| Dictionary of Earthquake Terminology |
| AFTERSHOCK - additional tremors that occur after the initial earthquake BODY WAVE - a vibration from an earthquake that moves through the interior of the earth COMPLEX FAULTS - a series of faults that may tilt rocks in many different directions COMPRESSIONAL WAVE - body wave that shakes the ground back and forth in the same direction and the opposite direction as the direction the wave is moving ; also known as a P wave CONTINENTAL DRIFT - when major plates are slowly but steadily moved apart CRUST - the outermost major layer of the earth, ranging from about 10 to 65 km in thickness worldwide. The uppermost 15-35 km of crust is brittle enough to produce earthquakes DISPLACEMENT - the difference between the initial position of a reference point and any later position. The amount any point affected by an earthquake has moved from where it was before the earthquake EARTHQUAKE - a trembling and shaking of the earth’s surface; a vibration or trembling of the ground caused by movement of the subsurface EPICENTER - the position on the earth’s surface above the focus of an earthquake FAULT - great fractures between masses of rock at the earth’s surface; a large crack or break in a series of rocks; where two plates slip past each other FOCUS - the place below ground where an earthquake starts FORESHOCK - a small tremor before a major earthquake GRABEN - a down-dropped block of the earth's crust resulting from extension, or pulling, of the crust HARMONIC TREMOR - continuous rhythmic earthquakes that can be detected by seimographs. Harmonic tremors often precede or accompany volcanic eruptions HORST - a block of rock thrown up between normal faults HYPOCENTER - the place below ground where an earthquake starts LANDSLIDE - a mass of loose rock and soil that slides down a steep slope LOVE WAVE - a type of surface wave where motion is horizontal and is transverse (or perpendicular) to the direction the wave is traveling MAGNITUDE - the size of an earthquake as measured on the Richter scale MERCALLI SCALE - a measure of an earthquake’s intensity, ranging from 1 to 12 NORMAL FAULT - a fault in which blocks of rock slip straight down; also called dip-slip faults OBLIQUE-SLIP FAULT - a fault in which blocks of rock slip up or down, and then past each other diagonally; when it happens on a large scale, they are known as transtension or transpression faults PRIMARY WAVE - fast-moving body waves that push and pull on rocks laterally; they move at 3 miles (5 km) per second RAYLEIGH WAVE - seismic surface wave causing the ground to shake in an elliptical motion, with no transverse, or perpendicular, motion REVERSE FAULT - a fault in which one block of rock slides up over another RICHTER SCALE - a scale ranging from 1 to 10 used to show the size of an earthquake RIFT VALLEY - a huge, trough-shaped valley created by faulting RING OF FIRE - the area around the Pacific Basin where a lot of seismic activity occurs, including the Western coast of North and South America and East Asian islands like Japan SECONDARY WAVE - a type of body wave, slightly slower than a primary wave, that moves rocks vertically or horizontally; they move at 2 miles (3 km) per second SEISMOGRAPH - instrument that makes an automatic record of the time, duration, direction, and intensity of earthquakes SEISMOLOGIST - scientist who studies earthquakes and their causes and results SHEAR WAVE - a seismic body wave that shakes the ground back and forth perpendicular to the direction the wave is moving ; also known as an S wave SHOCK WAVE - wave of energy that is produced underground as rocks snap; when they reach the surface they cause violent shaking STRESS - the intensity of two forces working against each other SURFACE WAVE - a vibration from an earthquake that travels at ground level TECT0NIC PLATES - large, thin, relatively rigid plates that move relative to one another on the outer surface of the Earth THRUST FAULT - when a reverse fault has an angle of 45º or less TREMOR - shaking caused by earthquakes TSUMAMI - a large sea wave caused by an earthquake; commonly referred to as a tidal wave WRENCH FAULT - a fault in which blocks of rock slip sideways past each other; also known as tear faults, strike-slip faults, or, when especially large, transcurrent faults |
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| California-Berkely |