1 Auxiliary material for paper 2 3 Dynamic triggering of microearthquakes in three geothermal/volcanic regions of California 4 Chastity Aiken and Zhigang Peng 5 Georgia Institute of Technology, School of Earth and Atmospheric Sciences, Atlanta, GA, USA 6 J. Geophys. Res. 7 Introduction 8 This auxiliary material contains two sections: Supplementary Figures and Supplementary Tables. 9 The Supplementary Figures section contains fifteen supplementary figures and their captions. 10 The Supplementary Tables section contains six tables and their captions. 11 12 1. Supplementary Figures 13 14 Figure S1. Hand-picked local earthquakes occurring in Long Valley Caldera around the 15 P-wave arrival for the 2005/06/15 M7.2 Mendocino earthquake. Symbols and notation are 16 the same as in Figure 2b. 17 18 Figure S2. Hand-picked local earthquakes occurring in Coso Geothermal Field around the 19 P-wave arrival of two earthquakes. (a) 2006/01/04 M6.6 Baja California (b) 2010/04/04 20 Mw7.2 Baja California. Symbols and notation are the same as in Figure 2b. 21 22 Figure S3. 23 Broadband transverse component recorded at station GDXB. (b) High-pass 10 Hz filtered Spectrogram of 2010/01/10 M6.5 Northern California earthquake. (a) 1 24 waveform. (c) Corresponding spectrogram indicating the 10 Hz high pass filter needed to avoid 25 contaminating body waves. 26 27 Figure S4. Recent example of earthquakes triggered in Geysers by a second moderate-size 28 earthquake occurring off the shore of Northern California. (a) Map indicating the Geysers 29 study region (black box) and location of the 2010/01/10 M6.5 and 2014/03/10 M6.1 Northern 30 California earthquakes. Plate boundaries are in light gray. (b) Broadband transverse, high- 31 passed > 5 Hz filtered envelopes, and broadband vertical waveforms are plotted. Red circles 32 indicate hand-picked earthquakes. Vertical bar indicates amplitude of broadband waveforms. β- 33 values are indicated. 34 35 Figure S5. Local earthquakes possibly triggered in Geysers Geothermal Field by the 36 2003/01/22 M7.6 and 2006/01/04 M6.6 Baja California earthquakes. Symbols and notation 37 are the same as in Figure 3. 38 39 Figure S6. Example of the 2012/10/28 Mw7.7 Haida Gwaii earthquake that did not trigger 40 earthquakes in the geothermal regions but did trigger tremor in Parkfield, CA. Symbols 41 and notation same as in Figure 8. 42 43 Figure S7. Transverse PGV and dynamic stress versus epicentral distance for 4 regions of 44 California. Symbols and notation are the same as in Figure 11. PGVs shown are measured 45 from low-passed 1-s waveforms. The dynamic stress is estimated using a shear rigidity of 30 2 46 GPa and a phase velocity of 4.1 km s-1. (a) Parkfield, (b) Long Valley, (c) Coso, and (d) 47 Geysers. 48 49 Figure S8. Vertical PGV and dynamic stress versus epicentral distance for 4 regions of 50 California. Symbols and notation are the same as in Figure 11. PGVs shown are measured 51 from low-passed 30-s waveforms. The dynamic stress is estimated using a shear rigidity of 30 52 GPa and a phase velocity of 3.5 km s-1. (a) Parkfield, (b) Long Valle, (c) Coso, and (d) Geysers. 53 54 Figure S9. Transverse PGV and dynamic stress versus epicentral distance for 4 regions of 55 California. Symbols are the same as in Figure 11. PGVs shown are measured from low-passed 56 30-s waveforms. The dynamic stress is estimated using a shear rigidity of 30 GPa and a phase 57 velocity of 4.1 km s-1. (a) Parkfield, (b) Long Valley Caldera, (c) Coso Geothermal Field, and 58 (d) Geysers Geothermal Field. 59 60 61 Figure S10. Surface wave spectra of instrument-corrected transverse displacement 62 waveforms for 4 regions of California. Colored lines = triggering and possible triggering 63 earthquakes. Gray lines = non-triggering events. (a) Parkfield, (b) Long Valley, (c) Coso, (d) 64 Geysers. 65 66 Figure S11. 67 California. Symbols and notation are the same as in Figure S10. (a) Parkfield, (b) Long Valley, 68 (c) Coso, (d) Geysers. Spectra of selected vertical displacement seismograms for 4 regions of 3 69 70 Figure S12. Examples of statistically significant triggering ± 5 days around mainshocks. (a) 71 2010 M7.2 Baja California sequence in Long Valley. (b) 2009 M6.9 Baja California sequence in 72 Coso. (c) 2001 M8.4 Peru sequence in Geysers. In each panel, circles represent earthquakes in 73 the ANSS and our hand-picked earthquakes. For the ANSS catalog, we use only events above 74 the Mc value (see Figure 12). For the hand-picked events, we estimated the magnitude as 75 described in the main text. Red line is cumulative number of earthquakes. β- and Z-values for 76 instantaneous triggering are indicated. 77 78 Figure S13. Example of increased local earthquake activity in Coso Geothermal Field 79 prior to the arrival of seismic waves of the 2004/12/26 M9.0 Sumatra earthquake. Color 80 depicts region: Yellow = Geysers, red = Long Valley, and turquoise = Coso. 81 82 Figure S14. Heat flow data for the three geothermal regions. The data was collected via 83 http://earthquake.usgs.gov/research/borehole/heatflow/map.php. In (a)-(c), the colored squares 84 indicate the location and magnitude of the heat flow measurements. The legend for the heat flow 85 magnitudes is in (d). The triangles in (d) represent the main reference stations, as represented in 86 Figure 1d. 87 88 Figure S15. Variation in β-value with CC value for tremor triggered by the 2012 Haida 89 Gwaii earthquake. (a) Cumulative CC sum across all stations vs. median CC value of all 90 stations used for LFE detection. Median of all median CC values from 2001-2012 and 1 times 91 the median absolution deviation (MAD) are indicated. (b) Instantaneous β-value vs. changing 4 92 median CC detection threshold. (c) Delayed β-value vs. changing median CC detection 93 threshold. 94 95 2. Supplementary Tables 96 97 Table S1. Earthquake parameters of 149 events analyzed in Long Valley Caldera. The 98 earthquake catalog information (origin time, location, magnitude) was obtained from the 99 Advanced National Seismic System (ANSS) catalog. The epicentral distance and back-azimuth 100 (BAZ) were computed relative to the broadband station OMM (stlo: -118.9994, stla: 37.6124). 101 The peak ground vertical (PGV_Z) and transverse (PGV_T) velocities were measured from the 102 broadband recordings of station OMM before 2002 and by station MCB and MDPB after 2002. 103 MDPB was only used if MCB data was not available or had poor quality. The PGVs are in units 104 of cm/s. The quality (Q) 1 marks events that are known triggers, 2 marks triggers identified in 105 this study, 3 marks those that possibly triggered earthquakes in Long Valley Caldera, and 0 106 marks those that did not. 107 108 Table S2. Earthquake parameters of 156 events analyzed in Coso Geothermal Field. The 109 earthquake catalog information (origin time, location, magnitude) was obtained from the 110 Advanced National Seismic System (ANSS) catalog. The epicentral distance and back-azimuth 111 (BAZ) were computed relative to the broadband station JRC2 (stlo: -117.8076, stla: 35.9823). 112 The peak ground vertical (PGV_Z) and transverse (PGV_T) velocities were measured from the 113 broadband recordings of station JRC before 2004 and by station JRC2 after 2004. The PGVs are 114 in units of cm/s. The quality (Q) 1 marks events that are known triggers, 2 marks triggers 5 115 identified in this study, 3 marks those that possibly triggered earthquakes in Coso Geothermal 116 Field, and 0 marks those that did not. 117 118 Table S3. Earthquake parameters of 148 events analyzed in Geysers Geothermal Field. 119 The earthquake catalog information (origin time, location, magnitude) was obtained from the 120 Advanced National Seismic System (ANSS) catalog. The epicentral distance and back-azimuth 121 (BAZ) were computed relative to the broadband station GDXB (stlo: -122.7947, stla: 38.8078). 122 The peak ground vertical (PGV_Z) and transverse (PGV_T) velocities were measured from the 123 broadband recordings of station HOPS before 2006 and by station GDXB after 2006. The PGVs 124 are in units of cm/s. The quality (Q) 1 marks events that are known triggers, 2 marks triggers 125 identified in this study, 3 marks those that possibly triggered earthquakes in Geysers Geothermal 126 Field, and 0 marks those that did not. 127 128 Table S4. Earthquake parameters of 153 events analyzed in Parkfield, CA. The earthquake 129 catalog information (origin time, location, magnitude) was obtained from the Advanced National 130 Seismic System (ANSS) catalog. The epicentral distance and back-azimuth (BAZ) were 131 computed relative to the broadband station PKD (stlo: -120.5416, stla: 35.9452). The peak 132 ground vertical (PGV_Z) and transverse (PGV_T) velocities were measured from the broadband 133 recordings of station PKD. The PGVs are in units of cm/s. The quality (Q) 1 marks events that 134 are known triggers, 2 marks triggers identified in this study, and 0 marks those that did not. 135 136 Table S5. β-values for events that appear to trigger tremor in Parkfield, CA and/or 137 microearthquakes in Long Valley, Coso, and Geysers. For Parkfield, we used the LFE-based 6 138 tremor catalog to compute the instantaneous (B_I) and delayed (B_D) β-statistic values. In the 139 geothermal/volcanic regions, we computed the β-values for both the instantaneous and delayed 140 triggering windows using all hand-picked events and those above a threshold equivalent to the 141 median S-wave amplitude of all hand-picked events occurring after the P-wave arrival of the 142 mainshock. We do not compute β-values using a median amplitude threshold for LFE-based 143 tremor, as the LFE amplitudes were not available. 144 threshold are in bold. β-statistic values computed without a 145 146 Table S6. Z-values for events that appear to trigger tremor in Parkfield, CA and/or 147 microearthquakes in Long Valley, Coso, and Geysers. For Parkfield, we used the LFE-based 148 tremor catalog to compute the instantaneous (Z_I) and delayed (Z_D) Z-statistic values. In the 149 geothermal/volcanic regions, we computed the Z-values for both the instantaneous and delayed 150 triggering windows using all hand-picked events and those above a threshold equivalent to the 151 median S-wave amplitude of all hand-picked events occurring after the P-wave arrival of the 152 mainshock. We do not compute Z-values using a median amplitude threshold for LFE-based 153 tremor, as the LFE amplitudes were not available. Z-statistic values computed without a 154 threshold are in bold. 155 7