earthquake
Natural earthquake (English: earthquake), also known as earth motion and earth vibration, is a natural phenomenon that causes vibrations during the rapid release of energy in the earth's crust, which will produce seismic waves during this period. The plates on the earth squeeze and collide with each other, causing staggering and rupture in the edges and inside the plates, which is the main cause of earthquakes. Earthquakes often occur instantly and can release a lot of energy in a short period of time.
Swimming pool in the major earthquake
February 27, 2010 local time 03:34, Chile suffered one of the strongest earthquakes in a century. The shock triggered a tsunami that destroyed coastal communities. The merger incident killed more than 500 people. The vibration is so powerful that according to NASA (NASA) estimates it moves the Earth's rotation axis by a full 8 cm.
Like almost all the strongest earthquakes, it is a huge thrust earthquake. It occurs in the subduction zone, where one plate is forced to press under the other. If these plates suddenly move, you will suffer a major earthquake. The Chile earthquake in 2010 was 8.8, and the intensity was enough to lift the building off the foundation.
We know very little about the subduction zone, which is why Professor Anne Socquet, a geophysicist at the University of Grenoble Alps in France, plans to visit Chile. She wants to install the earthquake monitoring instrument to collect data. She arrived a week after the earthquake. "That's terrible," she said. "There are cracks in the walls of the apartment we rented, so you can put your fists in." Professor
Socquet said that most people who study super-thrust earthquakes focus on the forequakes immediately before the main earthquake. However, an unusual feature of giant thrust earthquakes is that after a few years, they are often accompanied by a series of other very powerful giant thrust earthquakes, with epicenter hundreds of kilometers. For example, after the Chile earthquake in 2010, other events occurred in 2014, 2015 and 2016, focusing on the upper and lower areas of the Chilean coast. Professor Sockett wants to study these sequences of extreme thrust earthquakes and study the potential connections between these large earthquakes. This requires a closer inspection of earthquake and geodescending data than before.
Slow motion earthquake
Underground of the earth is a very active place. The movement and friction of plates deep underground form the landform we see on the surface, and the activities underground control the intensity of the danger above. Although Earth movements during earthquakes and volcanic eruptions have been recorded with sophisticated instruments, analyzed by researchers and constrained by statistics, they do not illustrate the entire story of the movement of the plate underfoot.
Over the past two decades, the arrival of GPS - including receivers with extremely sensitive sensors that capture millimeter-level motion - has allowed scientists to discover previously difficult-to-unremoval phenomena of earthquakes. These include so-called slow sliding events or slow moving earthquakes, which are different from ordinary earthquakes and are more like a "slow motion" earthquake.
These slow sliding events occur around the world and may help trigger larger earthquakes. The largest slow-sliding event occurred in the subduction zone, where one tectonic plate subduction below the other, eventually forming mountains and volcanoes over millions of years. New computer simulations produced by researchers at Stanford University and published online on June 15 in the journal Solid Mechanics and Physics may explain these hidden motions. "Slow slip is a fascinating phenomenon. Slow slip events are so common and so difficult to explain," said Eric Dunham, co-author of the
study. "This is a difficult problem that bothers us," said Professor of geophysics at Stanford University's School of Earth, Energy and Environmental Sciences (Stanford University School of Earth). "We have known that slow slips exist for more than 20 years, but people still know very little about why this phenomenon occurs." The
GPS site reveals the activity under Cascadia, where the seabed slides under North America.The plate interface is locked at a shallower depth (shaded area), but we see repeated slow sliding events (blue) decompressing the plate interface, resulting in tremors (black spots).
These events are particularly difficult to explain due to their unstable but slow nature. The motion of the fault does not slide smoothly, but periodically, accelerates, but never reaches the point where seismic waves are emitted enough for humans to detect. Although they are difficult to detect, slow sliding events may accumulate.
What is called "slow slip" or "silent" earthquakes behave more like conventional earthquakes than previously thought. This discovery opens the door for geoscientists to use these frequently occurring non-destructive events as easy-to-study analogies that will help them identify the causes of earthquakes. Slow sliding events that occur over several weeks may release the same energy as a magnitude 7.0 earthquake that lasts a minute. Because they occur deep in the earth and release energy slowly, surface deformation is small, although slow events can affect the area of thousands of square kilometers. Therefore, they are only noticed when GPS technology is improved to track very small changes. But not every time the friction slows down, slow slip events occur; so far, they have been found in only a few locations, including the Northwest Pacific region, Japan, Mexico and New Zealand .
In November 2016, New Zealand's second largest earthquake in history (the 7.8-magnitude Kaikura earthquake) hit the country's South Island . A GPS network operated by GeoNet, established in collaboration with GNS Science and the New Zealand Earthquake Commission, detected a slow slip event hundreds of miles below North Island . These events occur in shallow parts of the Hikuranyi subduction zone along and through New Zealand.
The above figure illustrates the slow slippage in centimeters that occurred after the 7.8-magnitude Kaikula earthquake in November 2016. This is the most common slow slippage found in New Zealand since scientists first observed this phenomenon in 2002.
GPS network detected a slow slip event at the boundary of the Hikurangi subduction zone plates in weeks and months after the Kaikura earthquake. Slow slip occurs less than 9 miles below the surface (or seabed) and is approximately 6,000 square miles from the Hawke Bay and Gisborne areas, which is comparable to the area occupied by New Jersey . Deeper slow slip events also occurred on the subduction zone 15-24 miles below the Kapiti Coast area west of the New Zealand capital Wellington . This deeper slow slip event near Wellington continues today.
Avouac’s team designed and applied innovative signal processing techniques to detect and image slow-slide events in the Cascadia subduction zone, Washington, where the North American tectonic plate slides southwest over the Pacific plate through a network of 352 GPS stations. The researchers analyzed data from 2007 to 2018 and were able to create a directory containing more than 40 slow-sliding events of different sizes. Their findings were published in the October 23 issue of Nature.
Past slow slip events have been linked to earthquakes, including the magnitude 9.0-magnitude Tohoku earthquake that attacked Japan in 2011 to destroy Fukushima nuclear power plant . The researchers also found that the slow slip event triggered by the Kaikura earthquake was a catalyst for other marine earthquakes. The east coast of the North Island includes the level 6.0 just offshore from the town of Porangahau on November 22, 2016.
Fukushima Nuclear Power Plant core melting diagram
Although scientists are still in an early stage of trying to understand the relationship between slow-sliding events and earthquakes, the results highlight other links between these processes.
Fan’s point of view: In my opinion, these slow motion slips are more like slowly elongated rubber bands, and when they break, they are the beginning of a major earthquake.
