scholarly journals Lithospheric Shortening and Ductile Deformation in a Back-Arc Setting: South Wanganui Basin, New  Zealand

2021 ◽  
Author(s):  
◽  
Erik Ewig
Keyword(s):  
New Zealand ◽  
Gravity Anomaly ◽  
Lower Crust ◽  
Receiver Function ◽  
Function Analysis ◽  
Strike Slip ◽  
High Angle ◽  
The West ◽  
Receiver Function Analysis ◽  
Velocity Layer

<p>South Wanganui Basin (SWB), New Zealand, is located behind the southern end of the Hikurangi subduction system. One of the most marked geophysical characteristics of the basin is the -150 mGal Bouguer/isostatic gravity anomaly. Sediment fill can only partly explain this anomaly. 3-D gravity models show that the gravity anomaly associated with the basin is generally consistent with a downwarp model of the entire crust. However, the downwarp of the Moho has to be 3-4 times larger than the downwarp of the sediment-basement interface to fit the observed gravity anomaly. Hence a model of lithospheric shortening where ductile thickening of the crust increases with depth is proposed. Finite element modelling demonstrates that the crust, in order to produce the ductile downwarp, is best modelled with at least two distinct different layers. The model requires the top 15-20 km of the crust to behave purely elastic and the lower part (10 km thick) to be viscoelastic with a viscosity of 10[to the power of 21 pascal-seconds]. The existence of this ductile lower continental crust can be explained due to fluids released from the subducting slab accumulating in the lower crust. This is supported by receiver function analysis results. These results propose a 10+/-2 km thick low S-wave velocity layer in the lower crust. The vertical loading necessary to create the basin is high (up to 200MPa) and is difficult to explain by slab pull forces transmitted via a strongly coupled subduction interface alone. An additional driving mechanism proposed is a thickened mantle lithosphere inducing normal forces on the base of the crust. However, the exact origin of the basin remains a puzzling aspect. Receiver function analysis shows that the crust of the subducting Pacific plate underneath the mainland in the lower North Island is abnormally thick ([approximates]10 km) for oceanic crust. This matches with results from the 3-D gravity modelling. Further features discovered with the receiver function analysis are an up to 6 km thick low-velocity layer on top of the slab, which is interpreted as a zone of crushed crustal material with subducted sediments. Furthermore, a deep Moho (39.5+/-1.5 km) is proposed underneath the northern tip of theMarlborough sounds. Shallow seismic and gravity investigations of the southeastern corner of the SWB reveal a complex faulting regime with high-angle normal and reverse faults as well as a component of strike slip. The overall style of faulting in the SWB changes from the west to the east. There are the low-angle thrust faults of the Taranaki Fault zone in the west, the high-angle mostly reverse faults in the eastern part of the basin and the strike slip faults, with a component of vertical movement, at the eastern boundary within the Tararua Ranges.</p>

scholarly journals Lithospheric Shortening and Ductile Deformation in a Back-Arc Setting: South Wanganui Basin, New  Zealand

2021 ◽  
Author(s):  
◽  
Erik Ewig
Keyword(s):  
New Zealand ◽  
Gravity Anomaly ◽  
Lower Crust ◽  
Receiver Function ◽  
Function Analysis ◽  
Strike Slip ◽  
High Angle ◽  
The West ◽  
Receiver Function Analysis ◽  
Velocity Layer

<p>South Wanganui Basin (SWB), New Zealand, is located behind the southern end of the Hikurangi subduction system. One of the most marked geophysical characteristics of the basin is the -150 mGal Bouguer/isostatic gravity anomaly. Sediment fill can only partly explain this anomaly. 3-D gravity models show that the gravity anomaly associated with the basin is generally consistent with a downwarp model of the entire crust. However, the downwarp of the Moho has to be 3-4 times larger than the downwarp of the sediment-basement interface to fit the observed gravity anomaly. Hence a model of lithospheric shortening where ductile thickening of the crust increases with depth is proposed. Finite element modelling demonstrates that the crust, in order to produce the ductile downwarp, is best modelled with at least two distinct different layers. The model requires the top 15-20 km of the crust to behave purely elastic and the lower part (10 km thick) to be viscoelastic with a viscosity of 10[to the power of 21 pascal-seconds]. The existence of this ductile lower continental crust can be explained due to fluids released from the subducting slab accumulating in the lower crust. This is supported by receiver function analysis results. These results propose a 10+/-2 km thick low S-wave velocity layer in the lower crust. The vertical loading necessary to create the basin is high (up to 200MPa) and is difficult to explain by slab pull forces transmitted via a strongly coupled subduction interface alone. An additional driving mechanism proposed is a thickened mantle lithosphere inducing normal forces on the base of the crust. However, the exact origin of the basin remains a puzzling aspect. Receiver function analysis shows that the crust of the subducting Pacific plate underneath the mainland in the lower North Island is abnormally thick ([approximates]10 km) for oceanic crust. This matches with results from the 3-D gravity modelling. Further features discovered with the receiver function analysis are an up to 6 km thick low-velocity layer on top of the slab, which is interpreted as a zone of crushed crustal material with subducted sediments. Furthermore, a deep Moho (39.5+/-1.5 km) is proposed underneath the northern tip of theMarlborough sounds. Shallow seismic and gravity investigations of the southeastern corner of the SWB reveal a complex faulting regime with high-angle normal and reverse faults as well as a component of strike slip. The overall style of faulting in the SWB changes from the west to the east. There are the low-angle thrust faults of the Taranaki Fault zone in the west, the high-angle mostly reverse faults in the eastern part of the basin and the strike slip faults, with a component of vertical movement, at the eastern boundary within the Tararua Ranges.</p>

Preliminary results from teleseismic tomography of the upper mantle beneath northern Borneo

2020 ◽  
Author(s):  
Simone Pilia ◽  
Nick Rawlinson ◽  
Felix Tongkul ◽  
Amy Gilligan ◽  
Dave Cornwell
Keyword(s):  
Upper Mantle ◽  
Receiver Function ◽  
Function Analysis ◽  
P Wave ◽  
The West ◽  
Tomographic Images ◽  
Teleseismic Tomography ◽  
North East ◽  
Receiver Function Analysis ◽  
Entire Network

&lt;p&gt;We present preliminary P-wave tomographic images of the upper mantle beneath northern Borneo (Sabah) using teleseismic earthquake data. Sabah underwent diachronous double-polarity subduction, one dipping to the southeast (terminated in the early Miocene) and the other to the northwest (terminated 5-6 Ma). With the goal of better understanding post-subduction processes in Sabah, 24 permanent seismic stations of MetMalaysia were augmented by the deployment of 46 temporary stations of the nBOSS network, which ran from March 2018 to January 2020. Relative P-wave traveltime residuals from nearly a thousand teleseismic events have been extracted from the continuous records using an adaptive stacking technique, which uses the coherency of global phases across the entire network. Using a grid-based eikonal solver and a subspace inversion technique implemented in FMTOMO, relative arrival time residuals are mapped as 3-D P-wave perturbations.&lt;/p&gt;&lt;p&gt;The most intriguing feature of the final tomographic model is a north-east trending lithospheric structure running across northern Borneo and separating relatively low to high wavespeeds to the west and east, respectively. This structure possibly indicates the suture between pre-Cenozoic lithosphere to the east and the Cenozoic accreted material to the west.&lt;/p&gt;&lt;p&gt;Results from receiver function analysis (i.e., crustal thickness) and crustal velocities from ambient noise tomography will be in the future incorporated in the tomographic inversion in order to obtain an integrated view of the crust-mantle system beneath Sabah.&lt;/p&gt;

scholarly journals Configuration and structure of the Philippine Sea Plate off Boso, Japan: constraints on the shallow subduction kinematics, seismicity, and slow slip events

2019 ◽  
Vol 71 (1) ◽  
Author(s):  
Aki Ito ◽  
Takashi Tonegawa ◽  
Naoki Uchida ◽  
Yojiro Yamamoto ◽  
Daisuke Suetsugu ◽  
...  
Keyword(s):  
Receiver Function ◽  
Function Analysis ◽  
Philippine Sea Plate ◽  
Slow Slip ◽  
Low Velocity ◽  
Slow Slip Events ◽  
Philippine Sea ◽  
Receiver Function Analysis ◽  
Eastern Edge ◽  
Upper Boundary

Abstract We applied tomographic inversion and receiver function analysis to seismic data from ocean-bottom seismometers and land-based stations to understand the structure and its relationship with slow slip events off Boso, Japan. First, we delineated the upper boundary of the Philippine Sea Plate based on both the velocity structure and the locations of the low-angle thrust-faulting earthquakes. The upper boundary of the Philippine Sea Plate is distorted upward by a few kilometers between 140.5 and 141.0°E. We also determined the eastern edge of the Philippine Sea Plate based on the delineated upper boundary and the results of the receiver function analysis. The eastern edge has a northwest–southeast trend between the triple junction and 141.6°E, which changes to a north–south trend north of 34.7°N. The change in the subduction direction at 1–3 Ma might have resulted in the inflection of the eastern edge of the subducted Philippine Sea Plate. Second, we compared the subduction zone structure and hypocenter locations and the area of the Boso slow slip events. Most of the low-angle thrust-faulting earthquakes identified in this study occurred outside the areas of recurrent Boso slow slip events, which indicates that the slow slip area and regular low-angle thrust earthquakes are spatially separated in the offshore area. In addition, the slow slip areas are located only at the contact zone between the crustal parts of the North American Plate and the subducting Philippine Sea Plate. The localization of the slow slip events in the crust–crust contact zone off Boso is examined for the first time in this study. Finally, we detected a relatively low-velocity region in the mantle of the Philippine Sea Plate. The low-velocity mantle can be interpreted as serpentinized peridotite, which is also found in the Philippine Sea Plate prior to subduction. The serpentinized peridotite zone remains after the subduction of the Philippine Sea Plate and is likely distributed over a wide area along the subducted slab.

scholarly journals Receiver Function Analysis & Applications to Seismic Imaging

2018 ◽  
Author(s):  
Chengping Chai ◽  
Monica Maceira ◽  
Charles Ammon ◽  
Carene Larmat ◽  
Sridhar Anandakrishnan ◽  
...  
Keyword(s):  
Seismic Imaging ◽  
Receiver Function ◽  
Function Analysis ◽  
Receiver Function Analysis

The CIELO Seismic Experiment

2021 ◽  
Author(s):  
Heather A. Ford ◽  
Maximiliano J. Bezada ◽  
Joseph S. Byrnes ◽  
Andrew Birkey ◽  
Zhao Zhu
Keyword(s):  
Receiver Function ◽  
Function Analysis ◽  
P Wave ◽  
Crust And Upper Mantle ◽  
Waveform Data ◽  
Wyoming Craton ◽  
Sensor Orientation ◽  
Seismic Experiment ◽  
Short Period ◽  
Receiver Function Analysis

Abstract The Crust and lithosphere Investigation of the Easternmost expression of the Laramide Orogeny was a two-year deployment of 24 broadband, compact posthole seismometers in a linear array across the eastern half of the Wyoming craton. The experiment was designed to image the crust and upper mantle of the region to better understand the evolution of the cratonic lithosphere. In this article, we describe the motivation and objectives of the experiment; summarize the station design and installation; provide a detailed accounting of data completeness and quality, including issues related to sensor orientation and ambient noise; and show examples of collected waveform data from a local earthquake, a local mine blast, and a teleseismic event. We observe a range of seasonal variations in the long-period noise on the horizontal components (15–20 dB) at some stations that likely reflect the range of soil types across the experiment. In addition, coal mining in the Powder River basin creates high levels of short-period noise at some stations. Preliminary results from Ps receiver function analysis, shear-wave splitting analysis, and averaged P-wave delay times are also included in this report, as is a brief description of education and outreach activities completed during the experiment.

scholarly journals Predictive models for the deep geometry of a thick-skinned thrust matched to crustal structure: Wind River Range, western USA

Lithosphere ◽  
2019 ◽  
Vol 11 (4) ◽  
pp. 448-464
Author(s):  
Richard H. Groshong ◽  
Ryan Porter
Keyword(s):  
Crustal Structure ◽  
Receiver Function ◽  
Function Analysis ◽  
Trailing Edge ◽  
Circular Arc ◽  
Wind River Range ◽  
Arc Model ◽  
Receiver Function Analysis ◽  
Kinematic Models ◽  
Teleseismic Receiver Function

Abstract The ability of models designed to use near-surface structural information to predict the deep geometry of a faulted block is tested for a thick-skinned thrust by matching the surface geometry to the crustal structure beneath the Wind River Range, Wyoming, USA. The Wind River Range is an ∼100-km-wide, thick-skinned rotated basement block bounded on one side by a high-angle reverse fault. The availability of a deep seismic-reflection profile and a detailed crustal impedance profile based on teleseismic receiver-function analysis makes this location ideal for testing techniques used to predict the deep fault geometry from shallow data. The techniques applied are the kinematic models for a circular-arc fault, oblique simple-shear fault, shear fault-bend fold, and model-independent excess area balancing. All the kinematic models imply that the deformation cannot be exclusively rigid-body rotation but rather require distributed deformation throughout some or all of the basement. Both the circular-arc model and the oblique-shear models give nearly the same best fit to the master fault geometry. The predicted lower detachment matches a potential crustal detachment zone at 31 km subsea. The thrust ramp is located close to where this zone dies out to the southwest. The circular-arc model implies that the penetrative deformation could be focused at the trailing edge of the basement block rather than being distributed uniformly throughout and thus helps to explain the line of second-order anticlines along the trailing edge of the Wind River block. Key points: (1) The circular-arc fault model and the oblique-shear model predict a lower detachment for the Wind River rotated block to be ∼31 km subsea, consistent with the crustal structure as defined by teleseismic receiver-function analysis. The thrust ramp starts where this zone dies out. (2) The kinematic models require distributed internal deformation within the basement block, probably concentrated at the trailing edge. (3) The uplift at the trailing edge of the rotated block is explained by the circular-arc kinematic model as a requirement to maintain area balance of a mostly rigid block above a horizontal detachment; the oblique-shear model can explain the uplift as caused by displacement on a dipping detachment.

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