Browsing by Author "Li, Guoliang"

Now showing 1 - 6 of 6
  • Thumbnail Image
    Item
    3D Shear Velocity Structure of the Caribbean—Northwestern South America Subduction Zone From Ambient Noise and Ballistic Rayleigh Wave Tomography
    (Wiley, 2024) Miao, Wenpei; Cornthwaite, John; Levander, Alan; Niu, Fenglin; Schmitz, Michael; Li, Guoliang; Dionicio, Viviana; Prieto, German
    The Caribbean-South America subduction zone is a flat subduction zone, with Laramide-style thick-skinned uplifts occurring in the Merida Andes, Sierra de Perija Range, and Santa Marta Massif. Geodetic measurements and historical seismicity show this region is storing strain energy and is capable of a mega-thrust earthquake (M ≥ 8.0). Previous seismic investigations of the lithosphere and upper mantle in this area are either very large scale, very local, or only peripheral to this area; therefore, details of the Caribbean plate subduction geometry beneath the Maracaibo block remain unclear. In this study, we used a new data set acquired by the Caribbean-Merida Andes seismic experiment (CARMA), which comprised 65 temporary broadband stations and 44 permanent stations from the Colombian and Venezuelan national seismic networks. We jointly inverted ambient noise Rayleigh wave Z/H ratios, phase velocities in the 8–30 s band and ballistic Rayleigh wave phase velocities in 30–80 s band to construct a 3-D S-wave velocity model in the area between 75°–65°W and 5°–12°N. The 3-D model reveals a general increase in crust thickness from the trench to the southeast. An anomalous area is the Lake Maracaibo, which is underlaid by the thinnest crystalline crust in the region. This observation may indicate that the Maracaibo block is experiencing a contortion deformation within the crust. We also identified a high velocity anomaly above the subducting Caribbean slab, likely representing a detached piece of eclogitized Caribbean large igneous province from the base of the Maracaibo block. Additionally, our Vs model clearly indicates a slab tear within the subducted Caribbean slab, approximately beneath the Oca-Ancon Fault.
  • Thumbnail Image
    Item
    Insights on Formation of the Gulf of Mexico by Rayleigh Surface Wave Imaging
    (Wiley, 2022) Nguyen, Luan C.; Levander, Alan; Niu, Fenglin; Morgan, Julia; Li, Guoliang
    We used cross-correlation of ambient noise records from seismic stations in the US, Mexico, and Cuba to extract dispersion data of Rayleigh surface wave. Our derived 3D shear-wave velocity model of the greater Gulf of Mexico (GOM) region captures variations in the crustal and lithospheric structures across the continental margins of the US Gulf Coast and Yucatan, Mexico. The model shows a zone of reduced velocity in the mantle lithosphere underlying the extended continental margin of the northwestern GOM. We attributed this velocity reduction to extensional deformation and melt-induced weakening of the lithosphere during the Triassic continental rifting that preceded the seafloor spreading that formed the GOM. Melt extraction might have been hindered by the greater lithospheric thickness in the western region along the US Gulf Coast margin that resulted in the westward decrease of rift-related volcanism/magmatism reported from previous studies. The clear asymmetry between the US Gulf Coast and its conjugate Yucatan margin suggests extension along a shear-zone that focused more deformation on the North American plate prior to breakup. In contrast to the counterclockwise rotation of the Yucatan block during seafloor-spreading, our analyses using deformable plate models demonstrate that continental rifting occurred in a predominantly northwest-southeast direction. This change in plate motion is attributed to the development of mantle shear-zones in the western part of the rift. We estimated the depth of the lithosphere-asthenosphere boundary and determined that the extended continental and oceanic lithospheres have mostly regained their thickness since the time of breakup.
  • Thumbnail Image
    Item
    Measurement of Rayleigh wave ellipticity and its application to the joint inversion of high-resolutionﾠSwave velocity structure beneath northeast China
    (Wiley, 2016) Li, Guoliang; Chen, Haichao; Niu, Fenglin; Guo, Zhen; Yang, Yingjie; Xie, Jun
    We present a new 3-D S wave velocity model of the northeast (NE) China from the joint inversion of the Rayleigh wave ellipticity and phase velocity at 8–40 s periods. Rayleigh wave ellipticity, or Rayleigh wave Z/H (vertical to horizontal) amplitude ratio, is extracted from both earthquake (10–40 s) and ambient noise data (8–25 s) recorded by the NorthEast China Extended SeiSmic Array with 127 stations. The estimated Z/H ratios from earthquake and ambient noise data show good consistency within the overlapped periods. The observed Z/H ratio shows a good spatial correlation with surface geology and is systematically low within the basins. We jointly invert the measured Z/H ratio and phase velocity dispersion data to obtain a refined 3-D S wave velocity model beneath the NE China. At shallow depth, the 3-D model is featured by strong low-velocity anomalies that are spatially well correlated with the Songliao, Sanjiang, and Erlian basins. The low-velocity anomaly beneath the Songliao basin extends to ~ 2–3 km deep in the south and ~5–6 km in the north. At lower crustal depths, we find a significant low-velocity anomaly beneath the Great Xing'an range that extends to the upper mantle in the south. Overall, the deep structures of the 3-D model are consistent with previous models, but the shallow structures show a much better spatial correlation with tectonic terranes. The difference in sedimentary structure between the southern and northern Songliao basin is likely caused by a mantle upwelling associated with the Pacific subduction.
  • Thumbnail Image
    Item
    Sedimentary and crustal structure of the US Gulf Coast revealed by Rayleigh wave and teleseismic P coda data with implications for continent rifting
    (Elsevier, 2022) Miao, Wenpei; Niu, Fenglin; Li, Guoliang; Levander, Alan
    We have developed an S-wave model of the south-central US focusing on the Gulf Coast sedimentary basin and its crust to understand continental rifting and regional tectonics. The model was derived by a joint inversion of Rayleigh wave phase velocities, Z/H ratios and P-coda data. The surface- and body-wave measurements were made, respectively, from ambient noise and teleseismic earthquakes recorded by 215 USArray stations in a rectangular area of 100°–87° west and 28°–37° north. We employed a cross-convolution function and H-κ analysis to better constrain sedimentary and Moho structure. We find that the southern edge of the Ouachita fold-and-thrust belt (OFTB) appears as a boundary in measured phase velocities, Z/H ratios, sediment basement depths, Moho depths, average crustal Vs and Vp/Vs ratios. The model shows southeastward thickening of the sedimentary basin, accompanied by thinning of the crystalline crust. The Moho gradient suggests that early rifting between North America and the Yucatan block commenced in a SE direction and involved most of the Pangea crust south of the OFTB boundary (i.e., Gondwana crust). We believe that a high velocity feature in the lowermost crust and upper mantle parallel to the southeast Texas coast was emplaced as a mafic body and is the source of the Houston magnetic anomaly. The seismic structures of the crust and uppermost mantle observed beneath the Mississippi Embayment and the Mississippi Valley Graben are consistent with plume induced Cretaceous uplift of the Mississippi Embayment as North America passed over the Bermuda hotspot.
  • Thumbnail Image
    Item
    Seismic evidence for lithospheric boudinage and its implications for continental rifting
    (The Geological Society of America, 2022) Nguyen, Luan C.; Levander, Alan; Niu, Fenglin; Morgan, Julia; Li, Guoliang
    The continental rifting that precedes the breakup of a continent and the formation of a new ocean basin is one of the key processes of plate tectonics. Although often viewed as a two-dimensional process, rifted margins exhibit significant variations along strike. We document along-strike variations developed during the ca. 200–160 Ma continental rifting that formed the margins of the Gulf of Mexico ocean basin. Rayleigh-wave ambient noise tomography reveals a zone of high and low seismic velocity resembling large scale geologic boudins in the mantle lithosphere of the northwestern Gulf of Mexico margin. These features become progressively less prominent eastward following the transition from a magma-poor to a magma-rich passive margin. We infer that mantle refertilization and thickness of the pre-rift lithosphere control deformation style and the along-strike variations in continental rifting. Our results also suggest that deformation during rifting produces long-lived features that persist long after breakup and, therefore, can be used to study rifted margins globally.
  • Thumbnail Image
    Item
    Temporal Variations of Near‐Surface Anisotropy Induced by Hydraulic Fracturing at a Shale Play Site in Southwest China
    (Wiley, 2018) Zuo, Qiankun; Tang, Youcai; Niu, Fenglin; Li, Guoliang; Chen, Haichao; Tao, Kai; Chen, Benchi
    Knowledge of the geometric properties of fractures and cracks in a petroleum reservoir is important to reservoir exploitation. When aligned and partially connected, fractures and cracks can act as conduits for fluid flow and thus can significantly increase the permeability of the reservoir. The aligned fractures and cracks, on the other hand, are an effective means to generate seismic anisotropy. In this study, we utilize the seismic data recorded by a vertical array installed in a shallow borehole at a shale play site in southwest China. By applying seismic interferometry to the ambient noise data recorded by 12 three‐component geophones, we extract P and S waves propagating vertically along the borehole. The S waves show up to 20% velocity variations with respect to their polarization directions. Such large S wave anisotropy can be explained by the horizontal transverse isotropic model and is likely caused by natural fractures that are widely present in the area and align approximately in the NE‐SW direction. During the 13‐day period of hydraulic fracking treatment, we also observe large and systematic temporal variations in S wave velocity, degree of S wave polarization anisotropy, and fast polarization direction. By comparing our observations with normal strain changes calculated with a half‐space elastic model, we speculate that strain changes induced by hydraulic injection and fracturing are likely to be responsible for the observed temporal variations in seismic anisotropy. As such, seismic interferometry with shallow borehole acquisition might provide an alternative means to monitor hydraulic fracturing and wastewater injection in the future.