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