1 00:00:05,200 --> 00:00:08,100 This is geology B with Oliver's trampled. 2 00:00:10,000 --> 00:00:13,200 We all know about the massive earthquake that occurred in 3 00:00:13,200 --> 00:00:16,200 March 2011 off the east coast of Japan. 4 00:00:17,000 --> 00:00:21,000 It had a registered magnitude greater than 9.0 making it the 5 00:00:21,000 --> 00:00:25,000 most powerful earthquake ever recorded in Japan and the fourth 6 00:00:25,000 --> 00:00:27,000 most powerful earthquake in the world. 7 00:00:27,300 --> 00:00:31,700 Since modern record keeping began in 1900, it triggered its 8 00:00:31,700 --> 00:00:35,800 tsunami with waves of up to 40 meters that swept ashore. 9 00:00:36,100 --> 00:00:39,600 Killing nearly 20,000 people and causing the Fukushima. 10 00:00:39,600 --> 00:00:42,900 And Nuclear disaster, the earthquake occurred. 11 00:00:42,900 --> 00:00:45,900 Where the Pacific Plate is subducting under the plate that 12 00:00:45,900 --> 00:00:48,500 Lies Beneath the Japanese island of Honshu. 13 00:00:49,400 --> 00:00:52,500 During the earthquake, the Eastern edge of the overriding 14 00:00:52,500 --> 00:00:55,400 plate. Jumped over 50 meters to the 15 00:00:55,400 --> 00:00:58,800 east over a length of about 500 kilometers. 16 00:00:59,900 --> 00:01:03,300 It was this unexpectedly large slip, that displaced enough 17 00:01:03,300 --> 00:01:06,300 water to set the giant tsunami in motion. 18 00:01:07,400 --> 00:01:10,800 Why was the slip so large? Was it something to do with the 19 00:01:10,800 --> 00:01:14,300 nature of the fault Zone on the boundary between the two plates 20 00:01:14,500 --> 00:01:19,500 as it nears, the Japan trench Patrick Fulton led a team that 21 00:01:19,500 --> 00:01:22,700 probe, the tohoku. Okay, earthquake fault, which is 22 00:01:22,700 --> 00:01:26,400 the Fault along which the main rupture occurred, his team, 23 00:01:26,400 --> 00:01:29,900 overcame enormous engineering challenges to install what he 24 00:01:29,900 --> 00:01:32,300 calls a temperature, Observatory? 25 00:01:32,400 --> 00:01:36,200 Right through the fault Zone, the observations revealed the 26 00:01:36,200 --> 00:01:38,800 temperature. I peek across the fault which in 27 00:01:38,800 --> 00:01:42,400 turn enabled him to estimate the coefficient of dynamic friction 28 00:01:42,400 --> 00:01:46,600 at the plate boundary and it turned out to be extremely low. 29 00:01:47,900 --> 00:01:51,000 Patrick Fulton is an assistant professor in the department of 30 00:01:51,000 --> 00:01:54,000 Earth and atmospheric sciences at Cornell University. 31 00:01:55,000 --> 00:01:57,500 Patrick Fulton, welcome to geology B. 32 00:01:57,800 --> 00:01:59,300 Thank you. And thank you for having me. 33 00:01:59,700 --> 00:02:02,000 Can we start with a bit of tectonic context for the 34 00:02:02,000 --> 00:02:04,500 subduction zone off? The east coast of Japan? 35 00:02:05,200 --> 00:02:08,900 Does Japan's sit on its own plate, or is it on the Eastern 36 00:02:08,900 --> 00:02:12,000 edge of a Eurasian plate? Japan is actually in a 37 00:02:12,000 --> 00:02:14,100 Confluence of a number of different plates. 38 00:02:14,500 --> 00:02:17,800 The northern part of Japan where this earthquake happened 39 00:02:18,200 --> 00:02:21,000 actually sits on the North American Plate. 40 00:02:21,500 --> 00:02:24,800 And some people will see that the plate goes all the way 41 00:02:24,800 --> 00:02:28,900 around, from the United States up through Canada, around from 42 00:02:28,900 --> 00:02:31,100 Alaska. And reaches down into the 43 00:02:31,100 --> 00:02:34,000 northern part of Japan. Some people call that little 44 00:02:34,000 --> 00:02:35,700 part of it. In Japan. 45 00:02:35,700 --> 00:02:39,000 The acoustic plate kind of a micro plate and then when it 46 00:02:39,000 --> 00:02:43,000 hits Mount Fuji, south of Tokyo, that's where it intersects with 47 00:02:43,000 --> 00:02:46,600 the Eurasian plate and how fast of the plates, converging in the 48 00:02:46,600 --> 00:02:49,700 region, where the earthquake occurred somewhere around eight 49 00:02:49,700 --> 00:02:52,300 centimeters per year. I think that must be one of the 50 00:02:52,300 --> 00:02:56,000 faster convergence speeds of plates around the planet. 51 00:02:56,300 --> 00:02:58,700 That's right, it's fast. And some of it's because the 52 00:02:58,700 --> 00:03:03,000 rocks are old and cold roughly, 130 million years and that old 53 00:03:03,000 --> 00:03:06,500 cold rocks are fairly tense. And it's trying to sink down 54 00:03:06,500 --> 00:03:09,500 into these the unisphere. So slab pull is especially 55 00:03:09,500 --> 00:03:13,600 effective for that reason. So what exactly happens when an 56 00:03:13,600 --> 00:03:18,000 earthquake occurs along a subduction zone, so when the 57 00:03:18,000 --> 00:03:22,800 down going oceanic plates are pulled down from their own 58 00:03:22,800 --> 00:03:25,500 weight. Into the steam is for they get 59 00:03:25,500 --> 00:03:29,900 stuck to the overlying plate and they build up elastic energy and 60 00:03:29,900 --> 00:03:33,100 every once in a while, they relieve that elastic energy, and 61 00:03:33,100 --> 00:03:37,000 that's what we observe is. And how deep down does the 62 00:03:37,200 --> 00:03:39,500 earthquake normally start? Does that stress? 63 00:03:39,500 --> 00:03:42,600 Get released. So in subduction zones, about 30 64 00:03:42,600 --> 00:03:45,700 kilometers depth is where we see a lot of earthquake starts. 65 00:03:45,700 --> 00:03:47,700 That's fine. The middle of the seismic Janek 66 00:03:47,700 --> 00:03:50,600 Zone on was the tohoku earthquake at that depth. 67 00:03:50,600 --> 00:03:53,100 It was it was about 30 kilometers deep. 68 00:03:53,400 --> 00:03:57,000 As I said in the introduction there was a 50 meter slip 69 00:03:57,100 --> 00:04:01,800 recorded at the surface and that was unexpectedly large. 70 00:04:02,100 --> 00:04:05,000 What would one normally expect for such an earthquake and and 71 00:04:05,000 --> 00:04:08,100 what can we infer from this enormously large slip? 72 00:04:08,600 --> 00:04:12,500 Yeah this was a very interesting and confusing earthquake. 73 00:04:12,600 --> 00:04:16,300 Generally we thought that most of the slip would happen where 74 00:04:16,300 --> 00:04:19,399 they start. So at 30 kilometers depth you 75 00:04:19,399 --> 00:04:23,500 mapped out on a map where the Contours of sip were you would 76 00:04:23,500 --> 00:04:27,000 see maybe at the beginning of the earthquake you had somewhere 77 00:04:27,200 --> 00:04:30,900 around 5 or 10 meters or sip and then it would Decay out as the 78 00:04:30,900 --> 00:04:34,800 rupture try to expand it would essentially hit the brakes. 79 00:04:35,000 --> 00:04:36,900 The surrounding rocks and died out. 80 00:04:37,100 --> 00:04:40,000 That was not the case in this earthquake. 81 00:04:40,200 --> 00:04:44,100 And this earthquake, most of the slip actually happened at the 82 00:04:44,100 --> 00:04:48,200 very shallowest parts. So where it was roughly 30 83 00:04:48,200 --> 00:04:51,700 meters, a huge amount of slip down where it started at the 84 00:04:51,700 --> 00:04:54,700 shallowest part. At the sea floor, it jumped as 85 00:04:54,700 --> 00:04:59,300 much as 50, 60 meters. That reminds me of the podcast I 86 00:04:59,308 --> 00:05:02,700 did with Roger bilham in which he talked about the earthquake 87 00:05:02,700 --> 00:05:07,800 in 2015, in goloka in the Paul. And in that case, the rupture 88 00:05:08,200 --> 00:05:11,600 did not propagate to the surface, the brakes, if you like 89 00:05:11,600 --> 00:05:15,900 were effective, thus, the stress was built up further along the 90 00:05:15,900 --> 00:05:18,900 fault, and everyone's expecting another big Quake sometime soon. 91 00:05:18,900 --> 00:05:22,500 They're so why do we think this one was so different? 92 00:05:22,900 --> 00:05:25,500 This is really kind of the big question and kind of motivated, 93 00:05:25,500 --> 00:05:29,000 some of our work on land. Like in the Corker earthquake, 94 00:05:29,000 --> 00:05:32,800 the rocks are strong and they are brittle and they break, but 95 00:05:32,800 --> 00:05:34,800 sometimes they don't go all the way to the surface. 96 00:05:34,900 --> 00:05:39,900 It's because they intersect areas where it's a bunch of soft 97 00:05:39,900 --> 00:05:43,100 sediments where the rupture kind of will dissipate into different 98 00:05:43,100 --> 00:05:45,900 areas or may deform more plastically. 99 00:05:45,900 --> 00:05:49,100 Some of the rocks and sediments above it here. 100 00:05:49,100 --> 00:05:52,100 We think in subduction zones, the rocks are often softer, 101 00:05:52,100 --> 00:05:55,100 especially when they get to the shadow parts that we almost 102 00:05:55,100 --> 00:05:59,600 never have really seen a surface break like this or at least of 103 00:05:59,600 --> 00:06:02,400 this magnitude. And so that led to a lot of 104 00:06:02,400 --> 00:06:07,300 questions about why the shallow part Slip so much was it because 105 00:06:07,300 --> 00:06:10,100 the shallow part was really strong and built up. 106 00:06:10,100 --> 00:06:13,500 A lot of elastic energy or was it really weak? 107 00:06:13,500 --> 00:06:16,000 And the rupture came through. And it just essentially 108 00:06:16,200 --> 00:06:18,800 hydroplaned didn't have any brakes on the show. 109 00:06:18,800 --> 00:06:22,700 Part that actually takes us to your work which was indeed to 110 00:06:23,000 --> 00:06:25,900 probe the fault Zone to see if you could gather data that would 111 00:06:25,900 --> 00:06:28,900 help us figure out what the friction walls along the 112 00:06:28,900 --> 00:06:32,000 surface. So how did you go about this one 113 00:06:32,000 --> 00:06:36,400 way that we can figure out how much She resistance or how much 114 00:06:36,400 --> 00:06:39,900 brakes were on the float when it slipped is by measuring, how 115 00:06:39,900 --> 00:06:42,700 much heat is generated during the earthquake. 116 00:06:42,700 --> 00:06:46,000 So, just like when you rub your hands together, it generates 117 00:06:46,000 --> 00:06:48,500 heat. And it's a function of how much 118 00:06:48,500 --> 00:06:51,700 you move them pass each other to displacement, but also how much 119 00:06:51,700 --> 00:06:55,500 force and friction is between your hands as you're sharing it. 120 00:06:55,500 --> 00:06:59,700 So if we could measure how much heat was generated on the fault, 121 00:06:59,700 --> 00:07:03,300 we could figure out this big question and to do that meant 122 00:07:03,300 --> 00:07:07,100 that we would have to drill down at depth where the earthquake 123 00:07:07,100 --> 00:07:11,700 happened and measured any temperature anomaly measure the 124 00:07:11,700 --> 00:07:15,700 excess heat across the fault after an earthquake, which is 125 00:07:15,700 --> 00:07:20,300 really challenging because that heat could generate really hot 126 00:07:20,300 --> 00:07:22,500 temperatures. May be up to 1000 degrees on the 127 00:07:22,500 --> 00:07:27,000 fault in a very thin Zone. Maybe it's CM thick during the 128 00:07:27,000 --> 00:07:30,100 earthquake, but then it diffuses into the surroundings. 129 00:07:30,500 --> 00:07:33,700 And so, we figured that we would have to be there within about a 130 00:07:33,707 --> 00:07:36,700 year or two. Afterwards to be able to do 131 00:07:36,700 --> 00:07:40,200 that. And this earthquake with a lot 132 00:07:40,200 --> 00:07:44,500 of slip will give it a very big signature, and because so much 133 00:07:44,500 --> 00:07:45,900 of that soup was that shallow depth? 134 00:07:45,900 --> 00:07:49,300 It meant that perhaps, we could actually drill into it and put 135 00:07:49,600 --> 00:07:52,600 sensors down there, to actually measure the temperature anomaly 136 00:07:52,600 --> 00:07:55,600 across the fall. How's anyone successfully 137 00:07:55,600 --> 00:07:59,700 measured temperature normally across the fault during all 138 00:07:59,700 --> 00:08:02,500 right. After an earthquake, not quite 139 00:08:02,500 --> 00:08:05,800 there has been a few attempts particularly After the chi chi 140 00:08:05,800 --> 00:08:08,800 earthquake in Taiwan large earthquake. 141 00:08:08,900 --> 00:08:12,600 But there it took many years before they could drill across 142 00:08:12,600 --> 00:08:16,100 the fault and I could only get one profile of temperature 143 00:08:16,100 --> 00:08:19,000 before the hole collapsed. So if you see something across 144 00:08:19,000 --> 00:08:21,400 the fault, you don't know whether that little temperature 145 00:08:21,400 --> 00:08:26,200 blip is really due to frictional heat does it diffuse over time 146 00:08:26,200 --> 00:08:29,600 as you would expect, or is it due to water flowing through a 147 00:08:29,600 --> 00:08:32,799 fracture? Or is it maybe just due to 148 00:08:32,799 --> 00:08:34,700 differences in rock type as you go? 149 00:08:34,799 --> 00:08:37,200 So we learned a lot from that experience. 150 00:08:37,200 --> 00:08:40,600 We learned that you really need to monitor the temperature over 151 00:08:40,600 --> 00:08:43,000 time. And you really need to get a 152 00:08:43,000 --> 00:08:45,200 good understanding of the Rocks themselves. 153 00:08:45,200 --> 00:08:47,700 Take core samples, and rock samples. 154 00:08:47,700 --> 00:08:51,500 There's also been a long-term study of trying to look for 155 00:08:51,500 --> 00:08:54,900 frictional, heat, not from a single earthquake, but over 156 00:08:54,900 --> 00:08:58,000 millions of years of shearing, along the San Andreas fault. 157 00:08:58,000 --> 00:09:01,500 And there you would expect a large increase over many 158 00:09:01,500 --> 00:09:06,100 kilometers of heat, coming out around the The fault Zone and 159 00:09:06,100 --> 00:09:09,100 there it was not observed, despite a lot of attempts, 160 00:09:09,100 --> 00:09:12,800 including some of my own during my PhD, which has led us to 161 00:09:12,800 --> 00:09:16,600 think that maybe rocks, aren't as strong as we think they are 162 00:09:16,600 --> 00:09:18,700 at least how they behave in the lab. 163 00:09:18,900 --> 00:09:21,200 Maybe there is something different during an earthquake 164 00:09:21,200 --> 00:09:24,200 or something different about mature plate. 165 00:09:24,200 --> 00:09:26,400 Boundary fault zones. That makes it all the more 166 00:09:26,400 --> 00:09:30,400 interesting that you actually were successful in determining a 167 00:09:30,400 --> 00:09:33,200 temperature anomaly. So, as I mentioned earlier, you 168 00:09:33,200 --> 00:09:35,800 went about this bye. Installing what you call a 169 00:09:35,808 --> 00:09:40,600 temperature Observatory, tell us about what that is and how you 170 00:09:40,600 --> 00:09:41,700 did that. Exactly. 171 00:09:41,900 --> 00:09:45,600 So one of the big challenges with this project is that 172 00:09:45,900 --> 00:09:48,600 perhaps we could drill Across The Fault in a place where it 173 00:09:48,600 --> 00:09:51,800 had a lot of slip and perhaps measure the temperature across 174 00:09:51,800 --> 00:09:54,800 it. But to do that, we were just at 175 00:09:54,800 --> 00:09:58,100 the limits of where technologically, we could 176 00:09:58,100 --> 00:10:01,100 actually drill. We're working in a water depth 177 00:10:01,100 --> 00:10:06,400 of 7 km and then the fault Zone. The Beneath that was another 178 00:10:06,400 --> 00:10:09,000 eight hundred and twenty meters below the sea floor. 179 00:10:09,000 --> 00:10:14,800 So, no one had ever drilled that deep within the ocean before let 180 00:10:14,800 --> 00:10:17,400 alone trying to put instruments under there. 181 00:10:17,400 --> 00:10:21,500 So to do that, we first had to characterize the hole, we 182 00:10:21,500 --> 00:10:24,400 drilled and found out exactly where the fault was first. 183 00:10:24,400 --> 00:10:27,900 We took core samples out. We did you physical lugging but 184 00:10:27,900 --> 00:10:31,300 now we drilled underneath the sea floor and we put a 185 00:10:31,300 --> 00:10:34,600 protective casing at the very shallow part just so that we 186 00:10:34,800 --> 00:10:37,600 Reenter the whole, then we built the observatories. 187 00:10:37,600 --> 00:10:42,700 So we built a 855 M, long steel pipe inside of it. 188 00:10:42,800 --> 00:10:45,400 We built our temperature Observatory, which was 189 00:10:45,400 --> 00:10:48,200 essentially a static climbing rope, or a rope. 190 00:10:48,200 --> 00:10:51,800 That does not stretch much where we had woven in temperature 191 00:10:51,800 --> 00:10:56,100 sensors, each of them with their own Data Logger and each of them 192 00:10:56,100 --> 00:10:59,800 encased in titanium. So all the electronics would not 193 00:11:00,000 --> 00:11:02,800 implode, do the huge pressures at those steps? 194 00:11:03,300 --> 00:11:05,700 And then the temperature sensors themselves, Elves have an 195 00:11:05,700 --> 00:11:09,600 accuracy of a thousandth of a degree celsius. 196 00:11:09,800 --> 00:11:13,200 We want to be able to see just the smallest little details in 197 00:11:13,200 --> 00:11:16,400 the smallest little increases of what the temperature is. 198 00:11:16,800 --> 00:11:20,100 So we then lower that down to the sea floor, and then 199 00:11:20,100 --> 00:11:23,800 re-entered the hole and install that bit of casing, all the way 200 00:11:23,800 --> 00:11:26,900 down. And then left it there, and went 201 00:11:26,900 --> 00:11:30,300 away for several months and then came back to collect the data, 202 00:11:30,300 --> 00:11:34,000 those temperature sensors, 55 of them, at different depths were 203 00:11:34,000 --> 00:11:37,800 measuring the You're at those steps over time and once the 204 00:11:37,800 --> 00:11:41,000 whole rig equilibrated, we could see if we saw a temperature 205 00:11:41,000 --> 00:11:43,800 anomaly Crossville just before we get to your results. 206 00:11:43,800 --> 00:11:48,900 I'm completely boggled by the idea that you could return to a 207 00:11:48,900 --> 00:11:51,800 hole that I don't know what is it about a meter across or 208 00:11:51,800 --> 00:11:56,000 something at the depth of 7 kilometers of water from a ship 209 00:11:56,000 --> 00:11:58,500 that's like floating on the waves above. 210 00:11:58,500 --> 00:12:02,900 How on Earth is that possible? Well it's just barely possible. 211 00:12:03,100 --> 00:12:09,100 So essentially we have 850 M long Observatory of steel pipe 212 00:12:09,300 --> 00:12:13,800 connected to another seven kilometers of drill pipe that 213 00:12:13,800 --> 00:12:16,400 bring it down to the sea floor and we're trying to re-enter 214 00:12:16,400 --> 00:12:19,900 that into the hole. There's no motor on the bottom 215 00:12:19,900 --> 00:12:22,600 of this. All we have is the ship, which 216 00:12:22,600 --> 00:12:26,600 can use Dynamic positioning to stay in one position on the 217 00:12:26,600 --> 00:12:30,400 surface of the water. But down below, we have a TV 218 00:12:30,400 --> 00:12:34,200 camera that can see only a few metres ahead of it at the 219 00:12:34,200 --> 00:12:35,900 bottom. Of the whole assembly. 220 00:12:36,300 --> 00:12:39,300 And so with the light on it we could see where we are. 221 00:12:39,400 --> 00:12:42,000 We tell the captain. Well we think it might be over 222 00:12:42,000 --> 00:12:46,500 to the north and he/she will move the ship over there. 223 00:12:46,600 --> 00:12:49,300 And then the whole thing, all that steel pipe below us it's 224 00:12:49,300 --> 00:12:50,700 like a wet. Spaghetti noodle. 225 00:12:51,000 --> 00:12:55,200 It's just hanging there in it. Slowly starts to wiggle over in 226 00:12:55,200 --> 00:12:59,300 that direction in response. And we did that for many hours 227 00:12:59,300 --> 00:13:03,100 until we see the observatory or the whole rather on the seafloor 228 00:13:03,300 --> 00:13:06,500 and little bit of Tubing that sits above the sea floor. 229 00:13:06,600 --> 00:13:08,700 And once we're above it, someone says now. 230 00:13:08,700 --> 00:13:12,500 Now now and then the Drillers drop everything into it. 231 00:13:13,000 --> 00:13:14,300 And luckily, it was a hole-in-one. 232 00:13:14,300 --> 00:13:17,500 We got straight in and then continue to lower it down. 233 00:13:17,800 --> 00:13:19,900 That's up to incredible. I want to off. 234 00:13:19,900 --> 00:13:23,200 So how you selected the precise location for the whole because 235 00:13:23,200 --> 00:13:27,800 it seems like you are 850 meters of Observatory that you could 236 00:13:27,800 --> 00:13:32,300 feed in below the level of the sea floor, the earthquake itself 237 00:13:32,300 --> 00:13:35,700 was at 30 kilometers depth. So, obviously, The fault zone of 238 00:13:35,700 --> 00:13:38,200 the fault plane makes it all the way up. 239 00:13:38,200 --> 00:13:40,300 Gradually to the surface, at some point. 240 00:13:40,300 --> 00:13:43,800 So how did you pick a point? Where the fault plane was at it 241 00:13:43,800 --> 00:13:48,100 about it said, 820 M down. We needed to find a place where 242 00:13:48,100 --> 00:13:51,600 we could drill across the fault at somewhere less than a 243 00:13:51,600 --> 00:13:54,600 kilometer deep. If it's too shallow, maybe we 244 00:13:54,600 --> 00:13:57,200 start to get to less weight acting on things. 245 00:13:57,200 --> 00:14:00,700 And so, we wanted to find very clear position of the fault. 246 00:14:00,700 --> 00:14:03,500 Less than a kilometer deep underneath the ground. 247 00:14:04,200 --> 00:14:08,000 We also Want to find a place where we knew the amount of sip 248 00:14:08,000 --> 00:14:09,900 fairly well and that it was large. 249 00:14:10,100 --> 00:14:13,800 Here is a position where there was clear evidence that it was 250 00:14:14,000 --> 00:14:17,500 roughly 50 meters of slip. The other kind of constraining 251 00:14:17,500 --> 00:14:22,000 thing was we needed to find a place where the water depth was 252 00:14:22,000 --> 00:14:25,900 less than 7 km. And the reason for that is we're 253 00:14:25,900 --> 00:14:28,400 going to put our temperature sensors down there and they're 254 00:14:28,400 --> 00:14:31,000 going to record but we need to get them back at some point in 255 00:14:31,000 --> 00:14:33,800 time. There is only one remotely 256 00:14:33,800 --> 00:14:38,400 operated Essentially an unmanned submarine that could go to those 257 00:14:38,400 --> 00:14:43,300 depths and pull the sensors out, get our data back out and its 258 00:14:43,300 --> 00:14:46,400 maximum operating depth with seven kilometers. 259 00:14:46,700 --> 00:14:51,100 So inside this pipe and you have your senses, I think you said 55 260 00:14:51,100 --> 00:14:54,000 of them. How far apart are they down 261 00:14:54,000 --> 00:14:58,000 inside that bowl? We want to make sure that we can 262 00:14:58,000 --> 00:15:01,300 really see the profile of an anomaly. 263 00:15:01,600 --> 00:15:04,500 And so we made our sensors one and a half. 264 00:15:04,700 --> 00:15:07,900 Meters apart from each other anticipating that the full 265 00:15:07,900 --> 00:15:11,500 anomaly, maybe over some tens of meters wide. 266 00:15:11,500 --> 00:15:14,900 And so most of them are about one and a half meters apart and 267 00:15:14,900 --> 00:15:18,000 then X shallower depths we have some other ones that have 268 00:15:18,100 --> 00:15:21,000 further spacing across that allow us to get some information 269 00:15:21,000 --> 00:15:24,200 about the background temperature gradient through the Earth. 270 00:15:24,400 --> 00:15:28,300 So you then seal the hole and left these senses to their own 271 00:15:28,300 --> 00:15:32,100 devices for about nine months. And then you return. 272 00:15:32,100 --> 00:15:34,500 So how did you pick that time interval and what were you? 273 00:15:34,700 --> 00:15:38,100 During that time with the senses, when you first drill the 274 00:15:38,100 --> 00:15:41,900 hole, you get all those broken up pieces of rock, out of the 275 00:15:41,900 --> 00:15:46,300 hole by circulating, cold, ocean water, so that drilling process 276 00:15:46,300 --> 00:15:49,700 actually cooled off the whole right around the edge of the 277 00:15:49,700 --> 00:15:53,200 bore hole for a while and it would take some time usually a 278 00:15:53,200 --> 00:15:56,400 few weeks to months to re-equilibrate with the 279 00:15:56,400 --> 00:16:00,500 formation temperatures. So then we went away we were 280 00:16:00,500 --> 00:16:04,500 anxious want to know the answer but this is still a very active. 281 00:16:04,700 --> 00:16:07,600 Of plate. Boundary fault Zone with lots of 282 00:16:07,600 --> 00:16:11,600 huge aftershocks, including a magnitude, 7.3 Aftershock, 283 00:16:11,600 --> 00:16:15,500 pretty much right at this site, on a deeper fault below our 284 00:16:15,500 --> 00:16:18,600 Observatory. And so, we were afraid that with 285 00:16:18,600 --> 00:16:21,400 all of these sensors hanging on a rope, if we left it too long, 286 00:16:21,400 --> 00:16:25,100 maybe the fault was moving and it would share through the 287 00:16:25,100 --> 00:16:28,300 observatory and grab hold of the sensors and no matter how much 288 00:16:28,300 --> 00:16:30,700 we tugged on them, we wouldn't get them back. 289 00:16:30,900 --> 00:16:34,500 So, when we first went back, we couldn't find the observatory. 290 00:16:34,900 --> 00:16:40,400 Some of that is just due to the challenges of navigating in 291 00:16:40,400 --> 00:16:44,500 seven kilometers of water depth, you can use GPS in the air on 292 00:16:44,500 --> 00:16:47,300 the ship but communicating to the ROV underneath. 293 00:16:47,300 --> 00:16:51,400 You just, the smallest little bits of imprecision in your 294 00:16:51,400 --> 00:16:54,900 communication can lead to you being several tens of meters 295 00:16:54,900 --> 00:16:56,300 away from where you think you are. 296 00:16:56,700 --> 00:17:00,300 But luckily some of our Japanese colleagues offered by us to use 297 00:17:00,300 --> 00:17:02,900 some of their time with the our review few weeks later. 298 00:17:02,900 --> 00:17:05,700 We went back and we were able Able to find it. 299 00:17:05,700 --> 00:17:08,800 And I grabbed hold of it with the ROV and we pulled it all the 300 00:17:08,800 --> 00:17:11,800 way back up to the seafloor and we recovered all of it. 301 00:17:11,800 --> 00:17:15,000 The fault and not moved. It had not shared through 302 00:17:15,099 --> 00:17:19,200 everything which was actually an important observation in itself. 303 00:17:19,400 --> 00:17:22,599 It meant that a lot of the observations on land where GPS 304 00:17:22,900 --> 00:17:26,200 sensors were showing that Japan was still moving to the east, 305 00:17:26,300 --> 00:17:30,600 maybe as much as a MM per day, it wasn't because of slip on the 306 00:17:30,608 --> 00:17:34,500 fault, it's probably due to movements within the man. 307 00:17:35,100 --> 00:17:39,100 The mantle recovering relaxing after having such a big 308 00:17:39,100 --> 00:17:40,800 earthquake. Well, that's fascinating. 309 00:17:40,800 --> 00:17:42,800 So you're saying the actual land. 310 00:17:42,800 --> 00:17:49,600 Mass of Honshu was moving, but the sea flow was not what part 311 00:17:49,600 --> 00:17:53,200 of the sea floor was, but that movement was not between the 312 00:17:53,200 --> 00:17:56,500 overlying plate in a downgoing plate, it was between both of 313 00:17:56,500 --> 00:18:00,800 those things and the mantle underneath was turning a little 314 00:18:00,800 --> 00:18:03,900 bit after the earthquake. So what's the GPS location of 315 00:18:03,900 --> 00:18:06,200 the ball? Actually slightly different when 316 00:18:06,200 --> 00:18:09,700 you came back after 9 months. Well, we don't have a very good 317 00:18:09,800 --> 00:18:14,700 GPS location of it. The main issue was that the 318 00:18:14,700 --> 00:18:17,600 position was correct. But our communication, for where 319 00:18:17,600 --> 00:18:21,700 we thought we were was slightly Miss calibrated, because of the 320 00:18:21,700 --> 00:18:24,300 wavelengths that you use to communicate from the ship to the 321 00:18:24,300 --> 00:18:27,100 ROV. It's just a very long path. 322 00:18:27,100 --> 00:18:31,600 Any little bit of imprecision just adds up and if your 1020 323 00:18:31,600 --> 00:18:35,400 meters away from where you think you are down there, You can't 324 00:18:35,400 --> 00:18:38,200 see very far ahead of you with an ROV light. 325 00:18:38,200 --> 00:18:40,900 Doesn't travel that well, through the water and at these 326 00:18:40,900 --> 00:18:44,200 steps, this is the deepest darkest trenches, it is very 327 00:18:44,200 --> 00:18:45,700 dark down there. Okay. 328 00:18:45,700 --> 00:18:49,200 Well, let's talk about what the temperature sensors had logged. 329 00:18:49,200 --> 00:18:52,600 During those nine months in the Bohol, what you found out as is 330 00:18:52,600 --> 00:18:54,900 the case, pretty much everywhere on Earth the temperature 331 00:18:54,900 --> 00:18:58,400 increases as you go deeper, it's roughly about three degrees on 332 00:18:58,400 --> 00:19:01,100 the sea floor, and then the temperature, it seems to 333 00:19:01,100 --> 00:19:04,800 increase down to about 25 degrees Celsius, kind of I'm 334 00:19:04,800 --> 00:19:08,300 temperature down at the bottom of the observatory and if we 335 00:19:08,300 --> 00:19:11,800 remove that background gradient, we see the anomalous 336 00:19:11,800 --> 00:19:15,000 temperatures at first. It was cold because of that 337 00:19:15,000 --> 00:19:18,800 drilling disturbance. But then we started to see a 338 00:19:18,800 --> 00:19:22,500 relatively big temperature, anomaly of about Point 3, 339 00:19:22,800 --> 00:19:27,200 degrees Celsius centered right on the fault Zone. 340 00:19:27,400 --> 00:19:31,100 The same position where we had logged in, have all these 341 00:19:31,100 --> 00:19:34,600 geophysical images of the fault, we've actually taken. 342 00:19:34,900 --> 00:19:37,700 Accor sample out from the Vault itself. 343 00:19:37,800 --> 00:19:40,600 Right there is where we see a very large temperature. 344 00:19:40,600 --> 00:19:44,400 Anomaly, that we interpret to be the frictional heat signature 345 00:19:44,500 --> 00:19:48,200 from the magnitude 9 earthquake. How wide is the Fault Zone down 346 00:19:48,200 --> 00:19:50,200 there? Very interesting. 347 00:19:50,600 --> 00:19:53,600 It's very thin compared to a lot of other fault zones. 348 00:19:53,600 --> 00:19:57,400 So, fault Zone has its main core. 349 00:19:57,500 --> 00:20:01,400 It's roughly a couple of meters or less than 4 meters, thick and 350 00:20:01,400 --> 00:20:04,600 filled with dense, clay and then around it. 351 00:20:04,700 --> 00:20:08,900 There are other subsidiary faults and fractures that really 352 00:20:08,900 --> 00:20:11,800 like a knife edge on these scales that were talking about. 353 00:20:11,800 --> 00:20:14,400 So you have your temperature signal and you already said you 354 00:20:14,400 --> 00:20:18,500 had to subtract out the thermal gradient associated with the 355 00:20:18,500 --> 00:20:21,000 steady state heat flow, that's coming up from the mantle to the 356 00:20:21,000 --> 00:20:24,000 surface. But whether any other effects 357 00:20:24,000 --> 00:20:26,400 that you had to account for an order to really understand the 358 00:20:26,408 --> 00:20:28,400 contribution of the earthquake to the temperature. 359 00:20:28,400 --> 00:20:33,700 Normally we didn't know if that anomaly was due to fluid flow or 360 00:20:33,700 --> 00:20:37,400 to determine Properties. We did lots of measurements on 361 00:20:37,400 --> 00:20:41,400 those core samples that we got to make sure that that anomaly 362 00:20:41,400 --> 00:20:44,700 that we saw could not be due to differences in thermal 363 00:20:44,700 --> 00:20:46,800 conductivity or other Rock property. 364 00:20:47,100 --> 00:20:51,100 We also looked at the data very closely to see is it very 365 00:20:51,100 --> 00:20:53,500 smooth? And does it look like the 366 00:20:53,500 --> 00:20:57,000 temperature is diffusing, as we would expect or are there? 367 00:20:57,000 --> 00:21:00,500 Lots of signatures of water moving through, open faults and 368 00:21:00,500 --> 00:21:03,600 fractures and in the plate, boundary fault itself. 369 00:21:03,600 --> 00:21:05,800 We did not see any Indications of that. 370 00:21:06,000 --> 00:21:10,300 But we did see water flowing through fractures away from the 371 00:21:10,300 --> 00:21:12,800 main fault and other faults and fractures. 372 00:21:13,100 --> 00:21:16,400 And that gave us a whole other insight into earthquake 373 00:21:16,400 --> 00:21:19,000 mechanics. During the nine months that you 374 00:21:19,000 --> 00:21:21,000 are logging the temperature down at that bull. 375 00:21:21,000 --> 00:21:23,300 Whole, did you see this temperature? 376 00:21:23,300 --> 00:21:26,400 Normally start to diffuse away through thermal conductivity? 377 00:21:26,400 --> 00:21:28,900 Did it Peter out. It was hard in that time, 378 00:21:28,900 --> 00:21:31,500 because we were still seeing a lot of the effects of the 379 00:21:31,500 --> 00:21:34,900 drilling disturbance, but generally the shape of it, The 380 00:21:34,900 --> 00:21:38,900 relative stable behavior of It Through Time, suggested to us 381 00:21:38,900 --> 00:21:43,000 that it was a very conductive signature just a moment ago. 382 00:21:43,000 --> 00:21:45,900 You were saying it was actually quite significant that you 383 00:21:45,900 --> 00:21:49,000 managed to pull your whole sense of string out of the whole 384 00:21:49,000 --> 00:21:52,600 intact without any of its snagging or getting caught. 385 00:21:53,000 --> 00:21:55,800 I assumed you meant the possibility that the whole was 386 00:21:55,800 --> 00:21:57,600 deformed during those nine months. 387 00:21:57,900 --> 00:22:00,800 The whole could have been shared across the fault, could have 388 00:22:00,800 --> 00:22:04,200 still been moving and we didn't see that some of the other 389 00:22:04,200 --> 00:22:06,500 things. Is that we measured while we 390 00:22:06,500 --> 00:22:11,300 were down there before we install the observatory was take 391 00:22:11,300 --> 00:22:17,600 the resistivity image 3D 360 degree image of the walls and we 392 00:22:17,600 --> 00:22:22,600 could see how the tectonic stresses were deforming that 393 00:22:22,600 --> 00:22:26,300 hole after we drilled it. So when we drilled it was a 394 00:22:26,308 --> 00:22:29,600 cylinder but we could see from those images that in some 395 00:22:29,600 --> 00:22:33,400 places, the tectonic stresses were forcing it a little bit to 396 00:22:33,400 --> 00:22:37,100 collapse in certain places. Where the hole was becoming more 397 00:22:37,100 --> 00:22:39,600 oval shaped. And that told us about the 398 00:22:39,600 --> 00:22:43,600 magnitude of the stress, has down near the fault Beyond. 399 00:22:43,600 --> 00:22:46,400 Just what we see in the temperature, that told us what 400 00:22:46,800 --> 00:22:48,800 the stresses were during the earthquake. 401 00:22:49,000 --> 00:22:53,000 So after the earthquake, we could see that the amount of 402 00:22:53,100 --> 00:22:56,000 shear stress on the fault, was essentially zero. 403 00:22:56,600 --> 00:23:00,400 So, not only did this fall Sip and have no brakes on it, and 404 00:23:00,400 --> 00:23:03,600 that the stress on the fault, went to a value that was very 405 00:23:03,700 --> 00:23:06,000 small. That after the earthquake at 406 00:23:06,000 --> 00:23:08,700 least in the year afterwards had not built up a lot of stress, 407 00:23:08,900 --> 00:23:11,100 that's interesting. So the coefficient of friction 408 00:23:11,100 --> 00:23:15,200 was very low and at the same time all the stress was relieved 409 00:23:15,200 --> 00:23:19,700 perhaps because of that in part. So did you manage to get some 410 00:23:19,700 --> 00:23:23,400 quantitative results from this that you were able to put in 411 00:23:23,400 --> 00:23:26,800 perspective with the parameters that we've observed another 412 00:23:26,800 --> 00:23:29,800 false around the world? Yeah, I guess I jumped ahead of 413 00:23:29,808 --> 00:23:33,100 myself there and so I told you that we saw this point three 414 00:23:33,400 --> 00:23:36,700 degrees Celsius I'm sure know me but I didn't tell you what it 415 00:23:36,700 --> 00:23:42,100 meant and so we could use that heat anomaly and the width of it 416 00:23:42,100 --> 00:23:45,600 to constrain and with the thermal properties of the Rocks 417 00:23:45,600 --> 00:23:49,900 down there to constrain how much heat must have been deposited on 418 00:23:49,900 --> 00:23:53,400 the fault during the earthquake. And I had said that the fault 419 00:23:53,400 --> 00:23:57,700 Zone was about two meters thick but they're in that two meters. 420 00:23:57,700 --> 00:24:02,600 Thick, there are lots of thousands, tens of thousands of 421 00:24:02,800 --> 00:24:06,600 little sip surfaces. From probably tens of thousands 422 00:24:06,900 --> 00:24:10,000 of past earthquakes across that fault. 423 00:24:10,600 --> 00:24:15,100 And so each of them are, as thin as even a few millimeters. 424 00:24:15,400 --> 00:24:19,800 And so, most of the slip can be in a very thin zone, or it could 425 00:24:19,800 --> 00:24:23,200 be distributed across those two meters, it's unknown, and it's 426 00:24:23,200 --> 00:24:26,500 not really that relevant for the calculation, we do. 427 00:24:27,200 --> 00:24:30,800 But what we found by figuring out how much heat energy was on 428 00:24:30,800 --> 00:24:33,600 the fault. Now, he energy per unit area 429 00:24:33,800 --> 00:24:37,300 related to the Stress or the shear resistance times the 430 00:24:37,308 --> 00:24:41,000 displacement, we take that defied up by 50 meters of slip. 431 00:24:41,300 --> 00:24:43,900 We get the average Shear resistance on the fault. 432 00:24:44,100 --> 00:24:47,000 We know that the average Shear resistance is related to the 433 00:24:47,000 --> 00:24:50,400 friction coefficient times, the normal stress, which is related 434 00:24:50,400 --> 00:24:53,100 to the weight of the Rocks. Calculate the weight of the 435 00:24:53,100 --> 00:24:56,400 rides based on their density and we end up with a friction 436 00:24:56,400 --> 00:24:59,000 coefficient. That is point zero eight. 437 00:24:59,300 --> 00:25:02,100 Which is outrageously small, most rocks. 438 00:25:02,300 --> 00:25:04,500 Have a friction coefficient of point 6. 439 00:25:04,600 --> 00:25:08,200 It's two point, eight. So it is told us that the fault 440 00:25:08,200 --> 00:25:11,700 had no brakes for very little resistance to slip. 441 00:25:11,700 --> 00:25:16,300 Once the rupture got into this shallow part, I might we explain 442 00:25:16,500 --> 00:25:18,700 such a very low coefficient of friction. 443 00:25:19,100 --> 00:25:22,700 Those sediments in The Fault Zone that are really slippery. 444 00:25:23,200 --> 00:25:26,700 They already have a low friction coefficient lot smaller than 445 00:25:26,700 --> 00:25:30,800 most rocks in general, and perhaps a combination of the 446 00:25:30,800 --> 00:25:34,200 rupture, going through them and other effects associated with 447 00:25:34,200 --> 00:25:38,000 the generic A tree of the fault being very shallow, or very 448 00:25:38,000 --> 00:25:43,200 horizontally dipping together, may have allowed the rupture to 449 00:25:43,200 --> 00:25:48,100 find a week playing in a set of diffusing out or rupturing into 450 00:25:48,100 --> 00:25:51,100 Hard Rock's. It affects found this easy 451 00:25:51,100 --> 00:25:54,800 Pathway to just continue to slip all the way to the sea floor. 452 00:25:55,400 --> 00:26:00,500 So, you mentioned clay, I guess Clay is a sort of lubricant as 453 00:26:00,500 --> 00:26:03,500 compared to say other materials like more, silica Rich, 454 00:26:03,500 --> 00:26:06,000 materials that many. Any sediments are formed. 455 00:26:06,000 --> 00:26:07,300 Is that right? Yeah. 456 00:26:07,300 --> 00:26:12,600 In the lab granular, materials Sands or crystalline materials, 457 00:26:12,800 --> 00:26:15,800 have very high friction coefficients of REM point six 458 00:26:16,000 --> 00:26:19,400 point eight, when you put them under stress, but Clays are 459 00:26:19,400 --> 00:26:21,800 interesting. Their material structure is 460 00:26:21,800 --> 00:26:23,700 different in their play D minerals. 461 00:26:24,000 --> 00:26:27,800 They tend to be a bit weaker in general and these particular 462 00:26:27,800 --> 00:26:32,500 Clays are sure smectite clay, which is largely Ash, not a lot 463 00:26:32,500 --> 00:26:36,100 of sediments from River. As I said, these are some of the 464 00:26:36,100 --> 00:26:40,500 oldest Oceanic rocks, 130, million years old or older, they 465 00:26:40,500 --> 00:26:44,000 are probably deposit out in the middle of the ocean, far away 466 00:26:44,000 --> 00:26:48,200 from any land at such great. Depths that all the animal life 467 00:26:48,200 --> 00:26:51,500 has dissolved when they get to these great depths where their 468 00:26:51,500 --> 00:26:53,700 deposit. So, pretty much all this 469 00:26:53,900 --> 00:26:57,500 material that sediment is ash from volcanoes that have gone 470 00:26:57,500 --> 00:27:00,300 through the atmosphere and found their way to the bottom of the 471 00:27:00,300 --> 00:27:04,900 ocean. So, ash from volcanoes, Is not 472 00:27:04,900 --> 00:27:07,900 in itself, necessarily clay-rich right is what happens. 473 00:27:07,900 --> 00:27:12,300 Once it goes down at depth, and you're below the depth at which 474 00:27:12,300 --> 00:27:15,100 carbon will read is also no carbonates are intact down. 475 00:27:15,100 --> 00:27:18,200 There, is that what happens? That's right, these soft 476 00:27:18,200 --> 00:27:21,500 particles and Ash when they go down and they're exposed to 477 00:27:21,500 --> 00:27:24,500 water and they can break down into these clay minerals. 478 00:27:24,800 --> 00:27:28,500 So obviously enough Quake, like this one has enormous 479 00:27:28,500 --> 00:27:33,600 destructive potential. Do these Studies have practical 480 00:27:33,600 --> 00:27:37,500 implications? For earthquake preparedness or 481 00:27:37,500 --> 00:27:41,000 maybe even for prospecting for economically important minerals 482 00:27:41,000 --> 00:27:44,300 that are deposited by the kinds of transient hydrothermal. 483 00:27:44,300 --> 00:27:46,900 Fluid flows, that you saw further up in the old borehole 484 00:27:46,900 --> 00:27:51,900 Observatory certainly. So we saw that other faults and 485 00:27:51,900 --> 00:27:57,500 fractures would respond to after shots pulses of fluid flow 486 00:27:57,500 --> 00:27:59,900 through them. They were opening up. 487 00:27:59,900 --> 00:28:03,000 And that's a very similar process to how we think a lot of 488 00:28:03,300 --> 00:28:05,800 ore minerals. Are precipitated. 489 00:28:06,000 --> 00:28:09,500 That's also another process that can change. 490 00:28:09,500 --> 00:28:11,900 The fluid pressure. Change the stress State as the 491 00:28:11,900 --> 00:28:14,800 fluids move through. They can redistribute fluid 492 00:28:14,800 --> 00:28:17,800 pressures, which affects stress State, and those changes in, 493 00:28:17,800 --> 00:28:20,800 stresses can trigger subsequent earthquakes. 494 00:28:21,000 --> 00:28:24,200 So, that tells us a lot about the processes that can affect 495 00:28:24,200 --> 00:28:26,800 aftershocks. But just in general, 496 00:28:26,900 --> 00:28:31,000 understanding something about our initial question was the 497 00:28:31,000 --> 00:28:34,100 shallow part locked in building up a lot of stress really 498 00:28:34,100 --> 00:28:36,600 strong. Or it was it really weak and 499 00:28:36,600 --> 00:28:41,400 just sit along for the ride that can have direct and important 500 00:28:41,400 --> 00:28:45,100 implications for earthquake and tsunami Hazard preparedness. 501 00:28:45,500 --> 00:28:48,700 Perhaps one of the more analogous parts of the world 502 00:28:48,700 --> 00:28:51,800 would be the Pacific northwest coast of the United States and 503 00:28:51,800 --> 00:28:56,600 Cascadia where people talk about a huge earthquake with tsunami 504 00:28:56,600 --> 00:28:59,500 potential waiting to happen. Is that a similar situation? 505 00:28:59,500 --> 00:29:03,600 There it is a similar situation. This is a place that also like 506 00:29:03,600 --> 00:29:06,000 the northern part of Japan. Japan has not had a lot of 507 00:29:06,100 --> 00:29:10,200 earthquakes in modern era. People had thought that Cascadia 508 00:29:10,200 --> 00:29:12,800 doesn't have big earthquakes, it's just quiet. 509 00:29:12,800 --> 00:29:15,800 Maybe it's just always gradually sliding, not building up any 510 00:29:15,800 --> 00:29:21,000 stress but Native American stories and also now, paleo 511 00:29:21,000 --> 00:29:24,700 seismological records evidence in the Rock record of past 512 00:29:24,700 --> 00:29:28,900 tsunamis that it does have big earthquakes, including a 513 00:29:28,900 --> 00:29:32,700 magnitude 9 earthquake in January 1700 there. 514 00:29:32,700 --> 00:29:34,400 The geology is a little bit different. 515 00:29:34,500 --> 00:29:37,600 But instead of having lots of ash and clay, there are a lot of 516 00:29:37,600 --> 00:29:40,400 sediments. It's not as easy to drill into 517 00:29:40,400 --> 00:29:42,400 the fall. Although we could perhaps do 518 00:29:42,400 --> 00:29:45,600 some follow-up survey shins to learn more about the seismic 519 00:29:45,600 --> 00:29:48,900 potential there as well. Patrick Fulton. 520 00:29:49,000 --> 00:29:53,000 Thank you very much. Thank you for more about geology 521 00:29:53,000 --> 00:29:57,000 b, as well as pictures and illustrations, that support this 522 00:29:57,000 --> 00:29:59,600 podcast, go to geology B.com.