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Observations From the Seafloor: Ultra-Low-Frequency Ambient Ocean-Bottom Nodal Seismology From the Gulf of Mexico

Description: 

Large-scale ocean-bottom node (OBN) arrays of 1000s of multi-component instruments deployed over 1000s of square kilometers have been used successfully for active-source seismic exploration activities including full waveform inversion (FWI) at frequencies above 2.0 Hz. The analysis of concurrently recorded lower-frequency ambient wavefield data, though, is only just beginning. A key long-term objective of such ambient wavefield analyses is to exploit the sensitivity of naturally occurring sub-2.0 Hz energy to build long-wavelength elastic models to facilitate FWI. However, doing so requires a detailed understanding of ambient wavefield information recorded on the seafloor including the types, frequency structure and effective source distribution of recorded surface-wave modes, the near-seafloor elastic model structure, and the sensitivity of recorded wave modes to model structure. We present an ambient wavefield analysis of (ultra)low-frequency ambient data (defined as <1.0 Hz) acquired on 2712 conventional OBN stations covering 2750 km² of the Gulf of Mexico. After applying prestack ambient data preprocessing and cross-coherence interferometry workflows, we demonstrate that: (1) the resulting virtual shot gather (VSG) volumes contain evidence for Scholte, leaky Rayleigh and guided P-wave mode propagation between the 0.001-1.0 Hz; (2) propagation remains coherent to distances of 80 km or more; and (3) surface-wave scattering from shallow salt-body structure is present in VSG data. Overall, these observations likely have important consequences for the early stages of initial model building for elastic FWI analysis in deep-water settings.

Session: Marine Seismoacoustics [Poster Session]

Type: Poster

Date: 5/1/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Jeffrey

Student Presenter: No

Invited Presentation: 

Authors