Through their recent work, geologists Matěj Peč and Daniel Ortega-Arroyo are shedding much needed light on the energy dynamics at work in earthquakes. Their study, published on August 28 in the journal AGU Advances, sheds light on how energy is distributed during seismic events. That’s because only about 10% of the energy produced in lab quakes actually goes into creating physical shaking, the research finds. At the same time, a whopping 80% is turned into heat.
Peč is an associate professor of geophysics at the Massachusetts Institute of Technology (MIT). He and his team created their own piezoelectric sensors to understand how rock samples vibrate when put under stress. The sensors — invented by co-author O’Ghaffari — allowed the researchers to easily quantify the energy budget of simulated earthquakes.
Unveiling the Energy Budget
In their own experiments, the researchers found that only a small percentage of a quake’s energy goes toward producing observable geological shifts. Less than 1% of the total energy produced is used to frac rocks or build new. The experiments used a precision built and modified apparatus for applying continuously increasing pressure on solid rock samples. This new device was specifically built to recreate the high pressure, high temperature conditions of Earth’s seismogenic layer, about 10-20 kilometers below the surface.
This study provides important new understandings about the ways energy dissipates during earthquakes. Such insights could improve our capacity to anticipate how an earthquake will act.
“Our experiments offer an integrated approach that provides one of the most complete views of the physics of earthquake-like ruptures in rocks to date.”
To make their measurements, the team developed an array of specially-designed piezoelectric sensors that were affixed to each end of the rock samples. This configuration enabled them to carefully quantify the shaking as stress was gradually introduced to the samples. In the best sample, the same fault displaced 100 microns. This slip movement corresponds to slip velocities of order 10m/s.
Methodology and Measurements
Daniel Ortega-Arroyo noted the importance of understanding the deformation history of rocks:
He went on to say that the paleohistory is very important for filling in unknown material properties within the rock. This context can further change the way the rock gives way in an earthquake.
“The deformation history—essentially what the rock remembers—really influences how destructive an earthquake could be.”
These results from Peč’s team have profound effects beyond deep-learning-based earthquake research, even into earthquake hazard mitigation and preparedness strategies. By putting a precise measure of the energy spread from quake lab simulations, they hope to improve today’s earthquake models. Peč remarked on the potential benefits of their work:
Implications for Earthquake Models
Ortega-Arroyo added that while it is challenging to observe daily patterns deep within the Earth, studying smaller-scale phenomena could yield valuable insights:
“This will provide clues on how to improve our current earthquake models and natural hazard mitigation.”
The research team hopes that by isolating and understanding these processes at a microscale, they can develop more accurate models that reflect natural conditions.
“Unlike the weather, where we can see daily patterns and measure a number of pertinent variables, it’s very hard to do that very deep in the Earth.”
The research team hopes that by isolating and understanding these processes at a microscale, they can develop more accurate models that reflect natural conditions.
“We are focusing on what’s happening on a really small scale, where we can control many aspects of failure and try to understand it before we can do any scaling to nature,” Ortega-Arroyo concluded.