1
(“Additional file 2”): Detailed descriptions of lithology, structure, and physical
2
properties of the damage zones in the Nobeoka Thrust
3
4
The hanging wall at 0–41.3 m below the ground surface (hereafter termed “mbgs”)
5
is composed of the Kitagawa Group (phyllite of alternating beds of sandstone and shale),
6
consisting of six intervals of three different types: (1) shale-dominant intervals,
7
characterized by a dense development of phyllitic cleavage, kink folds, and quartz vein
8
networks
9
sandstone-dominant intervals with disturbed foliations with ~2–20-mm-thick medium-
10
to fine-grained sandstone boudinage and fractures at 18.6–24.1 mbgs and 26.4–29.1
11
mbgs; and (3) the damage zone above the fault core, characterized by cataclastically
12
broken phyllite with thick (~20–100-mm) abundant medium- to fine-grained sandstone
13
blocks at 38.1–41.3 mbgs.
at
0–18.6
mbgs,
24.1–26.4
mbgs,
and
29.1–38.1
mbgs;
(2)
14
The footwall (41.3–255 mbgs) is composed of the Hyuga Group consisting of
15
foliated cataclasite of scaly shale, tuffacious shale, sandstone, and acidic tuff. Four
16
lithologic units were classified within the drilled range of the footwall, based on the
17
abundance of sandstone, silt, tuff, and the occurrence of structures, although lithology
18
and structure did not vary significantly with depth. Hyuga Unit 1 (42.1–80.0 mbgs) is
19
characterized by random-fabric cataclasite and foliated cataclasite with abundant
20
fragmented sandstone and tuffacious silt blocks. Hyuga Unit 2 (80.0–112.0 mbgs)
21
consists of foliated cataclasite containing elongated blocks of sandstone and tuffacious
22
silt. Hyuga Unit 3 (112.0–180.0 mbgs) consists of foliated cataclasite with especially
23
abundant tuff. Hyuga Unit 4 (180.0–255.0 m) is composed of foliated cataclasite with
24
sandstone and tuffacious silt blocks and boudinaged sandstone layers. These lithological
25
differences are clearly detected in the geophysical logging signatures of resistivity,
26
natural gamma rays, neutron porosity, and P-wave velocity (see Fig. 2 in the main text).
27
The footwall Hyuga Units 1 and 2 show lower resistivity (~232, ~226 m) and higher
28
porosity (~7.6%). Hyuga Unit 3 is characterized by a gradual increase in resistivity
29
(~280 m,), whereas in Hyuga Unit 4, the resistivity gradually decreases (~234 m).
30
These contrasts in physical properties across the lithologic units can be clearly seen in
31
the cross-correlation of porosity and resistivity (see Fig. 12 in the main text). The
32
regional dip of bedding and cleavage in footwall Hyuga Unit 1 is approximately 30°
33
toward the SE, but the orientation of structures is more scattered compared to the
34
hanging wall. Bedding- (cleavage)-parallel fractures, faults, and mineral veins and
35
structures striking SW and dipping to the NE are dominant in Unit 1. Bordering the
36
fracture zone at 73.0–80.0 mbgs, the orientation of fractures, faults, and mineral veins in
37
Unit 2 is more scattered compared to Unit 1. Bordering the fracture zone at 112.1–115.0
38
mbgs, the regional dip of bedding (cleavage), fractures, faults, and mineral veins in Unit
39
3 is approximately 30° toward the TN and strikes SSW to SSE. The overall orientation
40
of the structures is similar, and structures striking NW to NE occur only sporadically. In
41
Unit 4, the regional dip of bedding (cleavage), fractures, faults, and mineral veins in the
42
footwall is about 30–80° toward the NE and strikes SW to SSE. Sporadically, strike
43
directions to the SE, NW, and NE are also present. Bounded by the fault at ~242 mbgs,
44
structures below this depth dip 40–80° toward the NW to NE, with strike directions of
45
SE to SW.
46
Within the drilled range of the Nobeoka Thrust, seven sets of damage zones were
47
found in the hanging wall and footwall. The hanging wall damage zone just above the
48
fault core is characterized by cataclastically broken phyllite with thick (~20–100 mm)
49
abundant medium- to fine-grained sandstone blocks at 38.1–41.3 mbgs. The footwall
50
consists of six fracture zones within each lithologic unit (66.77–85.7 mbgs, 95.0–124.0
51
mbgs, 134.1–174.0 mbgs, 184.6–196.6 mbgs, 201.8–221.2 mbgs, and 222.5–247.3
52
mbgs), all of which include a brecciated zone intensively broken in the center
53
(75.1–80.0 mbgs, 112.1–115.0 mbgs, 157.0–159.0 mbgs, 188.1–189.0 mbgs,
54
210.0–212.0 mbgs, and 242.0–243.0 mbgs), sandwiched by a surrounding damage zone
55
with abundant cohesive faults, mineral veins, and sandstone blocks (66.7–75.0 mbgs,
56
80.1–85.7 mbgs, 95.0–112.0 mbgs, 115.1–124.0 mbgs, 134.1–156.9 mbgs, 159.1–174.0
57
mbgs, 184.6–188.0 mbgs, 189.1–196.6 mbgs, 201.8–209.9 mbgs, 212.1–221.2 mbgs,
58
222.5–241.9 mbgs, and 243.1–247.3 mbgs). These fracture zones were observed in both
59
cores and borehole images, and thus are not likely to be drilling-induced structures. In
60
this document, we describe lithology, structure, and geophysical logging data for each
61
damage zone in detail.
62
Note that the electric resistivity data presented in the supplementary material
63
describe the short-normal (SN) resistivity of the shorter distance between the electrodes
64
and the long-normal (LN) resistivity of the longer distance between the electrodes, two
65
of the three types of vertical electric resistivity data obtained in this project
66
(Supplementary Material “Additional file 1”).
67
68
11.5–41.3 mbgs: Hanging wall damage zone and fault core
69
At 0–29 mbgs, the number distribution of faults, fractures, and mineral veins
70
increases with depth, with a peak at ~30 mbgs. Faults are abundant with several
71
brecciated zones (10.00–10.86 mbgs, 11.50–11.84 mbgs, and 15.35–15.52 mbgs), which
72
are in the shale-dominated intervals of dense phyllitic cleavage. Within this interval, LN
73
resistivity increases from 274 Ω m to 579 Ω m, and SN resistivity increases from 180 Ω
74
m to 600 Ω m. Below 30 mbgs and toward the fault core, the structures are more
75
disturbed and cataclastic fragmentation of sandstone is more significant, characterized
76
by a decrease in resistivity (LN: 362 Ω m, SN: 282 Ω m). At 39–40 mbgs (just above
77
the fault core), the resistivity decreases to its lowest value (LN: 235 Ω m, SN: 140 Ω m),
78
and at 40.0–41.3 mbgs (just above the fault core or the upper fault core), the values
79
(LN: 297–315 Ω m, SN: ~233 Ω m) become stable. Within the damage zone, porosity
80
(~3.5%) begins to increase significantly at 39.5 mbgs.
81
82
66.7–85.7 mbgs: Footwall fracture zone at 70.9–83.9 mbgs
83
At 76 mbgs, high porosity up to 10.0–14.3%, P-wave velocities as lowt 76 mbgs,
84
high porosity up to 10.0–14.3%, P-wave velocities as low as 3.4 km s-1, and low
85
resistivity (LN: 232 Ω m, SN: 124 Ω m) at 78 mbgs. The brecciated zones have a low
86
density of described structures due to poor core recovery, but above and below the
87
brecciated zones, faults, fractures, and mineral veins are abundant at 73–75 mbgs and
88
80–81 mbgs. Above the fracture zone (64–71 mbgs), foliated cataclasite with elongated
89
sandstone and tuffacious, siliceous blocks, boudinage, and fragments are present. Faults
90
increase toward the fault zone with cataclastic fragmentation along the faults. Sharp and
91
high-angle faults with carbonate veins are characteristic, especially at ~64 mbgs. At
92
71–75 mbgs, cohesive faults increase within the foliated cataclasites and are often filled
93
by 0.3–1.0-cm-thick mineral veins of quartz and calcite. At ~71 mbgs, resistivity
94
fluctuates and reaches a local peak (LN: 365 Ω m, SN: 338 Ω m), then rises once again
95
(LN: 299 Ω m, SN: 244 Ω m) at ~80 mbgs. Within the fracture zone, porosity begins to
96
increase significantly with a decrease in resistivity from 7–8% at 73.5 mbgs (7.8%, SN:
97
271 Ω m) and 79.1 mbgs (8.3%, SN: 203 Ω m). The values for resistivity, P-wave
98
velocity, density, and porosity in the surrounding damage zones (~240 Ω m, ~4.3 km s-1,
99
~2.71 g cm-3, ~7.8%), the brecciated zones (~166 Ω m, ~3.9 km s-1, ~2.65 g cm-3,
100
~10.9%), and the intact zones (~232 Ω m, ~4.3 km s-1, ~2.71 g cm-3, ~7.6%) are shown
101
in Fig. 8 in the main text.
102
103
104.8–125.8 mbgs: Footwall fracture zone at 107.2-119.9 mbgs
104
Structures are highly brecciated at 112–115 mbgs, and though the brecciated zones
105
have a low density of described structures due to poor core recovery, the number
106
distribution of cohesive structures is high at 95–104 mbgs and 115–124 mbgs above and
107
below the brecciated zone. Disturbed foliation with fragmentation and elongated
108
sandstone blocks are intercalated between the fault breccias. At 115–116 mbgs,
109
sandstone-rich foliated cataclasites are characterized by frequent faults with cataclasites
110
of fine-grained clasts, bordering densely foliated zones. At 119–121 mbgs,
111
random-fabric cataclasites and blocks of tuffacious/siliceous sandstone become
112
abundant below the fault at ~121 mbgs. Below this fault, foliated cataclasites with thick
113
blocks or thin siliceous/tuffacious sandstone layers are characteristic at 122–123 mbgs.
114
At 123–126 mbgs, zones of well-fragmented and elongated cataclasites with disturbed
115
foliations are frequently cut by faults. At 112–113 mbgs, LN and SN resistivities
116
decrease (LN: ~187 Ω m, SN: ~68 Ω m), but rise again (LN: 398 Ω m, SN: 328 Ω m) at
117
119.5 mbgs. The temperature gradient in this fracture zone is ~27.5°C km-1, which is
118
higher than the gradients of all other units in the footwall. Above the fracture zone, the
119
resistivity and S-wave velocity increase, with a peak (LN: 343.6 Ω m, SN: 284.6 Ω m,
120
2.01 km s-1) at 102–107.5 mbgs. Within the fracture zone, porosity begins to increase
121
significantly with a decrease in resistivity from ~7–9% (~6.9%, SN: 169 Ω m) near
122
111.6 mbgs and (~9%, SN: 154 Ω m) near 115.5 mbgs. The values for resistivity,
123
P-wave velocity, density, and porosity in the surrounding damage zones (~251 Ω m,
124
~4.2 km s-1, ~2.70 g cm-3, ~7.6%), the brecciated zone (~79 Ω m, ~2.3 km s-1, ~2.08 g
125
cm-3, ~30.9%), and the intact zone (~226 Ω m, ~4.2 km s-1, ~2.7 g cm-3, ~7.6%) are
126
shown in Fig. 8 in the main text. The fracture zone at 107.2–119.9 mbgs contains the
127
most intensive brecciated zone, which may be due to the lithologic boundary where
128
abundant tuffacious and siliceous siltstone and sandstone appear and are intercalated
129
within the foliated cataclasite. The orientation of the structures also changes quite
130
markedly across the fracture zone (107.2–119.9 mbgs). The approximate curve of the
131
cross-plot between porosity and resistivity is also different below this lithologic
132
boundary (see Fig. 7 in the main text).
133
134
134.1–179.7 mbgs: Footwall fracture zone at 144.8–174 mbgs
135
Another fracture zone is found at 154.7–159.4 mbgs, which includes a brecciated
136
zone at 157–159 mbgs. The LN and SN resistivities exhibit low values (LN: 258 Ω m,
137
SN: 145 Ω m). The highly brecciated zones have a low density of described structures
138
due to poor core recovery, but note that above and below the breccias, structures are
139
concentrated, especially at 142–143 mbgs, 154–157 mbgs, and 162–170 mbgs. At
140
134–144 mbgs, sandstone blocks become relatively larger and more abundant within the
141
foliated cataclasites toward the fracture zone, with a higher occurrence of faults and
142
other structures. These foliated cataclasites continue at 144–155 mbgs, but with more
143
abundant and finer tuffacious and siliceous sandstone. Near the brecciated zone,
144
high-angle faults and mineral veins are frequent, and sandstone blocks and boudinages
145
are intercalated between the breccias. Below the breccias, foliation is disturbed, and
146
mud-rich zones increase at 160–164 mbgs. Several brecciated zones are found with
147
increasing numbers of sandstone blocks within the cataclasites at 164–174 mbgs, and
148
tuffacious, siliceous sandstone and siltstone increase from 174–180 mbgs. Below the
149
fracture zone at 152–156 mbgs, peaks are observed in LN and SN resistivities (~495 Ω
150
m) at ~170 mbgs, S-wave velocity (2.1 km s-1) at ~174.7 mbgs, and P-wave velocity
151
(4.69 km s-1) at ~171.4 mbgs. Within the fracture zone, porosity begins to increase
152
significantly with a decrease in resistivity at 153.2 mbgs (6.9%, SN: 365 Ω m) and
153
160.2 mbgs (6.6%, SN: 331 Ω m). The values for resistivity, P-wave velocity, density,
154
and porosity in the surrounding damage zones (~330 Ω m, ~4.4 km s-1, ~2.71 g cm-3,
155
~7.2%), the brecciated zone (~168 Ω m, ~4.0 km s-1, ~2.65 g cm-3, ~10.9%), and the
156
intact zone (~280 Ω m, ~4.3 km s-1, ~2.72 g cm-3, ~7.2%) are shown in Fig. 8 in the
157
main text.
158
159
180.9–198.4 mbgs: Footwall fracture zone at 184.6–196.6 mbgs
160
At ~188 mbgs, the number distribution of fractures, faults, and mineral veins
161
increases as the foliation becomes disturbed, and cohesive faults are abundant within the
162
foliated cataclasites consisting of sandstone clasts. Tuffacious sandstone is abundant,
163
especially at 182–183 mbgs, but the occurrence of coarser sandstone increases with
164
more frequent faults and veins. A highly brecciated zone is present at 197–199 mbgs,
165
where the number distribution of described structures is lower. Foliated cataclasite with
166
fragmented and elongated sandstone is characteristic, and structures including faults are
167
abundant near the brecciated zone. At 188–189 mbgs, the fracture zone is characterized
168
by a slight increase in neutron porosity up to 9.2%, a peak in S-wave velocity (1.95 km
169
s-1) at 194.9 mbgs, a low in SN resistivity (199.4 Ω m) at 188.5 m, followed br the
170
brecciated zone. At 188–189 mbgs, the fracture zone is characterized by a slight
171
increase in neutron porosity up to 9.2%, a peak in S-wave velocity (1.95 km s-1) at r the
172
brecciated zone. At 188–189 mbgs, the fracture zone is characterized by a slight
173
increase in neutron porosity up to 9.2%, a peak in S-wave velocity (1.95 km s-1) at
174
194.9 mbgs, a low in SN resistivity (199.4 Ω m) at 188.5 m, followed by an increase to
175
299.6 Ω m at 194.5 mbgs. In subunit 4-1 (180–210 mbgs), the spontaneous potential
176
increases sharply with a sharp linear slope of ~1090 V km-1, which is unique for this
177
subunit. Within the fracture zone, porosity begins to increase significantly with a
178
decrease in resistivity at 187.5 m (~7.1%, SN: 229 Ω m) and 189.9 m (6.5%, SN: 234 Ω
179
m). The values for resistivity, P-wave velocity, density, and porosity in the surrounding
180
damage zones (~270 Ω m, ~4.5 km s-1, ~2.73 g cm-3, ~6.7%), the brecciated zone (~205
181
Ω m, ~4.1 km s-1, ~2.69 g cm-3, ~8.4%), and the intact zone (~255 Ω m, ~4.4 km s-1,
182
~2.72 g cm-3, ~7.1%) are shown in Fig. 8 in the main text.
183
184
199.5–235.9 mbgs: Footwall fracture zone at 201.8–221.2 mbgs
185
Tuff and tuffacious/siliceous sandstone layers are abundant at 204–206 mbgs, and
186
below 207–225 mbgs, the number of faults, fractures, and mineral veins increases with
187
peaks at ~215 mbgs and ~220 mbgs. Within this zone, there is a highly brecciated
188
interval at 210-212 mbgs, characterized by a peak in neutron porosity (14.7%) and lows
189
in LN and SN resistivity (287 Ω m and 182 Ω m, respectively). Brecciated areas are
190
occasionally seen at 214-217 mbgs and 219-220 mbgs with deformed cataclasites
191
accompanied by abundant sandstone and siliceous fragments. At 221–222 mbgs,
192
tuffacious, siliceous sandstone is characteristic, followed by fragmented and boudinaged
193
sandstone. At 220–230 mbgs, faults and mineral veins are abundant, and LN and SN
194
resistivities increase to 468 Ω m and 463 Ω m, respectively. Foliated cataclasites with
195
elongated sandstone or silt/tuffacious blocks occasionally accompany boudinage and
196
disturbed foliation. Within the fracture zone, porosity begins to increase significantly
197
with a decrease in resistivity at 209.8 m (~6.1%, SN: 314 Ω m) and 212.2 m (6.9%, SN:
198
216 Ω m). The values for resistivity, P-wave velocity, density, and porosity in the
199
surrounding damage zones (~281 Ω m, ~4.3 km s-1, ~2.72 g cm-3, ~7.0%), the
200
brecciated zone (~209 Ω m, ~3.6 km s-1, ~2.59 g cm-3, ~9.4%), and the intact zone
201
(~282 Ω m, ~4.6 km s-1, ~2.71 g cm-3, ~6.4%) are shown in Fig. 8 in the main text.
202
203
215.2–252 mbgs: Footwall fracture zone at 225.6–247.3 mbgs
204
At 240–255 mbgs, cataclastic fragmentation of sandstone clasts is abundant within
205
the foliated cataclasite. Faults, fractures, and mineral veins increase at 239–242 mbgs,
206
followed by a brecciated zone at 242–243 mbgs. At 240–255 mbgs, foliation is
207
disturbed with elongated, boudinaged structures, and cataclastic fragmentation of
208
sandstone clasts is abundant within the foliated cataclasites. At ~250 mbgs, high-angle
209
faults border high-angle and low-angle foliations. The number distribution of structures
210
increases at 252–253 mbgs. At 251–254 mbgs, a low-angle disturbed foliated zone with
211
abundant elongated sandstone clasts and fragmentation can be seen. At 240–242 mbgs,
212
neutron porosity rises to 13.5%, with low LN and SN resistivities (170 Ω m and 90 Ω m,
213
respectively). P-wave velocity, S-wave velocity, and LN and SN resistivities decrease
214
towards the fracture zone at 240–242 mbgs, but increase slightly at 247 mbgs (P-wave:
215
4.7 km s-1, S-wave: 2.0 km s-1, LN: 226 Ω m, SN: 211 Ω m). Within the fracture zone,
216
porosity begins to increase significantly with a decrease in resistivity from ~6.8%, SN:
217
175 Ω m and 8%, SN: 128 Ω m at 240.6 m. The values for resistivity, P-wave velocity,
218
density, and porosity in the surrounding damage zones (~228 Ω m, ~4.5 km s-1, ~2.73 g
219
cm-3, ~6.6%), the brecciated zone (~101 Ω m, ~3.6 km s-1, ~2.65 g cm-3, ~10.1%), and
220
the intact zones (~234 Ω m, ~4.6 km s-1, ~2.73 g cm-3, ~6.4%) are shown in Fig. 8 in the
221
main text.
222