UCL Discovery
UCL home » Library Services » Electronic resources » UCL Discovery

Damage zone heterogeneity on seismogenic faults in crystalline rock; a field study of the Borrego Fault, Baja California

Ostermeijer, GA; Mitchell, TM; Aben, FM; Dorsey, MT; Browning, J; Rockwell, TK; Fletcher, JM; (2020) Damage zone heterogeneity on seismogenic faults in crystalline rock; a field study of the Borrego Fault, Baja California. Journal of Structural Geology , 137 , Article 104016. 10.1016/j.jsg.2020.104016. Green open access

[thumbnail of 1-s2.0-S0191814119303232-main.pdf]
Preview
Text
1-s2.0-S0191814119303232-main.pdf - Accepted Version

Download (5MB) | Preview

Abstract

Complex fracture damage around large faults is often simplified to fit exponential or power law decay in fracture density with distance from the fault. Noise in these datasets is attributed to large subsidiary faults or random natural variation. Through a field study of the Borrego Fault (Baja California) damage zone, combining mm-resolution structural mapping and point sampling, we show that such variations are the expression of systematic damage heterogeneity. The oblique-slip Borrego Fault comprises NW and SE segments that ruptured during the Mw7.2 2010 El Mayor-Cucapah earthquake. Measurements of fracture density along eight linear fault-perpendicular transects and from a high-resolution 68 m2 structural map display a power law decay and define footwall damage zone widths of ∼85 m and ∼120 m for the NW and SE segments respectively. Variance in fracture density decays with distance following an inverse exponential relationship, to background variance at ∼16 m. Spatial analysis of the high-resolution fracture map reveals a patchy distribution of high- and low-intensity clusters at metre- and decimetre-scales. We attribute high-intensity clusters at these scales to local complexity caused by interactions between minor subsidiary faults (101 m length and 10−2-10−1 m displacement). Fracture density differences between high- and low-intensity clusters decrease with distance from the fault, demonstrating a systematic change in outcrop-scale damage heterogeneity. Based on these observations we present a revised model for damage zone growth including growth of heterogeneity.

Type: Article
Title: Damage zone heterogeneity on seismogenic faults in crystalline rock; a field study of the Borrego Fault, Baja California
Open access status: An open access version is available from UCL Discovery
DOI: 10.1016/j.jsg.2020.104016
Publisher version: https://doi.org/10.1016/j.jsg.2020.104016
Language: English
Additional information: This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: damage zone; fault zone structure; fractures; damage heterogeneity; fracture density
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10093504
Downloads since deposit
177Downloads
Download activity - last month
Download activity - last 12 months
Downloads by country - last 12 months

Archive Staff Only

View Item View Item