LAST CHANCE!: February 8th, 2024 DGS Luncheon – Aaron Girard

Dr. Aaron Girard

Abstract:

Large-scale ocean-bottom node (OBN) arrays of thousands of multi-component instruments deployed over thousands of square kilometers have been used successfully for active-source seismic exploration activities at frequencies above 2.0 Hz. The analysis of concurrently recorded lower-frequency ambient wavefield data, though, is only just beginning. One 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 full waveform inversion (FWI). Doing so requires a detailed understanding of ambient wavefield information recorded on the seafloor including the types, frequency 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.

This talk will outline how using prestack ambient seismic data from the Gulf of Mexico and applying preprocessing and cross-coherence interferometry workflows allows analysis of ambient wavefields at (ultra)low-frequencies (defined as <1.0 Hz). The interferometric virtual shot gathers show evidence for Scholte, leaky Rayleigh and guided P-wave mode propagation between the 0.001-1.0 Hz. These waves remain coherent to distances of 80 km and have evidence of surface-wave scattering from shallow salt-body structure. Overall, these observations may have important consequences for the early stages of initial model building for elastic FWI analysis.

Dr. Aaron Girard completed his undergraduate degree in the Mines Geophysics Department, his MSc in the IDEA-League joint master program at TU Delft, ETH Zürich and RWTH Aachen, and his PhD at the University of Western Australia, where he explored imaging with ambient seismic wavefields. After graduation, he came back to Mines GP where he continues to develop methods for explorations with ambient seismic recordings.