This file was prepared 2022/05/06 by Sara Beth L. Cebry (sbl84@cornell.edu)
This file supplements data associated with the publication: "The Role of Background Stress State in Fluid-Induced Aseismic Slip and Dynamic Rupture on a 3-meter Laboratory Fault" JGR: Solid Earth
Authors: Sara Beth L. Cebry (sbl84@cornell.edu), Chun-Yu Ke (ck659@cornell.edu), Gregory C. McLaskey (gcm8@cornell.edu).

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Dataset Description:
These data are from Laboratory Earthquake Experiments from the Cornell 3 m apparatus in support of the following research: 

Fluid injection stimulates seismicity far from active tectonic regions, however the details of how fluids modify on-fault stresses and initiate seismic events remains poorly understood. We conducted laboratory experiments using a biaxial loading apparatus with a 3 m saw-cut granite fault and compared events induced at different background shear stress levels. Water was injected at 10 mL/min and normal stress was constant at 4 MPa. In all experiments, aseismic slip initiated on the fault near the location of fluid injection and dynamic rupture eventually initiated from within the aseismic slipping patch. When the fault was near critically stressed, seismic slip initiated only seconds after MPa-level injection pressures were reached and the dynamic rupture propagated beyond the fluid pressure perturbed region. At lower stress levels, dynamic rupture initiated hundreds of seconds later and was limited to regions where aseismic slip had significantly redistributed stress from within the pressurized region to neighboring locked patches. We found that slow slip initiation was broadly consistent with Coulomb failure criteria find that slow slip initiated when local stresses exceeded Coulomb failure criteria, but initiation of dynamic rupture required additional criteria to be met. Even high background stress levels required aseismic slip to modify on-fault stress to meet initiation criteria. We also observed slow slip events prior to dynamic rupture. Overall, our experiments suggest that initial fault stress, relative to fault strength, is a critical factor in determining whether a fluid-induced rupture will “runaway” or whether a fluid-induced rupture will remain localized to the fluid pressurized region.

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When utilizing this data, please cite as listed below, and provide reference to one or more of the following associated publications:

Dataset:
Cebry, S. B. L., Ke, C.-Y., and McLaskey, G. C. (2022) Data from: The role of background stress state in fluid-induced aseismic slip and dynamic rupture on a 3-meter laboratory fault [dataset]. Cornell University eCommons Repository. https://doi.org/10.7298/gdxn-e175

Publications:	
Cebry, S. B. L., Ke, C.-Y., and McLaskey, G. C. (2022) Data from: The role of background stress state in fluid-induced aseismic slip and dynamic rupture on a 3-meter laboratory fault, JGR: Solid Earth, submitted.

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This work was sponsored by National Science Foundation grants EAR-1847139.

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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.

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File labeling:

Experiments were conducted over the course of two days and several hours and utilized two data acquisition systems. One system recorded pressure and slip data from hydraulic pressure sensors and eddy current displacement sensors. The second system recorded strain data measured by semiconductor strain gauges glued at a 45 deg angle from the fault in a Wheatstone half bridge configuration. Data from each system was lined up according to the first slip event, then saved. Experiments were conducted in runs which consist of series of events. For catalog purposes a run called “FS01_054_4MPa_2” denotes experiments conducted on samples FS01, on day 54 of experiments with these samples, and within that day this is the second sequence run at ~4 MPa normal stress.

“FS01_054_4MPa_1” refers to the Case A in the paper.
“FS01_054_4MPa_2” refers to the Case B in the paper.
“FS01_054_4MPa_3” refers to the Case C in the paper.
“FS01_050_4MPa” refers to the shut-in test in the paper.

Each .mat file is a MATLAB structure with four structures ‘pressure’, ‘displacement’, ‘strain’, and ‘events’.

‘pressure’ is a MATLAB structure with four fields, ‘time’, ‘injection’, ‘normal’, and ‘shear’. 
‘time’ is a time vector describing the time stamp of each data point found in ‘pressure’. Data were recorded at 50 kHz and then averaged down to 5 kHz, which is provided here.
	‘shear’ and ‘normal’ are data from hydraulic pressure sensors in the array of shear loading cylinders (North side) and normal loading cylinders (East side), respectively. Data was collected in Volts where 5 V is 10,000 psi. This has been converted from Volts to sample average stress in MPa using the conversion: 6.4 MPa/V for the normal stress (East-side cylinders) and 3.2 MPa/V for the shear stress (North-side cylinders).
‘injection’ is data from pressure sensors connected to the injection well. Injection well data in MPa using a conversion factor of 5 V = 3,000 psi or 4.1 MPa/V.

‘displacement’ is a MATLAB structure with two fields: ‘slip’ and ‘time’.
	‘slip’ is data recorded from eddy current sensor channels E1 – E16, respectively. E1 is near the shear forcing end (North) and E16 is near the leading edge (South) of the sample. All data were recorded in units of Volts then converted using the factor of 128 microns/V.
	‘time’ is a time vector describing the time stamp of each data point found in ‘displacement’. Data were recorded at 50 kHz and then averaged down to 5 kHz, which is provided here.
	Note that no displacement data was saved for FS01_050_4MPa.

‘strain’ is a MATLAB structure with two fields: ‘time’, and ‘exy’.
	‘time’ is a time vector describing the time stamp of each data point found in ‘strain’. Data were recorded at 100 kHz and then averaged down to 1 kHz, which is provided here.
	‘exy’ is data recorded from 16 semiconductor strain gauges S1 – S16. S1 is nearest the shear forcing end (North) and S16 is nearest the leading edge (South) of the sample. All data were recorded in units of Volts and then converted using a factor of 9.3090e-04 strain/V.
	Note that no strain gauge data was saved for FS01_050_4MPa.

‘events’ is a MATLAB structure that contains a list of individual events measured from the ‘displacement’ data. Each event contains ‘timing’ within experiment (relative to ‘displacement.time’) and ‘highspeed’.
	‘timing’ is the event time in seconds relative to the start of the experiment measuring using ‘displacement.time’. Events were determined visually from the slip and strain measurements. 
	‘highspeed’ contains two structures ‘exy’ and ‘time’ for a 1.0 sec window centered around the slip event. Similar to the ‘strain’ data, ‘time’ is a time vector describing the time stamp of each data point found in ‘strain’. ‘exy’ is data recorded from 16 semiconductor strain gauges S1 – S16. S1 is nearest the shear forcing end (North) and S16 is nearest the leading edge (South) of the sample. ‘exy’ data were recorded in units of Volts and then converted using a factor of 9.3090e-04 strain/V. Data were recorded and saved at 100 kHz.
	Note that no strain gauge data was saved for FS01_050_4MPa.

Sensor Setup: Below are the approximate coordinates of the eddy displacement sensors E1-E16 and semiconductor strain gauges S1-S16. The origin of the coordinate system is the top NE corner of the stationary block. 

Sensor X (m)   Y (m)   Z (m)    Sensor X (m)   Y (m)   Z (m)

E1     0.050   0.000   0.000    S1     0.150   0.005   0.000

E2     0.250   0.000   0.000    S2     0.350   0.005   0.000

E3     0.450   0.000   0.000    S3     0.550   0.005   0.000

E4     0.650   0.000   0.000    S4     0.750   0.005   0.000

E5     0.850   0.000   0.000    S5     0.950   0.005   0.000

E6     1.050   0.000   0.000    S6     1.150   0.005   0.000

E7     1.250   0.000   0.000    S7     1.350   0.005   0.000

E8     1.450   0.000   0.000    S8     1.550   0.005   0.000

E9     1.650   0.000   0.000    S9     1.750   0.005   0.000

E10    1.850   0.000   0.000    S10    1.950   0.005   0.000

E11    2.050   0.000   0.000    S11    2.050   0.005   0.000

E12    2.250   0.000   0.000    S12    2.150   0.005   0.000

E13    2.450   0.000   0.000    S13    2.350   0.005   0.000

E14    2.650   0.000   0.000    S14    2.550   0.005   0.000

E15    2.850   0.000   0.000    S15    2.750   0.005   0.000

E16    3.050   0.000   0.000    S16    2.950   0.005   0.000