The Minimum Scale of Grooving on a Recently Ruptured Limestone Fault. Issue 21 (11th November 2019)

• Record Type: Journal Article
• Authors: Okamoto, K. K.; Brodsky, E. E.; Thom, C. A.; Smeraglia, L.; Billi, A.
• Is Part Of: Geophysical research letters. Volume 46:Issue 21(2019)
• Page Start: 11878
• Page End: 11885
• Publication Date: 2019-11-11
• Subjects: roughness -- earthquake nucleation -- deformation; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2019GL084889
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Faults have grooves that are formed by abrasion and wear during slip. Recent observations indicate that this grooving is only a large‐scale feature, indicating brittle behavior has a length scale limit. The connection between this scale and earthquake behavior remains limited because no examples exist from a proven seismogenic fault. Here, we address this problem and analyze differences in this scale between lithologies to further our understanding of the underlying mechanics. This study uses samples from the Mt. Vettoretto fault collected after the Norcia earthquake of 2016. We imaged fault topography with a white light interferometer and 10 μm resolution structure from motion and then calculated a Monte Carlo version of root mean square roughness. We found a minimum scale of grooving of ~100 μm. In comparing this fault to the Corona Heights fault, we find that this minimum grooving scale is consistent with predictions based on material properties. Plain Language Summary: As two surfaces slide past each other, harder material can cause grooves or scratches to form in the direction of slip. Recent work showed that on a fault, there exists a change in geometry, or roughness, within these grooves that is evidence of a change in how frictional contacts are deformed. At the micrometer scale, these contacts are deforming without breaking. To link this process to earthquakes, we aim to measure this scale on a fault that hosts known earthquakes. Here, we measure roughness on a fault slipped during the 2016 Norcia earthquake using interferometry and photography. We find this scale and show that it is predictable by measuring properties of the fault. This gives a link between laboratory and natural earthquakes by measuring a length scale and a deformation process that is common to both. Key Points: Lithological differences between faults explain the varying values of the minimum scale of grooving The small‐scale fault roughness of a seismogenic fault shows evidence of plastic deformation We develop micrometer scale structure from motion combined with Monte Carlo RMS analysis as a high‐resolution method to study roughness