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Abstract
In marine geophysics, high-resolution data collection is critical for investigating seafloor geomorphology and near-surface stratigraphy, particularly for geohazard assessments. The integration of multibeam bathymetry, sub-bottom profiling, deep multichannel seismic data, and well data provides valuable insights into both recent and ancient geological processes. These include studies of shallow crust deformation, volcanic history, fault geometry, paleoseismicity, mass wasting, and tsunami modeling.
The volcanism at the East Pacific Rise (EPR) and fast-spreading mid-ocean ridges is expected to be focused underneath the main axis, within ~10 km from the spreading center. The study of the relative age of off-axis volcanism along the 8º20’N seamount chain at the EPR, can define mantle processes and melt upwelling histories distribution away from the homogenizing effect of the steady-state magma chamber. High-resolution near-bottom CHIRP and bathymetric data collected by the autonomous underwater vehicle Sentry are used to test the hypothesis that seamount volcanism progresses in an age-sequence along the seamount chain. Since sediment thickness generally correlates with the exposure time of the seafloor, the distribution of sediment thickness along the volcanic constructs can serve as a proxy for the relative timing of volcanic activity. However, since sediment thickness does not increase linearly with distance from the spreading center, the observed data suggest that seamounts did not erupt sequentially with increasing distance from the EPR. This implies a prolonged and episodic melt upwelling history rather than a continuous, age-progressive volcanic sequence.
In the California Continental Borderland (CCB), the seafloor is composed of several basins and ridges aligned with strike-continuous fault segments. These tectonic structures influence the deformation and development of sedimentary basins along the offshore transform plate boundary between the Pacific and North American plates. High-resolution geophysical data collected during cruise SR2303 were used to investigate the relationship between tectonics and submarine mass wasting in the Cortes and Velero basins, located in the Outer California Borderland (OCB). More than 5 km³ of mass transport deposits (MTDs) have been mapped across Cortes Basin. These include slumps that accumulated adjacent to basin slopes and fault segments, along with distal turbidity currents that extend throughout the basin. In Velero Basin, a submarine fan system consisting of multiple lobes, with an estimated cumulative volume of ~1.4 km³, was identified, as well as a massive slope collapse resulting from two distinct failure events. The tectonic evolution of the CCB, coupled with the proximity of MTDs to active fault segments, suggests that mass wasting in the Cortes and Velero basins was likely triggered by slope steepening and uplift associated with fault reactivation. The alignment of several basins in the OCB, including Santa Cruz, San Nicholas, Tanner, Cortes, and Velero, along strike-continuous fault zones such as the Ferrelo fault zone, further suggests that earthquake-induced slope failures are a significant geohazard. These failures pose a considerable risk to the densely populated coastal regions of Southern California.
