This file was prepared 2023/12/11 by Jun Young Song (js2795@cornell.edu)

This file supplements data associated with the publication: " Laboratory earthquake ruptures contained by velocity strengthening fault patches"

Authors: Jun Young Song (js2795@cornell.edu) and Gregory C. McLaskey (gcm8@cornell.edu).

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Dataset Description:
These data are from Laboratory Earthquake Experiments from the Cornell 0.76 m apparatus in support of the following research: 

Many natural faults are believed to consist of velocity weakening (VW) patches surrounded by velocity strengthening (VS) sections. Numerical studies routinely employ this framework to study earthquake sequences including repeating earthquakes. In this laboratory study, we made a VW asperity, of length L, from a bare Poly(methyl methacrylate) PMMA frictional interface and coated the surrounding interface with Teflon to make VS fault sections. Behavior of this isolated asperity was studied as a function L (ranging from 100 mm to 400 mm) and the critical nucleation length, h*, which is inversely proportional to the applied normal stress (2 - 16 MPa). Consistent with recent numerical simulations, we observed aseismic slip for L/h* < 2, periodic slip for 2 < L/h* < 6, and non-periodic slip for 10 < L/h*. Furthermore, we compared the experiments where L was contained by VS material to standard stick-slip events where L was bounded by free surfaces (i.e., L = the total sample length). The free surface case produced ~10 times larger slip during stick-slip events compared to the contained fault ruptures, even with identical L/h*. This disparity highlights how standard, complete-rupture stick-slip events differ from contained events expected in nature, due to both the free surface conditions and the heterogeneous normal stress along the fault near the free ends, as confirmed by Digital Image Correlation (DIC) analysis. This study not only introduces the Teflon coating experimental technique for containing laboratory earthquake ruptures, but also highlights the utility of L/h* as a predictive parameter for earthquake behavior.
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This work was sponsored by National Science Foundation Grant EAR-2240376.

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These data are shared under a Creative Commons Universal Public Domain Dedication (CC0 1.0); the data will be openly available for re-use, modification and distribution; proper attribution to the original data creators is expected. See citation information above.

Please cite this dataset as: Jun Young Song, and Mclaskey, Gregory (2024). Data from: Laboratory earthquake ruptures contained by velocity strengthening fault patches [Dataset]. Cornell University Library eCommons Repository. https://doi.org/10.7298/dkwh-c932
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PT_slip:

File labeling:
Each MATLAB .mat file contains multiple stick-slip events. The filename is structured as “aPT_bMPa”, where ‘a’ represents the size of the VW patch in mm and ‘b’ indicates the applied normal stress

Each .mat file contains a MATLAB structure named ‘SS’ with 3 fields: ‘trigTime’, ‘t’, and ‘signal’.
Entry 1 of the MATLAB data structure is the continuously recorded data, recorded at 20 kHz (averaged down to 5 kHz here), and any subsequent entries in the MATLAB data structure are the triggered data, recorded at 2MHz (averaged down to 1 MHz here). 

‘trigTime’ means triggered time of the events.

‘t’ is a time matched with signal data. 

‘signal’: 
Rows 1-8 are data recorded from eddy current sensor channels E1-E8, respectively. All data is in units of Volts and the conversion factor is 128 μm/V. 

Rows 9-12 are data recorded from AE sensors from channels P1-P4, respectively, with a range from -25V to 25V. 

Rows 13-16 are the data same as Rows 9-12, respectively, but the range is from -1V to 1V.

Rows 17-18 are the hydraulic pressure sensors in units of Volts measured normal stress and shear stress, respectively. The conversion factor of normal stress and shear stress is 0.0535 V/MPa and 0.107 V/MPa, respectively.  

Row 19 is a piezoelectric sensor that measures vibrations due to the camera shutter for Digital Image Correlation (DIC). This allows us to obtain time synchronization of DIC images with the other data files.

Sensor Setup: Below are the approximate coordinates of the eddy displacement sensors E1-E8. The origin of the coordinate system is the fault at forcing end of the stationary block.
Sensor		X(m)	Y(m)	Z(m)
E1		0.03	0(fault)	0(Top surface)
E2		0.13	0	0
E3		0.23	0	0
E4		0.33	0	0
E5		0.43	0	0
E6		0.53	0	0
E7		0.63	0	0
E8		0.73	0	0

P sensor locations: Below are the coordinates of the piezoelectric sensors P1-P4. The origin of the coordinate system is the fault at forcing end of the stationary block.
Sensor		X (m)		Y(m)		Z(m)
P1     	0.08		-0.03		0(Top surface)
P2  		0.28		-0.03		0
P3		0.48		-0.03		0
P4		0.68		-0.03		0

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400FF_slip:
 
File labeling:
Each MATLAB .mat file contains multiple stick-slip events. The filename denotes free fault conditions (400FF) at 8 MPa normal stress.

Each .mat file contains a MATLAB structure named ‘SS’ with 3 fields: ‘trigTime’, ‘t’, and ‘signal’.
Entry 1 of the MATLAB data structure is the continuously recorded data, recorded at 20 kHz (averaged down to 5 kHz here), and any subsequent entries in the MATLAB data structure are the triggered data, recorded at 2MHz (averaged down to 1 MHz here). 

‘trigTime’ means triggered time of the events.

‘t’ is a time matched with signal data. 

‘signal’: 
Rows 1-4 are data recorded from eddy current sensor channels E1-E4, respectively. All data is in units of Volts and the conversion factor is 128 μm/V. 

Rows 5-8 are data recorded from AE sensors from channels P1-P4, respectively, with a range from -50V to 50V. 

Rows 9-10 are the hydraulic pressure sensors in units of Volts measured normal stress and shear stress, respectively. The conversion factor of normal stress and shear stress is 0.0563 V/MPa and 0.0563 V/MPa, respectively.  

Row 11 is a piezoelectric sensor that measures vibrations due to the camera shutter for Digital Image Correlation (DIC). This allows us to obtain time synchronization of DIC images with the other data files.

Sensor Setup: Below are the approximate coordinates of the eddy displacement sensors E1-E8. The origin of the coordinate system is the fault at forcing end of the stationary block.

Sensor		X(m)	Y(m)	Z(m)
E1		0.05	0(fault)	0(Top surface)
E2		0.15	0	0
E3		0.25	0	0
E4		0.35	0	0

P sensor locations: Below are the coordinates of the piezoelectric sensors P1-P4. The origin of The origin of the coordinate system is the fault at forcing end of the stationary block.

Sensor		X (m)		Y(m)		Z(m)
P1     	0.08		-0.03		0(Top surface)
P2  		0.28		-0.03		0
P3		0.48		-0.03		0
P4		0.68		-0.03		0

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760T_slip:

File labeling:
This file contains velocity step experiments. The filename is structured as “760T_aMPa_Expb_cmm”, where ‘a’ represents applied normal stress, ‘b’ indicates first or second experiment, and ‘c’ represents the cumulative slip before the recording started (see Appendix in Manuscript). Exp2' was conducted after 4 mm cumulative slip.

Each .mat file contains a MATLAB structure named ‘SS’ with 3 fields: ‘trigTime’, ‘t’, and ‘signal’.
Entry 1 of the MATLAB data structure is the continuously recorded data, recorded at 20 kHz (averaged down to 5 kHz here), and any subsequent entries in the MATLAB data structure are the triggered data, recorded at 2MHz (averaged down to 1 MHz here). 

‘trigTime’ means triggered time of the events.

‘t’ is a time matched with signal data. 

‘signal’: 
Rows 1 is data recorded from eddy current sensor channels E1. All data is in units of Volts and the conversion factor is 128 μm/V. 

Rows2-3 are the hydraulic pressure sensors in units of Volts measured normal stress and shear stress, respectively. The conversion factor of normal stress and shear stress is 0.0535 V/MPa and 0.107 V/MPa, respectively.  

Sensor Setup: Below are the coordinates of the eddy displacement sensor E1. The origin of the coordinate system is the fault at forcing end of the stationary block.

Sensor		X(m)	Y(m)	Z(m)
E1		0.03	0(fault)	0(Top surface)

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DIC_image:

File labeling:
DSC_*.jpg

6 images were taken using a Nikon D850 camera with ~93 μm/pixel resolution. The images were taken manually with a remote. 

DSC_3219 – Reference image without any stresses on the sample (400PT)
DSC_3218 – 8 MPa normal stress without shear stress (400PT)
DSC_3212 – 8 MPa normal stress with peak shear stress (400PT). The image was taken at 355.7 s, closely followed by a real peak shear stress at 360 s.
DSC_3402 – Reference image without any stresses on the sample (400FF)
DSC_3403 – 8 MPa normal stress without shear stress (400FF)
DSC_3419 – 8 MPa normal stress with peak shear stress (400FF). The image was taken at 731.6 s, closely followed by a real peak shear stress at 741.2 s.