{"id":28411,"date":"2025-09-17T08:52:27","date_gmt":"2025-09-17T03:07:27","guid":{"rendered":"https:\/\/www.revoscience.com\/en\/?p=28411"},"modified":"2025-09-17T08:53:01","modified_gmt":"2025-09-17T03:08:01","slug":"mit-geologists-discover-where-energy-goes-during-an-earthquake","status":"publish","type":"post","link":"https:\/\/www.revoscience.com\/en\/mit-geologists-discover-where-energy-goes-during-an-earthquake\/","title":{"rendered":"MIT geologists discover where energy goes during an earthquake\u00a0"},"content":{"rendered":"\n

Based on mini \u201clab-quakes\u201d in a controlled setting, the findings could help researchers assess the vulnerability of quake-prone regions. <\/strong><\/em><\/p>\n\n\n\n

\"\"<\/figure>\n\n\n

Jennifer Chu<\/p><\/div><\/div>\n\n\n

Cambridge, Mass. — The ground-shaking that an earthquake generates is only a fraction of the total energy that a quake releases. A quake can also generate a flash of heat, along with a domino-like fracturing of underground rocks. But exactly how much energy goes into each of these three processes is exceedingly difficult, if not impossible, to measure in the field. <\/p>\n\n\n\n

Now MIT geologists have traced the energy that is released by \u201clab quakes\u201d \u2014 miniature analogs of natural earthquakes that are carefully triggered in a controlled laboratory setting. For the first time, they have quantified the complete energy budget of such quakes, in terms of the fraction of energy that goes into heat, shaking, and fracturing. <\/p>\n\n\n\n

They found that only about 10 percent of a lab quake\u2019s energy causes physical shaking. An even smaller fraction \u2014 less than 1 percent \u2014 goes into breaking up rock and creating new surfaces. The overwhelming portion of a quake\u2019s energy \u2014 on average 80 percent \u2014 goes into heating up the immediate region around a quake\u2019s epicenter. In fact, the researchers observed that a lab quake can produce a temperature spike hot enough to melt surrounding material and turn it briefly into liquid melt.<\/p>\n\n\n\n

The geologists also found that a quake\u2019s energy budget depends on a region\u2019s deformation history \u2014 the degree to which rocks have been shifted and disturbed by previous tectonic motions. The fractions of quake energy that produce heat, shaking, and rock fracturing can shift depending on what the region has experienced in the past.  <\/p>\n\n\n\n

\u201cThe deformation history \u2014 essentially what the rock remembers \u2014 really influences how destructive an earthquake could be,\u201d says Daniel Ortega-Arroyo, a graduate student in MIT\u2019s Department of Earth, Atmospheric and Planetary Sciences (EAPS). \u201cThat history affects a lot of the material properties in the rock, and it dictates to some degree how it is going to slip.\u201d<\/p>\n\n\n\n

The team\u2019s lab quakes are a simplified analog of what occurs during a natural earthquake. Down the road, their results could help seismologists predict the likelihood of earthquakes in regions that are prone to seismic events. For instance, if scientists have an idea of how much shaking a quake generated in the past, they might be able to estimate the degree to which the quake\u2019s energy also affected rocks deep underground by melting or breaking them apart. This in turn could reveal how much more or less vulnerable the region is to future quakes. <\/p>\n\n\n\n

\u201cWe could never reproduce the complexity of the Earth, so we have to isolate the physics of what is happening, in these lab quakes,\u201d says Mat\u011bj Pe\u010d, associate professor of geophysics at MIT. \u201cWe hope to understand these processes and try to extrapolate them to nature.\u201d <\/p>\n\n\n\n

Pe\u010d (pronounced \u201cPeck\u201d) and Ortega-Arroyo reported their results in the journal AGU Advances<\/a><\/em>. Their MIT co-authors are Hoagy O\u2019Ghaffari and Camilla Cattania, along with Zheng Gong and Roger Fu at Harvard University and Markus Ohl and Oliver Pl\u00fcmper at Utrecht University in the Netherlands.<\/p>\n\n\n\n

Under the surface<\/strong><\/p>\n\n\n\n

Earthquakes are driven by energy that is stored up in rocks over millions of years. As tectonic plates slowly grind against each other, stress accumulates through the crust. When rocks are pushed past their material strength, they can suddenly slip along a narrow zone, creating a geologic fault. As rocks slip on either side of the fault, they produce seismic waves that ripple outward and upward.<\/p>\n\n\n\n

We perceive an earthquake\u2019s energy mainly in the form of ground shaking, which can be measured using seismometers and other ground-based instruments. But the other two major forms of a quake\u2019s energy \u2014 heat and underground fracturing \u2014 are largely inaccessible with current technologies.<\/p>\n\n\n\n

\u201cUnlike the weather, where we can see daily patterns and measure a number of pertinent variables, it\u2019s very hard to do that very deep in the Earth,\u201d Ortega-Arroyo says. \u201cWe don\u2019t know what\u2019s happening to the rocks themselves, and the timescales over which earthquakes repeat within a fault zone are on the century-to-millennia timescales, making any sort of actionable forecast challenging.\u201d<\/p>\n\n\n\n

To get an idea of how an earthquake\u2019s energy is partitioned, and how that energy budget might affect a region\u2019s seismic risk, he and Pe\u010d went into the lab. Over the last seven years, Pe\u010d\u2019s group at MIT has developed methods and instrumentation to simulate seismic events, at the microscale, in an effort to understand how earthquakes at the macroscale may play out. <\/p>\n\n\n\n

\u201cWe are focusing on what\u2019s 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,\u201d Ortega-Arroyo says. <\/p>\n\n\n\n

Microshakes<\/strong><\/p>\n\n\n\n

For their new study, the team generated miniature lab quakes that simulate a seismic slipping of rocks along a fault zone. They worked with small samples of granite, which are representative of rocks in the seismogenic layer \u2014 the geologic region in the continental crust where earthquakes typically originate. They ground up the granite into a fine powder and mixed the crushed granite with a much finer powder of magnetic particles, which they used as a sort of internal temperature gauge. (A particle\u2019s magnetic field strength will change in response to a fluctuation in temperature.) <\/p>\n\n\n\n

The researchers placed samples of the powdered granite \u2014 each about 10 square millimeters and 1 millimeter thin \u2014 between two small pistons and wrapped the ensemble in a gold jacket. They then applied a strong magnetic field to orient the powder\u2019s magnetic particles in the same initial direction and to the same field strength. They reasoned that any change in the particles\u2019 orientation and field strength afterward should be a sign of how much heat that region experienced as a result of any seismic event. <\/p>\n\n\n\n

Once samples were prepared, the team placed them one at a time into a custom-built apparatus that the researchers tuned to apply steadily increasing pressure, similar to the pressures that rocks experience in the Earth\u2019s seismogenic layer, about 10 to 20 kilometers below the surface. They used custom-made piezoelectric sensors, developed by co-author O\u2019Ghaffari, which they attached to either end of a sample to measure any shaking that occurred as they increased the stress on the sample. <\/p>\n\n\n\n

They observed that at certain stresses, some samples slipped, producing a microscale seismic event similar to an earthquake. By analyzing the magnetic particles in the samples after the fact, they obtained an estimate of how much each sample was temporarily heated \u2014 a method developed in collaboration with Roger Fu\u2019s lab at Harvard University. They also estimated the amount of shaking each sample experienced, using measurements from the piezoelectric sensor and numerical models. The researchers also examined each sample under the microscope, at different magnifications, to assess how the size of the granite grains changed \u2014 whether and how many grains broke into smaller pieces, for instance. <\/p>\n\n\n\n

From all these measurements, the team was able to estimate each lab quake\u2019s energy budget. On average, they found that about 80 percent of a quake\u2019s energy goes into heat, while 10 percent generates shaking, and less than 1 percent goes into rock fracturing, or creating new, smaller particle surfaces.  <\/p>\n\n\n\n

\u201cIn some instances we saw that, close to the fault, the sample went from room temperature to 1,200 degrees Celsius in a matter of microseconds, and then immediately cooled down once the motion stopped,\u201d Ortega-Arroyo says. \u201cAnd in one sample, we saw the fault move by about 100 microns, which implies slip velocities essentially about 10 meters per second. It moves very fast, though it doesn\u2019t last very long.\u201d<\/p>\n\n\n\n

The researchers suspect that similar processes play out in actual, kilometer-scale quakes. <\/p>\n\n\n\n

\u201cOur experiments offer an integrated approach that provides one of the most complete views of the physics of earthquake-like ruptures in rocks to date,\u201d Pe\u010d says. \u201cThis will provide clues on how to improve our current earthquake models and natural hazard mitigation.\u201d<\/p>\n\n\n\n

This research was supported, in part, by the National Science Foundation.<\/p>\n","protected":false},"excerpt":{"rendered":"

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