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CHIRP Acoustic Reflection Imaging: Toward Improved Signal Processing in Extant Glacial Lakes

Description: 

Compressed-High-Intensity-Radar-Pulse (CHIRP) acoustic reflection data acquired in lakes and other shallow water areas are generally recorded as an amplitude envelope for each trace. This format allows real-time imaging and optimizes planning for rapid follow-up invasive sediment sampling; however, improving the signal-to-noise ratio in this format using typical vendor visualization software is generally limited to simple gain and bandpass filtering functions. The resultant images are often capable of providing a usable representation of the shallow sub-bottom geology, but we find further signal processing (e.g., migration, weighted trace mixing, and/or FX deconvolution, etc.) can significantly improve overall image quality and provide enhanced ability to discriminate and interpret subtle earthquake-related features, as well as provide better comparisons with synthetic seismograms. However, these additional processing steps are precluded by the amplitude envelope format. To overcome this constraint, we calculate the first derivative of the amplitude envelope and apply a bandpass filter (and sometimes rotation) to simulate a representative full-reflection amplitude waveform, thus allowing it to be imported into seismic data processing software for the widest range of signal-to-noise enhancement algorithms. For investigators without access to, or expertise with, more sophisticated signal processing programs, these simple fundamental procedures are often also available in many seismic interpretation software packages. We provide examples of our processing workflow from two glacial lake basins in the western United States with a history of seismic hazards: Convict Lake (Sierra Nevada, California) and Jackson Lake (Grand Teton National Park, Wyoming). Both lakes have steep margin-adjacent topography and prominent axial deltas conducive to slope failures, which appears to help shape sub-lacustrine depositional processes during earthquakes. Extensive CHIRP and long sediment core datasets from these lakes, which differ considerably in bathymetric and stratal characteristics, provide the feedstock for method validation.

Session: Marine Seismoacoustics [Poster Session]

Type: Poster

Date: 5/1/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Kevin

Student Presenter: No

Invited Presentation: 

Authors