Velocity structure near IODP Hole U1309D, Atlantis Massif, from waveform inversion of streamer data and borehole measurements

Harding, A. J.; Arnulf, A. F.; Blackman, Donna K.

doi:10.1002/2016gc006312

Cited by 27 publications

(45 citation statements)

References 87 publications

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“…Atlantis massif (MAR, 30°N) is an inside‐corner OCC bounded by a transform fault and consisting of a large gabbroic core surrounded by serpentinized peridotites (e.g., Blackman et al, ; Harding et al, ). Collins et al () found that seismicity at the Atlantis massif (~55 events per day) was concentrated in the axial valley rather than beneath the massif itself, which is located outboard of the axial valley on the inside corner of a ridge transform intersection.…”

Section: Discussionmentioning

confidence: 99%

Local Seismicity of the Rainbow Massif on the Mid‐Atlantic Ridge

et al. 2018

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The Rainbow massif, an oceanic core complex located in a nontransform discontinuity on the Mid‐Atlantic Ridge (36°N), is notable for hosting high‐temperature hydrothermal discharge through ultramafic rocks. Here we report results from a 9 month microearthquake survey conducted with a network of 13 ocean bottom seismometers deployed on and around the Rainbow massif as part of the MARINER experiment in 2013–2014. High rates (~300 per day) of low‐magnitude (average ML ~ 0.5) microearthquakes were detected beneath the massif. The hypocenters do not cluster along deeply penetrating fault surfaces and do not exhibit mainshock/aftershock sequences, supporting the hypothesis that the faulting associated with the exhumation of the massif is currently inactive. Instead, the hypocenters demarcate a diffuse zone of continuous, low‐magnitude deformation at relatively shallow (< ~3 km) depths beneath the massif, sandwiched in between the seafloor and seismic reflectors interpreted to be magmatic sills driving hydrothermal convection. Most of the seismicity is located in regions where seismic refraction data indicate serpentinized ultramafic host rock, and although the seismic network we deployed was not capable of constraining the focal mechanism of most events, our analysis suggests that serpentinization may play an important role in microearthquake generation at the Rainbow massif.

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Section: Discussionmentioning

confidence: 99%

Local Seismicity of the Rainbow Massif on the Mid‐Atlantic Ridge

et al. 2018

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“…Under these circumstances, the inversion result suffers from velocity-depth ambiguity. Streamer TTT exploits the dense and even spatial distribution of MCS data and is further improved upon by DC, which allows for the inclusion of shallower refractions that were only previously obtainable using either seafloor receivers and sources (Henig, 2013). It is important to notice that these highlighted phases would correspond to ray paths in the upper region of the subseafloor section.…”

Section: Discussionmentioning

confidence: 99%

Full-waveform inversion of short-offset, band-limited seismic data in the Alboran Basin (SE Iberia)

et al. 2019

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Abstract. We present a high-resolution P-wave velocity model of the sedimentary cover and the uppermost basement to ∼3 km depth obtained by full-waveform inversion of multichannel seismic data acquired with a 6 km long streamer in the Alboran Sea (SE Iberia). The inherent non-linearity of the method, especially for short-offset, band-limited seismic data as this one, is circumvented by applying a data processing or modelling sequence consisting of three steps: (1) data re-datuming by back-propagation of the recorded seismograms to the seafloor; (2) joint refraction and reflection travel-time tomography combining the original and the re-datumed shot gathers; and (3) full-waveform inversion of the original shot gathers using the model obtained by travel-time tomography as initial reference. The final velocity model shows a number of geological structures that cannot be identified in the travel-time tomography models or easily interpreted from seismic reflection images alone. A sharp strong velocity contrast accurately defines the geometry of the top of the basement. Several low-velocity zones that may correspond to the abrupt velocity change across steeply dipping normal faults are observed at the flanks of the basin. A 200–300 m thick, high-velocity layer embedded within lower-velocity sediment may correspond to evaporites deposited during the Messinian crisis. The results confirm that the combination of data re-datuming and joint refraction and reflection travel-time inversion provides reference models that are accurate enough to apply full-waveform inversion to relatively short offset streamer data in deep-water settings starting at a field-data standard low-frequency content of 6 Hz.

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“…All ultramafic samples analyzed in this study come from the detachment shear zone that is documented to be 100 m thick at the southern wall (Karson et al, ; Schroeder & John, ). On the contrary, the detachment shear zone is thin (<20 m) at the Central Dome (Harding et al, ), and the mafic samples come mostly from the deeper and broader deformation zone, well below the detachment shear zone. The experimental rig that we used for the physical properties measurements requires cylindrical samples of 5‐cm diameter and ~2‐cm height.…”

Section: Methodsmentioning

confidence: 99%

Anisotropic Physical Properties of Mafic and Ultramafic Rocks From an Oceanic Core Complex

Bayrakci

Falcón-Suarez

Minshull

et al. 2018

Geochem Geophys Geosyst

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We analyzed the physical properties of altered mafic and ultramafic rocks drilled at the Atlantis Massif (Mid‐Atlantic Ridge, 30°N; Integrated Ocean Discovery Program Expeditions 304‐305 and 357). Our objective was to find a physical property that allows direct distinction between these lithologies using remote geophysical methods. Our data set includes the density, the porosity, P and S wave velocities, the electrical resistivity, and the permeability of mafic and ultramafic samples under shallow subsurface conditions (confining pressure up to 50 MPa equivalent to ~2‐km depth). In shallow subsurface conditions, mafic and ultramafic samples showed distinct differences in the density, the seismic wave velocities, and the electrical resistivity (mafic samples: 2,840 to 2,860 kg/m3, 5.92 to 6.70 km/s, and 60 to 221 Ω m; ultramafic samples: 2,370 to 2,790 kg/m3, 3.36 and 3.62 km/s, and 8 to 44 Ω m). However, we observed an overlap between physical properties of mafic and ultramafic rocks when we compared our measurements with those acquired from similar environments. The anisotropic homogeneous electrical resistivity inversion shows transverse isotropy symmetry, which is typical of a foliated microstructure. In both the inversion results and the thin sections, the direction of high resistivity axes of ultramafic rock samples is systematically perpendicular to the equivalent axes in mafic rock samples analyzed in this study. Our sample scale study suggests that electrical resistivity anisotropy may allow us to distinguish mafic and ultramafic lithologies via controlled source electromagnetic surveys. When surface conduction is negligible, the electrical resistivity can be used as proxy for permeability.

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Velocity structure near IODP Hole U1309D, Atlantis Massif, from waveform inversion of streamer data and borehole measurements

Cited by 27 publications

References 87 publications

Local Seismicity of the Rainbow Massif on the Mid‐Atlantic Ridge

Local Seismicity of the Rainbow Massif on the Mid‐Atlantic Ridge

Full-waveform inversion of short-offset, band-limited seismic data in the Alboran Basin (SE Iberia)

Anisotropic Physical Properties of Mafic and Ultramafic Rocks From an Oceanic Core Complex

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