Article
Geosciences, Multidisciplinary
Jonathan Wolf, Maureen D. Long
Summary: We investigate the applicability of the PS-SKS splitting technique using global wavefield simulations and apply this technique to measure upper mantle anisotropy beneath the Pacific Ocean basin. Our results suggest that the upper mantle anisotropy in this region is mainly influenced by shearing due to the Pacific plate. Furthermore, we observe a rotation of fast polarization directions north of Fiji, possibly indicating far-field mantle flow effects associated with the subduction of the Australian plate beneath the Pacific.
GEOPHYSICAL RESEARCH LETTERS
(2023)
Article
Geochemistry & Geophysics
Erica M. Lucas, Andrew A. Nyblade, Natalie J. Accardo, Andrew J. Lloyd, Douglas A. Wiens, Richard C. Aster, Terry J. Wilson, Ian W. Dalziel, Graham W. Stuart, John Paul O'Donnell, J. Paul Winberry, Audrey D. Huerta
Summary: In this study, we examined the anisotropy of the upper mantle in the Antarctic continent. The results showed that the fast polarization directions across Antarctica mostly oriented in the NE-SW direction, with a clockwise rotation when moving from west to east. The observed anisotropy is likely a result of regionally variable contributions from both lithospheric and sub-lithospheric mantle sources.
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
(2022)
Article
Geochemistry & Geophysics
Julia Rewers, Piotr Sroda
Summary: In this study, seismic data was used to analyze the structure and evolution of the upper mantle beneath the Polish Sudetes. The results indicate a large-scale anisotropy trend with NW-SE to WNW-ESE orientation, possibly related to the formation of asthenospheric flow.
Article
Geochemistry & Geophysics
Eric Loeberich, Goetz Bokelmann
Summary: Shear-wave splitting measurements can be used to map the orientation of geodynamically induced fabrics in the mantle. However, it has been challenging to differentiate between asthenospheric and lithospheric origins of observed seismic anisotropy. This study investigates seismic anisotropy in the Central Alps and suggests that the anisotropy is likely of asthenospheric origin.
PHYSICS OF THE EARTH AND PLANETARY INTERIORS
(2022)
Article
Geochemistry & Geophysics
C. Erman, S. Yolsal-Cevikbilen, T. Eken, F. Tilmann, D. Keles, T. Taymaz
Summary: This study investigates the azimuthal anisotropy in the back-arc region of the Hellenic subduction zone and its relation to geodynamical processes. The results reveal NE-SW oriented fast polarization directions and delay times between 0.65 and 2.2 s. The observed seismic anisotropy is mainly attributed to the internal deformation of the mantle lithosphere and asthenosphere.
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
(2022)
Article
Geochemistry & Geophysics
Hanting Wu, Zhouchuan Huang
Summary: By measuring SKS splitting, this study reveals the complex deformation of the upper mantle in western Mongolia. The predominant NW-SE-oriented fast polarization directions are consistent with lithospheric deformation and asthenospheric flow. The shape of the Siberian Craton influences the extent of lithospheric deformation and causes the deflection of asthenospheric flow.
Article
Geochemistry & Geophysics
A. Christian Stanciu, Eugene D. Humphreys
Summary: New P and S teleseismic tomography models of the upper mantle beneath California and Nevada have been presented, showing stronger and narrower structures beneath prominent tectonic features in the region. These structures suggest the presence of partial melting in the upper mantle and imply variations in the upper mantle that ultimately impact the overlying crust in California and Nevada. The incorporation of modern crustal velocity models and technical advancements in tomographic methods have improved image resolution and seismic structure definition.
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
(2021)
Article
Geochemistry & Geophysics
Wu YiYing, Deng SiZhuang, Niu FengLin, He Wei, Wu HanNing
Summary: The Qinling Orogenic Belt is an east-west extended Proterozoic mountain range with overall E-W fast polarization direction of seismic anisotropy. However, there are slight variations at its western and eastern ends, and significant difference in fast polarization direction between crust and upper mantle deformation in the eastern part of the belt.
CHINESE JOURNAL OF GEOPHYSICS-CHINESE EDITION
(2021)
Article
Geochemistry & Geophysics
S. Pondrelli, J. M. Confal, P. Baccheschi
Summary: In this paper, a new seismic anisotropy dataset is described for Central Italy. The new measurements reveal changes in the fast polarisation directions and the presence of mantle flow from the Adriatic Sea to the Tyrrhenian Sea.
Article
Geochemistry & Geophysics
Kailun Ba, Stephen S. Gao, Jianguo Song, Kelly H. Liu
Summary: Seismic azimuthal anisotropy beneath Australia is investigated using splitting of the teleseismic phases. The observed azimuthal anisotropy can mostly be related to simple shear in the rheologically transition layer between the lithosphere and asthenosphere.
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
(2023)
Article
Geochemistry & Geophysics
Enbo Fan, Yumei He, Yinshuang Ai, Stephen S. Gao, Kelly H. Liu, Mingming Jiang, Guangbing Hou, Chit Thet Mon, Myo Thant, Kyaing Sein
Summary: This study conducted the first campaign-style teleseismic shear wave splitting investigation in central Myanmar, revealing that the Indo-Burma Ranges (IBR) have mostly N-S fast orientations while the Central Basin (CB) and the Shan Plateau (SP) exhibit slightly larger splitting times compared to normal.
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
(2021)
Article
Geochemistry & Geophysics
Jonathan Wolf, Daniel A. Frost, Maureen D. Long, Edward Garnero, Adeolu O. Aderoju, Neala Creasy, Ebru Bozdag
Summary: Shear-wave splitting measurements are commonly used to resolve seismic anisotropy in both the upper and lowermost mantle. However, practical constraints such as limited suitable phases and poor signal-to-noise ratios or large measurement uncertainties limit the application of these techniques. This study investigates how a beamforming methodology can improve shear-wave splitting measurement confidence intervals and shows the potential of beamforming to improve the detection of lowermost mantle anisotropy.
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
(2023)
Article
Geochemistry & Geophysics
Lindsey M. Kenyon, Ikuko Wada
Summary: The study investigates the evolution of olivine crystal preferred orientation and its effect on shear wave splitting in the mantle wedge of oblique subduction zones. Model simulations show that seismic fast axis does not always align with flow direction in these zones. The research demonstrates significant variations in SWS parameters with subduction obliquity and initial polarization, requiring a range of shear waves to interpret accurately.
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
(2022)
Article
Geochemistry & Geophysics
E. Loeberich, M. D. Long, L. S. Wagner, E. Qorbani, G. Bokelmann
Summary: Shear-wave splitting observations of SKS and SKKS phases are used to map azimuthal anisotropy and constrain upper mantle deformation directions caused by olivine. Predicting the azimuthal variation of splitting parameters for different olivine fabrics helps infer upper mantle water content, with E-type olivine likely present in the back-arc of the Cascadia subduction zone.
GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS
(2021)
Article
Geochemistry & Geophysics
Zhengyang Qiang, Qingju Wu, Yonghua Li
Summary: This study estimated over 2,000 shear wave splitting parameters from 84 teleseismic earthquakes to constrain lithospheric deformation and mantle flow in the western and central North China Craton. The results revealed stable terrane with thick Archean cratonic keel in the Ordos Block, and systematic directional deviation from the absolute plate motion direction in the southern Trans-North China Orogen. Active mantle flow and a mantle plume beneath the Datong Volcano were also inferred from the analysis.
Article
Geochemistry & Geophysics
Jonathan Wolf, Maureen D. Long, Kuangdai Leng, Tarje Nissen-Meyer
Summary: Observations of seismic anisotropy at the base of the mantle provide insights into geodynamic scenarios and patterns of flow at the base of the mantle. However, limitations in current studies include the use of ray theoretical framework in forward modelling and lack of consideration of finite-frequency wave propagation effects.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2022)
Article
Geochemistry & Geophysics
Yantao Luo, Maureen D. Long, Paul Karabinos, Yvette D. Kuiper, Stephane Rondenay, John C. Aragon, Lucas Sawade, Peter Makus
Summary: Southern New England displays diverse geological features resulting from past tectonic events. Seismological studies in Connecticut have revealed deep Moho variations, potential remnants of past subduction events, and a negative velocity gradient at the base of the lithosphere. These features suggest complex tectonic processes shaping the region's geology.
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
(2021)
Article
Geochemistry & Geophysics
Neala Creasy, Angelo Pisconti, Maureen D. Long, Christine Thomas
Summary: Observations of seismic anisotropy just above the core-mantle boundary provide insights into the dynamics of the lowermost mantle. By combining different data types in modeling approaches, constraints on the geometry and mechanisms of seismic anisotropy can be tightened, with post-perovskite or bridgmanite models showing the best fit to observations. The best-fitting models suggest a dominant shear direction to the southwest or northeast at the base of the mantle, consistent with flow towards the Perm anomaly driven by slab remnants at the core-mantle boundary.
GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS
(2021)
Article
Geochemistry & Geophysics
Jonathan Wolf, Maureen D. Long, Kuangdai Leng, Tarje Nissen-Meyer
Summary: This study systematically assesses the accuracy and limitations of several methods for resolving seismic anisotropy in the deep mantle. The research reveals inaccuracies and suggests modifications to improve the reliability of the measurement techniques. Recommendations are also provided to ensure accurate comparisons and measurements of lowermost mantle anisotropy.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2022)
Article
Geology
Gillian B. Goldhagen, Heather A. Ford, Maureen D. Long
Summary: Using data from the SEISConn seismic experiment, this study characterizes the upper-mantle structure beneath southern New England. The researchers identify a well-defined lithosphere-asthenosphere boundary, a thin lithosphere, and a possible extension of the Northern Appalachian Anomaly. They also suggest the preservation of inherited structure in the present-day lithosphere.
Article
Geosciences, Multidisciplinary
Yantao Luo, Maureen D. Long, Stephane Rondenay, Paul Karabinos, Yvette D. Kuiper
Summary: This study reveals the significant offset and dipping discontinuities of the Moho beneath the New England Appalachians, indicating tectonic movements in the Paleozoic or younger. By using scattered wavefield migration, new insights are obtained, including the discovery of a doubled Moho and mafic underplating.
GEOPHYSICAL RESEARCH LETTERS
(2022)
Article
Geochemistry & Geophysics
Jonathan Wolf, Maureen D. Long
Summary: Flow in the mantle's bottom boundary layer is crucial for shaping structures and processes in the deep mantle. This study investigates the influence of remnant slabs on lowermost mantle flow and reveals their significant role in driving the behavior of the lowermost mantle.
EARTH AND PLANETARY SCIENCE LETTERS
(2022)
Article
Geochemistry & Geophysics
Angelo Pisconti, Neala Creasy, James Wookey, Maureen D. Long, Christine Thomas
Summary: Recent advances in seismic anisotropy studies have provided significant insights into the structure and deformation of the D '' region beneath the South Atlantic. By analyzing seismic phases, researchers have detected a discontinuity within the D '' region and evidence of anisotropy. The study proposes a regional variation in mineralogy and deformation, suggesting the presence of distinct domains within and outside the large low seismic velocity province.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2023)
Article
Geochemistry & Geophysics
Ved Mittal, Maureen D. Long, Rob L. Evans, Joseph S. Byrnes, Maximiliano Bezada
Summary: The Central Appalachian Anomaly (CAA) is a region beneath eastern North America with abnormal seismic velocity, seismic attenuation, and electrical conductivity structure. Through the Mid-Atlantic Geophysical Integrative Collaboration (MAGIC) experiment, new observations from teleseismic earthquakes at MAGIC stations provide insights into the structure and properties of the upper mantle in the CAA region. These observations, combined with previous estimates of attenuation and conductivity, suggest that 1%-2% partial melt is necessary to explain the anomalies in velocity, attenuation, and electrical conductivity beneath the MAGIC array.
GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS
(2023)
Article
Geochemistry & Geophysics
Jonathan Wolf, Daniel A. Frost, Maureen D. Long, Edward Garnero, Adeolu O. Aderoju, Neala Creasy, Ebru Bozdag
Summary: Shear-wave splitting measurements are commonly used to resolve seismic anisotropy in both the upper and lowermost mantle. However, practical constraints such as limited suitable phases and poor signal-to-noise ratios or large measurement uncertainties limit the application of these techniques. This study investigates how a beamforming methodology can improve shear-wave splitting measurement confidence intervals and shows the potential of beamforming to improve the detection of lowermost mantle anisotropy.
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
(2023)
Article
Geochemistry & Geophysics
Jonathan Wolf, Maureen D. D. Long
Summary: The study reveals that ultralow velocity zones (ULVZs) and seismic anisotropy are commonly detected in the lowermost mantle at the edges of large low velocity provinces (LLVPs). By jointly investigating ULVZ structure and lowermost mantle anisotropy near the Pacific LLVP, the study provides insights into the geodynamic scenarios for flow in the deep mantle. The findings contribute to our understanding of mantle flow processes at the edges of LLVP structures.
GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS
(2023)
Article
Geosciences, Multidisciplinary
Shangxin Liu, Scott D. King, Maureen D. Long, Margaret H. Benoit, John C. Aragon
Summary: Using high-resolution seismic data along the MAGIC profile, we found a shallowing trend of both the 410-km and 660-km discontinuities beneath the central Appalachian region. This could be explained by hydro-thermal upwelling and hot upwelling return flow associated with the descending lower mantle Farallon slab. The rising hydrous hot upwelling may trigger dehydration melting atop the 410-km discontinuity, leading to the low velocity upper mantle anomaly observed in the region.
GEOPHYSICAL RESEARCH LETTERS
(2023)
Article
Geochemistry & Geophysics
Jonathan Wolf, Maureen D. Long, Mingming Li, Edward Garnero
Summary: This study utilizes a global digital database to examine the seismic anisotropy distribution in the D '' layer of Earth's mantle and assess whether it is more likely to be located at the edges of the two large-low velocity provinces. The findings indicate that this hypothesis lacks statistical justification when considering previous observations of lowermost mantle anisotropy. The study also highlights the uneven global ray coverage of the lowermost mantle, with the edges and interiors of LLVPs being less well-sampled.
GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS
(2023)
Article
Geosciences, Multidisciplinary
Jonathan Wolf, Maureen D. Long
Summary: We investigate the applicability of the PS-SKS splitting technique using global wavefield simulations and apply this technique to measure upper mantle anisotropy beneath the Pacific Ocean basin. Our results suggest that the upper mantle anisotropy in this region is mainly influenced by shearing due to the Pacific plate. Furthermore, we observe a rotation of fast polarization directions north of Fiji, possibly indicating far-field mantle flow effects associated with the subduction of the Australian plate beneath the Pacific.
GEOPHYSICAL RESEARCH LETTERS
(2023)
Article
Geochemistry & Geophysics
Haiying Gao, Maureen D. Long
Summary: The Cascadia subduction zone represents a thermally hot endmember of global subduction systems with complex and three-dimensional heterogeneities. However, consensus on many important aspects of its magmatic, tectonic, and geodynamic setting remains elusive.