SUPPLEMENTARY INFORMATION

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1 SUPPLEMENTARY INFORMATION DOI: /NGEO1992 Seismic detection of an active subglacial magmatic complex in Marie Byrd Land, Antarctica TABLE OF CONTENTS 1. Additional Study Information 1.1 Station Locations 1.2 Local Velocity Model 1.3 Ice Thickness 2. Additional Analysis 2.1 Event Temporal Distribution 2.2 b-value 2.3 Testing Depth Constraint 2.4 Cross-correlation Analysis 2.5 Eruptive Energy Calculation 2.6 Amount of Ice Melted Calculation 3. References NATURE GEOSCIENCE 1

2 Supplementary Materials 1.1 Station Locations Station Latitude Longitude Elevation ST km SILY km ST km ST km ST km ST km ST km ST km ST km Supplementary Table S1.1 Location of stations used in this study. 2

3 Supplementary Materials 1.2 Local Velocity Model Depth (km) P velocity (km/s) S velocity (km/s) Supplementary Table S1.2 Local velocity model used in relative relocation. We base our local velocity model on the shear velocity structure determined from noise correlation using the POLENET/ANET stations by Sun et al. (2009) 1. P velocities are calculated from the S velocities assuming a P/S ratio of P and S velocities in the firn and ice layers are taken from Albert (1998) 1-2. The ice thickness is estimated from the average value of ice thickness in BEDMAP for the box with coordinates (-77.88, ), (-78.63, ), (-76.52, ), (-75.58, ) 3. The Moho depth of 29.5 km was determined by averaging the values determined from receiver functions by Chaput et al. (2012) for the stations ST08 and SILY 4. Supplementary Materials 1.3 Ice Thickness Supplementary Figure S1.3 Ice thickness in study area from Bedmap2 3. Ice is approximately 1600 m thick above cluster epicenters (area circled in black). 3

4 Supplementary Materials 2.1 Event Temporal Distribution The vast majority of events occur during swarm activity, and even outside of swarms events tend to occur close in time. 89.7% of events occurred during the two swarms (68.2% in January to February 2010 and 21.5% in March 2011). In mid-late January 2010 (first relevant instruments were deployed on January 17, 2010 and all relevant stations were deployed by January 21, 2010) 628 events were located, this is the equivalent of almost 42 events per day taking into account the number of days analyzed. February 2010 and March 2011 average about 300 events or about 12.8 events per day whereas a typical month during a non-swarm period only averages 6.55 events or 0.62 events per day. Supplementary Figure S2.1 Histogram of DLP events detected in by month. Events are binned by number of arrivals. 4

5 log(n) Seismic Detection of an Active Subglacial Magmatic Complex in Marie Byrd Land, Antarctica Supplementary Materials 2.2 b-value b = Supplementary Figure S2.2 Graph showing b-value calculation on DLP events. The b- value of 2.75 is indicative of the overwhelming swarm like behavior of the events. It is consistent with the strong falloff of numbers of smaller events relative to tectonic seismicity commonly observed in volcanic earthquake swarms. ml 5

6 Depth (km) Seismic Detection of an Active Subglacial Magmatic Complex in Marie Byrd Land, Antarctica Supplementary Materials 2.3 Testing Depth Constraint Residual Supplementary Figure S2.3.1 Plot of residual versus depth for fixed depths calculated with the local velocity model. The minimum residual is near 35 km depth. We test the validity of depth constraints by solving for various fixed depths with our local velocity model. In every case the residual is greatest at shallow levels, decreases with depth to a minimum around km and increases with depth but does not reach the maximum at shallows levels until deeper than 70 km. We also tested ISAP91 with the same results. Our depth are well constrained at km. Sample waveforms from the event used to generate Fig. S2.3.1 are shown in Fig. S Supplementary Figure S2.3.2 Three component seismograms of an example event (same event used to demonstrate depth constraints in Fig. S2.3.1). Waveforms are bandpass filtered between 1.5 and 4.0 Hz. P and S wave arrivals are marked. 6

7 Supplementary Materials 2.4 Cross-correlation Analysis We performed a cross-correlation analysis on ST08 and SILY stations to determine the similarity in waveforms. Supplementary Fig. S2.4 and Supplementary Fig. S2.5 show the results of cross-correlation with dates labeled on the axes. Warm colors indicate higher levels of correlation. Both stations show weak correlations, except during swarm periods. Waveforms seem to correlate best with those closest in time. For example, there is a strong correlation at ST08 for events on January 20-22, The cluster analysis also showed low correlation values, and events tend to cluster into two main groups based on year. This is also apparent in the cross-correlation, especially at ST08 where events from 2011 have very low correlation values with events from 2010 (far right of Supplementary Fig. S2.4). Supplementary Figure S2.4.1 Cross correlation values for ST08 station on entire dataset. Warm colors indicate a high correlation. Highest correlations occur during swarms. 7

8 Supplementary Materials 2.4 Cross-correlation Analysis Supplementary Figure S2.4.2 Cross correlation values for SILY station on entire dataset. Warm colors indicate a high correlation. Highest correlations occur during swarms. 8

9 Supplementary Materials 2.5 Eruptive Energy Calculation The thermal energy require to melt ice is: E = H fus * ρ ice * V ice H fus the heat of fusion for ice is 334 kj/kg ρ ice the density of glacial ice is 850 kg/m 3 V ice is the volume of ice being melted. 5 km diameter cylinder of ice 1 km thick: E = (2500m*2500m*1000m*π)*(334 kj/kg)*(850 kg/m 3 ) = 6 X kj 20 km diameter cylinder of ice 1 km thick: E = (10000m*10000m*1000m*π)*(334 kj/kg)*(850 kg/m 3 ) = 9 X kj Volcano Year Total Energy (kj) Santorini, Aegean Sea 1500 B.C.E 1.0 x Laki, Iceland 1783 C.E. 8.6 x Tambora, Indonesia 1815 C.E. 8.4 x Krakatau, Indonesia 1883 C.E. ~1.0 x Vesuvio, Italy 1906 C.E. 1.7 x Katmai-Novarupta, Alaska 1912 C.E. 2.0 x Sakura-jima, Japan 1914 C.E. 4.6 x Mauna Loa, Hawaii 1950 C.E. 1.4 x Oshima, Japan C.E. 9.4 x Kilauea, Hawaii 1952 C.E. 1.8 x Bezymianny, Kamchatka C.E. 2.2 x Capelinhos (Fayal), Azores 1957 C.E. 4.0 x Agung, Bali 1963 C.E. 4.5 x Surtsey, Iceland 1963 C.E. 1.9 x Taal, Philippines 1965 C.E. 1.0 x Arenal, Costa Rica 1968 C.E. 1.0 x Mount St Helens, USA 1980 C.E. ~5.0 x Supplementary Table S2.5 Examples of energy released in various volcanic eruptions 5. 9

10 Supplementary Materials 2.6 Volume of Ice Melted Calculation The volume of ice melted for a given eruption is: V ice = E / H fus / ρ ice H fus the heat of fusion for ice is 334 kj/kg ρ ice the density of glacial ice is 850 kg/m 3 For a typical eruption ( kj) the amount of ice melted is: V ice = kj / 334 kj/kg / 850 kg/m 3 = 3.5 X 10 6 m 3 = km 3 V ice = kj / 334 kj/kg / 850 kg/m 3 = 3.5 X 10 7 m 3 = km 3 For a large eruption ( kj) the amount of ice melted is: V ice = kj / 334 kj/kg / 850 kg/m 3 = 3.5 X m 3 = 35 km 3 V ice = kj / 334 kj/kg / 850 kg/m 3 = 3.5 X m 3 = 350 km 3 10

11 Supplementary Materials 3. References 1. Sun, X., et al. Crust and upper mantle shear wave structure of Antarctica from seismic ambient noise. American Geophysical Union, Fall Meeting 2009, Abstract #U51C Albert, D.G. Theoretical modeling of seismic noise propegation in firn at the South Pole, Antarctica. Geophysical Research Letters, 25, (1998). 3. Fretwell, P. et al. Bedmap2: improved ice bed, surface and thickness datasets for Antarctica. The Cryosphere Discuss. 6, (2012). 4. Chaput, J., Aster, R., Sun, X., Wiens, D., Nyblade, A., Anandakrishnan, S., Huerta, A., Winberry, J., & Wilson, T., Crustal thickness across West Antarctica, in review, Blong, R.J. Volcanic Hazards A Sourcebook on the Effects of Eruptions. (Academic Press, Orlando, 1984). 11