Bayesian Seismic Refraction Inversion for Critical Zone Science and Near‐Surface Applications. (25th May 2021)

• Record Type: Journal Article
• Authors: Huang, Mong‐Han; Hudson‐Rasmussen, Berit; Burdick, Scott; Lekic, Vedran; Nelson, Mariel D.; Fauria, Kristen E.; Schmerr, Nicholas
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 22:Number 5(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-05-25
• Subjects: active source seismic refraction -- critical zone science -- near surface geophysics -- Transdimensional Hierarchical Bayesian inversions; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1029/2020GC009172
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: The critical zone (CZ) is the region of the Earth's surface that extends from the bottom of the weathered bedrock to the tree canopy and is important because of its ability to store water and support ecosystems. A growing number of studies use active source shallow seismic refraction to explore and define the size and structure of the CZ across landscapes. However, measurement uncertainty and model resolution at depth are generally not evaluated, which makes the identification and interpretation of CZ features inconclusive. To reliably resolve seismic velocity with depth, we implement a Transdimensional Hierarchical Bayesian (THB) framework with reversible‐jump Markov Chain Monte Carlo to generate samples from the posterior distribution of velocity structures. We also perform 2D synthetic tests to explore how well THB traveltime inversion can resolve different subsurface velocity structures. We find that THB recovers both sharp changes in velocity as well as gradual velocity increases with depth. Furthermore, we explore the velocity structure in a series of ridge‐valley systems in northern California. The posterior velocity model shows an increasing thickness of low velocity material from channels to ridgetops along a transect parallel to bedding strike, implying a deeper weathering zone below ridgetops and hillslopes than below channels. The THB method enhances the ability to reliably image CZ structure, and the model uncertainty estimates it yields provides an objective way to interpret deep CZ structure. The method can be applied across other near‐surface studies, especially in the presence of significant surface topography. Key Points: An open‐source Transdimensional Hierarchical Bayesian (THB) inversion code can resolve seismic structure and measurement uncertainty from active source seismic refraction surveys Comprehensive synthetic tests demonstrate the reliability of using seismic refraction for critical zone research A field survey with THB inversion shows changes of weathering structure thickness in a ridge‐channel system landscape