Earthquakes happen every day all over the world, along both tectonic plate edges and interiors. Earthquakes occur along faults, which are fractures between blocks of rock that allow the blocks to move relative to one another. Faults are caused by the bumping and sliding that plates do and are more common near the edges of the plates.
Plates, Motion, Faults, Energy Release
The Earth's crust (the outer layer of the planet) is made up of several pieces called tectonic plates and most earthquakes occur along their edges. The plates under the oceans are called oceanic plates. Plates that are not under the ocean are continental plates. The plates are moved around by the motion of a deeper part of the earth (the mantle) that lies underneath the crust, and by the weight of oceanic plates that pulls them down below oceanic plates. These plates are always moving apart, bumping, or sliding past each other at about the same speed that your fingernails grow. Earthquakes usually occur where two plates are running into each other or sliding past each other.
Earthquakes Can Happen Along Intraplate Faults
Earthquakes can occur along faults far from the edges of plates. Although these earthquakes are much less common, they are due to the same forces that cause earthquakes along plate boundaries.
Types of Faults
Faults are defined by the kind of motion that happens where they are. Normal faults show cracks where one block of rock is sliding down and away from another block of rock. These faults usually occur in areas where the crust is very slowly stretching or where two plates are pulling away from each other. A normal fault is defined by the hanging wall (a term that comes from mining) moving down relative to the footwall (where the miner would stand), which is moving up.
Normal Fault
The "footwall" is on the "upthrown" side of the fault, moving upwards. The "hanging wall" is on the "downthrown" side of the fault, moving downwards.
Reverse Faults
Reverse faults are formed where the Earth’s crust is under compression. They also occur where the crust is folding up because it's being compressed by another plate pushing against it. At these faults, one block of rock is sliding underneath another block or one block is being pushed up over the other. A reverse fault is defined by the hanging wall moving up relative to the footwall, which is moving down.
Reverse Fault
This time, the "footwall" is on the "downthrown" side of the fault, moving downwards, and the "hanging wall" is on the "upthrown" side of the fault, moving upwards. When the hanging wall is on the upthrown side, it "hangs" over the footwall.
Strike-slip Faults
Strike-slip faults lie between two sides of the crust that slide past each other and are common in places like California where the Pacific Plate is moving northwest relative to the North American Plate. In a pure strike-slip fault, there is no motion up or down along the fault. The well-known San Andreas fault is predominantly strike-slip.
Strike-slip Fault
The motion shows a left-lateral strike-slip fault. No matter which side of the fault you are on, the other side is moving to the left. For a right lateral strike-slip fault (not shown), no matter which side of the fault you are on, the other side is moving to the right.
Fun Fact: The Keweenaw Peninsula—home to Michigan Tech and UPSeis, is also known for the massive slip fault that marks our landscape. The Keweenaw Fault is the result of activity more than one billion years ago and presents no current danger. In other words, don’t fear the fault!
FAQs
Where Do Earthquakes Happen? | UPSeis | Michigan Tech? ›
Earthquakes happen every day all over the world, along both tectonic plate edges and interiors. Earthquakes occur along faults, which are fractures between blocks of rock that allow the blocks to move relative to one another.
Where do earthquakes usually occur? ›Over 80 per cent of large earthquakes occur around the edges of the Pacific Ocean, an area known as the 'Ring of Fire'; this where the Pacific plate is being subducted beneath the surrounding plates. The Ring of Fire is the most seismically and volcanically active zone in the world.
Where do earthquakes occur explain your answer? ›Earthquakes occur along fault lines, cracks in Earth's crust where tectonic plates meet. They occur where plates are subducting, spreading, slipping, or colliding. As the plates grind together, they get stuck and pressure builds up. Finally, the pressure between the plates is so great that they break loose.
How do earthquakes happen? ›The tectonic plates are always slowly moving, but they get stuck at their edges due to friction. When the stress on the edge overcomes the friction, there is an earthquake that releases energy in waves that travel through the earth's crust and cause the shaking that we feel.
What is an earthquake answer? ›An earthquake is what happens when two blocks of the earth suddenly slip past one another. The surface where they slip is called the fault or fault plane.
When and where do earthquakes start? ›Earthquakes are usually caused when underground rock suddenly breaks and there is rapid motion along a fault. This sudden release of energy causes the seismic waves that make the ground shake.
Do earthquakes only happen on Earth? ›Do Earthquakes Only Happen on Earth? Earthquake is a name for seismic activity on Earth, but Earth isn't the only place with seismic activity. Scientists have measured quakes on Earth's Moon, and see evidence for seismic activity on Mars, Venus and several moons of Jupiter, too!
In which 3 areas are earthquakes most common? ›- the Circum-Pacific belt,
- the Alpide belt,
- the mid-Atlantic Ridge.
While most earthquakes are caused by the slipping of tectonic plates, minor earthquakes can also be caused by volcanic eruptions, collapse of rock formations on Earth's surface, or underground explosions.
What are three ways earthquakes can occur? ›Movement in narrow zones along plate boundaries causes most earthquakes. Most seismic activity occurs at three types of plate boundaries—divergent, convergent, and transform. As the plates move past each other, they sometimes get caught and pressure builds up.
What are the 5 main causes of earthquakes? ›
The Main Causes of Earthquakes are the Movement of Tectonic Plates, Volcanic Eruptions, Underground Explosions, Induced Quaking (Human Activities), etc. Apart from these, earthquakes can be caused by a number of geological factors, natural phenomena, and human activity.
What is during an earthquake? ›COVER your head and neck (and your entire body if possible) underneath a sturdy table or desk. If there is no shelter nearby, get down near an interior wall or next to low-lying furniture that won't fall on you, and cover your head and neck with your arms and hands.
How is an earthquake called? ›An earthquake also known as a temblor, quake, tremor is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's crust that creates seismic waves.
Where do 90% of earthquakes occur? ›The “Ring of Fire” also called the Circum-Pacific belt, is the zone of earthquakes surrounding the Pacific Ocean — about 90% of the world's earthquakes occur there.
Where are 95% of all earthquakes located? ›Nearly 95% of all earthquakes take place along one of the three types of tectonic plate boundaries, but earthquakes do occur along all three types of plate boundaries. About 80% of all earthquakes strike around the Pacific Ocean basin because it is lined with convergent and transform boundaries.