Friday, October 7, 2016

Caltech Researchers Discover Deep-Level Earthquakes in the Mantle

For a very long time, seismologists (people who study earthquakes) believed that earthquakes could only happen in the Earth's crust layer, no more than 15 miles below the surface. A recent discovery by researchers at Caltech turned that assumption on its head. As Rong-Gong Lin II wrote in his L.A. Times article, it turns out that some earthquakes actually have the ability to travel deep under the surface, to the mantle level, which can multiply the quake's power many times.

Some of the earthquakes took place so far under the surface that the state-of-the-art sensors employed by the Caltech researchers barely sensed them, which explains why conventional seismometers have failed to pick up the signals in the past. Basically, what the researchers discovered is that the largest earthquakes are those that spent some time percolating in the mantle. One example was the 8.6 earthquake that happened in the middle of the Indian Ocean in 2012. At the time, science's understanding of how earthquakes work could not explain how an earthquake that large had happened.

If these greater-strength quakes were possible, areas around the Newport-Inglewood fault or the San Andreas fault could be at risk. Fortunately, the researchers have so far only found evidence of microquakes (2.0 or less) that originated in the deeper layers. It is possible that the deeper-level quakes are more spread out and don't usually join together, which could mean that they would only cause small microquakes. If a quake on the scale of magnitude 3 or 4 were to be detected in the mantle, concerns would likely be raised, but right now, researchers have asked for more time to study and learn more about the way earthquakes work.

Additionally, research performed in areas other than the Long Beach portion of the Newport-Inglewood fault line did not show nearly as much evidence of deep quakes. Some evidence points to liquids flowing up from the mantle in certain beachside areas, so that may contribute to Long Beach's increased risk for deep quakes. At the moment, there is no way to tell if deep-level quakes are as large a risk as they could be. Perhaps it is only an issue in Long Beach; maybe it's only an issue in cities that border the ocean. Only time and a lot more research will reveal the truth.

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