Along-strike fault core thickness variations of a fault in poorly lithified sediments, Miri (Malaysia)

Abstract

This version is available at https://strathprints.strath.ac.uk/65335/ Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.Any correspondence concerning this service should be sent to the Strathprints administrator: strathprints@strath.ac.ukThe Strathprints institutional repository (https://strathprints.strath.ac.uk) is a digital archive of University of Strathclyde research outputs. It has been developed to disseminate open access research outputs, expose data about those outputs, and enable the management and persistent access to Strathclyde's intellectual output. The degree to which a fault will impede fluid flow is only as great as its most permeable point. Processes that determine areas of the fault surface containing transmissible fault rocks must be utilized to produce reliable predictions of cross-fault fluid flow. We use a study site in Miri, Malaysia, to investigate in detail the fault-core thickness variations along-strike and down dip, and to quantify the risk of discontinuities in the clay-rich fault core. Four fault-core types have been identified: foliated clay-rich fault core, chaotic clay-rich fault core, anastomosing sandy shear zones and sandy breccia. We performed a geostatistical analysis, showing a correlation over 3 m scale, suggesting the presence of 'patches' of thin and thick fault core generally less than 3 m in length in profile.We interpret this geometry as superimposition of two or more different deformation processes at a smaller and a larger scale. We speculate about the processes that could produce the observed distribution of thickness and composition, and in particular, processes that could have disrupted the through-going clay-rich core.

The growth of faults and fracture networks in a mechanically evolving, mechanically stratified rock mass: a case study from Spireslack Surface Coal Mine, Scotland

“…While the fault core at Spireslack SCM is typically thin (Table 2), similar to previous studies (e.g. McKay et al, 2019;De Rosa et al, 2018) thickness was found to be highly heterogeneous both along strike and down dip. Much of this variability is caused by the lithological juxtapositions observed across the fault (Fig.…”

“…Carboniferous basins that have axes oblique to the main trend of the Midland Valley (e.g. Central Scottish Coalfield; Francis, 1991) can reach over 6 km in thickness (Dean et al, 2011). Faults with associated, localised folding have a complex history of reactivation caused by sinistral strike and oblique-slip movement during the Tournaisian and dextral strike and obliqueslip movement during Viséan to Westphalian times (Browne and Monro, 1987;Rippon et al, 1996;Ritchie et al, 2003;Underhill et al, 2008).…”

Supplemental Material: Fault permeability from stochastic modeling of clay smears

“…Although this is a simplification of reality, data on along-strike smear segmentation is too limited to justify a more complex approach here. Finally, while natural and experimental fault core thickness varies along-strike (e.g., Kettermann et al, 2016;Sosio de Rosa et al, 2018), PREDICT models each realization with constant thickness. This is reasonable given that each realization considers a relatively short f L (equal to the fault displacement), and that, by running multiple realizations, the effect of varying fault core thickness is accounted for.…”

Fault fictions: systematic biases in the conceptualization of fault-zone architecture

“…An experienced geologist may approach an outcrop 'how they always have' because 'everyone knows' 'that's how to do it', and so may lack the awareness to prevent bias from affecting the mental models they develop. In fact, they may simply be adapting a pre-existing mental model of one fault zone to another, and in doing so omit key and unique fault properties such as the rare fault rocks reported by Sosio de Rosa et al (2018). Alternatively, their experiences may aid their decision making, and prevent the mind from jumping to conclusions (which we often have to coax geology students away from) and becoming vulnerable to anchoring bias.…”