A snapshot of the earliest stages of normal fault growth

This is a Preprint and has not been peer reviewed. The published version of this Preprint is available: https://doi.org/10.55575/tektonika2023.1.2.29. This is version 2 of this Preprint.

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Authors

Ahmed Alghuraybi, Rebecca E. Bell, Christopher Aiden-Lee Jackson 

Abstract

Observations of how faults lengthen and accrue displacement during the very earliest stages of their growth are limited, reflecting the fact that the early syn-kinematic sediments that record this growth are often deeply buried and difficult to image with geophysical data. Here, we use borehole and high-quality 3D seismic reflection data from offshore Norway to quantify the lateral propagation (c. 0.38 – 3.4 mm/year) and displacement accumulation (c. 0.0062 – 0.025 mm/year) rates (averaged over 6.2 Myr) for several long (up to 43 km), moderate displacement (up to 155 m), layer-bound faults that we argue provide a unique, essentially ‘fossilised’ snapshot of the earliest stage of fault growth. We show that lateral propagation rates were up to 300 times faster than displacement rates during the initial ~25% of fault lifespan, suggesting that these faults lengthened much more rapidly than they accrued displacement. Our inference of rapid lengthening is also supported by geometric observations including: (i) low Dmax-Lmax (<0.01) scaling relationships, ii) high (>5) length/height aspect ratios, iii) broad, bell-shaped throw-length profiles, and iv) hangingwall depocenters forming during deposition of the first seismically detectable stratigraphic unit spanning the length of the fault. We suggest that the unusually high ratio between lateral propagation rate and displacement rate is likely due to relative immaturity of the studied fault system, an interpretation that supports the ‘constant-length’ fault growth model. Our results highlight the need to document both displacement and lateral propagation rates to further our understanding of how faults evolve across various temporal and spatial scales.

DOI

https://doi.org/10.31223/X5634T

Subjects

Earth Sciences, Geology, Tectonics and Structure

Keywords

normal fault growth, Displacement rate, Lateral propagation rate

Dates

Published: 2021-12-22 11:49

Last Updated: 2022-12-06 22:45

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License

CC BY Attribution 4.0 International