Understanding Earthquake Energy Distribution

Earthquakes, with their immense destructive power, are among the most astonishing natural phenomena. When the ground shakes, earthquakes can cause cracks in the earth, topple buildings, and trigger massive rockslides. However, this high destructive capability is only a small fraction of the total energy of an earthquake. A recent study sheds light on how this energy is distributed and its impact on the earth.

Seismic Energy: Between Vibration and Heat

In a new study published in AGU Advances, it was found that vibrations account for only 1 to 8 percent of the energy released by an earthquake, while up to 98 percent dissipates as heat. This intense heating occurs due to the friction of massive rock blocks against each other, raising the earth’s temperature to over 1700 degrees Celsius, enough to melt quartz and other minerals.

The main challenge lies in measuring the amount of energy that goes into vibrations versus rock breaking and sudden heating, especially since earthquakes originate deep within the earth and occur unexpectedly. To understand this energy budget, researcher Daniel Ortega-Arroyo and his colleagues created small laboratory earthquakes by compressing centimeter-sized chips of granite powder and magnetic particles between aluminum pistons until they slipped or broke. They used thermometers and piezoelectric sensors to simulate real earthquake measurements.

Laboratory Results: Rapid and Sudden Heating

Even small laboratory earthquakes experienced a rapid rise in temperature. “The heat rose from room temperature to over 900 degrees Celsius in just a few microseconds,” says Ortega-Arroyo.

The researchers found that between 68 and 98 percent of the energy released by these laboratory earthquakes dissipated as heat. Breaking the chip consumed between less than 1 percent to up to 32 percent of the energy, while vibrations accounted for 8 percent or less. Samples that experienced more deformation before breaking saw slightly less heating, suggesting that the rock’s history in the fault may affect how much energy goes into heating, rock breaking, and vibrations in the next earthquake.

The Importance of Research in Earthquake Modeling

The new research indicates that the energy budget of earthquakes remains a “big unknown,” says Rachel Abercrombie, a seismologist at Boston University who was not involved in the study but discussed the experiments with the authors before publication. “It is fundamental to understanding earthquakes and thus the ability to model them.” Computer models of earthquakes are used for everything from determining how resistant local buildings are to earthquakes to trying to predict when the next fault break will occur and how large the resulting earthquake will be.

Applications of Laboratory Processes in the Real World

The advantage of the work is the use of a new technique that measures the alignment of magnetic minerals in heated rocks to help interpret temperature changes, says Heather Savage, a seismologist at the University of California, Santa Cruz. Savage, who was not involved in the study, conducts field analyses of molten rocks on ancient fault lines. These real-world studies also use magnetic analysis, and she says having the same measurements in the real world and in the lab can help extend results from a centimeter-sized chip to a fault spanning several kilometers.

Conclusion

This study highlights the significant importance of understanding energy distribution in earthquakes, not only to comprehend the natural phenomenon itself but also to develop accurate models that help predict the effects of future earthquakes. With the use of new techniques and detailed laboratory analysis, scientists can now better understand how the geological history of rocks affects seismic energy distribution, opening new avenues for earthquake prediction and risk reduction for society.