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May23
The Stress on Faults: Fundamental Physics of Earthquakes
Prof. Emily Brodsky, University of California / Santa Cruz
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Earthquakes occur by overcoming fault friction, and therefore quantifying the resistance of faults is central to earthquake physics. Both static and dynamic friction values are required, and the latter is especially difficult to determine on natural faults. Perhaps the only way to solve the problem is to drill into a fault after an extremely large earthquake. The Japan Trench Fast Drilling Project (JFAST) did just this after the 2011 Mw 9.1 Tohoku earthquake and showed that the shear strength during the earthquake was substantially below that predicted by Byerlee’s law, which was a touchstone of earthquake physics for a generation. The very low dynamic stress implies a complete reset of the earthquake cycle. The JFAST data also reopens the conundrum of why earthquakes have depth-independent stress drops that are smaller than would be anticipated if friction drops completely. We recreate the phenomenon in the laboratory by imaging ruptures in a transparent, analog model. Surprisingly, the laboratory stress drops are like the natural ones and independent of normal stress apparently due to self-organization of the stress field in a confined rupture.
About Prof. Emily Brodsky
Emily Brodsky is a professor and earthquake physicist at the University of California, Santa Cruz. Her research focuses on connecting empirical observations of earthquakes with fundamental physical processes. Her expertise spans several fields relevant to induced seismicity including seismology, hydrogeology and rock mechanics. Prof. Brodsky earned her A.B. from Harvard in 1995 and Ph.D. from Caltech in 2001. She is the recipient of the inaugural 2005 Charles Richter Early Career award from the Seismological Society of America, the 2008 James Macelwane Medal from the American Geophysical Union (AGU), the 2019 Woolard Award from the Geological Society of America (GSA), the 2019 Gutenberg Lectureship, the 2020 Price Medal of the Royal Astronomical Society (RAS), and is a Fellow of both AGU and GSA. She was selected as a Distinguished Lecturer for the NSF Earthscope program, the Geo-Prisms program, International Ocean Discovery Program (IODP) and the National Science Board. She has served on the Board of Directors of the Southern California Earthquake Center (SCEC), Incorporated Research Institutes for Seismology (IRIS) and is currently chair of SZ4D. She has published over 130 peer-reviewed articles, has an h-index of 59 and presented over 150 invited lectures in 30 states and 13 countries. Her work has been featured in major press outlets such as the BBC, NPR, Time Magazine, NY Times, Nature, Reuters, LA Times and The Wall Street Journal. She has mentored 17 postdocs, 16 PhD students, 3 Masters and 21 Undergraduate research students, many of whom have gone on to be leaders in the field.
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