This file was prepared 20191108 by Gregory C. McLaskey (gcm8@cornell.edu) This file supplements data associated with the publication: "Earthquake Initiation from Laboratory Observations and Implications for Foreshocks" Journal of Geophysical Research Author: Gregory C. McLaskey (gcm8@cornell.edu) Alternate contacts: Chun-Yu Ke (ck659@cornell.edu) Bill S. Wu (sw842@cornell.edu) -------------------------- Dataset Description: These data are from Laboratory Earthquake Experiments from the Cornell 3 m apparatus in support of the following research: This paper reviews laboratory observations of earthquake initiation and describes new experiments on a 3 m rock sample where the nucleation process is imaged in detail. Many of the laboratory observations are consistent with previous work that showed a slow and smoothly accelerating earthquake nucleation process that expands to a critical nucleation length scale Lc, before it rapidly accelerates to dynamic fault rupture. The experiments also highlight complexities not currently considered by most theoretical and numerical models. This includes a loading rate dependency where a “kick” above steady state produces smaller and more abrupt initiation. Heterogeneity of fault strength also causes abrupt initiation when creep fronts coalesce on a stuck patch that is somewhat stronger than the surrounding fault. Taken together, these two mechanisms suggest a rate-dependent “cascade-up” model for earthquake initiation. This model simultaneously accounts for foreshocks that are a byproduct of a larger nucleation process and similarities between initial P wave signatures of small and large earthquakes. A diversity of nucleation conditions are expected in the Earth’s crust, ranging from slip limited environments with Lc < 1 m, to ignition-limited environments with Lc > 10 km. In the latter case, Lc fails to fully characterize the initiation process since earthquakes nucleate not because a slipping patch reaches a critical length but because fault slip rate exceeds a critical power density needed to ignite dynamic rupture. -------------------------- When utilizing this data, please cite as listed below, and provide reference to one or more of the following associated publications: Dataset: McLaskey, G. C. (2019) Data from: Earthquake Initiation from Laboratory Observations and Implications for Foreshocks [dataset]. Cornell University eCommons Repository. https://doi.org/10.7298/yqbn-fn15 Publications: McLaskey, G. C. (2019) Earthquake Initiation from Laboratory Observations and Implications for Foreshocks, Journal of Geophysical Research, https://doi.org/10.1029/2019JB018363 Wu, B. S., & McLaskey, G. C. (2019). Contained laboratory earthquakesranging from slow to fast.Journal of Geophysical Research: Solid Earth 124(10):10270-10291. https://doi.org/10.1029/2019JB017865 Ke, C.-Y., McLaskey, G. C., Kammer, D. S. (2018) Rupture Termination in Laboratory-Generated Earthquakes. Geophysical Research Letters 45(23):12784-12792. https://doi.org/10.1029/2018GL080492 -------------------------- This work was sponsored by USGS Earthquake hazards grant G18AP00010 and National Science Foundation grants EAR-1645163, EAR-1763499, and EAR-1847139 -------------------------- 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. -------------------------- File labelling: Experiments were conducted in runs which consist of series of events. Each data file is associated with an experimental run. We refer to the run generated after a large increase in normal stress as a Poisson expansion sequence, denoted “P” or “Poisson”. A run generated after a large decrease in normal stress is denoted "Reverse Poisson" or "RP”. For catalog purposes a run called “FS01_27_10MPaP” denotes the Poisson expansion sequence at ~10 MPa normal stress in the 27th overall day of experiments on the first set of blocks used on the Cornell 3 m apparatus. Individual slip events are labeled by their time (in seconds) since the beginning of the slip sensor data file. -------------------------- Dataset Description: Each .mat file contains a MATLAB structure with 2 fields: ‘t’ and ‘signal’. ‘t’ is a time vector describing the time stamp of each data point found in ‘signal’. All data were recorded at 50 kHz and then averaged down to 5 kHz, which is provided here. ‘signal’: Rows 1-16 are data recorded from eddy current sensor channels E1 - E16, respectively. E1 is near the forcing end (North) and E16 is near the leading edge (South) of the sample. All data is in units of Volts and the conversion factor is 128 microns/V. ‘signal’: Rows 19 - 20 are data from hydraulic pressure sensors in the array of normal loading cylinders (East side) and shear loading cylinders (North side), respectively. Data is in Volts where 5 V is 10,000 psi. The conversion from Voltage to sample average stress is 6.4 MPa/V for the normal stress (East-side cylinders) and 3.2 MPa/V for the shear stress (North-side cylinders). ‘signal’: Rows 17 and 18 were used for either (1) a piezoelectric sensor signal that was split and recorded for precise time synchronization between this data and data that was recorded on a separate digitizer, or (2) an additional eddy current sensor that measured slip on the low-friction Teflon-steel interface or another interface on the machine such as the rock/steel interface on the West side of the stationary rock block. For most of the experimental runs described here the slip sensors were evenly spaced down the length of the 3 m fault, with location listed below. The exceptions are experiments listed under FS01_021, where the slip sensors were located both on the top and bottom surfaces of the rock slab, as shown in Figure 8 of McLaskey (2019) DOI 10.1029/2019JB018363. The approximate locations of the slip sensors are listed below: Sensor X (m) Y (m) Z (m) E1 0.050 0.000 0.000 E2 0.250 0.000 0.000 E3 0.450 0.000 0.000 E4 0.650 0.000 0.000 E5 0.850 0.000 0.000 E6 1.050 0.000 0.000 E7 1.250 0.000 0.000 E8 1.450 0.000 0.000 E9 1.650 0.000 0.000 E10 1.850 0.000 0.000 E11 2.050 0.000 0.000 E12 2.250 0.000 0.000 E13 2.450 0.000 0.000 E14 2.650 0.000 0.000 E15 2.850 0.000 0.000 E16 3.050 0.000 0.000 Experimental Runs associated with each Figure of McLaskey (2019) DOI 10.1029/2019JB018363 are provided below. Figures 4-7 FS01_035_4MPaP Figure 8 FS01_021_7MPaRP Figure 9 – select events from the following runs: FS01_007_4MPaP FS01_007_4MPa FS01_007_7MPaP FS01_019_7MPaP FS01_026_4MPaP FS01_033_12MPaP FS01_033_2MPaP2 FS01_033_12MPaP2 FS01_034_10MPaP FS01_035_4MPaP FS01_035_10MPaP2 FS01_036_2MPaP FS01_036_7MPaP FS01_036_7MPa Figure 10 (a-o) FS01_009_640kPa FS01_022_1MPaP FS01_022_1MPa FS01_035_2MPaRP FS01_017_4MPaRP FS01_018_4MPaP2 FS01_008_4MPaP FS01_007_4MPa FS01_019_7MPaP FS01_022_7MPa FS01_016_7MPa FS01_031_7MPaP FS01_019_8MPa FS01_023_10MPa FS01_024_10MPaP3 Figure 12 FS01_036_7MPaP Figure 14 FS01_033_2MPaP2