The efficient option is to gradually accelerate once and then decelerate once. Ye uses an analogy to explain how earthquake energy varies: Consider driving a car from point A to point B. For example, the Sumatra earthquake had a REEF value of 2.0, meaning the energy released in the complex rupture was much bigger than the potential minimum amount of energy released in a magnitude-9.2 earthquake. High REEF values mean high complexity - and high energy release. The result gives researchers an idea of the complexity of a rupture. REEF is the ratio of an earthquake’s radiated energy (measured by seismic instruments) to the theoretical minimum possible energy that an event of equal seismic moment and duration of rupture could produce. Now, she and her colleagues have developed a different way to measure energy release, called the Radiated Energy Enhancement Factor, or REEF, which can provide scientists with a more nuanced picture of variations among megathrust earthquakes. “However, we do not have a parameter, a number, to complexities ,” Ye says. The way a megathrust ruptures - either continuously or sporadically, with stops and starts - can contribute to the release of different amounts of energy, says Lingling Ye, a seismologist at Sun Yat-sen University in China and lead author of the study in Science Advances. However, during the Tohoku quake, the fault slipped primarily along one area for three minutes, whereas in the Sumatra quake, the fault ruptured in multiple areas at once and shook for eight long minutes. For example, the 2011 magnitude-9.1 Tohoku megathrust quake and the 2004 magnitude-9.2 Sumatran megathrust quake were similar in magnitude. But two earthquakes with the same moment magnitude can have very different styles of rupture. Now, a team of scientists has come up with a new model to help crack the complexity and nature of megathrust earthquakes using global historical records.Įarthquakes are currently measured on the moment magnitude scale, which describes the size of earthquakes based on the amount of energy they release: Large earthquakes are labeled with bigger numbers. Yet, there are many unknown factors that control how much energy is released in each earthquake. Bradley.Īs tectonic plates collide and sink in subduction zones, huge megathrust earthquakes can produce devastation above. Navy photo by Mass Communication Specialist 1st Class Matthew M. And if a building's normal movement changes after an earthquake, that data can alert engineers to potentially hidden structural damage.Understanding how megathrust earthquakes like the 2011 magnitude-9.1 Tohoku event might rupture, including how long shaking might last, could help scientists prepare for future hazards. The information helps researchers learn how the ground and buildings move differently during everyday disturbances, such as truck traffic, and during earthquakes. The system collects continuous three-dimensional data about position and acceleration with accelerometers similar to those used in smartphones to reorient screens. Caltech's Zhongwen Zhan and his colleagues have used this approach to track aftershocks from California's 2019 Ridgecrest earthquake sequence and create a citywide earthquake-detecting network in Pasadena.Īccelerometer arrays: In this type of network, pioneered over the past decade through Caltech's Community Seismic Network, small sensors installed in the ground and hundreds of public schools and other buildings send motion data to the cloud. DAS sensors send beams of light down cables and detect differences in the travel time of reflected light when seismic waves jostle the cables. Earthquakes may produce smaller or larger waves when they encounter different soils and where bedrock is near the surface or buried deep under sediments.ĭistributed Acoustic Sensing (DAS): These networks employ fiber-optic communications cables that are already installed underground. Intensity also can vary depending on geology. Think of a lightbulb: It has one wattage, but the brightness that energy produces decreases with distance as the light spreads out. The waves get smaller as they travel away from the fault. While an earthquake has just one magnitude, its levels of intensity decrease with distance from the epicenter. Today, scientists also can measure instrumental intensity directly, calculating and assigning intensities based on recorded ground shaking in different locations. For instance, if the shaking is strong enough to awaken most people, then the intensity will be assigned a level of V. This definition of intensity requires a subjective judgment by an observer. In the United States and many other locations, intensity values are described with Roman numerals from I (barely perceptible) to X (widespread destruction), using the Modified Mercalli Intensity scale. Intensity describes how strong the shaking is at a given location.
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