Supplementary material: The relation between viscosity and acoustic emissions as a laboratory analogue for volcano seismology

Transcription

1 GSA Data Repository 1918 Supplementary material: The relation between viscosity and acoustic emissions as a laboratory analogue for volcano seismology James Clarke*, Ludmila Adam*, Joel Sarout, Kasper van Wijk*, Ben Kennedy and Jeremy Dautriat *University of Auckland, Auckland, New Zealand. CSIRO Energy, Perth, Australia. University of Canterbury, Christchurch, New Zealand. This supplementary material contains: I. Contents of this file Figure DR1: Experimental set-up with a description of depressurization conditions. Figure DR: Cumulative number of acoustic emissions induced by each fluid over a one hour period for the P e f f = 5 MPa experiment on linear axis scales. Figure DR3: Cumulative number of acoustic emissions induced by each fluid over a one hour period for the P e f f = MPa experiment on linear axis scales. Figure DR: X-ray computerized tomography slice of the rock fracture network which intersects Cluster and selected superposed, D projected event locations for both sets of depressurization experiments. Figure DR5: Waveforms, power spectra and spectrograms for long duration, monochromatic, tremor-like signal recorded during P e f f = 5 MPa nitrogen depressurization experiment on two time scales. Figure DR6: Waveforms, power spectra and spectrograms of two LP events and tremor signal recorded during P e f f = 5 MPa nitrogen depressurization experiment. Text DR7: Note on magma viscosity and rheology in relation to the depressurization experiments. Video DR1 1

2 II. Supplementary Material To Actuator Pump Ball Valve Connective Mesh Fluid Lines Triaxial Stress Cell Plattern Sample Fracture Network Transducer Jacket Fluid Pump Figure DR1: Experimental schematic showing the sample inside the triaxial stress cell. Axial load is applied via the actuator pump to fracture the dry sample. Pressurized pore fluids are supplied via the fluid pump and subsequently depressurized upon opening of the ball valve. Experiments are conducted for two effective pressure conditions; P e f f = 5 MPa and P e f f = MPa. For the P e f f = 5 MPa experiment, a confining pressure (P c ) of MPa and a pore pressure (P p ) of 35 MPa are used for all fluids with the exception of nitrogen gas for which P c = 5 MPa and P p = MPa. This pressure difference is due to the necessity of supplying nitrogen gas from a MPa pressurized bottle, rather than the fluid pump. For the P e f f = MPa experiment, P c = MPa and P p = MPa for all fluids.

3 Nitrogen Water 6% Glyc 85% Glyc % Glyc Figure DR: Cumulative number of acoustic emissions induced by fluid type for the P e f f = 5 MPa experiment during 1 hour post depressurization and data for the first 3 seconds post depressurization (inset plot). Time t = s represents the pressure release moment of each fluid relative to nitrogen venting. 3

4 Nitrogen Water 6% Glyc % Glyc Figure DR3: Cumulative number of acoustic emissions induced by fluid type for the P e f f = MPa experiment during 1 hour post depressurization and data for the first 1 seconds post depressurization (inset plot). Time t = s represents the pressure release moment of each fluid relative to nitrogen venting.

5 A) B) %Glyc 85%Glyc Z(cm) Z(cm) 6%Glyc Water 1 1 Y(cm) 1 1 Y(cm) Nitrogen Figure DR: X-ray computerised tomography slice with projected Acoustic Emission (AE) locations. Panel A) shows the induced fracture network. Panel B) shows the fracture network with superposed (D projected) AE locations for both sets of depressurization experiments, color-coded by the fluid type which induced the event. Only AEs located in the region X=-.75 to.75 cm are plotted. Cluster AEs are highlighted by the black circle. These events are associated with a complex zone of intersecting fractures with tortuous fluid pathways. Please note that the data has been rotated into the plane of the XRCT image and so the Y axis is defined differently from that in Figure 1 and DR8. A) 3 B) Figure DR5: Waveforms, power spectra and spectrograms for long duration, monochromatic, tremor-like signal generated during Peff=5 nitrogen depressurization. The full tremor signals are recorded over a duration of 1.17 seconds and.56 seconds of the depressurization experiments for P e f f = 5 MPa and P e f f = MPa respectively. Panel A) 3 µs record of continuous tremor (Event 9, S18). Note the higher frequency, broader band Volcano-Tectonic (VT) event observed at 8 µs. Panel B) Magnified perspective of the signal over the time range µs. 5

6 A) B) C) Figure DR6: Waveforms, power spectra and spectrograms for Long Period (LP) events and tremor signal generated during Peff=5 nitrogen depressurization. A) Event 1, Sensor 18 - An LP event that immediately precedes the onset of tremor signal, B) Event 11, Sensor 1 - An LP event recorded during the tremor period, C) Event 5, Sensor 18 - One pulse of tremor signal. Power spectra are computed over a time window of µs in each case. 6

7 DR 7: A note on magma viscosity and rheology in relation to the depressurization experiments: Our experiments aim to shed some light into the role fluid viscosity has on volcano seismicity. In magmatic and hydrothermal systems, fluids have a logarithmic range of viscosities as a result of fluid type, temperature and rheological processes. Magma rheology is complex including varying gas volumes and fractional crystalization. Moreover, the rheological response of magma is both total strain (Kendrick et al., 13) and strain rate controlled (Lavallée et al., 7). Indeed magma itself can fracture (Lavallée et al., 8). Our experiments target understanding viscosity as a first order control on acoustic emissions. Accounting for complex magma rheology, the presence of multiple phases, or fluid flow type (e.g. laminar or turbulent) is beyond the scope of this study. References Kendrick, J. E., Lavallée, Y., Hess, K. U., Heap, M. J., Gaunt, H. E., Meredith, P. G., and Dingwell, D. B. (13). Tracking the permeable porous network during strain-dependent magmatic flow. Journal of Volcanology and Geothermal Research, 6: Lavallée, Y., Hess, K. U., Cordonnier, B., and Dingwell, D. B. (7). Non-Newtonian rheological law for highly crystalline dome lavas. Geology, 35(9): Lavallée, Y., Meredith, P. G., Dingwell, D. B., Hess, K. U., Wassermann, J., Cordonnier, B., Gerik, A., and Kruhl, J. H. (8). Seismogenic lavas and explosive eruption forecasting. Nature, 53(719):