What are conservative plate margins and Transform Faults?
Conservative plate margins occur at plate boundaries where two tectonic plates slide past each other horizontally. They are most commonly found on the ocean floor with only a few exposed on land. Transform faults are a sort of miniature conservative plate margin that connect the end of one plate boundary to the end of another. There are 3 types of transform fault:
- Those connecting two destructive plate margins together
- Those connecting two constructive plate margins together
- Those connecting a constructive and a destructive plate margin together
Transform faults are very common at ridges such as the Mid-Atlantic Ridge (shown below), because the plates move obliquely and the nature of the lithosphere causes some parts of the plates to move faster than others.
Typical features of conservative plate margins
There is no volcanic activity at conservative plate margins as there is no lithosphere being created or destroyed. This is because no subduction takes place, and as the plates are not moving apart there is no space for magma to rise up. However, there is lots of seismic activity at conservative plate margins in the form of shallow focus earthquakes. These occur because there is a huge amount of friction between the two plates as they slide past each other, and so occasionally they get stuck. Pressure builds up rapidly, and, once it becomes greater than the friction causing the plates to get stuck, is released by the sudden movement of the plates past each other. This release of pressure sends shockwaves through the earths crust as a shallow focus earthquake, which is often devastating to any urban areas nearby.
an exampe of a conservative plate margin
The most famous example of a conservative plate margin is the San Andreas Fault on the west coast of North America. It is around 800 miles long, 15km deep and has been active for over 20 million years. It runs through California which has resulted in some devastating earthquakes, such as one in Los Angeles in 1994, and one in San Francisco in 1989, both of which killed tens of people and injured thousands, destroying many buildings in the process. The San Andreas Fault is under constant surveillance from Seismologists and other scientists due to the devastating consequences the earthquakes have previously caused.
In 1989, an earthquake (centred NE of Santa Cruz on the San Andreas Fault line) occurred in Northern California on October 17th. It was named the “Loma Prieta earthquake”, due to the mountain peak in the Santa Cruz mountains nearby. There were several foreshocks in June foreshadowing a major earthquake – as that segment of the San Andreas fault had been so quiet that no large earthquake had occurred in that region since 1906. The earthquake was rated IX (Violent) on the Mercalli scale and 6.9 on the Richter scale. The Loma Prieta earthquake killed 63 people and left 3,757 injured.
In 1989, an earthquake (centred NE of Santa Cruz on the San Andreas Fault line) occurred in Northern California on October 17th. It was named the “Loma Prieta earthquake”, due to the mountain peak in the Santa Cruz mountains nearby. There were several foreshocks in June foreshadowing a major earthquake – as that segment of the San Andreas fault had been so quiet that no large earthquake had occurred in that region since 1906. The earthquake was rated IX (Violent) on the Mercalli scale and 6.9 on the Richter scale. The Loma Prieta earthquake killed 63 people and left 3,757 injured.
Report by Alex Luke