The tectonic configuration of the Banda region in southeast Asia captures the spatial transition ... more The tectonic configuration of the Banda region in southeast Asia captures the spatial transition from subduction of Indian Ocean lithosphere to subduction and collision of the Australian continental lithosphere beneath the Banda Arc. An ongoing broadband seismic deployment funded by NSF is aimed at better understanding the mantle and lithospheric structure in the region and the relationship of the arc–continent collision to orogenesis. Here, we present results from ambient noise tomography in the region utilizing this temporary deployment of 30 broadband instruments and 39 permanent stations in Indonesia, Timor Leste, and Australia. We measure dispersion curves for over 21,000 inter-station paths resulting in good recovery of the velocity structure of the crust and upper mantle beneath the Savu Sea, Timor Leste, and the Nusa Tenggara Timur (NTT) region of Indonesia. The resulting three dimensional model indicates up to ∼25% variation in shear velocity throughout the plate boundary region; first-order velocity anomalies are associated with the subducting oceanic lithosphere, subducted Australian continental lithosphere, obducted oceanic sediments forming the core of the island of Timor, and high velocity anomalies in the Savu Sea and Sumba. The structure in Sumba and the Savu Sea is consistent with an uplifting forearc sliver. Beneath the island of Timor, we confirm earlier inferences of pervasive crustal duplexing from surface mapping, and establish a link to underlying structural features in the lowermost crust and uppermost mantle that drive upper crustal shortening. Finally, our images of the volcanic arc under Flores, Wetar, and Alor show high velocity structures of the Banda Terrane, but also a clear low velocity anomaly at the transition between subduction of oceanic and continental lithosphere. Given that the footprint of the Banda Terrane has previously been poorly defined, this model provides important constraints on tectonic reconstructions that formerly have lacked information on the lower crust and uppermost mantle.
We incorporate the effects of anisotropy to refine the continental-scale 3-D isotropic velocity m... more We incorporate the effects of anisotropy to refine the continental-scale 3-D isotropic velocity model previously produced for India and Tibet by inverting 52,050 teleseismic P wave residuals. We have exploited a total of 1648 individual SKS splitting parameters to calculate the P wave travel time corrections due to azimuthal anisotropy. Our results suggest that anisotropy affects the P wave delays significantly (20.3 to 10.5 s). Integration of these corrections into the 3-D modeling is achieved in two ways: (a) a priori adjustment to the delay time vector and (b) inverting only for anisotropic delays by introducing strong damping above 80 km and below 360 km depths and then subtracting the obtained anisotropic artifact image from the isotropic image, to get the corrected image. Under the assumption of azimuthal anisotropy resulting from lattice preferred orientation (LPO) alignment due to horizontal flow, the bias in isotropic P wave tomographic images is clear. The anisotropy corrected velocity perturbations are in the range of 61.2% at depths of around 150 km and reduced further at deeper levels. Although the bias due to anisot-ropy does not affect the gross features, it does introduce certain artifacts at deeper levels.
The time for a seismic wave to travel from earthquake source to receiver can be expressed as a fu... more The time for a seismic wave to travel from earthquake source to receiver can be expressed as a function of the path the energy followed, a model of the subsurface structure, and an initial guess at the hypocentral parameters, location and origin time. When this travel time is expressed for the myriad of observation stations, the resultant equations can be
An 80 station broadband seismic array (FAME-Flex Array MEnodocino) across the greater northern Ca... more An 80 station broadband seismic array (FAME-Flex Array MEnodocino) across the greater northern California area has been deployed. We present results of P-wave tomography using finite-frequency sensitivity kernels. Data analyzed includes 50 Transportable Array stations and 80 stations from FAME, spanning a time period from July 2005 to September 2008. Preliminary results show fast velocity anomalies beneath the northern Great
Subduction near to a deep continental root is modeled with finite elements. The root restricts as... more Subduction near to a deep continental root is modeled with finite elements. The root restricts asthenospheric corner flow, which increases mantle-wedge suction. The suction pulls the continental root toward the subduction zone, simultaneously promoting trenchward continental motion and compressive tectonics in the lithosphere between the root and the subduction zone. In a 2-D model with a root that extends to
The southern terminus of the Juan de Fuca plate provides an excellent example of asthenospheric f... more The southern terminus of the Juan de Fuca plate provides an excellent example of asthenospheric flow around descending oceanic lithosphere. Using the Flex Array Mendocino Experiment data set, we have developed P- and S-wave mantle tomography models, including P/S joint inversions. Approximate finite-frequency kernels, corrections for 3-D crustal structure, and dense station spacing allow for high-resolution of lithosphere/asthenosphere interaction near
ABSTRACT The most prominent features of the Andean range are the Altiplano and Puna plateaus, whi... more ABSTRACT The most prominent features of the Andean range are the Altiplano and Puna plateaus, which were constructed by crustal shortening and uplift over the past ~45 Myrs. The localization in space and time of this intense tectonism in the Central Andes remains enigmatic. Proposed models have suggested that an abrupt acceleration in relative motion between the Farallon/Nazca plate and the South American plate at ~30 Ma may have led to compression of the continent. However, the major plate motion change occurred at 25-23 Ma. Paleogmagnetic rotations and crustal shortening of the Andean forearc require that the Arica Bend formed prior to about ~25 Ma, calling into question the causal links between shortening/uplift in the Altiplano and relative plate motions. The history of flat slab subduction along the Altiplano section of the Andean margin, and the structure of the adjacent South American cratonic shield combine to suggest an alternate scenario based partly upon oceanic-continental plate interactions in subduction zones. We consider the following regimes: (1) Oblique subduction along the central Andean margin during the Oligocene accompanied by down-dip alignment with the center of the Amazonian Shield. Flat slab activity in this phase of orogenesis may have been caused by a combination of cratonic root enhanced tectonics and oceanic plateau subduction. (2) An abrupt transition to trench-normal subduction after ~25 Ma toward the thinner, more distal Sao Francisco Craton accompanied by a return to normal angle subduction.
The western termination of the Chugach Metamorphic Complex in southern Alaska provides an excelle... more The western termination of the Chugach Metamorphic Complex in southern Alaska provides an excellent example of a down-plunge crustal section that we are utilizing to examine strike-slip/transpressional plate boundary behavior. This exhumed section was developed in monolithologic forearc accretionary sediments (Valdez group), which eliminates rheologic complications associated with heterogeneous crust. Following an "attachment zone" model of Teyssier et al. (2003),
The tectonic configuration of the Banda region in southeast Asia captures the spatial transition ... more The tectonic configuration of the Banda region in southeast Asia captures the spatial transition from subduction of Indian Ocean lithosphere to subduction and collision of the Australian continental lithosphere beneath the Banda Arc. An ongoing broadband seismic deployment funded by NSF is aimed at better understanding the mantle and lithospheric structure in the region and the relationship of the arc–continent collision to orogenesis. Here, we present results from ambient noise tomography in the region utilizing this temporary deployment of 30 broadband instruments and 39 permanent stations in Indonesia, Timor Leste, and Australia. We measure dispersion curves for over 21,000 inter-station paths resulting in good recovery of the velocity structure of the crust and upper mantle beneath the Savu Sea, Timor Leste, and the Nusa Tenggara Timur (NTT) region of Indonesia. The resulting three dimensional model indicates up to ∼25% variation in shear velocity throughout the plate boundary region; first-order velocity anomalies are associated with the subducting oceanic lithosphere, subducted Australian continental lithosphere, obducted oceanic sediments forming the core of the island of Timor, and high velocity anomalies in the Savu Sea and Sumba. The structure in Sumba and the Savu Sea is consistent with an uplifting forearc sliver. Beneath the island of Timor, we confirm earlier inferences of pervasive crustal duplexing from surface mapping, and establish a link to underlying structural features in the lowermost crust and uppermost mantle that drive upper crustal shortening. Finally, our images of the volcanic arc under Flores, Wetar, and Alor show high velocity structures of the Banda Terrane, but also a clear low velocity anomaly at the transition between subduction of oceanic and continental lithosphere. Given that the footprint of the Banda Terrane has previously been poorly defined, this model provides important constraints on tectonic reconstructions that formerly have lacked information on the lower crust and uppermost mantle.
We incorporate the effects of anisotropy to refine the continental-scale 3-D isotropic velocity m... more We incorporate the effects of anisotropy to refine the continental-scale 3-D isotropic velocity model previously produced for India and Tibet by inverting 52,050 teleseismic P wave residuals. We have exploited a total of 1648 individual SKS splitting parameters to calculate the P wave travel time corrections due to azimuthal anisotropy. Our results suggest that anisotropy affects the P wave delays significantly (20.3 to 10.5 s). Integration of these corrections into the 3-D modeling is achieved in two ways: (a) a priori adjustment to the delay time vector and (b) inverting only for anisotropic delays by introducing strong damping above 80 km and below 360 km depths and then subtracting the obtained anisotropic artifact image from the isotropic image, to get the corrected image. Under the assumption of azimuthal anisotropy resulting from lattice preferred orientation (LPO) alignment due to horizontal flow, the bias in isotropic P wave tomographic images is clear. The anisotropy corrected velocity perturbations are in the range of 61.2% at depths of around 150 km and reduced further at deeper levels. Although the bias due to anisot-ropy does not affect the gross features, it does introduce certain artifacts at deeper levels.
The time for a seismic wave to travel from earthquake source to receiver can be expressed as a fu... more The time for a seismic wave to travel from earthquake source to receiver can be expressed as a function of the path the energy followed, a model of the subsurface structure, and an initial guess at the hypocentral parameters, location and origin time. When this travel time is expressed for the myriad of observation stations, the resultant equations can be
An 80 station broadband seismic array (FAME-Flex Array MEnodocino) across the greater northern Ca... more An 80 station broadband seismic array (FAME-Flex Array MEnodocino) across the greater northern California area has been deployed. We present results of P-wave tomography using finite-frequency sensitivity kernels. Data analyzed includes 50 Transportable Array stations and 80 stations from FAME, spanning a time period from July 2005 to September 2008. Preliminary results show fast velocity anomalies beneath the northern Great
Subduction near to a deep continental root is modeled with finite elements. The root restricts as... more Subduction near to a deep continental root is modeled with finite elements. The root restricts asthenospheric corner flow, which increases mantle-wedge suction. The suction pulls the continental root toward the subduction zone, simultaneously promoting trenchward continental motion and compressive tectonics in the lithosphere between the root and the subduction zone. In a 2-D model with a root that extends to
The southern terminus of the Juan de Fuca plate provides an excellent example of asthenospheric f... more The southern terminus of the Juan de Fuca plate provides an excellent example of asthenospheric flow around descending oceanic lithosphere. Using the Flex Array Mendocino Experiment data set, we have developed P- and S-wave mantle tomography models, including P/S joint inversions. Approximate finite-frequency kernels, corrections for 3-D crustal structure, and dense station spacing allow for high-resolution of lithosphere/asthenosphere interaction near
ABSTRACT The most prominent features of the Andean range are the Altiplano and Puna plateaus, whi... more ABSTRACT The most prominent features of the Andean range are the Altiplano and Puna plateaus, which were constructed by crustal shortening and uplift over the past ~45 Myrs. The localization in space and time of this intense tectonism in the Central Andes remains enigmatic. Proposed models have suggested that an abrupt acceleration in relative motion between the Farallon/Nazca plate and the South American plate at ~30 Ma may have led to compression of the continent. However, the major plate motion change occurred at 25-23 Ma. Paleogmagnetic rotations and crustal shortening of the Andean forearc require that the Arica Bend formed prior to about ~25 Ma, calling into question the causal links between shortening/uplift in the Altiplano and relative plate motions. The history of flat slab subduction along the Altiplano section of the Andean margin, and the structure of the adjacent South American cratonic shield combine to suggest an alternate scenario based partly upon oceanic-continental plate interactions in subduction zones. We consider the following regimes: (1) Oblique subduction along the central Andean margin during the Oligocene accompanied by down-dip alignment with the center of the Amazonian Shield. Flat slab activity in this phase of orogenesis may have been caused by a combination of cratonic root enhanced tectonics and oceanic plateau subduction. (2) An abrupt transition to trench-normal subduction after ~25 Ma toward the thinner, more distal Sao Francisco Craton accompanied by a return to normal angle subduction.
The western termination of the Chugach Metamorphic Complex in southern Alaska provides an excelle... more The western termination of the Chugach Metamorphic Complex in southern Alaska provides an excellent example of a down-plunge crustal section that we are utilizing to examine strike-slip/transpressional plate boundary behavior. This exhumed section was developed in monolithologic forearc accretionary sediments (Valdez group), which eliminates rheologic complications associated with heterogeneous crust. Following an "attachment zone" model of Teyssier et al. (2003),
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