MOSCOW (MIPT) — Thousands of earthquakes happen across the world each day, shaking the Earth’s surface, reshaping the landscape, and at times posing a threat to the population. While seismologists have come a long way understanding the processes behind earthquakes, the recent events in California show we are still a long way off from reliable predictions.
Geophysicist Sergey Turuntaev from the Moscow Institute of Physics and Technology is available to comment on the July 4-6 Ridgecrest earthquakes and other related issues. Professor Turuntaev is chair of theoretical and experimental physics of geosystems at MIPT and the director of the Institute of Geosphere Dynamics of the Russian Academy of Sciences. He is known for research on human-induced geodynamic processes.
Here are some ideas to get you started.
Q: Why do earthquakes happen?
A: Most of them are related to tectonic processes within our planet and occur at the boundaries of tectonic plates, which make up the Earth’s lithosphere. These plates may either spread apart, creating new crust, or clash into each other, resulting in the thinner plate sinking underneath the thicker crust.
Q: Are their causes well-studied?
A: Yes, mostly. An earthquake occurs when strain builds up in tectonic faults — fractures in the Earth’s crust — and then releases. Fluids are among the known factors that may trigger such stress relaxation. Researchers are discussing how seismic activity may be affected by geothermal energy use, which involves water injection. The abundance of geothermal sites in California has attracted considerable research interest.
However, apart from the natural quakes, there are also man-made ones. Certain activities, such as mineral resource mining, drilling, water injection into oil or geothermal wells, and water reservoir filling have been found to trigger earthquakes. This is why the number of earthquakes has increased dramatically in central U.S., where fluid has been used to increase rock permeability for shale oil production.
Q: So why is California constantly rocked by earthquakes?
A: Because that state lies along a plate boundary. As the Pacific Plate moves in the northwestern direction, it grinds against the North American Plate, producing the so-called “strike-slip” earthquakes. This is why the recent seismic events in California were not unexpected.
Q: What was unusual about the July earthquakes?
A: It was the fact that the right-lateral faulting in the first quake was followed by northwestward movement later on, forming an intersection. This means that the focal mechanism orientations between the two were different. A similar situation was observed during the Gazli earthquakes of 1976 and 1984.
Q: Some parts of the world are earthquake risk zones. But how can we know a quake is coming?
A: Actually, it is still pretty difficult to predict the time, location, and magnitude of an earthquake. We can forecast them on the scale of decades, and we are trying hard to do it for the less distant future: months or even hours before the event.
While short-term predictions are difficult to make, seismic monitoring can produce viable intermediate-term forecasts, yet there remains much to accomplish in this field. Hence today the world favors probabilistic predictions: How likely is a seismic event of a given “size” to happen during a certain time interval?
Q: Given the limitations of earthquake prediction, how can we protect ourselves?
A: Since some areas are more susceptible to earthquakes, precautions should be taken. This involves creating seismic zoning maps, advising people to avoid building in these regions or opt for earthquake-proof structures. On Kamchatka, for example, reinforced walls are used to make buildings resistant to earthquakes.
Also, soil conditions have to be considered, as seismic wave attenuation depends on soil properties and may either be increased or decreased by them. For example, creating a sandpit underneath a building effectively reduces seismic vibrations.
When it comes to minimizing the damage done by earthquakes, timing is of the essence. A group of young researchers on Sakhalin Island came up with a Telegram bot which analyzes seismic data and sends notifications to its users the moment an earthquake hits.
Q: Is it possible to control an earthquake?
A: I think, yes. By targeting the Earth’s crust and either triggering an earthquake before it actually happens or inducing a series of smaller quakes instead of a big one. But to do so, we have to know where the tension has accumulated and basically predict an earthquake.
Another way to control an earthquake is to look for fault areas with high earthquake potential and use high-pressure fluid injection to disrupt the fault in an attempt to lower seismic activity in the region. This is what we and our colleagues from around the world have been working on lately. But testing these ideas requires fairly expensive experiments.
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