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We present a new compilation and analysis of broad-band ocean bottom seismometer noise properties from 15 yr of seismic deployments. We compile a comprehensive data set of representative four-component (seismometer and pressure gauge) noise spectra and cross-spectral properties (coherence, phase and admittance) for 551 unique stations spanning 18 U.S.-led experiments. This is matched with a comprehensive compilation of metadata parameters related to instrumentation and environmental properties for each station. We systematically investigate the similarity of noise spectra by grouping them according to these metadata parameters to determine which factors are the most important in determining noise characteristics. We find evidence for improvements in similarity of noise properties when grouped across parameters, with groupings by seismometer type and deployment water depth yielding the most significant and interpretable results. Instrument design, that is the entire deployed package, also plays an important role, although it strongly covaries with seismometer and water depth. We assess the presence of traditional sources of tilt, compliance, and microseismic noise to characterize their relative role across a variety of commonly used seismic frequency bands. We find that the presence of tilt noise is primarily dependent on the type of seismometer used (covariant with a particular subset of instrument design), that compliance noise follows anticipated relationships with water depth, and that shallow, oceanic shelf environments have systematically different microseism noise properties (which are, in turn, different from instruments deployed in shallow lake environments). These observations have important implications for the viability of commonly used seismic analysis techniques. Finally, we compare spectra and coherences before and after vertical channel tilt and compliance noise removal to evaluate the efficacy and limitations of these now standard processing techniques. These findings may assist in future experiment planning and instrument development, and our newly compiled noise data set serves as a building block for more targeted future investigations by the marine seismology community.

The breakup of supercontinent Pangea occurred ∼200 Ma forming the Eastern North American Margin (ENAM). Yet, the precise timing and mechanics of breakup and onset of seafloor spreading remain poorly constrained. We investigate the relict lithosphere offshore eastern North America using ambient‐noise Rayleigh‐wave phase velocity (12–32 s) and azimuthal anisotropy (17–32 s) at the ENAM Community Seismic Experiment (CSE). Incorporating previous constraints on crustal structure, we construct a shear velocity model for the crust and upper ∼60 km of the mantle beneath the ENAM‐CSE. A low‐velocity lid (V_Sof 4.4–4.55 km/s) is revealed in the upper 15–20 km of the mantle that extends ∼200 km from the margin, terminating at the Blake Spur Magnetic Anomaly (BSMA). East of the BSMA, velocities are fast (>4.6 km/s) and characteristic of typical oceanic mantle lithosphere. We interpret the low‐velocity lid as stretched continental mantle lithosphere embedded with up to ∼15% retained gabbro. This implies that the BSMA marks successful breakup and onset of seafloor spreading ∼170 Ma, consistent with ENAM‐CSE active‐source studies that argue for breakup ∼25 Myr later than previously thought. We observe margin‐parallel Rayleigh‐wave azimuthal anisotropy (2%–4% peak‐to‐peak) in the lithosphere that approximately correlates with absolute plate motion (APM) at the time of spreading. We hypothesize that lithosphere formed during ultra‐slow seafloor spreading records APM‐modified olivine fabric rather than spreading‐parallel fabric typical of higher spreading rates. This work highlights the importance of present‐day passive margins for improving understanding of the fundamental rift‐to‐drift transition.

Seismic anisotropy produced by aligned olivine in oceanic lithosphere offers a window into mid‐ocean ridge (MOR) dynamics. Yet, interpreting anisotropy in the context of grain‐scale deformation processes and strain observed in laboratory experiments and natural olivine samples has proven challenging due to incomplete seismological constraints and length scale differences spanning orders of magnitude. To bridge this observational gap, we estimate an in situ elastic tensor for oceanic lithosphere using co‐located compressional‐ and shear‐wavespeed anisotropy observations at the NoMelt experiment located on ∼70 Ma seafloor. The elastic model for the upper 7 km of the mantle, NoMelt_SPani7, is characterized by a fast azimuth parallel to the fossil‐spreading direction, consistent with corner‐flow deformation fabric. We compare this model with a database of 123 petrofabrics from the literature to infer olivine crystallographic orientations and shear strain accumulated within the lithosphere. Direct comparison to olivine deformation experiments indicates strain accumulation of 250%–400% in the shallow mantle. We find evidence for D‐type olivine lattice‐preferred orientation (LPO) with fast [100] parallel to the shear direction and girdled [010] and [001] crystallographic axes perpendicular to shear. D‐type LPO implies similar amounts of slip on the (010)[100] and (001)[100] easy slip systems during MOR spreading; we hypothesize that grain‐boundary sliding during dislocation creep relaxes strain compatibility, allowing D‐type LPO to develop in the shallow lithosphere. Deformation dominated by dislocation‐accommodated grain‐boundary sliding (disGBS) has implications for in situ stress and grain size during MOR spreading and implies grain‐size dependent deformation, in contrast to pure dislocation creep.

To investigate the controls on continental rifting in the western branch of the East Africa Rift System, we conduct shear velocity imaging of the crust and uppermost mantle beneath the weakly extended Malawi Rift and the Rungwe Volcanic Province (RVP). We use local‐scale measurements of Rayleigh wave phase velocities between 9‐ and 100‐s periods combined with constraints on basin architecture and crustal thickness to invert for shear velocity from the surface to ~135 km. Our resulting 3‐D model reveals a localized low‐velocity anomaly associated with the RVP extending from the crust and through the upper mantle, which can be explained with modestly elevated temperatures. Away from the RVP, velocities within mantle flanking the rift are fast (>4.6 ± 0.1 km/s), suggesting depleted lithospheric mantle to depths of ~100 and >135 km to the west and east of the rift, respectively. The upper mantle beneath the rift axis is characterized by thinned lithosphere with slower velocities than the surrounding plateau, suggestive of thermal and/or chemical modification by the rifting process. Slowest velocities are mildly asymmetric about the rift axis, with the lowest velocities observed beneath the rift and adjacent footwall escarpments. The underlying asthenosphere is only moderately slow (~4.25 ± 0.1 km/s), including beneath the RVP, precluding the presence of significant volumes of partial melt. The positions of localized lithospheric modification and basin‐bounding border faults correlate with the location of Proterozoic mobile belts, suggesting that these sutures provide lithospheric‐scale weakening mechanisms necessary for localizing strain and allowing extension to occur in the Malawi Rift.