by Hannah Rabinowitz
This summer, Heather and I had the opportunity to go to the Istituto Nazionale di Geofisica e Vulcanologia (INGV) in Rome. In addition to spending a lot of time making our way through the gelaterias of Rome, we were able to run a couple of series of experiments on two different deformation apparatuses in the rock mechanics lab there.
Taste-testing gelato at a gelateria recommended by Kevin Uno
The apparatuses we used this summer in Rome. SHIVA is on the left and BRAVA on the right.
One set of these experiments was conducted with Giulio di Toro and Elena Spagnuolo on the Slow to HIgh Velocity Apparatus (SHIVA). SHIVA is a high velocity rotary shear apparatus that can slide either intact rocks or gouge layers at high velocity and high normal stress. This is actually the apparatus that first got me interested in rock mechanics research. After seeing a video of one of the first SHIVA tests in which solid rock samples were sheared to form pseudotachylite (frictional melt) during a class in undergrad, I went straight to my professor’s office to ask to work in his lab. Though I did experiments on a different deformation apparatus for my undergraduate research (a Griggs rig), I was lucky enough to get to go use SHIVA with my undergrad advisor the summer before starting at Lamont. So in a way, I’ll always feel I owe more to this apparatus than just the cool results that it can give us! But really, who could watch this video and not fall in love with rock mechanics?
In our experiments this summer on SHIVA, we sheared gouge at high velocity to induce frictional heating. The goal of these experiments is to expand the kinetics of biomarker thermal maturity to shorter timescales than is achievable in our hydrous pyrolysis apparatus at Lamont. We also conducted slow velocity shearing experiments to test the impact of shear without significant heating on biomarker thermal maturity. This will be important when using biomarker thermal maturity to estimate temperature rise on faults. If shear strain can have similar effects to heating on biomarker maturity, then these effects must both be considered when we try to determine the size of the earthquake that could have produced a biomarker anomaly. However, if the shear strain does not impact biomarker maturity significantly, then we can be more confident that a signal in the biomarker record is recording an earthquake.
Heather prepping a sample of Woodford Shale to run on SHIVA.
Our second set of experiments were conducted with Cristiano Collettini and Brett Carpenter on the Brittle Rock deformAtion Versatile Apparatus (BRAVA), a new biaxial deformation apparatus with which we could control pore fluid pressure as well as confining pressure. In this set of experiments, we deformed samples of sediments that are being fed into subduction zones. We chose samples from two subduction zones in order to have a range of different carbonate content in our experiments and address the question of how compositional heterogeneity can affect the different seismic character of subduction zones.
We were fortunate to finish our planned experiments with plenty of time to spare. Because of this, we were able to go out into the field and collect samples from a couple of faults in the Apennines. Specifically we got to sample the Monte Maggio (a normal fault) and Spoleto (a thrust fault). These faults were completely spectacular and we were able to drill samples from both of the fault surfaces as well as several off fault samples to use for the biomarker paleoseismic indicator project.
Drill holes from our samples on the razor sharp contact between the footwall Scaglia group red limestones and the hanging wall cataclasites at the Spoleto fault.
Heather and Brett sampling the Monte Maggio fault. Our hosts were amused by our commitment to wearing purple gloves in the field.
Heather and I in front of the Monte Maggio slip surface.