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Kid's Tour to Mars

Earthquakes

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"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

Earthquake Fault DiagramEarthquakes 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. (Diagram adapted from a USGS diagram.)

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.

Plate Tectonics

Click for larger view of Continental PlatesScientists 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.

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Spokane Earthquake History and Geology
Pacific Northwest Seismograph Network (PNSN)
U of Washington: Surfing the Internet for Earthquake Data
 
USGS Earthquake Information
USGS Geohazards Information
USGS Western Region Earthquake Information
USGS National Earthquake Information Center

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Geology Terms

Here are some basic terms used in the tour. Find more geology terms in the Glossary.

Basalt
Volcanic rock caused by partial melting of the Earth's crust.
Epicenter
The spot on the surface of the Earth directly above the area where an earthquake took place.
Fault
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.
Hypocenter
The area inside the Earth where an earthquake happened. Also known as the Focus.
Intensity
The observed effects that an earthquake shaking the ground has on people, buildings, man-made structures and natural features.
Magnitude
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.

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