What is formed in a subduction zone? This is a question that I am asked quite often from people that work in the petroleum exploration and development industry. The answer to this question varies from area to area.
One of the biggest factors that determine what is formed in a subduction zone is whether or not there has been fluid movement within that zone. If that has happened then it can be classified as being formed in that zone. If the fluid has not moved, or has not moved in a significant amount then it is not formed there.
What is formed in a zone around the earth’s crust when there is fluid movement? That is something that geologists find out through research. They use sophisticated equipment to determine what is forming in the soil layers beneath the surface. Once they determine what is forming in that zone then they can remove that area and sample it to see if and how much fluid movement is happening there.
One scientist explained to me that when tectonic plates are moving apart, sometimes there will be a movement of fluid. If that fluid is not going to move with the tectonic plate, then it can form into voids. These voids can become bottlenecks. If the fluids that fill these bottlenecks are moving, then sometimes they can cause the land beneath them to slip away. This can cause an earthquake or even a major slip on a lake or river.
How can you tell if there is fluid moving in your region? If you have an active volcano, then there should be a change in the ground water level on a regular basis. This means that the volcano is working. The USGS does an analysis called Isotopic Depth Studies which is done to determine if there has been any changes in the earth’s crust. If there is a significant change in the depth of the crust, then it is possible that there may be significant movement of fluid in a subduction zone.
Subduction zones are important because there is one large fault running underneath most of them. The faults are sometimes called rupture zones because they do contain large amounts of fluid. They can be made from different types of rock, but most commonly they are made out of tectonic material (like granite, limestone, and marble) with faults that run horizontally.
The fluid in a subduction zone can move to the south and cause movement of the land. When this happens, you actually have two faults that are sliding along with the land. You must know when and where to expect earthquakes caused by fluid movement.
You can expect to see this type of earthquake near large areas of slip. These slip areas are often underneath mountains or behind other large structures. The fault can be close enough to the surface to cause a massive earthquake. Also, the rupture zone is not always close to a large body of water. Sometimes, it can be underneath the ocean. Seismologists are very good at studying the behavior of fluid and the way it behaves under various conditions.
One area where these faults can lead to earthquakes is near oil fields. Oil can move slowly underneath the ocean, and it moves slowly enough that it does not cause much friction when it hits the soil. However, there are times when oil gets hot and causes areas of slippage or slip. When this happens, there could be a large earthquake nearby that was caused by the rupture zone. Knowing what is formed in a subduction zone before an earthquake can make things easier for scientists and emergency planners.