How do plate boundary fault cores evolve and why? : a case study of the highland boundary fault, Scotland

Student thesis: Doctoral Thesis

Abstract

Understanding the internal structure (i.e., fault core composition, thickness and geometry) of large faults is crucial because their fault structure and properties control how and where earthquakes occur. Compilations of data from multiple fault studies show that fault cores get thicker on average with increasing total displacement (and hence slip events). However, the majority of faults in these datasets are from intraplate settings (faults within the interior of tectonic plates). Plate boundary faults have largely been excluded. As such there are no studies that systematically compare the two fault systems. This study aims to address this knowledge gap: compiling and harmonising a global dataset of intraplate and plate boundary fault core thickness and total displacement data in order to examine whether these fault systems evolve in a similar way with repeated slip events. The Highland Boundary fault (HBF), an ancient plate boundary fault in Scotland, is used as a field site to provide a case study for examining the internal structure and inferring the evolution of a plate boundary fault core. Detailed field, laboratory and mineralogical work reveal that the HBF core consists of four distinct units that remain unmixed. Not every unit is continuous along-strike and each unit varies in thickness (between 2.95 and 10.7 m). The units remain distinct as they formed at different stages of faulting and by different mechanisms affecting the faults ability to host earthquakes through time. For the first time, this work discovers quantitatively that plate boundary fault cores are narrower than predicted by the trend for intraplate faults and highlights that, for this reason, plate boundary faults do not dissipate as much energy as intraplate faults during earthquakes. These results are crucial for understanding the internal structure and evolution of plate boundary fault cores and have implications for understanding how earthquakes behave.
Date of Award1 Sep 2021
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsEPSRC (Engineering and Physical Sciences Research Council) & University of Strathclyde
SupervisorZoe Shipton (Supervisor) & Rebecca Lunn (Supervisor)

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