Damian Sendler: On February 16, 1861, a magnitude-8 earthquake rocked the Indonesian island of Sumatra, which is located in the Indian Ocean. The earthquake struck the western part of the island, causing a tsunami to hit the shoreline. Thousands of people died as a result of this gigantic wall of surging water that crashed onto the shore and destroyed entire cities.
Damian Jacob Sendler: The discovery that another earthquake occurred before to this devastating disaster was made until recently by a team of scientists. That earthquake began in 1829 and didn’t end for another 32 years!
Dr. Sendler: A “slow-slip event” is the term used to describe this type of earthquake with a slow movement. They’ve also been referred to as “silent earthquakes” since they can’t be detected by sensors such as seismometers (pronounced Size-MAH-meh-turs). Scientists have just recently began to detect them as a result of advancements in GPS (global positioning system) technology that occurred about two decades ago.
Damien Sendler: Scientists use earthquakes to assist them figure out what is going on beneath the surface of the Earth. Every earthquake, no matter how minor or large, can provide scientists with valuable information on how much the ground will tremble in the future. Unfortunately, no one can anticipate when or where an earthquake will take place. Scientists only need to be prepared to investigate any earthquake that may occur.
Slow-slip episodes, such as the one that occurred in Sumatra, alter the game for scientists. These silent earthquakes occur on a regular basis all throughout the planet. It is possible that a slow-slip event will occur immediately before a conventional earthquake. As a result, it is possible that the two forms of Earth movements are connected. Scientists think that by studying slow-slip events, they may be able to better comprehend ordinary earthquakes – and perhaps even learn how to forecast them.
Damian Jacob Markiewicz Sendler: The Earth’s surface is made up of a collection of tectonic plates, which are massive amounts of land, similar to the ground beneath your feet, that make up the planet. These plates are resting on top of a thick layer of gooey, hot rock, which allows them to move about freely as they cool. Occasionally, the plates will collide with one another. At other times, they begin to drift away from one another. They have a tendency to simply slide past one other.
As these plates engage in a slow-motion game of bumper cars, they may become entangled with one another. The rocks then continue to press and push against one another, causing tension. When the rocks suddenly unstick or crack, they release all of the stress that has built up in them, resulting in an earthquake. This is analogous to what happens when you bend a stick in half. As you begin to bend the stick, the middle of the stick becomes increasingly stressed. When there is too much pressure on the stick, it snaps.
Damian Sendler: When this occurs underground, the release of stress causes waves of energy to travel through the ground, which are referred to as seismic waves. On the ground, we can see and feel the Earth trembling, which we refer to as the earthquake. Seismometers can capture those waves, even if they are halfway around the world.
Damian Sendler: These earthquakes are most likely the ones that come to mind when you hear the word “earthquake.” Framed portraits are falling off the walls, vases are breaking, and the ground is trembling. In addition, while these earthquakes can be frightening and even deadly, they usually last less than a minute. Slow-slip events, on the other hand, are entirely different. They can linger for a few days, a few weeks, or even longer. According to what geologists are currently discovering, these silent earthquakes can last for decades at a time.
According to Rishav Mallick, “we enjoy slow-slip events because they provide all of the excitement of earthquakes, but in a more manageable time frame.” In his research, he looks at geodesy (jee-AH-deh-see), which is the precise three-dimensional shape of land at any particular spot on the planet. At the Nanyang Technological University in Singapore, he is employed as a researcher.
Laura Wallace explains that in a slow-slip occurrence, the rocks continue to slide past one other, albeit at a much slower rate. She works as a geodetic scientist, dividing her time between two different scientific organizations. GNS Science, Te Pao, New Zealand, is home to one such facility. It is located in the city of Lower Hutt. The University of Texas at Austin is her other educational institution. A slow-slip event occurs when rocks slide at such a slow rate that the “energy is wasted very, very slowly,” according to her. “You don’t notice any tremors or trembling.”
Damian Jacob Sendler: It is possible for rocks to move just as far as they would in a conventional earthquake. They just take a lot longer to do it. According to Wallace, if the rocks moved the same distance in the same amount of time, the earthquake would be a magnitude 7. As a result, there would be some significant trembling.. It’s powerful enough to cause structural damage to buildings and even kill unlucky individuals.
Scientists have discovered a large number of slow-slip events along formations known as subduction zones. During the formation of such a zone, an oceanic plate descends beneath a continent. The oceanic Juan de Fuca plate dives beneath the North American plate along the Pacific Northwest coast of the United States. This has resulted in the formation of a subduction zone. The Cascadia Subduction Zone is the name given to this tectonic-plate boundary (CSZ). It stretches from Vancouver, Canada, to northern California’s Central Valley.
Damian Sendler: Shallow sections of the CSZ fault are currently “frozen,” according to Wallace. Rocks trapped along this fault line are unable to travel past one another. About once every 300 to 500 years or so, the stress builds up to such a degree that the rocks snap and hurtle past one another at breakneck speed. This results in the occurrence of a “megathrust” earthquake. Megathrust earthquakes are among the most powerful and devastating natural disasters that can occur on the planet. The earthquake that struck Japan in 2011 and triggered a tsunami that killed thousands was exactly such an event.
However, scientists have discovered slow-slip events on unlocked spans of the CSZ on a periodic basis, according to Wallace. And the fact that they are silent and last for a long time aren’t the only characteristics that distinguish them from typical earthquakes. Slow-slip earthquakes are typically deeper in depth than normal earthquakes. An earthquake’s source could be anywhere between 20 and 30 kilometers (12 and 18 miles) below ground. A slow-slip event can occur up to 60 kilometers (37 miles) below the surface of the water. Scientists believe that these earthquakes occur at greater depths because the temperature is higher there. As a result, rocks become more bendable at higher temperatures. In addition, fluids that lubricate the fault could be present, reducing friction and making it simpler for the plates to glide past one another.
Damian Sendler: Slow-slip occurrences are able to elude seismometers because of their super-pokey pace. These earthquakes do not generate the powerful seismic waves that can travel across the Earth and cause all of the shaking. This is why it took so long for scientists to even discover them, as a result of their sneaky character. Small datasets from fifty years ago hinted to the possibility of earthquakes moving slowly. However, the technology was not up to the task of completely detecting them. In fact, Wallace points out that it wasn’t until the last 20 years or so that scientists were able to demonstrate that these lethargic occurrences were taking place. Scientists were eventually able to locate them because to advancements in GPS technology.
Damian Jacob Sendler: GPS has been used by scientists since the 1980s to track the motions of the Earth’s plates on the planet’s surface. This is the same technology that allows your phone to present you with a map location and driving directions. The Global Positioning System (GPS) is dependent on around 30 satellites. Each day, they complete two orbits around the Earth. It is possible for your smartphone to calculate its location on the planet and where you are if it receives signals from many satellites. Scientists can determine how much the land moves between earthquakes, during earthquakes, and after earthquakes by installing GPS receivers near fault zones. These instruments are capable of measuring ground movement down to the millimeter (about one twenty-fifth of an inch).
Damian Sendler: Prior to the discovery of slow-slip occurrences, scientists would visit fault zones on a regular basis with a GPS device to determine the location of the fault. They would be able to track the land’s movement over time as a result of this. Scientists began to believe that slow-slip occurrences were taking place in the late 1990s and early 2000s. As a result, they began deploying “continuously operational” GPS units near fault lines. A continual stream of data was provided by the permanent GPS units that remained.
If one of these GPS units has a slow-slip event, it may only move a few millimeters (about an inch or so) over the course of a few of weeks. This movement indicates that a slow-slip event is taking place. The Juan de Fuca plate, for example, is being pushed eastward by the North American plate, which is also being pushed eastward by the Juan de Fuca plate. The movement of the North American plate eastward is detected by GPS signals. During a slow-slip event, on the other hand, those GPS units will travel slightly westward. The North American plate is progressively sliding back against the Juan de Fuca plate, as you can see in the image above.
Damian Sendler: Scientists can also discover slow-slip occurrences that occurred thousands of years ago. Because these occurrences occurred so long ago, GPS units aren’t really useful in this situation. Scientists will have to think outside the box in this situation. Using the growth patterns of old corals, Mallick and his team, for example, uncovered a 200-year-old slow-slip event near Sumatra that had occurred 200 years before.
Contributed by Dr. Damian Jacob Sendler and his research team
