How do differences in interpreting seismic images affect estimates of geological slip rates? An example of a shear fault-bend fold

Abstract

Abstract. Uncertainties of geological structural geometry constructed based on seismic reflections can stem from data acquisition, processing, analysis, or interpretation. Especially uncertainties arising from structural interpretations and subsequent estimates of geological slip have been little quantified and discussed. To illustrate the implications of interpretation uncertainties for seismic potential and structural evolution, I use an example of a shear fault-bend fold in the Central Himalaya. I apply a simple solution from the kinematic model of shear fault-bend folding to resolve the geological slip, and then compare the result with a previous study to show how differences in structural interpretations could impact dependent conclusions. The findings show that only a little variance in interpretations owing to subjectivity and an unclear seismic image could yield geological slip rates differing by up to ~10 mm/yr, resulting in significantly different scenarios of seismic potential. To reduce unavoidable subjectivity, this study also suggests that the epistemic uncertainty in raw data should be included in interpretations and conclusions.

How do differences in interpreting seismic images affect estimates of geological slip rates?

“…Shear fault-bend folds are commonly identified in thrust belts worldwide (e.g. Moore et al, 1990;Suppe et al, 2004;Shaw et al, 2005;Corredor et al, 2005;Yue et al, 2011;Almeida et al, 2018;Le Béon et al, 2019), and they are distinctly characterized by long, gentle, and rotated backlimbs. These characteristics are caused by shear strain in décollement layers (Suppe et al, 2004;Shaw et al, 2005;Hardy and Connors, 2006).…”

“…Moore et al, 1990;Suppe et al, 2004;Shaw et al, 2005;Corredor et al, 2005;Yue et al, 2011;Almeida et al, 2018;Le Béon et al, 2019), and they are distinctly characterized by long, gentle, and rotated backlimbs. These characteristics are caused by shear strain in décollement layers (Suppe et al, 2004;Shaw et al, 2005;Hardy and Connors, 2006). Based on shear strain mechanisms, two end-members of kink-style kinematic models for shear fault-bend folding have been proposed (Suppe et al, 2004).…”

“…These characteristics are caused by shear strain in décollement layers (Suppe et al, 2004;Shaw et al, 2005;Hardy and Connors, 2006). Based on shear strain mechanisms, two end-members of kink-style kinematic models for shear fault-bend folding have been proposed (Suppe et al, 2004). First, the simple shear fault-bend fold has externally imposed bedparallel and homogeneous simple shear accommodated by the basal shear layer, with no basal fault slip (Fig.…”

“…1b); instead, its shortening is evenly accommodated by pure shear within the décollement layer, which moves along the basal fault. Suppe et al (2004) derived geometric relations among features in shear fault-bend folds of both types based on assumptions of conservation of area, line length, and bed thickness in the plane profile. Since these geometric relations are powerful for predicting unknown geometry based on partially revealed features, they are widely and successfully utilized in interpreting seismic reflections.…”

“…Here, I illustrate such an issue with a case of an unclear seismic image of a shear fault-bend fold in the central Himalaya. Firstly, I highlight a simple solution derived in Suppe et al (2004). This solution can directly acquire the input displacement accommodated by shear layers in shear fault-bend folds based on the features in the shallow part of seismic images.…”