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.

Author ORCID Identifier

James P. Evans



Document Type




File Format

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

Viewing Instructions

***A zipped version of the complete dataset is available. Contact RDMS ( for more details.*** 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



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


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


Data collection described within each subfolder.

Start Date


End Date



Elizabeth Lake, California



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


Description of files:

Appendix 1 - Los Angeles Department of Water and Power geotechnical final report. Linked to published report stored at

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.


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


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




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