (2006) (an electronic version of Mouslopoulou (2006) can be obtained upon request from the School of Geological Sciences at Victoria University of Wellington, New Zealand). ...
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Intersecting strike-slip and normal fault systems form either two or three plate configurations. In circumstances where they intersect to form a triple junction, internal block deformation produces a quasi-stable 3-D configuration permitting maintenance of both the regional geometry and kinematics of the intersection. This paper examines the temporal stability of such a triple junction in New Zealand over a range of timescales, from individual earthquakes to millions of years, and discusses the factors that impact its stability. Using seismic-reflection, gravity, drill-hole and outcrop data, the accumulation of vertical displacements is examined, both on individual faults and across the intersection zone between the strike-slip North Island Fault System (NIFS) and the Taupo Rift. Fault-throws and throw rates for the NIFS and Taupo Rift suggest that despite a threefold increase in throw rates in both fault systems at about 0.3 Ma, which may have modified the orientation of the slip vectors and therefore the contemporary kinematics of the triple junction, the intersection of the two fault systems has functioned coherently for the last 0.6e1.5 Myr accumulating vertical displacements interdependently since the early stages of rifting. The apparent arrest of a large magnitude earthquake on the rift-bounding fault adjacent to the intersection, suggests that the short-term dynamic behaviour of the system is relatively complex compared to the more coherent long-term kinematics.
... In formal plate tectonic terms, this type of triple junction is considered unstable (rigid blocks) (York, 1973). The intersection of the NIFS and Taupo Rift may, however, have been stable at a regional scale since 300 kyr, when throw rates on the principal faults in the NIFS and the rift increased by a factor of three (Mouslopoulou, 2006). The present fault geometries show no outward signs that strike-slip faults are displacing the rift or that the present kinematics of the active faults differ from those recorded in the last 300 kyr. ...
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The Rotorua 1:250 000 geological map covers 24 800 km2 of the Bay of Plenty, Waikato, Hawke's Bay, Gisborne and Manawatu-Wanganui regions in the North Island, New Zealand. The Hauraki Plains and Kaimai Range extend into the northwest quadrant of the map and the Hauhungaroa and Rangitoto ranges are close to the western margin. The Urewera ranges and Waikaremoana hill country in the east are separated from these by a NNE-trending belt of volcanoes, lakes, volcanic plateaus and grabens of the Taupo Volcanic Zone (TVZ) and Taupo Rift. Offshore, the 23-30 km wide continental shelf slopes gently to water depths of 120-150 m; it is surmounted by a number of volcanic islands, the largest of which are Motiti, Moutohora (Whale) and White (Whakaari) islands. The heads of the submarine Tauranga and White Island canyons extend into the map area from beyond the continental shelf. Complexly deformed Mesozoic sedimentary rocks underlie the entire area. Rocks of the Jurassic Manaia Hill Group of the Waipapa (composite) terrane form the western hill country and are probably juxtaposed against Torlesse (composite) terrane beneath volcanic deposits of the TVZ. Kaweka terrane is the westernmost of the Torlesse terranes exposed, and it is separated from the Early Cretaceous Pahau terrane (Waioeka petrofacies) to the east by either the Whakatane Melange or Whakatane Fault. East of the Whakatane Fault, sub-vertical and deformed rocks of Pahau terrane are overlain by gently dipping, little-deformed, Early Cretaceous to Paleogene marine sandstone and mudstone, the oldest of which is only 5-14 million years younger than the underlying basement rocks. A short but intense period of deformation, uplift and erosion was associated with the amalgamation of Kaweka and Pahau terranes and the formation of the Whakatane Melange. In the Late Cretaceous to Paleogene periods, the Tinui and Mangatu groups were deposited during a period of plate boundary quiescence. Renewed plate boundary convergence is signalled in the southeast by a late Paleogene to earliest Neogene unconformity overlain by a thick Early Miocene to Pliocene sequence of clastic, largely bathyal sediments of the Tolaga and Mangaheia groups. Middle Miocene shelf deposits of the King Country Basin are preserved in the extreme southwest of the map area. Andesitic to rhyodacitic Miocene to Pliocene volcanic rocks crop out in the Kaimai Range and Tauranga area. Early Quaternary andesitic volcanic rocks, including Titiraupenga, Pureora and Hauhungaroa volcanoes, and predominantly rhyolitic ignimbrites from the Mangakino Volcanic Centre, crop out to the west of the TVZ and mark initiation of TVZ eruptive activity. Rhyolitic ignimbrites from a period of intense explosive volcanism in the middle Quaternary dominate volcanic deposits of the map area. The more recent Oruanui (27 ka) and Taupo (1.8 ka) ignimbrites are widespread across central and southern parts. At least eight caldera volcanoes were sources of widespread TVZ ignimbrites. While the Taupo and Rotorua calderas have remained prominent landscape features, others are obscured by younger deposits. Throughout the central TVZ, rhyolite (and minor dacite) lava domes and dome complexes, such as Maroa and Tarawera-Haroharo, represent non-explosive rhyolite volcanism, of smaller volume than the pyroclastic deposits. Rhyolite lava also forms many isolated domes, such as Mount Maunganui, Mount Ngongotaha, the Horohoro cliffs and several peninsulas around Lake Taupo. Small basalt scoria cones, lava flows and tuff rings, and several andesite stratovolcanoes (including Mount Edgecumbe/Putauaki) are present within the map area. The surface expression of TVZ hydrothermal systems includes hot pools, mud pools, steam vents and geysers. 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Since 1840, at least eleven tsunami have been recorded within the Bay of Plenty. Rock and mineral resources include aggregate, pumice, diatomite, zeolite and perlite. Some gold-silver mineralisation is known. High-temperature geothermal steam is used to generate c. 600 MW of electricity from several geothermal systems, providing about 10% of the nation's supply, and production will increase as new stations come on stream. Hydrothermal areas within the TVZ are significant tourist attractions.
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