Darley Dale Sandstone AE Dataset (Confinement 20 MPa)

AE data (.seg2 files) contain AE recordings from all 12 sensors (recloc.mat) for individual events. These events have been picked (pktimes_ml.mat) and located using a Time Difference of Arrival methodology (sourceloc_ml.mat).

Darley dale sandstone (DDS) is a brown-yellow, feldspathic sandstone with a modal composition of quartz (69%), feldspars (26%), clay (3%) and mica (2%) (Heap et al., 2009). Previous studies report a connected porosity of 13.3% ± 0.8% with grain sizes varying from 100-800 µm (Zhu & Wong, 1997). The unconfined compressive strength is 160 MPa (Baud & Meredith, 1997). At the scale analysed here, no distinct layering or laminations were present. A cylindrical rock sample was cored using a diamond tipped hollow coring drill to prepare a 4 cm diameter sample that was then trimmed to 10 cm length with a diamond saw. End faces are accurately ground using a lathe fitted with a cross-cutting diamond grinding disk with surfaces flat and parallel to within 0.01 mm.

Deformation was performed using a conventional triaxial deformation cell installed at the Rock Mechanics Laboratory, University of Portsmouth (Fazio, 2017). The sample presented here was deformed until brittle failure at a confining pressure of 20 MPa at a constant deformation rate of 3.6 mm/hr. Experimentation was performed under fully drained conditions to avoid any fluid-driven effects on AE frequency content (Benson et al., 2010). These environmental conditions ensure that a high number of AE are obtained and any time-dependent variations in the signal waveform are predominantly due to the scattering effects of microfractures, thus allowing for the sampling of a diverse range of deformation structure. Axial displacement is measured with a non-contact Eddy Displacement system mounted to the apparatus. It comprises of three sensors that accurately (sub-micron) measure the distance to a target steel plate attached to the driving piston. These readings are averaged and are used to set the target deformation rate via feedback to an axial stress intensifier. Differential stress (MPa) and sample strain (%) are in attached .txt files.

For AE data acquisition the protocol of Benson et al. (2007) was followed. The dry sample was positioned inside an engineered rubber jacket fitted with ports for an array of twelve 1 MHz single-component Piezo-Electric Transducers (PZTs, model PAC Nano30) were embedded. These sensors have a relatively flat frequency response between 125-750 KHz. Sensor output is connected to preamplifiers set to 40 dB, focusing on data quality over quantity. An ITASCA-Image “Milne” recorder operate in a standard ‘trigger’ model, downloading all twelve channels when any single channel passes a set 100 mV threshold (e.g. Gehne, 2018).

Heap, M. J., Baud, P., Meredith, P. G., Bell, A. F., & Main, I. G. (2009). Time‐dependent brittle creep in Darley Dale sandstone. Journal of Geophysical Research: Solid Earth, 114(B7).

Zhu, W., & Wong, T. (1997). The transition from brittle faulting to cataclastic flow: Permeability evolution. Journal of Geophysical Research: Solid Earth, 102(B2), 3027–3041.

Baud, P., & Meredith, P. (1997). Damage accumulation during triaxial creep of Darley Dale sandstone from pore volumometry and acoustic emission. International Journal of Rock Mechanics and Mining Sciences, 34(3–4), 24-e1.

Fazio, M. (2017, January). Dynamic Laboratory Simulations of Fluid-Rock Coupling with Application to Volcano Seismicity and Unrest (PhD Thesis). University of Portsmouth, School of Earth and Environmental Sciences.

Benson, P. M., Vinciguerra, S., Meredith, P. G., & Young, R. P. (2010). Spatio-temporal evolution of volcano seismicity: A laboratory study. Earth and Planetary Science Letters, 297(1–2), 315–323.

Benson, P. M., Thompson, B. D., Meredith, P. G., Vinciguerra, S., & Young, R. P. (2007). Imaging slow failure in triaxially deformed Etna basalt using 3D acoustic-emission location and X-ray computed tomography. Geophysical Research Letters, 34(3). https://doi.org/10.1029/2006gl028721

Gehne, S. (2018). A laboratory study of fluid-driven tensile fracturing in anisotropic rocks. University of Portsmouth.