This wordbook includes words normally accustomed describe the character of earthquakes, however they occur, and their effects, likewise as a discussion of the instruments accustomed record earthquake motion. every word or phrase that's in blue within the text is explained during this wordbook.
Accelerograph
A measuring device whose output is proportional to ground acceleration (in comparison to the standard measuring device whose output is proportional to ground velocity). Accelerographs area unit generally used as instruments designed to record terribly sturdy ground motion helpful in engineering design; seismographs normally record off scale in these circumstances. Normally, sturdy motion instruments don't record unless triggered by sturdy ground motion.
Aftershock
One of several earthquakes that usually occur throughout the times to months once some larger earthquake (mainshock) has occurred. Aftershocks occur within the same general region because the mainshock and area unit believed to be the results of minor readjustments of stress at places within the fault zone.
Amplitude
The amplitude of a unstable wave is that the quantity the bottom moves because the wave passes by. (As AN illustration, the amplitude of AN ocean wave is simple fraction the space between the height and trough of the wave. The amplitude of a unstable wave will be measured from the signal recorded on a seismogram.)
Aseismic creep
Movement on a fracture within the Earth that happens while not inflicting earthquakes. This movement is therefore slow that it's not recorded by standard seismographs.
Collision
A term generally applied to the convergence of 2 plates within which neither plate subducts. Instead, the perimeters of the plates crumple and area unit severely misshapen.
Convection
The motion of a liquid driven by gravity and temperature variations within the material. within the Earth, wherever pressure and temperature area unit high, rocks will act like viscous fluids on a continuance of immeasurable years. Thus, scientists believe that convection is a crucial method within the rocks that structure the world.
Convergent boundary
The boundary between 2 plates that approach each other. The convergence could end in geological process if one plate yields by diving deep into the world, obduction if one plate is thrust over the opposite, or collision if the plates merely ram into one another and area unit misshapen.
Core
The Earth's central region, believed to be composed principally of iron. The core features a radius of three,477 kilometers and is enclosed by the Earth's mantle. At the middle of the melted outer core may be a solid inner core with a radius of one,213 kilometers.
Earthquake
The release of keep clastic energy caused by fulminant fracture and movement of rocks within the world. a part of the energy free produces unstable waves, like P, S, and surface waves, that travel outward all told directions from the purpose of initial rupture. These waves shake the bottom as they surpass. AN earthquake is felt if the shaking is robust enough to cause ground accelerations extraordinary close to one.0 centimeter/second' (Richter, 1958).
Epicenter
The location on the surface of the world directly higher than the main focus, or place wherever AN earthquake originates. AN earthquake caused by a fault that offsets options on the Earth's surface could have AN epicentre that doesn't lie on the trace of that fault on the surface. happens|this happens} if the fault plane isn't vertical and also the earthquake occurs below the Earth's surface.
Fault
A break within the Earth on that movement happens. fulminant movement on a fault produces earthquakes. Slow movement produces aseismic creep.
Fault plane resolution
The calculation of the orientation, dip, and slip direction of a fault that created the bottom motion recorded at measuring device stations. generally known as a focal mechanism resolution.
Focus
The place within the Earth wherever rock initial breaks or slips at the time of AN earthquake; additionally known as the hypocenter. the main focus may be a single purpose on the surface of a burst fault. throughout an excellent earthquake, which could rupture a fault for many kilometers, one might be standing on the rupturing fault, nevertheless be many kilometers from the main focus.
Intensity
A live of the severity of shaking at a specific web site. it's sometimes calculable from descriptions of injury to buildings and parcel of land. The intensity is usually greatest close to the earthquake epicentre. Today, the changed scale is usually accustomed rank the intensity from I to XII per the type and quantity of injury created. Before 1931 earthquake intensifies were typically according exploitation the Rossi-Forel scale (Richter, 1958).
Kilometers and alternative metric units of measure:
Conversion formulae:
Millimeters x zero.039 = inches
Centimeters x zero.394 = inches
Meters x 3.28 = feet
Kilometers x zero.621 = statute miles
Square kilometers x zero.386 = sq. miles
Cubic kilometers x zero.240 = cuboid miles
Liquifaction
A process, in which, throughout ground shaking, some sandy, water-saturated soils will behave like liquids instead of solids.
Magnitude
A amount characteristic of the overall energy free by AN earthquake, as contrasted with intensity, that describes its effects at a specific place. variety of earthquake magnitude scales exist, together with native (or Richter) magnitude (ML), body wave magnitude (Mb), surface wave magnitude (Ms), moment magnitude (Mw), and conclusion magnitude (Mc). As a general rule, a rise of 1 magnitude unit corresponds to 10 times larger ground motion, a rise of 2 magnitude units corresponds to a hundred times larger ground motion, and then on during a power series. Commonly, earthquakes area unit recorded with magnitudes from zero to eight, though sometimes massive ones (M = 9) and extremely little ones (M = -I or -2) also are recorded. close earthquakes with magnitudes as little as a pair of to three area unit oft felt. the particular ground motion for, say, a magnitude five earthquake is concerning zero.04 millimeters at a distance of a hundred kilometers from the epicenter; it's one.1 millimeters at a distance of one0 kilometers from the epicentre.
Mainshock
The largest during a series of earthquakes occurring closely in time and area. The mainshock is also preceded by foreshocks or followed by aftershocks.
Mantle
A rock layer, about 2,894 kilometers thick, between the crust and core. just like the crust, the higher a part of the mantle is comparatively brittle. Together, the higher brittle a part of the mantle and also the crust type tectonic plates.
Modified Mercalli Intensity Scale
A scale for measurement ground shaking at a web site, and whose values vary from I (not felt) to XII (extreme harm to buildings and land surfaces).
NEHRP
The federal National Earthquake Hazard Reduction Program, enacted in 1977, to scale back potential losses from earthquakes by funding analysis in earthquake prediction and hazards and to guide the implementation of earthquake loss reduction programs.
Normal Fault
A normal fault may end up from vertical motion of 2 adjacent blocks underneath horizontal tension. (It additionally happens in rocks underneath compression if stress is unequal in numerous directions. during this case, the minimum and most compressive stresses should be applied horizontally and vertically severally.) during a common fault, the higher of the 2 adjacent blocks of rock slips comparatively downward.
P (Primary) waves
Also known as compressional or longitudinal waves, P waves area unit the quickest unstable waves created by associate degree earthquake. They oscillate the bottom back and forth on the direction of wave travel, in a lot of a similar method as sound waves, that are compressional, move the air back and forth because the waves travel from the sound supply to a sound receiver.
Plates
Pieces of crust and brittle topmost mantle, maybe a hundred kilometers thick and lots of or thousands of kilometers wide, that cowl the Earth's surface. The plates move terribly slowly over, or presumably with, a viscous layer within the mantle at rates of a couple of centimeters p.a..
Plate boundaries
The edges of plates or the junction between plates. confer plates, convergent (both collision and subduction), spreading, and rework boundaries.
Plate tectonics
A wide accepted theory that relates most of the earth science options close to the Earth's surface to the movement and interaction of comparatively skinny rock plates. the speculation predicts that the majority earthquakes occur once plates move past one another.
Return times
Sometimes known as the return time or return interval. The come time, or additional properly the common come time, of associate degree earthquake is that the range of years between occurrences of associate degree earthquake of a given magnitude in an exceedingly specific space. as an example, if the common time of associate degree earthquake having magnitude bigger than or adequate seven is a hundred years, then, on the common, such earthquakes can occur each a hundred years. If such earthquakes occur haphazardly in time, there's perpetually the possibility that the particular measure between the events are less or bigger than a hundred years. come time is best delineate in terms of possibilities. within the case of associate degree earthquake having a 100-year average come time, there's regarding associate degree eighteen p.c probability that such associate degree earthquake can occur within the next twenty years and a sixty three p.c probability than it'll occur within the next a hundred years. On the opposite hand, there's a fourteen p.c probability that it'll not occur within the next two hundred years.
Reverse Fault
A rupture that results from vertical motion of 2 adjacent blocks caused by horizontal compression. typically known as a overthrust fault. in an exceedingly overthrust fault, the higher of the 2 adjacent blocks moves comparatively upward.
Richter Magnigtude Scale
An earthquake magnitude scale, additional properly known as native magnitude scale, supported measurements of the amplitude of earthquake waves recorded on a customary Wood-Anderson kind measuring system at a distance of but 600 kilometers from the geographic point (Richter, 1958).
S (Secondary or shear) waves
S waves oscillate the bottom perpendicular to the direction of wave travel. They travel regarding one.7 times slower than P waves. as a result of liquids won't sustain shear stresses, S waves won't travel through liquids like water, liquified rock, or the Earth's outer core.
Seiche
A wave in an exceedingly closed body of water like a lake or bay. It are often characterised because the sloshing of water within the insertion basin. Seiches are often created by unstable waves from earthquakes. The permanent tilting of lake basins caused by near fault motions has created terribly energetic seiches.
Seismic waves
A undulation disturbance within the Earth that travels at speeds of many kilometers per second. There area unit 3 main kinds of unstable waves within the earth: P (fastest), S (slower), and surface waves (slowest). unstable waves area unit created by earthquakes.
Seismogram
A graph showing the motion of the bottom versus time.
Seismograph
A sensitive instrument that may notice, amplify, and record ground vibrations too little to be perceived by kith and kin.
Site response
Local vibrating response to unstable waves. Some sites expertise additional or less violent shaking than others, counting on factors like the character and thickness of loose sediments and/or the configuration of the underlying bedrock.
Strike-slip fault
Horizontal motion of 1 block relative to a different on a fault plane. If one stands on one aspect of the fault associate degreed observes that associate degree object on the opposite aspect moves to the proper throughout an earthquake, the fault is named a right-lateral fracture (like California's San Andreas fault). If the article moves to the left, the fault is named a left-lateral fracture.
Subduction zone boundary
The region between convergency plates, one amongst that dives at a lower place the opposite. The Cascadia geological process zone boundary is associate degree example.
Subduction earthquake
A thrust-type earthquake caused by slip between convergency plates in an exceedingly geological process zone. Such earthquakes sometimes occur on the shallow a part of the boundary and might exceed magnitude eight.
Surface waves
Seismic waves, slower than P or S waves, that propagate on the Earth's surface instead of through the deep interior. 2 principal kinds of surface waves, Love and John William Strutt waves, area unit generated throughout associate degree earthquake. John William Strutt waves cause each vertical and horizontal ground motion, and Love waves cause horizontal motion solely. They each manufacture ground shaking at the Earth's surface however little or no motion deep within the Earth. as a result of the amplitude of surface waves diminishes less apace with distance than the amplitude of P or S waves, surface waves area unit usually the foremost vital part of ground shaking faraway from the earthquake supply.
Transform boundary
A boundary between plates wherever the relative motion is horizontal. The San Andreas fault could be a rework boundary between the North America plate and also the Pacific plate. The whiten fracture zone could be a rework boundary between the Juan Diamond State Fuca and also the Pacific plates.
Tsunami
A moving ridge could be a series of terribly long wavelength ocean waves caused by the fulminant displacement of water by earthquakes, landslides, or submarine slumps. Ordinarily, tsunamis area unit created solely by earthquakes exceptional magnitude seven.5. within the open ocean, moving ridge waves travel at speeds of 600-800 kilometers/hour, however their wave heights area unit sometimes solely a couple of centimeters. As they approach shallow water close to a coast, moving ridge waves travel additional slowly, however their wave heights could increase to several meters, and so they'll become terribly harmful.
World-wide commonplace measuring system Network
A network of regarding a hundred and ten equally tag measuring system stations that area unit distributed throughout the globe. The network was originally established within the early Sixties, and its operation is currently coordinated by the U.S. earth science Survey. every station has six seismometers that live vertical and horizontal ground motion in 2 frequency ranges.