Work Description

README (Yihe Huang 07/24/2019)

Contacts: De Barros, Louis (debarros@geoazur.unice.fr, Université Côte d’Azur); Huang, Yihe (yiheh@umich.edu, University of Michigan)

Data was collected in an injection experiment funded by French government through the HYDROSEIS project under contract ANR-13-JS06-0004-01.

Methodology: The seismic data is collected from an injection experiment at 280 m depth within the Low Noise Underground Laboratory facility (LSBB, http://lsbb.eu) in France (Guglielmi et al, 2015). A series of eleven injection tests were performed to reactivate selected geological features belonging to the damaged zone (20 m thick) of a kilometer-long inactive fault (Figure 1). A borehole probe, called SIMFIP (Guglielmi et al., 2014), was used to inject water into 2.4 m long sections isolated between packers in vertical boreholes. At the injection point, this probe was also used to monitor the fluid pressure, the flowrate and the deformation through optical fiber sensors. To monitor seismicity, 14 vertical and 8 3-component accelerometers were set on the gallery floor and on adjacent boreholes, respectively, at distances of 3-20 meters from the injection. These 10Hz-4kHz sensors allow the analysis of the seismicity in a broad frequency range. For more details about this experiment, we refer the reader to Duboeuf et al. (2017) and De Barros et al. (2018). We use seismic data recorded by the vertical component of the 22 sensors at a rate of 10000 samples/s to carry out a spectral ratio analysis of events with highly-similar waveforms (Abercrombie, 2015; Huang et al., 2016). We cross-correlate waveforms of previously detected earthquakes, including both P– and S– waves filtered between 200 and 2000 Hz, and identify pairs of earthquakes that have cross-correlation coefficients higher than 0.8 at more than 3 stations.

References:

Abercrombie, R. E. (2015). Investigating uncertainties in empirical Green's function analysis of earthquake source parameters. Journal of Geophysical Research: Solid Earth, 120, 4263–4377. https://doi.org/10.1002/2015JB011984

De Barros, L., Guglielmi, Y., Rivet, D., Cappa, F., & Duboeuf, L. (2018). Seismicity and fault aseismic deformation caused by fluid injection in decametric in-situ experiments. Comptes Rendus Geoscience, 350(8), 464-475. https://doi.org/10.1016/j.crte.2018.08.002

Duboeuf, L., De Barros, L., Cappa, F., Guglielmi, Y., Deschamps, A., & Seguy, S. (2017). Aseismic motions drive a sparse seismicity during fluid injections into a fractured zone in a carbonate reservoir. Journal of Geophysical Research: Solid Earth, 122(10), 8285-8304. https://doi.org/10.1002/2017JB014535

Guglielmi, Y., Cappa, F., Lancon, H., Janowczyk, J., Rutqvist, J., Tsang, C.-F., & Wang, J. S. Y. (2014). ISRM suggested method for Step-Rate Injection Method for Fracture In-Situ Properties (SIMFIP): Using a 3-components borehole deformation sensor. Rock Mechanics and Rock Engineering, 47(1), 303–311. doi.org/10.1007/s00603-013-0517-1

Guglielmi, Y., Cappa, F., Avouac, J.-P., Henry, P., & Elsworth, D. (2015). Seismicity triggered by fluid injections induced aseismic slip. Science, 348(6240), 1224–1226. https://doi.org/10.1126/science.aab0476

Huang, Y., Beroza, G. C., & Ellsworth, W. L. (2016). Stress drop estimates of potentially induced earthquakes in the Guy‐Greenbrier sequence. Journal of Geophysical Research: Solid Earth, 121(9), 6597-6607. https://doi.org/10.1002/2016JB013067

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The MAT files contain the seismic data, time, station information used in the spectral ratio analysis.

The file names document the injection test number, event numbers, cross-correlation coefficient and data duration (in seconds). For example, TEST3-1_data_cluster16_27_cc08_t120.mat contains 120 second long data for earthquakes 16 and 27 that have cross-correlation coefficient of 0.8 in injection test 3-1.

The seismic data, time (in seconds), station information can be extracted in MATLAB as follows:
infotime=load('TEST3-1_time_cluster16_27_cc08_t120.mat');
infodata=load('TEST3-1_data_cluster16_27_cc08_t120.mat');
infostation=load('TEST3-1_station_cluster16_27_cc08_t120.mat');
time=infotime.time_short;time=time';
data_all=infodata.event_dataraw_short;
station_all=infostation.station_cc;