Japan Geoscience Union Meeting 2022

Presentation information

[J] Oral

S (Solid Earth Sciences ) » S-SS Seismology

[S-SS07] Fault Rheology and Earthquake Physics

Mon. May 23, 2022 3:30 PM - 5:00 PM 105 (International Conference Hall, Makuhari Messe)

convener:Makiko Ohtani(Earthquake Research Institute, the University of Tokyo), convener:Keishi Okazaki(Japan Agency for Marine-Earth Science and Technology), Ryo Okuwaki(Mountain Science Center, Faculty of Life and Environmental Sciences, University of Tsukuba), convener:Shunya Kaneki(Disaster Prevention Research Institute, Kyoto University), Chairperson:Shunya Kaneki(Disaster Prevention Research Institute, Kyoto University), Keishi Okazaki(Japan Agency for Marine-Earth Science and Technology)

4:30 PM - 4:45 PM

[SSS07-11] Microscopic Defect Dynamics of a Brittle-to-Ductile Transition

Hamed Ghaffari1, Uli Mok1, Hilary Chang1, Tushar Mittal1, Alejandra Quintanilla Terminel1, Brian Evans1, *Matej Pec1 (1.Massachusetts Institute of Technology)

Keywords:brittle-ductile transition, rheology, acoustic emission

The strength of the Earth’s crust likely reaches a peak in the “brittle-to-ductile“ transition region where fracturing gives way to crystal-plastic deformation. The activity and interactions of microscopic defects such as cracks, twins and dislocations are important elements in determining whether rocks creep steadily or fail abruptly resulting in an earthquake. Here, we use ultrasound probes to study acoustic emissions in marbles that are deforming within the brittle-to-ductile transition. The acoustic signals provide insight into the microscopic defect dynamics. We identify three dominant classes of emitted waveforms: 1) long-period signals, abundant at low confining pressures associated with microcracking, 2) short-period signals localized in frequency domain associated with twinning, and 3) low-amplitude, high-frequency signals common at higher pressures associated with glide of dislocations. With increasing pressure, the dominant frequency of events increases from ~0.5 MHz to >40 MHz and deformation de-localizes on the sample scale; cracking is suppressed, and twinning and dislocation glide become dominant. Complex hybrid events indicate that interactions between the defects are common over the whole studied pressure range.