Earthquakes
Vocabulary for Catastrophic Events - Earthquakes
Terms
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- Liquefaction
- this happens when loose, moist soil or sand is shaken so hard that individual grains separate, turning the earth into a soft, fluid slurry that can swallow entire buildings.
- Thrust fault
- occurs when the rocks move almost horizontally with the older rocks being piled on top of the younger rocks.
- Longitudinal (compressional) waves
- are a primary wave that travels by compressing the crust in front of it and stretching the crust in back of it. They travel the fastest. They originate from the earthquake's focus and spread in all directions. They can travel through solids, liquids,a nd gases. They move rock back and forth between a squeeaed and stretched portion. They move umderground, causing structures on the surface to move back and forth. They cause high-frequency vibrations that cause low buildings to vibrate more than tall structures.
- Magnitude
- measurement of energy released by an earthquake; maximum motion shown on a seismograph.
- Focus
- the point underground where the earthquake started.
- Fold
- a bend in rock that forms where part of the earth's crust is compressed. During folding, the stress can cause an anticline (ground mounds upward) or a syncline (ground sinks downsward).
- liquefaction
- is a process by which water-saturated sediment temporarily loses strength and acts as a fluid, like when you wiggle your toes in the wet sand near the water at the beach. This effect can be caused by earthquake shaking.
- Seismogram
- A record written by a seismograph in response to ground motions produced by an earthquake, explosion, or other ground-motion sources.
- Syncline
- a downward fold in rock.
- Aftershocks
- earthquakes of lesser intensity than the mainshock. They may occur minutes, hours, days, weeks, or years after the first quake.
- Rayleigh wave
- is a type of surface wave caused by the earth's surface rolling like ocean waves.
- Convection
- is the heat transfer involving the movement of fluids, liquids and gases. during convection, heated particles of fluid begin to flow, transferring heat energy from one part of the fluid to another. When a liquid or gas is heated, the particles move faster. As the particles move faster, they spread apart. Because they are farther apart, they occupy more space. The density decreases.
- tsunami
- A sea wave of local or distant origin that results from large-scale seafloor displacements associated with large earthquakes, major submarine slides, or exploding volcanic islands.
- Intensity
- the effect of the earthquake on the earth's surface, humans, and structures.
- Seismic waves
- are elastic waves generated by an impulse such as an earthquake or an explosion. They may travel either along or near the earth's surface (Rayleigh and Love waves) or through the earth's interior (P and S waves).
- lithosphere
- The upper solid part of the earth, including the crust and uppermost mantle. It is about 100 km thick, although its thickness is age dependent. It's below the crust is brittle enough at some locations to produce earthquakes by faulting.
- Seismologist
- scientist who studies earthquakes.
- Richter Scale
- measures magnitude or energy released at the focus of an earthquake.
- Richter Scale
- an objective measure of the strength of an earthquake. It measures the degree of magnitude.
- Moho
- The boundary between the crust and the mantle in the earth. This is a depth where seismic waves change velocity and there is also a change in chemical composition. The boundary is between 25 and 60 km deep beneath the continents and between 5 and 8 km deep beneath the ocean floor.
- Lithosphere
- the uppermost layer of the earth, which consists of all solid rock. It includes both the crust and the upper mantle.
- Tension
- a form of stress that pulls and stretches the earth's crust, causing it to become thinner in the middle.
- Intensity
- the amount of shaking and type of damage at a particular location. Intensity can be greater or weaker depending on the distance from the epicenter.
- Normal fault
- occurs when the two sides of a fault pull apart. The rocks on one side drop down lower than the other side. This is the result of two divergent boundaries undergoing tension. The hanging wall moves downward.
- Fault
- a break in the earth's crust where slabs of rock slip past each other.
- Focus
- the source of the earthquake inside the earth, where the rock first begins to break.
- velocity
- How fast a point on the ground is shaking as a result of an earthquake.
- Crust
- the top layer of the earth, which consists of solid rock. Both the continental crust (land masses) and oceanic crust (the land beneath the ocean) belong to the crust.
- Mantle
- the layer beneath the crust. The upper mantle is solid rock; the lower mantle is molten rock.
- Reverse fault (dip-slip)
- occurs when the two sides of a fault push together. The rocks on one side get pushed up over the rocks on the other side. This is the result of convergent plates undergoing compression, and the hanging wall moves upward.
- Fault
- a break or separation in rock, usually between two or more tectonic plates.
- S-wave
- stands for secondary or shear waves. This is a seismic body wave that shakes the ground back and forth perpendicular to the direction the wave is moving. These occur when the motion of the particles move at right angles to the direction of the wave (also called transverse waves).
- Epicenter
- the point directly above the focus or source of the earthquake.
- Tectonic Plates
- individual sections of the lithosphere of the earth. They fit together in a way similar to a jigsaw puzzle, but are always moving very slowly, floating on the molten rock of the lower mantle.
- L-wave
- stands for Love or surface wave caused by the earth's surface moving side to side.
- Convergent
- a boundary where earth's tectonic plates move toward each other. This causes a collision or subduction. This will result in the formation of volcanoes and mountain ranges.
- Mercalli Scale
- a subjective measure of the strength of an earthquake. It measures the degree of intensity.
- Dip-slip fault
- another name for a reverse or a normal fault. In a reverse fault, compression from pushing together (convergent plates) causes the hanging wall to move up. In a normal fault, tension from pulling apart (divergent plates) causes the hanging wall to move down.
- Compression
- a form of stress that pushes rocks together until they fold or break.
- Ring of Fire
- This is the zone of earthquakes surrounding the Pacific Ocean which is called the Circum-Pacific Belt. About 90% of the world's earthquakes occur there. The next most seismic region (5-6% of earthquakes) is the Alpide Belt (estends from Mediterranean region, eastward through Turkey, Iran and northern India.
- Seismograph
- instrument that plots the intensity of earthquake waves on a roll of specially marked graph paper.
- Stress
- a pushing or a pulling force that causes changes on or below the earth's surface.
- Convection current
- is the flow that transfers heat within a fluid. The heat from the earth's mantle and core causes convection currents to form in the astenosphere and throughout the mantle. The heating and cooling of the fluid, changes in the fluid's density, and the force of gravity combine to set convection currents in motion.
- Magnitude
- the amount of energy released from the earthquake. The size of the seismic waves at the epicenter, which can be determined by the size of the wavy lines on the seismogram.
- Seismogram
- written recording of the earth's vibrations, produced by a seismograph.
- Strike-slip Fault
- occurs when the blocks of rock have mostly moved horizontally (laterally). This horizontal movement happens at transform boundaries undergoing transverse movement.
- Seismic Waves
- vibrations that move through the earth in a way similar to waves moving in water. They can travel through solids and liquids.
- Shear
- a form of stress that pushes a rock in two opposite horizontal directions.
- Anticline
- an upward fold in rock.
- Transverse waves
- occur when the motion of the particles move at right angles to the direction of the wave. Examples would be S waves or shear waves. These are secondary waves. They travel the slowest. They can only travel through solids. They spread out in all directions from the focus. They move rocks beneath the earth's surface from side to side, giving tbuildings a good shaking and causing much damage. They may also move in a vertical direction and are strong enough to launch you out of your seat. They cause high-frequency vibrations that cause low buildings to vibrate more than tall structures.
- Epicenter
- the point on the earth's surface directly over the focus.
- P-wave
- stands for primary waves caused by an earthquake (also called longitudinal or compressional waves).
- Divergent
- a boundary where earth's tectonic plates move away from each other. This causes formations like mid-ocean ridges and rift valleys.
- asthenosphere
- The bottom layer of the earth's mantle that lies beneath the lithosphere and consists of several hundred kilometers of deformable rock.