WorldWide Drilling Resource

23 WorldWide Drilling Resource ® MARCH 2019 Open the Doorway to all the Event Photos during Utah Ground Water Association 2019. To see all the photos from this event, go to www.worldwidedrillingresource.com or click here. Feel free to download at will and print the photo(s) of your choice. Compliments of WorldWide Drilling Resource ® . Photos are copyrighted and released for personal use only - no commercial use permitted. Studying Seismology in the Nankai Trough Adapted from Information by the University of Wisconsin-Madison Hiroki Sone, assistant professor of civil and environmental engineering at the University of Wisconsin-Madison and Ph.D. student Zirou Jin are part of a team of scientists working on the Nankai Trough Seismogenic Zone Experiment, the deepest scientific oceanic drilling project ever. Part of the 11-year experiment involves drilling below the Nankai Trough, the meeting point of the Eurasian and Philippine Sea tectonic plates, the source of repeated earthquakes. If successful, it would be the first time scientists have reached the depth where earthquakes spawn in a subduction zone. The drilling, which reached a record depth in early December 2018 and will continue through the spring of 2019, will pro- vide samples and allow the team to install sensors, potentially discovering new clues about the processes behind earth- quakes. “We want to understand what kind of forces are accumulating in this plate boundary, because that’s the driving force for ground motion during earthquakes,” said Sone. “To be directly in there and see the ma- terial, really improves our understanding of what is actually happening.” Growing up in a Japanese society understandably wary of earth- quakes, Sone is well aware of the long history of seismic activity in the country. As a graduate student at Kyoto University, he was studying a deadly earthquake in Taiwan for his thesis when he found out about plans for the first NanTroSEIZE Integrated Ocean Drilling Program expedition, which launched in 2007. Six years later, he joined his first expedition on the Nankai Trough. This time, he’s leading the physical properties team. When drill cut- tings come to the surface, his team examines them to calculate changes in porosity, the percentage of empty space in the rock that’s filled by water. Typically the porosity would decrease with depth, but researchers are looking for exceptions which may indicate higher-than-expected fluid pressure. Scientists have long suspected fluid pressure along tectonic plate interfaces is abnormally high, which could en- courage a plate to slip. According to Sone, no one has measured the fluid pressure at this depth. “This is a good opportunity to test those hypotheses and validate theories, or maybe disprove some of them,” he stated. Even though work days are long aboard the drilling vessel Chikyu, with 12-hour shifts and limited internet access, the promise of rock core samples, a much larger and more useful sample than the drill cuttings, provide the motivation to continue. Jin is currently studying cores from a previous expedition for her Ph.D. work on the viscoplastic properties, which is how mate- rials flow and deform over time, in Nankai Trough’s accretionary prism, the collection of rocks and sediment formed during plate subduction. By taking cores from the plate interface and slowly deforming them in the lab, scientists will be able to understand the forces that build up during the 100-400 years between the tsunami-generating earthquakes in the Nankai Trough. “It’s important to understand how the earth ruptures during these large earthquakes that happen in a matter of minutes, and scientists have focused on that for many decades,” Sone said. “But what happens in between the 100 years? How does the force accumulate to get ready for the next earthquake? That is an equally, if not more, important questions to ask that we have not addressed in the community. We’d like to make a breakthrough there to better forecast seismic hazards around the world.” Civil and Environmental Engineering Assistant Professor Hiroki Sone stands on the drilling vessel Chikyu’s heliport. Photo courtesy Hiroki Sone. ENV