Tectonic and structural features of the Pacific/Indo-Australian plate boundary in the North Fiji-Lau Basin regions, southwest Pacific

1993 ◽  
Vol 13 (2) ◽  
pp. 126-131 ◽  
Author(s):  
D. L. Tiffin
Keyword(s):  
Plate Boundary ◽  
Structural Features ◽  
Lau Basin ◽  
Southwest Pacific ◽  
The North ◽  
Australian Plate ◽  
The Pacific

Dynamics of the extension in the Fonualei Rift in the northern Lau Basin at 16 °S

2021 ◽  
Author(s):  
Anna Jegen ◽  
Anke Dannowski ◽  
Heidrun Kopp ◽  
Udo Barckhausen ◽  
Ingo Heyde ◽  
...  
Keyword(s):  
Velocity Gradient ◽  
Lower Crust ◽  
Pacific Plate ◽  
P Wave ◽  
Upper Crust ◽  
Lau Basin ◽  
Australian Plate ◽  
The Pacific ◽  
Refraction Seismic ◽  
Roll Back

<p>The Lau Basin is a young back-arc basin steadily forming at the Indo-Australian-Pacific plate boundary, where the Pacific plate is subducting underneath the Australian plate along the Tonga-Kermadec island arc. Roughly 25 Ma ago, roll-back of the Kermadec-Tonga subduction zone commenced, which lead to break up of the overriding plate and thus the formation of the western Lau Ridge and the eastern Tonga Ridge separated by the emerging Lau Basin.</p><p>As an analogue to the asymmetric roll back of the Pacific plate, the divergence rates decline southwards hence dictating an asymmetric, V-shaped basin opening. Further, the decentralisation of the extensional motion over 11 distinct spreading centres and zones of active rifting has led to the formation of a composite crust formed of a microplate mosaic. A simplified three plate model of the Lau Basin comprises the Tonga plate, the Australian plate and the Niuafo'ou microplate. The northeastern boundary of the Niuafo'ou microplate is given by two overlapping spreading centres (OLSC), the southern tip of the eastern axis of the Mangatolu Triple Junction (MTJ-S) and the northern tip of the Fonualei Rift spreading centre (FRSC) on the eastern side. Slow to ultraslow divergence rates were identified along the FRSC (8-32 mm/a) and slow divergence at the MTJ (27-32 mm/a), both decreasing southwards. However, the manner of divergence has not yet been identified. Additional regional geophysical data are necessary to overcome this gap of knowledge.</p><p>Research vessel RV Sonne (cruise SO267) set out to conduct seismic refraction and wide-angle reflection data along a 185 km long transect crossing the Lau Basin at ~16 °S from the Tonga arc in the east, the overlapping spreading centres, FRSC1 and MTJ-S2, and extending as far as a volcanic ridge in the west. The refraction seismic profile consisted of 30 ocean bottom seismometers. Additionally, 2D MCS reflection seismic data as well as magnetic and gravimetric data were acquired.</p><p>The results of our P-wave traveltime tomography show a crust that varies between 4.5-6 km in thickness. Underneath the OLSC the upper crust is 2-2.5 km thick and the lower crust 2-2.5 km thick. The velocity gradients of the upper and lower crust differ significantly from tomographic models of magmatically dominated oceanic ridges. Compared to such magmatically dominated ridges, our final P-wave velocity model displays a decreased velocity gradient in the upper crust and an increased velocity gradient in the lower crust more comparable to tectonically dominated rifts with a sparse magmatic budget.</p><p>The dominance of crustal stretching in the regional rifting process leads to a tectonical stretching, thus thinning of the crust under the OLSC and therefore increasing the lower crust’s velocity gradient. Due to the limited magmatic budget of the area, neither the magnetic anomaly nor the gravity data indicate a magmatically dominated spreading centre. We conclude that extension in the Lau Basin at the OLSC at 16 °S is dominated by extensional processes with little magmatism, which is supported by the distribution of seismic events concentrated at the northern tip of the FRSC.</p>

scholarly journals A Microearthquake Study of the Plate Boundary, North Island, New Zealand

2021 ◽  
Author(s):  
◽  
Martin Everardus Reyners
Keyword(s):  
Plate Boundary ◽  
Pacific Plate ◽  
Focal Mechanisms ◽  
Phase Changes ◽  
Indian Plate ◽  
Depth Range ◽  
The North ◽  
The Pacific ◽  
Deep Activity ◽  
Set Up

<p>The seismicity, structure and tectonics of the North Island plate boundary have been studied by means of a microearthquake traverse oriented in the direction of dip of the subducted Pacific plate and stretching from southern Hawke's Bay to northern Taranaki. The geometry of the top of the Pacific plate is inferred from a band of concentrated microearthquake activity which can be identified with the crust of the plate. The Pacific plate appears to have two knee-like bends, one between the east coast and the Ruahine Range, where the top of the plate is about 25 km deep, the other below the volcanic front, where it is about 70 km deep. The shallower bend and subsequent restraightening of the plate can be related to phase changes in the plate, while the deeper bend can be related to volcanism. Composite focal mechanisms indicate that seaward of its shallower bend the Pacific plate is being loaded by the Indian plate, whereas landward of this bend the Pacific plate is sinking under its own weight. Both composite focal mechanisms and the distribution of microseismicity in the Pacific plate suggest the existence of a major discontinuity striking down the dip of the plate and passing beneath the Tongariro volcanic centre. A conspicuous lack of microseismicity in the Indian plate in the eastern North Island revealed in this study can be related to the plates being unlocked in this region. A feature of the seismicity of the Indian plate in the region of the Wanganui Basin is the concentration of activity in the 25-42 km depth range, shallower activity being largely confined to the northeast edge of the basin, near Mt Ruapehu and Waiouru. Composite focal mechanisms suggest the 25-42 km deep activity reflects stresses set up by locking and unlocking of the plates, while the shallower activity reflects local stresses related to volcanic phenomena.</p>

scholarly journals Scenario-based numerical modelling and the palaeo-historic record of tsunamis in Wallis and Futuna, Southwest Pacific

2015 ◽  
Vol 3 (4) ◽  
pp. 2283-2346 ◽  
Author(s):  
G. Lamarche ◽  
S. Popinet ◽  
B. Pelletier ◽  
J. Mountjoy ◽  
J. Goff ◽  
...  
Keyword(s):  
Numerical Models ◽  
Plate Boundary ◽  
South Pacific ◽  
Tsunami Hazard ◽  
Time Of Arrival ◽  
Barrier Reef ◽  
Outer Reef ◽  
Southwest Pacific ◽  
The North ◽  
The Impact

Abstract. We investigated the tsunami hazard in the remote French territory of Wallis and Futuna, Southwest Pacific, using the Gerris flow solver to produce numerical models of tsunami generation, propagation and inundation. Wallis consists of the inhabited volcanic island of Uvéa that is surrounded by a lagoon delimited by a barrier reef. Futuna and the island of Alofi forms the Horn Archipelago located ca. 240 km east of Wallis. They are surrounded by a narrow fringing reef. Futuna and Alofi emerge from the North Fiji Transform Fault that marks the seismically active Pacific-Australia plate boundary. We generated fifteen tsunami scenarios. For each, we calculated maximum wave elevation (MWE), inundation distance, and Expected Time of Arrival (ETA). The tsunami sources were local, regional and distant earthquake faults located along the Pacific Rim. In Wallis, the outer reef may experience 6.8 m-high MWE. Uvéa is protected by the barrier reef and the lagoon, but inundation depths of 2–3 m occur in several coastal areas. In Futuna, flow depths exceeding 2 m are modelled in several populated areas, and have been confirmed by a post-September 2009 South Pacific tsunami survey. The channel between the islands of Futuna and Alofi amplified the 2009 tsunami, which resulted in inundation distance of almost 100 m and MWE of 4.4 m. This first-ever tsunami hazard modelling study of Wallis and Futuna compares well with palaeotsunamis recognised on both islands and observation of the impact of the 2009 South Pacific tsunami. The study provides evidence for the mitigating effect of barrier and fringing reefs from tsunamis.

scholarly journals A Magnetic Survey of the Southwest Pacific Ocean

2021 ◽  
Author(s):  
◽  
David Irwin Ross
Keyword(s):  
New Zealand ◽  
Pacific Ocean ◽  
Ross Sea ◽  
Magnetic Survey ◽  
Southwest Pacific ◽  
The North ◽  
Magnetic Pattern ◽  
The Pacific ◽  
Profiling Techniques ◽  
Ocean Ridge

<p>The design and construction of a free precession proton magnetometer which give a reading of the field directly in gamma is described. This instrument has been used to obtain magnetic profiles across the Southwest Pacific Ocean during the 1963-65 summer Antarctic supply cruises of H.M.N.Z.S. Endeavour. The magnetic and bathymetric profiler obtained on these cruises have been analysed to determine the nature and structure of the oceanic crust in this region. The region is divided into four divisions. (l) The New Zealand Plateau, with an almost continental crustal thickness. (2) The Southwest Pacific Basin, at a depth of 3,000 fathoms. (3) The Pacific-Antarctic Ridge, pert of the world encircling mind-ocean ridge system. (4) The Ross Sea, an epicontinental sea across the Antarctic continental shelf. Subtraction of the regional field form the magnetic results has enabled a regional field map of the area to be drawn. Comparison with earlier results indicates a westward drift of the earth's field of approximately 0.25 degrees /yr. Some discussion of regional anomalies (~ 100 miles period) has been given. Because of the excellent correlation of magnetic anomalies from track to track across the basin it has been possible to draw an anomaly contour map of this part. This map illustrates the predominantly east-west trend of features over the basin. To the north the features parallel the edge of the New Zealand Plateau. To the south the features swing more towards the Pacific-Antarctic Ridge. A major discontinuity is indicated along a direction 9 degrees E of S meeting the Plateau just southwest of Antipodes Islands. If this discontinuity is extrapolated south to the ridge it meets it at approximately 180 degrees E, where the ridge turns N-E towards Easter Island. Across the ridge the magnetic pattern shows three distinct regions. Over the northern flanks large anomalies are evident but the correlation of anomalies from track to track is very poor. Further south, across the upper flanks, the magnetic records are very much subdued. The extent of this region varies appreciably from track to track. Over the axis of the ridge large, steep-sided anomalies are obtained. These correlate well over part of the region studied. The southern flanks of the ridge are hidden by the Balleny Plateau which seems to form a link between Antarctica and the ridge in this region. The bathymetry records obtained indicate a step-type formation over the ridge. A narrow median valley appears to exist along the axis of the ridge. Some preliminary experimentation has been carried out with continual seismic profiling techniques over the region. The equipment that has been developed and the preliminary results obtained with it are discussed.</p>

scholarly journals A Magnetic Survey of the Southwest Pacific Ocean

2021 ◽  
Author(s):  
◽  
David Irwin Ross
Keyword(s):  
New Zealand ◽  
Pacific Ocean ◽  
Ross Sea ◽  
Magnetic Survey ◽  
Southwest Pacific ◽  
The North ◽  
Magnetic Pattern ◽  
The Pacific ◽  
Profiling Techniques ◽  
Ocean Ridge

<p>The design and construction of a free precession proton magnetometer which give a reading of the field directly in gamma is described. This instrument has been used to obtain magnetic profiles across the Southwest Pacific Ocean during the 1963-65 summer Antarctic supply cruises of H.M.N.Z.S. Endeavour. The magnetic and bathymetric profiler obtained on these cruises have been analysed to determine the nature and structure of the oceanic crust in this region. The region is divided into four divisions. (l) The New Zealand Plateau, with an almost continental crustal thickness. (2) The Southwest Pacific Basin, at a depth of 3,000 fathoms. (3) The Pacific-Antarctic Ridge, pert of the world encircling mind-ocean ridge system. (4) The Ross Sea, an epicontinental sea across the Antarctic continental shelf. Subtraction of the regional field form the magnetic results has enabled a regional field map of the area to be drawn. Comparison with earlier results indicates a westward drift of the earth's field of approximately 0.25 degrees /yr. Some discussion of regional anomalies (~ 100 miles period) has been given. Because of the excellent correlation of magnetic anomalies from track to track across the basin it has been possible to draw an anomaly contour map of this part. This map illustrates the predominantly east-west trend of features over the basin. To the north the features parallel the edge of the New Zealand Plateau. To the south the features swing more towards the Pacific-Antarctic Ridge. A major discontinuity is indicated along a direction 9 degrees E of S meeting the Plateau just southwest of Antipodes Islands. If this discontinuity is extrapolated south to the ridge it meets it at approximately 180 degrees E, where the ridge turns N-E towards Easter Island. Across the ridge the magnetic pattern shows three distinct regions. Over the northern flanks large anomalies are evident but the correlation of anomalies from track to track is very poor. Further south, across the upper flanks, the magnetic records are very much subdued. The extent of this region varies appreciably from track to track. Over the axis of the ridge large, steep-sided anomalies are obtained. These correlate well over part of the region studied. The southern flanks of the ridge are hidden by the Balleny Plateau which seems to form a link between Antarctica and the ridge in this region. The bathymetry records obtained indicate a step-type formation over the ridge. A narrow median valley appears to exist along the axis of the ridge. Some preliminary experimentation has been carried out with continual seismic profiling techniques over the region. The equipment that has been developed and the preliminary results obtained with it are discussed.</p>

scholarly journals A Microearthquake Study of the Plate Boundary, North Island, New Zealand

2021 ◽  
Author(s):  
◽  
Martin Everardus Reyners
Keyword(s):  
Plate Boundary ◽  
Pacific Plate ◽  
Focal Mechanisms ◽  
Phase Changes ◽  
Indian Plate ◽  
Depth Range ◽  
The North ◽  
The Pacific ◽  
Deep Activity ◽  
Set Up

<p>The seismicity, structure and tectonics of the North Island plate boundary have been studied by means of a microearthquake traverse oriented in the direction of dip of the subducted Pacific plate and stretching from southern Hawke's Bay to northern Taranaki. The geometry of the top of the Pacific plate is inferred from a band of concentrated microearthquake activity which can be identified with the crust of the plate. The Pacific plate appears to have two knee-like bends, one between the east coast and the Ruahine Range, where the top of the plate is about 25 km deep, the other below the volcanic front, where it is about 70 km deep. The shallower bend and subsequent restraightening of the plate can be related to phase changes in the plate, while the deeper bend can be related to volcanism. Composite focal mechanisms indicate that seaward of its shallower bend the Pacific plate is being loaded by the Indian plate, whereas landward of this bend the Pacific plate is sinking under its own weight. Both composite focal mechanisms and the distribution of microseismicity in the Pacific plate suggest the existence of a major discontinuity striking down the dip of the plate and passing beneath the Tongariro volcanic centre. A conspicuous lack of microseismicity in the Indian plate in the eastern North Island revealed in this study can be related to the plates being unlocked in this region. A feature of the seismicity of the Indian plate in the region of the Wanganui Basin is the concentration of activity in the 25-42 km depth range, shallower activity being largely confined to the northeast edge of the basin, near Mt Ruapehu and Waiouru. Composite focal mechanisms suggest the 25-42 km deep activity reflects stresses set up by locking and unlocking of the plates, while the shallower activity reflects local stresses related to volcanic phenomena.</p>

Holocene subsidence at the transition between strike-slip and subduction on the Pacific-Australian plate boundary, Marlborough Sounds, New Zealand

2010 ◽  
Vol 29 (5-6) ◽  
pp. 648-661 ◽  
Author(s):  
Bruce W. Hayward ◽  
Hugh R. Grenfell ◽  
Ashwaq T. Sabaa ◽  
Jon Kay ◽  
Rhiannon Daymond-King ◽  
...  
Keyword(s):  
New Zealand ◽  
Plate Boundary ◽  
Strike Slip ◽  
Australian Plate ◽  
The Pacific
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