Kaijian Liu - Academia.edu (original) (raw)
Papers by Kaijian Liu
... A. Levander, F. Niu, MS Miller, Y. Zhai, K. Liu, and X. Cheng Department of Earth Science, Ri... more ... A. Levander, F. Niu, MS Miller, Y. Zhai, K. Liu, and X. Cheng Department of Earth Science, Rice University MS-126, 6100 Main ... arc and Sierra Nevada batholith, the Snake River Plain and Columbia flood basalts, the Basin and Range, part of the Southern Rocky Mountains, and ...
... Authors: Levander, A.; Niu, F.; Miller, MS; Zhai, Y.; Liu, K. ... At present the Transportabl... more ... Authors: Levander, A.; Niu, F.; Miller, MS; Zhai, Y.; Liu, K. ... At present the Transportable Array extends as far west as ~108° to 113°W, crossing the Snake River Plain and Columbia flood basalts, most of the Basin and Range, part of the Rocky Mountains, and about half of the ...
1] The Colorado Plateau is a physiographic province in the western US with an average elevation o... more 1] The Colorado Plateau is a physiographic province in the western US with an average elevation of $1.9 km where, in contrast to neighboring provinces, there is little evidence of large scale tectonic deformation or magmatism. Recent availability of Earthscope/ USArray seismic data allow us to better examine the crust and upper mantle structure beneath the region and test proposed explanations for the plateau's uplift and relative stability. Using phase velocities for fundamental mode Rayleigh waves and P receiver functions, we perform over 800 joint inversions for 1-D shear wave velocity V S profiles sampling the plateau and surrounding regions down to 150 km depth. We image a sharp change in crustal thickness at the western edge of the Colorado Plateau with a more gradual increase eastward moving into the Rocky Mountains. A relatively thick (≳100 km) lithosphere beneath the plateau extends into the Rocky Mountains to the north. We use empirical scaling relations to estimate densities from our V S results, and predict the associated gravity anomalies, which are inconsistent with the observed distribution of the Bouguer gravity anomalies. We somewhat reconcile the prediction and observations by assuming that lateral density variations below 50 km can be ignored and the lithospheric root is therefore neutrally buoyant. While there is some evidence for small scale convection and lithospheric removal at its edges, the shape of the lithospheric mantle anomaly is consistent with a large scale uplift of the plateau by heating since removal of the Farallon slab. We conclude that the lithospheric root is key to the long term stability of the Colorado Plateau, leading to a colder, stronger crust. Citation: Bailey, I. W., M. S. Miller, K. Liu, and A. Levander (2012), V S and density structure beneath the Colorado Plateau constrained by gravity anomalies and joint inversions of receiver function and phase velocity data,
1] We present a 3-D shear wave velocity model for the crust and upper mantle of the western Medit... more 1] We present a 3-D shear wave velocity model for the crust and upper mantle of the western Mediterranean from Rayleigh wave tomography. We analyzed the fundamental mode in the 20-167 s period band (6.0-50.0 mHz) from earthquakes recorded by a number of temporary and permanent seismograph arrays. Using the two-plane wave method, we obtained phase velocity dispersion curves that were inverted for an isotropic Vs model that extends from the southern Iberian Massif, across the Gibraltar Arc and the Atlas mountains to the Saharan Craton. The area of the western Mediterranean that we have studied has been the site of complex subduction, slab rollback, and simultaneous compression and extension during African-European convergence since the Oligocene. The shear velocity model shows high velocities beneath the Rif from 65 km depth and beneath the Granada Basin from 70 km depth that extend beneath the Alboran Domain to more than 250 km depth, which we interpret as a near-vertical slab dangling from beneath the western Alboran Sea. The slab appears to be attached to the crust beneath the Rif and possibly beneath the Granada Basin and Sierra Nevada where low shear velocities (3.8 km/s) are mapped to >55 km depth. The attached slab is pulling down the Gibraltar Arc crust, thickening it, and removing the continental margin lithospheric mantle beneath both Iberia and Morocco as it descends into the deeper mantle. Thin lithosphere is indicated by very low upper mantle velocities beneath the Alboran Sea, above and east of the dangling slab and beneath the Cenozoic volcanics.
... At large scale, for example, P and S body wave traveltime tomography (eg Humphreys and Dueker... more ... At large scale, for example, P and S body wave traveltime tomography (eg Humphreys and Dueker, 1994a, b; Burdick et al, 2008) and surface wave tomography (eg van der Lee and No let, 1997) both characterized the western US by pronounced low P and S velocity ...
Physics Letters A, 2007
The currentvoltage (IV) characteristics of single ZnO nanowires have been studied in the humid ... more The currentvoltage (IV) characteristics of single ZnO nanowires have been studied in the humid air, dry air, vacuum, and under ultraviolet (UV) irradiation. A model of a single ZnO nanowire connected with two opposite diodes was proposed to calculate the observed IV ...
... Romain A. Bouchet, Janne Blichert-Toft Université de Lyon, CNRS, UMR 5276, Laboratoire de Géo... more ... Romain A. Bouchet, Janne Blichert-Toft Université de Lyon, CNRS, UMR 5276, Laboratoire de Géologie de Lyon, Ecole Normale Supérieure de Lyon, 46 Allée d'Italie, 69364 Lyon Cedex 07, France Alan Levander, Kaijian Liu Department of Earth Science, Rice University, 6100 ...
We have measured Rayleigh wave phase velocities to determine the shear velocity structure of the ... more We have measured Rayleigh wave phase velocities to determine the shear velocity structure of the crust and upper mantle beneath the high-elevation (~2 km) and tectonically stable Colorado Plateau (CP), and adjacent Basin and Range Province (BR), the Rio Grande Rift (RGR), and the Southern Rocky Mountain (RM), using data from the USArray Transportable Array (TA) network. Approximately 60 teleseismic earthquakes with epicentral distance between 30°-120°, magnitude >= 6.0, and depth = 42 km in the plateau. A smaller region with thinner crust (< 30 km) in the northern BR was found near the Wasatch front. Our results show slower upper mantle shear velocities than previous studies (Lastowka et al. 2001, West et al. 2004 etc.). We observe a consistent low velocity feature extending to ~200 km beneath Mt. Taylor along the NE trending Jemez lineament to the west of the RGR. Relative low velocity signatures in the upper mantle from ~50 to 100 km beneath the southernmost RM to the east edge of the plateau, and along the axis of the RGR, suggest warm upper mantle and small amount of partial melt. The central plateau shows a thicker crust and faster mantle lithosphere compared to the eastern, southwestern and northwestern transition zones towards the RM and BRP, indicating a cooler stronger lithosphere, consistent with the moderate surface heat flow and high Pn velocity compared to those of the plateau edges, where Pn velocity are relatively low and shallow upper mantle low velocity zones have been observed (Benz &McCarthy 1994, Henstock et al., 1998). We compare the surface wave results with the PdS and SdP receiver functions presented by Miller et al. (2009, this meeting). Bibtex entry for this abstract Preferred format for this abstract (see Preferences) Find Similar Abstracts: Use: Authors Title Keywords (in text query field) Abstract Text Return: Query Results Return items starting with number Query Form Database: Astronomy Physics arXiv e-prints
We present results from joint inversions of surface wave phase velocities and teleseismic receive... more We present results from joint inversions of surface wave phase velocities and teleseismic receiver functions, recently computed from USArray data, to analyze structure beneath the Colorado Plateau. The Colorado Plateau is a tectonic province characterized by high elevations (>1.5 km) of almost uniformly horizontally bedded rocks. To understand how such significant uplift has occurred without major changes in the bedding
ABSTRACT We combine teleseismic P and S body-wave and Rayleigh wave tomography with Ps and Sp rec... more ABSTRACT We combine teleseismic P and S body-wave and Rayleigh wave tomography with Ps and Sp receiver functions to image the west-central Colorado Plateau (CP). The images, made largely with USArray data, resolve a high-velocity drip extending from the base of the crust to more than 200 km depth. Ps receiver functions clearly define the upper surface of this body, which dips from the lower crust to depths of 70-90 km. The bottom of the remaining crust above the drip has a shape almost identical to the top of the drip, with an elevated Moho and a low seismic contrast. We interpret the high-velocity structure as an ongoing delamination-style downwelling of the lowermost crust and the Proterozoic age CP continental lithospheric mantle. The structure of the lithosphere-asthenosphere boundary (LAB), imaged with the receiver functions and the Rayleigh wave tomography, support this view. We associate this delamination feature with Pliocene and ongoing uplift of the CP, and envision uplift driven by a succession of these events propagating inward from the Plateau margins, associated with the magmatic invasion of the CP from its margins. Petrologic and geochemical observations suggest that Laramide-age flat-slab subduction thinned, hydrated and weakened the CP lithosphere and that mid-Cenozoic to Recent magmas infiltrated this mantle, creating the negative buoyancy required to destabilize the lithosphere. Using Grand Canyon incision rates and the patterns of Pliocene and younger basalts, we suggest that substantial plateau uplift resulted from underlying delaminations over the last ~6 Ma. We also note that these two processes together can destabilize cratons: 1) Weakening by hydration followed by 2) Invasion of the craton edges by melts that then freeze, increasing the bulk density of the pre-existing lithosphere.
1] The Colorado Plateau is a physiographic province in the western US with an average elevation o... more 1] The Colorado Plateau is a physiographic province in the western US with an average elevation of $1.9 km where, in contrast to neighboring provinces, there is little evidence of large scale tectonic deformation or magmatism. Recent availability of Earthscope/ USArray seismic data allow us to better examine the crust and upper mantle structure beneath the region and test proposed explanations for the plateau's uplift and relative stability. Using phase velocities for fundamental mode Rayleigh waves and P receiver functions, we perform over 800 joint inversions for 1-D shear wave velocity V S profiles sampling the plateau and surrounding regions down to 150 km depth. We image a sharp change in crustal thickness at the western edge of the Colorado Plateau with a more gradual increase eastward moving into the Rocky Mountains. A relatively thick (≳100 km) lithosphere beneath the plateau extends into the Rocky Mountains to the north. We use empirical scaling relations to estimate densities from our V S results, and predict the associated gravity anomalies, which are inconsistent with the observed distribution of the Bouguer gravity anomalies. We somewhat reconcile the prediction and observations by assuming that lateral density variations below 50 km can be ignored and the lithospheric root is therefore neutrally buoyant. While there is some evidence for small scale convection and lithospheric removal at its edges, the shape of the lithospheric mantle anomaly is consistent with a large scale uplift of the plateau by heating since removal of the Farallon slab. We conclude that the lithospheric root is key to the long term stability of the Colorado Plateau, leading to a colder, stronger crust. Citation: Bailey, I. W., M. S. Miller, K. Liu, and A. Levander (2012), V S and density structure beneath the Colorado Plateau constrained by gravity anomalies and joint inversions of receiver function and phase velocity data,
ABSTRACT We have developed a 3-D shear velocity model using finite-frequency Rayleigh wave phase ... more ABSTRACT We have developed a 3-D shear velocity model using finite-frequency Rayleigh wave phase velocity dispersion, PdS receiver functions, and ambient noise tomography to better understand the complex lithosphere/asthenosphere structures in the Mendocino Triple Junction (MTJ) region. Using approximately 100 events (July 2007-December 2008) recorded by the stations of the Flexible Array Mendocino Experiment (FAME), the USArray Transportable Array (TA) network, and the Berkeley Digital Seismograph network, we have obtained the phase velocities (20-100s) from the finite-frequency Rayleigh wave tomography, which agrees well with the ambient noise tomography results (7-40 s, Porritt & Allen, 2010) in the overlapping period range. We subsequently inverted for a 3-D Vs model on a 0.25°x0.25° grid from the combined dispersion datasets, constrained by interface depths from the PdS receiver functions (Zhai & Levander, 2010). The resulting crustal and upper mantle Vs model (~150 km) reveals strong lateral heterogeneity in the subduction and transform regimes of the Mendocino Triple Junction region where the Gorda, Pacific, and North American plates intersect. The subducting Gorda slab is well-imaged as an eastward-dipping high-velocity anomaly to ~100 km depth. At the same depth to the east we observe a large-scale low velocity zone, which is the mantle wedge beneath the North American Plate. The southern edge of the Gorda plate (SEDGE) is imaged at 80-100 km depth and is in excellent agreement with measurements made from PdS receiver functions, body-wave tomography (Schmandt & Humphreys, 2010; Obrebski et al., 2010), and active source studies. At depths greater than 80 km, we interpret low velocities under the Cascadia subduction zone as the asthenosphere below the Gorda plate, in agreement with measured LAB depths from RFs. South of the SEDGE shallow strong low-velocities appear beneath the transform region, which we interpret as the asthenosphere in the slab-gap region left by the northward migration of the MTJ, consistent with the `slab window' hypothesis. The Rayleigh wave data image low velocity upper mantle directly beneath the crust as far north as the Lake Pillsbury region, a site of modern basaltic intrusion. This probably marks the northernmost extent of the slab free window beneath the California Coast Ranges. We will examine the trade-off between receiver function amplitudes and velocity gradients for a better estimate of the lithosphere-asthenosphere boundary (LAB) depths beneath the Gorda plate and beneath the transform regime.
1] We present a 3-D shear wave velocity model for the crust and upper mantle of the western Medit... more 1] We present a 3-D shear wave velocity model for the crust and upper mantle of the western Mediterranean from Rayleigh wave tomography. We analyzed the fundamental mode in the 20-167 s period band (6.0-50.0 mHz) from earthquakes recorded by a number of temporary and permanent seismograph arrays. Using the two-plane wave method, we obtained phase velocity dispersion curves that were inverted for an isotropic Vs model that extends from the southern Iberian Massif, across the Gibraltar Arc and the Atlas mountains to the Saharan Craton. The area of the western Mediterranean that we have studied has been the site of complex subduction, slab rollback, and simultaneous compression and extension during African-European convergence since the Oligocene. The shear velocity model shows high velocities beneath the Rif from 65 km depth and beneath the Granada Basin from 70 km depth that extend beneath the Alboran Domain to more than 250 km depth, which we interpret as a near-vertical slab dangling from beneath the western Alboran Sea. The slab appears to be attached to the crust beneath the Rif and possibly beneath the Granada Basin and Sierra Nevada where low shear velocities (3.8 km/s) are mapped to >55 km depth. The attached slab is pulling down the Gibraltar Arc crust, thickening it, and removing the continental margin lithospheric mantle beneath both Iberia and Morocco as it descends into the deeper mantle. Thin lithosphere is indicated by very low upper mantle velocities beneath the Alboran Sea, above and east of the dangling slab and beneath the Cenozoic volcanics.
ABSTRACT Under a number of Cascade volcanoes we have identified a characteristic seismic signatur... more ABSTRACT Under a number of Cascade volcanoes we have identified a characteristic seismic signature in individual station Ps receiver functions and in Ps CCP image volumes made from USArray Transportable Array and Flexible Array stations. In the mantle wedge, the CCP images and the RFs show a strong negative event just below the Moho, paired with a weak to moderate positive event between 50-70 km, and a strong slab event. At most of these volcanoes, a strong negative signal also appears between 15 and 25 km depth in the crust. The signature is particularly clear under Mt. Lassen and Mt. Shasta in data from FAME (Flexible Array Mendocino Experiment), where instruments were close to the volcanic centers. Comparing the average Cascadia volcano signature to those of stations throughout the western U.S. and specifically those of the Cascadia backarc region, shows that this signal is unique to the Cascadia volcanoes. Joint inversion of the Ps receiver functions and ambient noise Rayleigh wave phase velocities (Porritt et al., 2011; Liu et al., submitted) for those volcanoes with the paired events provides 1D shear velocity profiles having common characteristics. A strong sub-Moho low velocity zone from 5 to 15 km thick gives rise to the paired negative-positive signals in the receiver functions. The sub-Moho low velocity zones, with velocities of 3.7 < Vs < 4.0 km/s, are evident in 15 of the 22 stations we examined. Stations not exhibiting this pattern also show a characteristic seismic structure: There is no abrupt velocity increase at Moho depths, instead Vs increases gradually from the lower crust to as deep as ~70 km, forming a thick, relatively high velocity layer (4.0 < Vs <4.5 km/s). This project was initiated as part of the CIDER 2011 summer program.
ABSTRACT The goal of this study is to compare imaging with scattered teleseismic wavefields using... more ABSTRACT The goal of this study is to compare imaging with scattered teleseismic wavefields using 3-D Kirchhoff- and Born-approximate inversion methods. Kirchhoff and Born-approximate inversions have been well developed in exploration seismology based on the inverse scattering framework (e.g. Beylkin and Burridge, 1990) to image subsurface structure that generates secondary wavefields due to localized heterogeneities. Application of these methods in global seismology has been somewhat limited to 1-D reference models due to high computational cost and the lack of dense receiver arrays (Bostock, 2002, Frederiksen and Revenaugh, 2004; Cao et al., 2010). Due to the deployment of the USArray Transportable and Flexible arrays across the United States and dense array recordings in other countries, we seek to extend teleseismic scattered wavefield imaging with each of these approximations from 2-D to 3-D for both scalar and vector wavefields to resolve the contrast of material parameters in the lowermost crust and the upper mantle. Following Bostock and coworkers (2001, 2002), making each approximation allows us to derive the 3-D multimode (P-to-P, P-to-S etc.) inversion formulae by phrasing the problem in terms of a generalized Radon transform (or its inverse) and then inverting the scattered waves. To demonstrate the relative accuracy of the two different inversions, we examine several synthetic cases with a variety of discontinuity surfaces. In the forward scattering modeling, we extend the method to utilize a 3-D background velocity model by calculating 3-D finite-difference traveltimes and amplitudes, backprojected from the receivers using an eikonal solver. We compare our Kirchhoff- and Born-approximation imaging with the common-conversion point (CCP) stacked receiver function imaging for the synthetic data. We apply these methods to USArray data.
ABSTRACT We have developed a 3-D teleseismic imaging technique for scattered elastic wavefields u... more ABSTRACT We have developed a 3-D teleseismic imaging technique for scattered elastic wavefields using the Kirchhoff approximation. Kirchhoff migration/inversion have been well developed in exploration seismology within the inverse scattering framework (e.g. Miller et al., 1987; Beylkin and Burridge, 1990) to image subsurface structure that generates secondary wavefields caused by localized heterogeneities. Application of this method in global seismology has been largely limited to 2-D images made with 1-D reference models due to high computational cost and the lack of adequately dense receiver arrays (Bostock, 2002, Poppeliers and Pavlis, 2003; Frederiksen and Revenaugh, 2004; Cao et al., 2010). The deployment of the USArray Transportable and Flexible arrays in the United States and dense array recordings in other countries motivate developing teleseismic scattered wavefield imaging with the Kirchhoff approximation for 3-D velocity models for both scalar and vector wavefields to improve upper mantle imaging. Following Bostock's development of the 2-D problem (2002), we derive the 3-D P-to-S scattering inversion formula by phrasing the inverse problem in terms of the generalized Radon transform (GRT) and singular functions of discontinuity surfaces. In the forward scattering modeling, we extend the method to utilize a 3-D migration velocity model by calculating 3-D finite-difference traveltimes, backprojected from the receivers using an eikonal solver. To demonstrate the relative accuracy of the inversion, we examine several synthetic cases with a variety of discontinuity surfaces (sinuous, dipping, dome- and crater-shaped discontinuity interfaces, point scatterers, etc.). The Kirchhoff GRT imaging can successfully recover the shapes of these structures very well. We compare our Kirchhoff approximation imaging with the Born-approximate results, as well as the common-conversion point (CCP) stacked receiver function imaging for the various synthetic cases, and show a field example using USArray data.
ABSTRACT Under a number of Cascade volcanoes we have identified a characteristic seismic signatur... more ABSTRACT Under a number of Cascade volcanoes we have identified a characteristic seismic signature in individual station Ps receiver functions and in Ps CCP image volumes made from USArray Transportable Array and Flexible Array stations. In the mantle wedge, the CCP images and the RFs show a strong negative event just below the Moho, paired with a weak to moderate positive event between 50-70 km, and a strong slab event. At most of these volcanoes, a strong negative signal also appears between 15 and 25 km depth in the crust. The signature is particularly clear under Mt. Lassen and Mt. Shasta in data from FAME (Flexible Array Mendocino Experiment), where instruments were close to the volcanic centers. Comparing the average Cascadia volcano signature to those of stations throughout the western U.S. and specifically those of the Cascadia backarc region, shows that this signal is unique to the Cascadia volcanoes. Joint inversion of the Ps receiver functions and ambient noise Rayleigh wave phase velocities (Porritt et al., 2011; Liu et al., submitted) for those volcanoes with the paired events provides 1D shear velocity profiles having common characteristics. A strong sub-Moho low velocity zone from 5 to 15 km thick gives rise to the paired negative-positive signals in the receiver functions. The sub-Moho low velocity zones, with velocities of 3.7 < Vs < 4.0 km/s, are evident in 15 of the 22 stations we examined. Stations not exhibiting this pattern also show a characteristic seismic structure: There is no abrupt velocity increase at Moho depths, instead Vs increases gradually from the lower crust to as deep as ~70 km, forming a thick, relatively high velocity layer (4.0 < Vs <4.5 km/s). This project was initiated as part of the CIDER 2011 summer program.
Teleseismic imaging techniques utilizing mode converted/scattered waves are gaining importance du... more Teleseismic imaging techniques utilizing mode converted/scattered waves are gaining importance due to the deployment of increasingly dense broad-band seismograph arrays. Although common-conversion point (CCP) stacking is widely used to determine structure from Ps or Sp scattered wavefields isolated by receiver function (RF) processing, this method is limited due to its assumption of a layered medium: Dipping events and diffractions are not treated correctly. As an extension of previous 2-D generalized Radon transform (GRT) imaging methods, we present a 3-D Kirchhoff-approximate imaging technique to migrate scattered waves in 3-D. We first derive the 3-D migration formula for P-to-S conversions using the GRT solution to the linear inverse elastic wave scattering problem. Then we illustrate the Kirchhoff method using finite-difference synthetic seismograms from several 3-D models.
... A. Levander, F. Niu, MS Miller, Y. Zhai, K. Liu, and X. Cheng Department of Earth Science, Ri... more ... A. Levander, F. Niu, MS Miller, Y. Zhai, K. Liu, and X. Cheng Department of Earth Science, Rice University MS-126, 6100 Main ... arc and Sierra Nevada batholith, the Snake River Plain and Columbia flood basalts, the Basin and Range, part of the Southern Rocky Mountains, and ...
... Authors: Levander, A.; Niu, F.; Miller, MS; Zhai, Y.; Liu, K. ... At present the Transportabl... more ... Authors: Levander, A.; Niu, F.; Miller, MS; Zhai, Y.; Liu, K. ... At present the Transportable Array extends as far west as ~108° to 113°W, crossing the Snake River Plain and Columbia flood basalts, most of the Basin and Range, part of the Rocky Mountains, and about half of the ...
1] The Colorado Plateau is a physiographic province in the western US with an average elevation o... more 1] The Colorado Plateau is a physiographic province in the western US with an average elevation of $1.9 km where, in contrast to neighboring provinces, there is little evidence of large scale tectonic deformation or magmatism. Recent availability of Earthscope/ USArray seismic data allow us to better examine the crust and upper mantle structure beneath the region and test proposed explanations for the plateau's uplift and relative stability. Using phase velocities for fundamental mode Rayleigh waves and P receiver functions, we perform over 800 joint inversions for 1-D shear wave velocity V S profiles sampling the plateau and surrounding regions down to 150 km depth. We image a sharp change in crustal thickness at the western edge of the Colorado Plateau with a more gradual increase eastward moving into the Rocky Mountains. A relatively thick (≳100 km) lithosphere beneath the plateau extends into the Rocky Mountains to the north. We use empirical scaling relations to estimate densities from our V S results, and predict the associated gravity anomalies, which are inconsistent with the observed distribution of the Bouguer gravity anomalies. We somewhat reconcile the prediction and observations by assuming that lateral density variations below 50 km can be ignored and the lithospheric root is therefore neutrally buoyant. While there is some evidence for small scale convection and lithospheric removal at its edges, the shape of the lithospheric mantle anomaly is consistent with a large scale uplift of the plateau by heating since removal of the Farallon slab. We conclude that the lithospheric root is key to the long term stability of the Colorado Plateau, leading to a colder, stronger crust. Citation: Bailey, I. W., M. S. Miller, K. Liu, and A. Levander (2012), V S and density structure beneath the Colorado Plateau constrained by gravity anomalies and joint inversions of receiver function and phase velocity data,
1] We present a 3-D shear wave velocity model for the crust and upper mantle of the western Medit... more 1] We present a 3-D shear wave velocity model for the crust and upper mantle of the western Mediterranean from Rayleigh wave tomography. We analyzed the fundamental mode in the 20-167 s period band (6.0-50.0 mHz) from earthquakes recorded by a number of temporary and permanent seismograph arrays. Using the two-plane wave method, we obtained phase velocity dispersion curves that were inverted for an isotropic Vs model that extends from the southern Iberian Massif, across the Gibraltar Arc and the Atlas mountains to the Saharan Craton. The area of the western Mediterranean that we have studied has been the site of complex subduction, slab rollback, and simultaneous compression and extension during African-European convergence since the Oligocene. The shear velocity model shows high velocities beneath the Rif from 65 km depth and beneath the Granada Basin from 70 km depth that extend beneath the Alboran Domain to more than 250 km depth, which we interpret as a near-vertical slab dangling from beneath the western Alboran Sea. The slab appears to be attached to the crust beneath the Rif and possibly beneath the Granada Basin and Sierra Nevada where low shear velocities (3.8 km/s) are mapped to >55 km depth. The attached slab is pulling down the Gibraltar Arc crust, thickening it, and removing the continental margin lithospheric mantle beneath both Iberia and Morocco as it descends into the deeper mantle. Thin lithosphere is indicated by very low upper mantle velocities beneath the Alboran Sea, above and east of the dangling slab and beneath the Cenozoic volcanics.
... At large scale, for example, P and S body wave traveltime tomography (eg Humphreys and Dueker... more ... At large scale, for example, P and S body wave traveltime tomography (eg Humphreys and Dueker, 1994a, b; Burdick et al, 2008) and surface wave tomography (eg van der Lee and No let, 1997) both characterized the western US by pronounced low P and S velocity ...
Physics Letters A, 2007
The currentvoltage (IV) characteristics of single ZnO nanowires have been studied in the humid ... more The currentvoltage (IV) characteristics of single ZnO nanowires have been studied in the humid air, dry air, vacuum, and under ultraviolet (UV) irradiation. A model of a single ZnO nanowire connected with two opposite diodes was proposed to calculate the observed IV ...
... Romain A. Bouchet, Janne Blichert-Toft Université de Lyon, CNRS, UMR 5276, Laboratoire de Géo... more ... Romain A. Bouchet, Janne Blichert-Toft Université de Lyon, CNRS, UMR 5276, Laboratoire de Géologie de Lyon, Ecole Normale Supérieure de Lyon, 46 Allée d'Italie, 69364 Lyon Cedex 07, France Alan Levander, Kaijian Liu Department of Earth Science, Rice University, 6100 ...
We have measured Rayleigh wave phase velocities to determine the shear velocity structure of the ... more We have measured Rayleigh wave phase velocities to determine the shear velocity structure of the crust and upper mantle beneath the high-elevation (~2 km) and tectonically stable Colorado Plateau (CP), and adjacent Basin and Range Province (BR), the Rio Grande Rift (RGR), and the Southern Rocky Mountain (RM), using data from the USArray Transportable Array (TA) network. Approximately 60 teleseismic earthquakes with epicentral distance between 30°-120°, magnitude >= 6.0, and depth = 42 km in the plateau. A smaller region with thinner crust (< 30 km) in the northern BR was found near the Wasatch front. Our results show slower upper mantle shear velocities than previous studies (Lastowka et al. 2001, West et al. 2004 etc.). We observe a consistent low velocity feature extending to ~200 km beneath Mt. Taylor along the NE trending Jemez lineament to the west of the RGR. Relative low velocity signatures in the upper mantle from ~50 to 100 km beneath the southernmost RM to the east edge of the plateau, and along the axis of the RGR, suggest warm upper mantle and small amount of partial melt. The central plateau shows a thicker crust and faster mantle lithosphere compared to the eastern, southwestern and northwestern transition zones towards the RM and BRP, indicating a cooler stronger lithosphere, consistent with the moderate surface heat flow and high Pn velocity compared to those of the plateau edges, where Pn velocity are relatively low and shallow upper mantle low velocity zones have been observed (Benz &McCarthy 1994, Henstock et al., 1998). We compare the surface wave results with the PdS and SdP receiver functions presented by Miller et al. (2009, this meeting). Bibtex entry for this abstract Preferred format for this abstract (see Preferences) Find Similar Abstracts: Use: Authors Title Keywords (in text query field) Abstract Text Return: Query Results Return items starting with number Query Form Database: Astronomy Physics arXiv e-prints
We present results from joint inversions of surface wave phase velocities and teleseismic receive... more We present results from joint inversions of surface wave phase velocities and teleseismic receiver functions, recently computed from USArray data, to analyze structure beneath the Colorado Plateau. The Colorado Plateau is a tectonic province characterized by high elevations (>1.5 km) of almost uniformly horizontally bedded rocks. To understand how such significant uplift has occurred without major changes in the bedding
ABSTRACT We combine teleseismic P and S body-wave and Rayleigh wave tomography with Ps and Sp rec... more ABSTRACT We combine teleseismic P and S body-wave and Rayleigh wave tomography with Ps and Sp receiver functions to image the west-central Colorado Plateau (CP). The images, made largely with USArray data, resolve a high-velocity drip extending from the base of the crust to more than 200 km depth. Ps receiver functions clearly define the upper surface of this body, which dips from the lower crust to depths of 70-90 km. The bottom of the remaining crust above the drip has a shape almost identical to the top of the drip, with an elevated Moho and a low seismic contrast. We interpret the high-velocity structure as an ongoing delamination-style downwelling of the lowermost crust and the Proterozoic age CP continental lithospheric mantle. The structure of the lithosphere-asthenosphere boundary (LAB), imaged with the receiver functions and the Rayleigh wave tomography, support this view. We associate this delamination feature with Pliocene and ongoing uplift of the CP, and envision uplift driven by a succession of these events propagating inward from the Plateau margins, associated with the magmatic invasion of the CP from its margins. Petrologic and geochemical observations suggest that Laramide-age flat-slab subduction thinned, hydrated and weakened the CP lithosphere and that mid-Cenozoic to Recent magmas infiltrated this mantle, creating the negative buoyancy required to destabilize the lithosphere. Using Grand Canyon incision rates and the patterns of Pliocene and younger basalts, we suggest that substantial plateau uplift resulted from underlying delaminations over the last ~6 Ma. We also note that these two processes together can destabilize cratons: 1) Weakening by hydration followed by 2) Invasion of the craton edges by melts that then freeze, increasing the bulk density of the pre-existing lithosphere.
1] The Colorado Plateau is a physiographic province in the western US with an average elevation o... more 1] The Colorado Plateau is a physiographic province in the western US with an average elevation of $1.9 km where, in contrast to neighboring provinces, there is little evidence of large scale tectonic deformation or magmatism. Recent availability of Earthscope/ USArray seismic data allow us to better examine the crust and upper mantle structure beneath the region and test proposed explanations for the plateau's uplift and relative stability. Using phase velocities for fundamental mode Rayleigh waves and P receiver functions, we perform over 800 joint inversions for 1-D shear wave velocity V S profiles sampling the plateau and surrounding regions down to 150 km depth. We image a sharp change in crustal thickness at the western edge of the Colorado Plateau with a more gradual increase eastward moving into the Rocky Mountains. A relatively thick (≳100 km) lithosphere beneath the plateau extends into the Rocky Mountains to the north. We use empirical scaling relations to estimate densities from our V S results, and predict the associated gravity anomalies, which are inconsistent with the observed distribution of the Bouguer gravity anomalies. We somewhat reconcile the prediction and observations by assuming that lateral density variations below 50 km can be ignored and the lithospheric root is therefore neutrally buoyant. While there is some evidence for small scale convection and lithospheric removal at its edges, the shape of the lithospheric mantle anomaly is consistent with a large scale uplift of the plateau by heating since removal of the Farallon slab. We conclude that the lithospheric root is key to the long term stability of the Colorado Plateau, leading to a colder, stronger crust. Citation: Bailey, I. W., M. S. Miller, K. Liu, and A. Levander (2012), V S and density structure beneath the Colorado Plateau constrained by gravity anomalies and joint inversions of receiver function and phase velocity data,
ABSTRACT We have developed a 3-D shear velocity model using finite-frequency Rayleigh wave phase ... more ABSTRACT We have developed a 3-D shear velocity model using finite-frequency Rayleigh wave phase velocity dispersion, PdS receiver functions, and ambient noise tomography to better understand the complex lithosphere/asthenosphere structures in the Mendocino Triple Junction (MTJ) region. Using approximately 100 events (July 2007-December 2008) recorded by the stations of the Flexible Array Mendocino Experiment (FAME), the USArray Transportable Array (TA) network, and the Berkeley Digital Seismograph network, we have obtained the phase velocities (20-100s) from the finite-frequency Rayleigh wave tomography, which agrees well with the ambient noise tomography results (7-40 s, Porritt & Allen, 2010) in the overlapping period range. We subsequently inverted for a 3-D Vs model on a 0.25°x0.25° grid from the combined dispersion datasets, constrained by interface depths from the PdS receiver functions (Zhai & Levander, 2010). The resulting crustal and upper mantle Vs model (~150 km) reveals strong lateral heterogeneity in the subduction and transform regimes of the Mendocino Triple Junction region where the Gorda, Pacific, and North American plates intersect. The subducting Gorda slab is well-imaged as an eastward-dipping high-velocity anomaly to ~100 km depth. At the same depth to the east we observe a large-scale low velocity zone, which is the mantle wedge beneath the North American Plate. The southern edge of the Gorda plate (SEDGE) is imaged at 80-100 km depth and is in excellent agreement with measurements made from PdS receiver functions, body-wave tomography (Schmandt & Humphreys, 2010; Obrebski et al., 2010), and active source studies. At depths greater than 80 km, we interpret low velocities under the Cascadia subduction zone as the asthenosphere below the Gorda plate, in agreement with measured LAB depths from RFs. South of the SEDGE shallow strong low-velocities appear beneath the transform region, which we interpret as the asthenosphere in the slab-gap region left by the northward migration of the MTJ, consistent with the `slab window' hypothesis. The Rayleigh wave data image low velocity upper mantle directly beneath the crust as far north as the Lake Pillsbury region, a site of modern basaltic intrusion. This probably marks the northernmost extent of the slab free window beneath the California Coast Ranges. We will examine the trade-off between receiver function amplitudes and velocity gradients for a better estimate of the lithosphere-asthenosphere boundary (LAB) depths beneath the Gorda plate and beneath the transform regime.
1] We present a 3-D shear wave velocity model for the crust and upper mantle of the western Medit... more 1] We present a 3-D shear wave velocity model for the crust and upper mantle of the western Mediterranean from Rayleigh wave tomography. We analyzed the fundamental mode in the 20-167 s period band (6.0-50.0 mHz) from earthquakes recorded by a number of temporary and permanent seismograph arrays. Using the two-plane wave method, we obtained phase velocity dispersion curves that were inverted for an isotropic Vs model that extends from the southern Iberian Massif, across the Gibraltar Arc and the Atlas mountains to the Saharan Craton. The area of the western Mediterranean that we have studied has been the site of complex subduction, slab rollback, and simultaneous compression and extension during African-European convergence since the Oligocene. The shear velocity model shows high velocities beneath the Rif from 65 km depth and beneath the Granada Basin from 70 km depth that extend beneath the Alboran Domain to more than 250 km depth, which we interpret as a near-vertical slab dangling from beneath the western Alboran Sea. The slab appears to be attached to the crust beneath the Rif and possibly beneath the Granada Basin and Sierra Nevada where low shear velocities (3.8 km/s) are mapped to >55 km depth. The attached slab is pulling down the Gibraltar Arc crust, thickening it, and removing the continental margin lithospheric mantle beneath both Iberia and Morocco as it descends into the deeper mantle. Thin lithosphere is indicated by very low upper mantle velocities beneath the Alboran Sea, above and east of the dangling slab and beneath the Cenozoic volcanics.
ABSTRACT Under a number of Cascade volcanoes we have identified a characteristic seismic signatur... more ABSTRACT Under a number of Cascade volcanoes we have identified a characteristic seismic signature in individual station Ps receiver functions and in Ps CCP image volumes made from USArray Transportable Array and Flexible Array stations. In the mantle wedge, the CCP images and the RFs show a strong negative event just below the Moho, paired with a weak to moderate positive event between 50-70 km, and a strong slab event. At most of these volcanoes, a strong negative signal also appears between 15 and 25 km depth in the crust. The signature is particularly clear under Mt. Lassen and Mt. Shasta in data from FAME (Flexible Array Mendocino Experiment), where instruments were close to the volcanic centers. Comparing the average Cascadia volcano signature to those of stations throughout the western U.S. and specifically those of the Cascadia backarc region, shows that this signal is unique to the Cascadia volcanoes. Joint inversion of the Ps receiver functions and ambient noise Rayleigh wave phase velocities (Porritt et al., 2011; Liu et al., submitted) for those volcanoes with the paired events provides 1D shear velocity profiles having common characteristics. A strong sub-Moho low velocity zone from 5 to 15 km thick gives rise to the paired negative-positive signals in the receiver functions. The sub-Moho low velocity zones, with velocities of 3.7 < Vs < 4.0 km/s, are evident in 15 of the 22 stations we examined. Stations not exhibiting this pattern also show a characteristic seismic structure: There is no abrupt velocity increase at Moho depths, instead Vs increases gradually from the lower crust to as deep as ~70 km, forming a thick, relatively high velocity layer (4.0 < Vs <4.5 km/s). This project was initiated as part of the CIDER 2011 summer program.
ABSTRACT The goal of this study is to compare imaging with scattered teleseismic wavefields using... more ABSTRACT The goal of this study is to compare imaging with scattered teleseismic wavefields using 3-D Kirchhoff- and Born-approximate inversion methods. Kirchhoff and Born-approximate inversions have been well developed in exploration seismology based on the inverse scattering framework (e.g. Beylkin and Burridge, 1990) to image subsurface structure that generates secondary wavefields due to localized heterogeneities. Application of these methods in global seismology has been somewhat limited to 1-D reference models due to high computational cost and the lack of dense receiver arrays (Bostock, 2002, Frederiksen and Revenaugh, 2004; Cao et al., 2010). Due to the deployment of the USArray Transportable and Flexible arrays across the United States and dense array recordings in other countries, we seek to extend teleseismic scattered wavefield imaging with each of these approximations from 2-D to 3-D for both scalar and vector wavefields to resolve the contrast of material parameters in the lowermost crust and the upper mantle. Following Bostock and coworkers (2001, 2002), making each approximation allows us to derive the 3-D multimode (P-to-P, P-to-S etc.) inversion formulae by phrasing the problem in terms of a generalized Radon transform (or its inverse) and then inverting the scattered waves. To demonstrate the relative accuracy of the two different inversions, we examine several synthetic cases with a variety of discontinuity surfaces. In the forward scattering modeling, we extend the method to utilize a 3-D background velocity model by calculating 3-D finite-difference traveltimes and amplitudes, backprojected from the receivers using an eikonal solver. We compare our Kirchhoff- and Born-approximation imaging with the common-conversion point (CCP) stacked receiver function imaging for the synthetic data. We apply these methods to USArray data.
ABSTRACT We have developed a 3-D teleseismic imaging technique for scattered elastic wavefields u... more ABSTRACT We have developed a 3-D teleseismic imaging technique for scattered elastic wavefields using the Kirchhoff approximation. Kirchhoff migration/inversion have been well developed in exploration seismology within the inverse scattering framework (e.g. Miller et al., 1987; Beylkin and Burridge, 1990) to image subsurface structure that generates secondary wavefields caused by localized heterogeneities. Application of this method in global seismology has been largely limited to 2-D images made with 1-D reference models due to high computational cost and the lack of adequately dense receiver arrays (Bostock, 2002, Poppeliers and Pavlis, 2003; Frederiksen and Revenaugh, 2004; Cao et al., 2010). The deployment of the USArray Transportable and Flexible arrays in the United States and dense array recordings in other countries motivate developing teleseismic scattered wavefield imaging with the Kirchhoff approximation for 3-D velocity models for both scalar and vector wavefields to improve upper mantle imaging. Following Bostock's development of the 2-D problem (2002), we derive the 3-D P-to-S scattering inversion formula by phrasing the inverse problem in terms of the generalized Radon transform (GRT) and singular functions of discontinuity surfaces. In the forward scattering modeling, we extend the method to utilize a 3-D migration velocity model by calculating 3-D finite-difference traveltimes, backprojected from the receivers using an eikonal solver. To demonstrate the relative accuracy of the inversion, we examine several synthetic cases with a variety of discontinuity surfaces (sinuous, dipping, dome- and crater-shaped discontinuity interfaces, point scatterers, etc.). The Kirchhoff GRT imaging can successfully recover the shapes of these structures very well. We compare our Kirchhoff approximation imaging with the Born-approximate results, as well as the common-conversion point (CCP) stacked receiver function imaging for the various synthetic cases, and show a field example using USArray data.
ABSTRACT Under a number of Cascade volcanoes we have identified a characteristic seismic signatur... more ABSTRACT Under a number of Cascade volcanoes we have identified a characteristic seismic signature in individual station Ps receiver functions and in Ps CCP image volumes made from USArray Transportable Array and Flexible Array stations. In the mantle wedge, the CCP images and the RFs show a strong negative event just below the Moho, paired with a weak to moderate positive event between 50-70 km, and a strong slab event. At most of these volcanoes, a strong negative signal also appears between 15 and 25 km depth in the crust. The signature is particularly clear under Mt. Lassen and Mt. Shasta in data from FAME (Flexible Array Mendocino Experiment), where instruments were close to the volcanic centers. Comparing the average Cascadia volcano signature to those of stations throughout the western U.S. and specifically those of the Cascadia backarc region, shows that this signal is unique to the Cascadia volcanoes. Joint inversion of the Ps receiver functions and ambient noise Rayleigh wave phase velocities (Porritt et al., 2011; Liu et al., submitted) for those volcanoes with the paired events provides 1D shear velocity profiles having common characteristics. A strong sub-Moho low velocity zone from 5 to 15 km thick gives rise to the paired negative-positive signals in the receiver functions. The sub-Moho low velocity zones, with velocities of 3.7 < Vs < 4.0 km/s, are evident in 15 of the 22 stations we examined. Stations not exhibiting this pattern also show a characteristic seismic structure: There is no abrupt velocity increase at Moho depths, instead Vs increases gradually from the lower crust to as deep as ~70 km, forming a thick, relatively high velocity layer (4.0 < Vs <4.5 km/s). This project was initiated as part of the CIDER 2011 summer program.
Teleseismic imaging techniques utilizing mode converted/scattered waves are gaining importance du... more Teleseismic imaging techniques utilizing mode converted/scattered waves are gaining importance due to the deployment of increasingly dense broad-band seismograph arrays. Although common-conversion point (CCP) stacking is widely used to determine structure from Ps or Sp scattered wavefields isolated by receiver function (RF) processing, this method is limited due to its assumption of a layered medium: Dipping events and diffractions are not treated correctly. As an extension of previous 2-D generalized Radon transform (GRT) imaging methods, we present a 3-D Kirchhoff-approximate imaging technique to migrate scattered waves in 3-D. We first derive the 3-D migration formula for P-to-S conversions using the GRT solution to the linear inverse elastic wave scattering problem. Then we illustrate the Kirchhoff method using finite-difference synthetic seismograms from several 3-D models.