Title

Digital Appendix of Masters Thesis "Constraining deformation mechanisms of damage zones: A case study of the shallow San Andreas Fault at Elizabeth Lake, Southern California

Description

We performed macroscopic, optical petrographic, scanning electron microscopy, and geochemical analyses on rock core acquired across the San Andreas Fault at Elizabeth Lake, California, in order to understand the distribution and accommodation of fault-related slip and energy within the shallow damage zone of this continental scale strike-slip fault. We characterized the deformation structures, alteration textures, and elemental variabilities to constrain the properties of the uppermost ~2 km fault-related damage zone at this site. We identified evidence for coseismic slip in the form of pulverized rocks, injection veins, clay-clast aggregates, and pseudotachylyte, and aseismic slip through calcite twins, dilatant vein fills, and possibly by a network of aligned chlorite, biotite, and muscovite cleavages. Alteration assemblages indicate a temperature range of ~50-250°C with calcite, zeolite, chlorite, and pseudomorphic plagioclase as the most common mineral alterations. The geochemical data do not exhibit trends as a function of distance from the fault core but pointed to distinct geochemical signatures for fault-rock types including the Si-rich pulverized rocks and a relative enrichment in the fault gouge Fe concentrations as compared to the quartzo-feldspathic protolith. The cross-cutting relationships of deformation microstructures and the distribution of the observed deformation and alteration textures indicate that coseismic and aseismic slip mechanisms are active throughout the shallow fault zone at this site. We document brittle-plastic cross cutting relationships within thin sections indicating that the slip mechanisms vary in their nature and style over multiple earthquake cycles. We show that the fault zone at Elizabeth Lake consists of a complex of superimposed fault strands that recycle and rework fault-related products and likely distribute the seismically generated energy throughout the damage zone through a combination of brittle and semi-brittle processes, and geochemical alterations. The observed deformation and alteration textures decrease the seismic velocities and reduce the overall rheologic strength of the fault-related rocks, and likely enable seismically radiated energy to be distributed throughout the fault damage zone. The distribution, nature, and degree of deformation and alteration found here may help explain how fault-related low-velocity zones form, and characterize the rocks within which shallow co-seismic slip deficits, if real, may develop.

OCLC

1255179684

Document Type

Dataset

DCMI Type

Dataset

File Format

.txt, .zip, .docx, .xlsx, .jpg, .tif, .png, pdf

Viewing Instructions

The main file contains the entire dataset. The individual appendices are listed separately as supplemental .zip files. .zip files will need to have their content files extracted prior to use.

Publication Date

5-21-2021

Funder

Fonds du Recherche Nature et Technologies

Geological Society of America

Utah State University

Association of Women Geologists

NSF, Division of Earth Sciences (EAR)

Southern California Earthquake Center

Publisher

Utah State University

Award Number

Fonds du Recherche Nature et Technologies - International Research Internship Grant Fall 2019; Geological Society of America - Continental Scientific Drilling Division Grant Spring 2019; Geological Society of America - Graduate Student Research Grant 2020; Utah State University - J. Stewart Williams Graduate Fellowship Spring 2019; Utah State University - Summit Scholarship Spring 2020; Association of Women Geologists - Salt Lake Chapter Research Grant Winter 2019; NSF, Division of Earth Sciences (EAR) 1824852; Southern California Earthquake Center Grant #18077

Award Title

NSF, Division of Earth Sciences (EAR) 1824852: Examining temperatures and microgeochemical processes on fault slip surfaces with synchrotron methods

Methodology

Data collection described within each subfolder.

Start Date

2017

End Date

2019

Location

Elizabeth Lake, California

Language

eng

Code Lists

Definitions of Acronyms:

a. mineralogies: qtz - quartz; plag - plagioclase; feld - feldspar; bio - biotite; chl - chlorite; ep - epidote; opq - opaques; phyllo - phyllosilicates; hnbl - hornblende, amph - amphibole, zeo - zeolite; opt opq mat - optically opaque matrix

b. textures: CCA - clay clast aggregate; inj vein - injection vein; ptach - pseudotachylyte; pulv - pulverized

Comments

Description of files:

Appendix 1 - Los Angeles Department of Water and Power geotechnical final report. Linked to published report stored at https://osf.io/2vn6x/

Appendix 2 - Sampled Core with descriptions. 1 Excel sheet of core descriptions. 84 JPG images of epoxied and cut core samples.

Appendix 3 - Thin Section Imagery. High resolution plane polarized and cross polarized light JPG images of 19 large (38 images) and 73 standard (146 images) thin sections.

Appendix 4 - Thin Section Descriptions. 7 word documents (1 for each borehole) containing descriptions of the collected thin sections. e.

Appendix 5 - Scanning Electron Microscopy. 15 subfolders of individual thin sections imaged with scanning electrom microscopy. Each thin section folder contains an image map and associated SEM images.

Appendix 6 - Electron Dispersive Spectroscopy. 11 subfolders of individual thin sections analyzed with electron dispersive spectroscopy. Each thin section folder contains an image map and associated EDS reports.

Appendix 7 - X-Ray Dispersive (XRD) Data. 1 Excel sheet containing identified mineralogies from XRD analysis. 1 subfolder containing JPEG images of each XRD sample's spectra.

Appendix 8 - X-ray Fluorescence(XRF) Data. 1 Excel file containing 3 sheets. Samples - sample descriptions, XRF data - raw data for major and trace element concentrations, and External Data containing protolith values from neighboring sites.

Appendix 9 - Core Box Photos. 7 PDF files of core box photos sorted by borehole.

Appendix 10 - Complete Sample Log. Identification of samples analyses including thin sections, SEM, XRD, and XRF. Descriptions include the distance (ft) from the inferred primary fault strand, sample lithology, single point resistance and key features identified in thin section.

Appendix 11 - Additional Mapped Thin Sections. 4 thin sections with mapped zones. 8 files - 2 for each thin section. 1 map overlaying the thin section and 1 plain map.

Disciplines

Earth Sciences | Geology | Geophysics and Seismology | Tectonics and Structure

License

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

Identifier

https://doi.org/10.26078/mv7c-q808

Checksum

fdf9c3b508cc2a4acb440e67548041a1

Additional Files

README.txt (8 kB)
MD5: 3a5136abd54c28177452e3fc012c2774

Appendix_1_LADWP_2019_Final_Report.zip (9 kB)
MD5: 7afa2d24504514219a11c67c80d5b0b2

Appendix_2_Macroscopic_Core_Data.zip (167216 kB)
MD5: 816609a02ec3d8052a3830b59682f953

Appendix_3_Thin_Section_Images.zip (8738251 kB)
MD5: 0e99cf3bb07cd6e01781dda608747ffe

Appendix_4_Thin_Section_Descriptions.zip (60924 kB)
MD5: 98fd36d4e2d51fbea06780bc3d3eb725

Appendix_5_Scanning_Electron_Microscopy.zip (2492599 kB)
MD5:3ccac691b8caf5efd8d48894d8dd574c

Appendix_6_Electron_Dispersive_Spectroscopy.zip (1329181 kB)
MD5: e67d1f35b490fff372164ac468d507b6

Appendix_7_X-Ray_Diffraction_Data.zip (8677 kB)
MD5: 25bcccfa20aae361636e157b4ddfb259

Appendix_8_X-Ray_Flourescence_Data.zip (42 kB)
MD5: 214b98781ce74e83bff1c17c0dda00bb

Appendix_9_LADWP_Core_Box_Photos.zip (1079801 kB)
MD5: e5c966bd28e353ad0646866277c11669

Appendix_10_Complete_Sample_Log.zip (32 kB)
MD5: f00a29ef87383357c891875fca2deb34

Appendix_11_Mapped_Thin_Sections.zip (493952 kB)
MD5: aa39fbde254077eb0c15c6b0ff45bb91

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