A layer of fine-grained talc and other minerals makes some faults much weaker.
Click on image for full size
Credit: Zina Deretsky, NSF
It’s Not Your Fault – A Typical Fault, Geologically Speaking, That Is
News story originally written on December 16, 2009
Some faults look strong and like they wouldn’t cause an earthquake. But it turns out that they can slip and slide like weak faults causing earthquakes. Scientists have been looking at one of these faults in a new way to figure out why.
The faults that are thought to be very stable are called low-angle normal faults. They dip into the ground at an angle less than the angle of a typical roof.
However, they are not always stable. They do slip.
Scientists who are watching actual low-angle faults have found that they move. Scientists wanted to know how this happens.
An unusual low-angle normal fault on the Italian Island of Elba allowed scientists figure out how this happens. The fault sits exposed on the island’s beach so it is easy to examine the rocks from the fault. Often, scientists only get to work with small bits of rock from faults that are collected by drilling underground. But in this case they had an entire beach of rock to examine.
They found that the rock was very weak in one direction. The rock was made up of small wafers that slid almost like a deck of cards when pushed. Small patches of talc and clay minerals allowed the fault to slide.
Shop Windows to the Universe Science Store!
Our online store
on science education, classroom activities in The Earth Scientist
specimens, and educational games
You might also be interested in:
The ground underfoot might seem like it’s not going anywhere but it is. It moves. If it moves all of a sudden the ground shakes. That’s an earthquake! Earthquakes happen as pieces of the Earth’s crust...more
There are at least 2000 minerals on Earth. That's a lot of minerals! But you don't need to know all of them to spot the minerals lurking in the rocks of your backyard. That is because only a small number...more
Scientists have learned that Mount Hood, Oregon's tallest mountain, has erupted in the past due to the mixing of two different types of magma. Adam Kent, a geologist at Oregon State University, says this...more
The Earth's mantle is a rocky, solid shell that is between the Earth's crust and the outer core. The mantle is made up of many different reservoirs that have different chemical compositions. Scientists...more
Some faults look strong and like they wouldn’t cause an earthquake. But it turns out that they can slip and slide like weak faults causing earthquakes. Scientists have been looking at one of these faults...more
The sun goes through cycles that last approximately 11 years. These solar cycle include phases with more magnetic activity, sunspots, and solar flares. They also include phases with less activity. The...more
Studying tree rings doesn't only tell us the age of that tree. Tree rings also show what climate was like while the tree was alive. This means that tree rings can tell us about climates of the past. Two...more