*** Dominantly Aseismic Nucleation of Laboratory Earthquakes: A Quantitative Investigation *** 

Authors: S. Marty, H.S. Bhat, J. Aubry, R. Madariaga, E. Fukuyama, A. Schubnel

 Corresponding author: S. Marty

Contact Information: 

sam92son@gmail.com

Laboratoire de Géologie, Ecole Normale Supérieure, PSL Research University, Paris
24 rue Lhomond
75001
Paris
France

 ***General Introduction*** 

This data set contain all the mechanical and acoustic data that were used to produce the results in the present 
study. Data were collected at the Laboratoire de Géologie of the Ecole Normale Supérieure in Paris between October 2016 and October 2019.

***Purpose of the test campaign*** 

The purpose of this study was to use acoustic emissions generated during rock friction experiments as a proxy to foreshocks prior to earthquakes in order to better constrain the physical parameters relevant to the occurence of foreshocks.

***The experiments** 

Rock friction experiments were conducted on cylindrical samples of Indian metagabbro (about 80 mm long) under tri-axial conditions and  at upper crustal stress conditions (30-60 MPa). The mechanical data was collected by external pressure and displacement sensors and the acoustic data were collected by acoustic sensors in direct contact with the surface sample.

***Description of the data in this data set*** 

At each stress condition (30, 45 and 60 MPa)  we provide 5 .mat files:

1- def_(30,45,60)

The mat_files def_(30,45,60) contain the accumulated strain of the rock sample during the experiments, recorded at 10 Hz.

2- p_diff_(30,45,60)

The mat_files p_diff_(30,45,60) contain the differential stress (in MPa) acting on the fault place during the experiments, recorded at 10 Hz.

3- mainshocks_(30,45,60)

The mat_files mainshocks_(30,45,60) contain three matrix: 

- matrice_nuc, for which the rows correspond to the stick-slip index, the two first columns correspond to stick-slip locations and the third column corresponds to the location uncertainty (in seconds).

- Out_Mat contain the acoustic waveforms recorded during stick-slip instabilities, the first, second and third dimensions of this matrix refer to, respectively, the stick-slip index, the acoustic sensor index, and the waveform.

- Param_Mat contain the first P-wave arrival times (columns) for each stick-slip (rows). Arrival times are given in microseconds.

4- matrice_fs_(30,45,60)

The mat_files matrice_fs_(30,45,60) contain three matrix: 

- matrice_fs_f, for which the rows correspond to the acoustic emissions (AE) index, the two first columns correspond to AE locations and the third column corresponds to the location uncertainty (in seconds).

- Out_Mat contain the acoustic waveforms of the AEs, the first, second and third dimensions of this matrix refer to, respectively, the AE index, the acoustic sensor index, and the waveform.

- Param_Mat_fs_f contain the first P-wave arrival times (columns) for each AE (rows). Arrival times are given in microseconds.

5- time_before_event_(30,45,60)_f

The mat_files time_before_event_(30,45,60)_f contain the AEs occurence time (normalized by the time between two successives stick-slips)  relative to failure. The times of occurence are sorted in descending order.

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The spatial coordinates of the acoustic sensors are given by the mat_file coor_ca. The rows correspond to the acoustic sensors index and the columns to X, Y and Z.


Finally, the matrix FAULT (81x41x3) can be used to visualize the fault plane during our experiments and AEs or stick-slip locations on the fault. The fault is discretized into 81x41 points (two first dimensions of the matrix FAULT) the spatial coordinates of each point are given y the third dimension (X,Y,Z).

In our study we imposed that the AEs and stick-slip locate on the fault plane, therefore the spatial coordinates of the AEs (matrice_fs_f, 2 first columns) and the stick-slip (matrice_nuc, 2 first columns) indicate a specific point on the fault plane (for example if an AE is located at the position 64,31 on the fault plane, its spatial coordinates are FAULT(64,31,1), FAULT(64,31,2) and FAULT(64,31,3)).


