"Are there 'earthquakes' on Mars? What's inside the Earth and Mars? What causes earthquakes and how are they measured? What is Plate Tectonics?"
Slip, Sliding Away
Earthquakes are caused by forces deep within the Earth's crust. As continents collide, ocean floors split, magma flows, volcanoes erupt and other natural processes occur pressure is released making vibrations within the ground which we call earthquakes. Where one block of the Earth's crust interacts with another they may slip, slide or push each other resulting in a fault. This movement in the Earth is called tectonics. The interior of Mars has very little movement and does not have quakes that have been measured.
A fault is a fracture in the Earth's crust where two blocks of crust have slipped against each other. In the diagram at right figure A is a Normal Fault where the blocks are pulled apart allowing for one block to slip down on the other. Figure B indicates a Thrust Fault which occurs when blocks are pushed against each other raising one of the blocks. A Strike-Slip Fault, figure C, occurs when stress causes the blocks to move horizontally past one another.
The severity of an earthquake is related to magnitude, that is, the seismic energy recorded on a seismograph and intensity meaning the observed effects that the ground shaking has on people, buildings, man-made structures and natural features. The epicenter of an earthquake is the spot on the surface directly above the area where the quake took place. The focus or hypocenter is the area inside the Earth where the event happened.
Scientists have developed a theory called "Plate Tectonics" to explain why earthquakes continue to occur. In this theory the continents float on the surface of the Earth on a continental plate and slide, collide or push other continental plates. The heat and pressure from this movement causes rock deep within the Earth to melt (magma) and force its way to the surface to create volcanoes.
Click on image for a detail view.
Plate movements are also believed to cause about 90 percent of all earthquakes. Less than 10 percent of earthquakes occur within plate interiors. In Washington the pressure between the North American Plate and the Juan de Fuca Plate (center of diagram) causes earthquakes to occur around Puget Sound and the Seattle area. It is believed that at one time in the distant past all of the plates formed one huge continent called Pangea. In the diagram the yellow lines indicate plate boundaries and the red lines mark areas of volcanic action.
Find out about earthquakes in Spokane, Seattle and earthquake hazards below.
All external links open in a new tab.
Close the tab to return to Kid's Cosmos.
Here are some basic terms used in the tour. Find more geology terms in the Glossary.
- Volcanic rock caused by partial melting of the Earth's crust.
- The spot on the surface of the Earth directly above the area where an earthquake took place.
- A split or fracture in the Earth's crust where two blocks of crust have slipped, slid or pushed against each other.
- Focus (Earthquake)
- The area inside the Earth where an earthquake happened. Also known as the Hypocenter.
- The area inside the Earth where an earthquake happened. Also known as the Focus.
- The observed effects that an earthquake shaking the ground has on people, buildings, man-made structures and natural features.
- The seismic (earthquake) energy recorded on a seismograph.
- Mercalli Intensity Scale, Modified
- Earthquake intensity measured on a scale that has 12 increasing levels. The scale takes into account how people "felt" the quake and the observed structural damage.
- Richter Magnitude Scale
- A scale that mathematically rates how much force an earthquake releases based on seismograph readings.
Kids' Cosmos… Expanding Minds Beyond the Limits of the Universe
P.O. Box 14077, Spokane, WA 99206-4077
© 2011 Kid's Cosmos
This tour created with the support of: