By: Meghomita Das (www.meghomita.com) with inputs from John deSanto
David Schimdt is the chief scientist for the Cascadia leg of the Near Trench Geodetic Community Cascadia edition. A critical part of the trio, along with the ship captain and Jason operations leader, who gets to call all the shots on this ship. He is a geophysicist who uses both satellite and surface data to study the deformation of the earth's crust, which is at times very subtle to be detected by other means. His primary focus is to study these slow and silent earthquakes that rumbles through the Pacific Northwest along the Cascadia Subduction Zone. Here, I got to sit down (re:bother) him with questions about his role, goals and passion for this research cruise and any interesting stories that he has to share with us.
Slow slip or slow earthquakes are an interesting phenomena that defines earthquake behavior on a spectrum. Instead of regular earthquakes that cause felt shaking and propagate through the surface within seconds to minues, slow slip or slow earthquakes are well, slow. Their propagation takes days to weeks to months and they do not produce any strong shaking (hence, silent). They were first detected in Japan followed shortly by similar events along the Cascadia Subduction Zone (CSZ) in the Pacific Northwest. They are important behavior as they control the total earthquake budget along these margins and can influence the behavior of the large magnitude quakes that is forecast to happen along the Pacific Northwest.
 |
| David (center, blue sweater) with some of the research crew participants. Photo credit: Meghomita Das |
Q: Can you give a brief primer on how GNSS-Acoustic works and what those data tell us about interseismic locking along the Cascadia margin?
Global Navigation Satellite Systems (GNSS) allow us to position a point on the earth with great precision using signals from a constellation of satellites. With GNSS, we can track how the position of a benchmark changes over time, which tells us about the deformation of Earth's crust from tectonics and the buildup of elastic energy that will be released in a future earthquake. However, those satellite signals cannot penetrate water. In order to measure the position on the seafloor where there are undersea faults, we have to use the two-way travel time of acoustic signals through the ocean. Therefore, GNSS-Acoustic is a method for measuring the position of a benchmark on the seafloor that uses a craft floating at the sea surface. GNSS is used to locate the position of the surface craft, while acoustic signal from the surface craft help to triangulate the position of benchmarks on the seafloor.
 |
| Screen grab of Jason (Remote operated vehicle) sending us pictures of the signal-emitting devices called transponders (orange balls) as they were placed on the ocean bottom |
Q: What are your major goals for this research cruise?
There are the 4 main goals for the 2024 Cascadia cruise. We want to replace the batteries at two GNSS-Acoustic sites. Then take measurements of temperature and salinity of the seawater column. These values are then put into a model that calculates the acoustic sound velocity of a sound wave through a portion of the water column. The velocity is further converted to estimate the travel time between the acoustic-wave emitter and acoustic-wave receiver and correct for any drifts in the measurements. Next on the agenda is servicing a seafloor fiber optic strainmeter. It is an ingenious instrument that literally measures strain (or deformation) within an optical fiber that allows us to see and quantify the deformation between the two tectonic plates. Finally, we are deploying a Wave Glider that glides along the waves and records three measurements: GNSS position of the antenna on the glider, rotation of the glider as it swims along the waves, and the travel time between the acoustic-signal emitting device (on board the glider) and the acoustic-signal receiving device (located on the bottom of the ocean on a well-placed benchmark site). These might seem like a lot but they are crucial pieces of information that allows geophysicists and geodecists like myself to make precious measurements concerning the movement of the plate as it subducts underneath the North American plate.
Q: What inspired you to study slow earthquakes?
When I began my academic career, slow earthquakes were just discovered in Cascadia. This phenomenon was new and exciting. It provided the first information about what was happening on the deep part of the subduction zone, down dip of the megathrust-earthquake generating zone. Prior to these discoveries, we did not know the mode of strain release at these depths and how that affected the overall plate deformation along Cascadia.
Q: How did the Near Trench Geodetic community form? What are some of the highlights that this community has produced that has improved our understanding of slow slip behavior?
The community experiment formed from an earlier effort to acquire seafloor geodetic instrumentation. Limited access to seafloor geodetic instrumentation has been a barrier for the geodetic community to expand from on-land to off-shore measurements. A group of us first wrote an infrastructure proposal to acquire the instruments. When that was successful, we then wrote a second proposal to actually deploy the instruments and collect data. It was then decided to structure this as a community experiment, where the data and tools would be made available to the geodetic community. It is a novel project that allows collaborations between researchers and across different academic research stages.
Q: Time for some ship stories: the crazy ones first that seriously made you reconsider everything in life? And the really cool ones that blew your mind and motivates you to do this more often?
I am always impressed by the technology that is used to conduct research at sea. The research vessels work like small cities, providing water, power, food, and sanitation to everyone on board. And they require a trained professional crew to operate safely. It is always unnerving when the seas are rough and furniture starts to slide across the room. Seeing wildlife is always fun. Sometimes the seas are calm enough to see shark fins breaking the surface around the boat. Dolphin pods and whales bring a lot of spectacle.
 |
| David is in charge of writing down the plan of action for each day. But since things change at sea rapidly, we call the notice board "The Board of Lies". Photo credit: Meghomita Das |
Q: What are you thoughts on going on research cruises like these? Any closing words for people who might want to join this cruise in the future?
Going to sea on a research expedition is an immersive experience. And whether you are a scientist, engineer, technician, or ship's crew, everyone has a specific role to play; yet everyone must work as a team to accomplish the goals of the expedition. It's a great opportunity to experience science in action. Keep your eyes peeled for future opportunities.
Great interview!
ReplyDelete