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259 Cards in this Set
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A type of seismograph used to measure ground acceleration as a function of time. |
Accelerograph |
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A fault along which slip has occurred in recent geological time, or where earthquake foci are located. |
Active fault |
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Continental margin characterized by earthquakes and volcanic activity (i.e. location of transform fault or subduction zone). |
Active margin |
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An earthquake that occurs after a "mainshock" (or larger earthquake). |
Aftershock |
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The maximum height of a wave crest or depth of a trough. |
Amplitude (wave) |
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An ordered arrangement of seismometers or geophones, the data from which feeds into a central receiver. |
Array |
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The appearance of seismic energy on a seismic record. |
Arrival |
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The time at which a particular wave phase arrives at a detector. |
Arrival time |
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Not associated with an earthquake |
Aseismic |
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Area with no record of earthquakes |
Aseismic zone |
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Roughness on the fault surface posing local resistance to slip. |
Asperities (fault) |
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The layer below the lithosphere that is marked by low seismic-wave velocities and high seismic- wave attenuation. |
Asthenosphere |
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The reduction in amplitude of a wave with time or distance travelled. |
Attenuation |
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A plane orthogonal to the fault plane. |
Auxiliary fault-plane |
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An area of fault surface that is resistant to slip because of geometrical or structural changes. |
Barrier (fault) |
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A narrow zone, defined by earthquake foci, that is tens of kilometers thick dipping from the surface under the Earth's crust to depths of up to 700 kilometers. |
Benioff zone / Wadati-Benioff zone |
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A deep crustal thrust-fault with no or only indirect surface expression such as a fold structure. |
Blind thrust |
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A seismic wave that can travel through the interior of the earth. |
Body wave |
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Examples of body waves |
P-waves and S-waves |
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Magnitude of an earthquake as estimated from the amplitude of body waves. |
Body-wave magnitude |
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A fault along which it is mechanically feasible for sudden slip to occur. |
Capable fault |
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The mass per unit volume of a substance, commonly expressed in grams per cubic centimetre. |
Density |
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The value given is the depth below the surface of the mean spheroid. |
Depth of an earthquake |
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The increase in the volume of rocks mainly due to pervasive microcracking. |
Dilatancy (of rocks) |
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The angle by which a rock layer or fault plane deviates from the horizontal. The angle is measured in a plane perpendicular to the strike. |
Dip |
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A fault in which the relative displacement is along the direction of dip of the fault plane; the offset is either normal or reverse. |
Dip-slip fault |
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The spreading out of a wave train due to each wavelength travelling with its own velocity. |
Dispersion (wave) |
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Time interval between the first and last peaks of strong ground motion above a specified amplitude. |
Duration (of strong shaking) |
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The sudden release of stored elastic energy caused by the sudden fracture and movement of rocks along a fault. Some of the energy released is in the form of seismic waves, that cause the ground to shake. |
Earthquake |
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The average interval of time between the occurrence of earthquakes in a particular region. |
Earthquake occurrence (recurrence) interval |
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A series of minor earthquakes, none of which may be identified as the main shock, occurring in a limited area and time. |
Earthquake swarm |
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An earthquake with a size and generating mechanism typical for a particular fault source. |
Characteristic earthquake |
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The layer of rock located immediately below the earth's surface. Beneath continents, it is typically about 35 km thick, and composed of granite. Under the ocean, it is about 5-10 kilometres thick and composed mainly of basalt. |
Earth's crust |
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A wave that is propagated by some kind of elastic deformation, that is, a change in shape that disappears when the stresses are removed. A seismic wave is a type of this. |
Elastic wave |
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The concluding train of seismic waves that follows the principal waves from an earthquake. |
Coda |
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Tightly packed. Composed of particles that are not easily separated. |
Consolidated |
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The theory, first advanced by Alfred Wegener, that Earth's continents were originally one land mass. Pieces of the land mass split off and migrated to form the continents. |
Continental Drift |
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Part of the continental margin between the coast and the continental slope. |
Continental shelf |
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The innermost layers of the Earth. |
Core |
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Solid and has a radius of about 1300 kilometres |
Inner core |
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Fluid and is about 2300 kilometres thick. S-waves cannot travel through |
Outer core |
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Loss of energy in wave motion due to transfer into heat by frictional forces. |
Damping |
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The mass per unit volume of a substance, commonly expressed in grams per cubic centimetre. |
Density |
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The layer of rock located immediately below the earth's surface. Beneath continents, it is typically about 35 km thick, and composed of granite. Under the ocean, it is about 5-10 kilometres thick and composed mainly of basalt. |
Earth's crust |
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A wave that is propagated by some kind of elastic deformation, that is, a change in shape that disappears when the stresses are removed. A seismic wave is a type of this. |
Elastic wave |
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The point on the earth's surface directly above the focus (hypocentre) of an earthquake. |
Epicentre |
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A zone of fractures or breaks in rocks, where movements occur. Earthquakes often occur along these because they are weak zones in the rock. |
Fault |
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The plane that most closely coincides with the rupture surface of a fault. |
Fault plane |
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The first recorded signal attributed to seismic wave travel from a source. |
First arrival |
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More-or-less symmetrical splays into sub-faults near the intersection of the main fault with the ground surface. |
Flower structure |
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An earthquake that is smaller than, and precedes, a "mainshock". |
Foreshock |
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Number of oscillations per unit time; unit is Hertz (Hz),which equals 1 cycle per second. |
Frequency |
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In a fault zone, crushed, sheared, and powdered rock altered to clay. |
Gouge |
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The value given is the depth below the surface of the mean spheroid. |
Depth of an earthquake |
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A crustal block of rock generally long and narrow, that has dropped down along boundary faults relative to the adjacent rocks. |
Graben |
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An earthquake having a magnitude of 8 or greater on the Richter scale. |
Great Earthquake |
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Discontinuity in seismic velocity that marks the boundary between the core and the mantle. |
Gutenberg discontinuity |
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A situation that has the possibility of occurring. |
Hazard |
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The unit of frequency equal to 1 cycle per second, or 2 PI radians per second. |
Hertz |
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The current geological time period that started about 10,000 years ago. |
Holocene |
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The subsurface location (focus) at which the energy of an earthquake is released. Earthquakes generally occur at depths less than about 30 km, but may occur to a depth of 600 km or more in some areas. |
Hypocentre |
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An index of the resistance of an elastic body, such as a rock, to volume change. |
Incompressibility |
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Central solid region of the Earth's core, probably mostly iron; radius about 1221 kilometers, discovered by Inge Lehmann in 1936. |
Inner core |
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The Modified Mercalli Scale is a numerical scale used to catagorize earthquakes based on descriptions of how the earthquake was felt. These effects may range from I (not felt except by a very few under especially favourable conditions) and XII (total damage). |
Intensity |
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The increase in the volume of rocks mainly due to pervasive microcracking. |
Dilatancy (of rocks) |
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Earthquake with its focus on a plate boundary. Offshore earthquakes of western Canada are of this type. |
Interplate earthquake |
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The angle by which a rock layer or fault plane deviates from the horizontal. The angle is measured in a plane perpendicular to the strike. |
Dip |
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A fault in which the relative displacement is along the direction of dip of the fault plane; the offset is either normal or reverse. |
Dip-slip fault |
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The spreading out of a wave train due to each wavelength travelling with its own velocity. |
Dispersion (wave) |
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Time interval between the first and last peaks of strong ground motion above a specified amplitude. |
Duration (of strong shaking) |
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The sudden release of stored elastic energy caused by the sudden fracture and movement of rocks along a fault. Some of the energy released is in the form of seismic waves, that cause the ground to shake. |
Earthquake |
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The average interval of time between the occurrence of earthquakes in a particular region. |
Earthquake occurrence (recurrence) interval |
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A series of minor earthquakes, none of which may be identified as the main shock, occurring in a limited area and time. |
Earthquake swarm |
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Earthquake with its focus within a tectonic plate. Eastern Canadian earthquakes are of this type. |
Intraplate earthquake |
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A surface wave which travels through the continental crust. This wave type is the one which causes damage during large Eastern Canadian earthquakes. |
Lg Wave |
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Chain of islands above a subduction zone (e.g., Japan, Aleutians). |
Island arc |
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A line connecting points on the Earth's surface at which earthquake intensity is the same. It is usually a closed curve around the epicentre. |
Isoseismal Line |
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The way in which the lithosphere 'floats' on the asthenosphere. |
Isostasy |
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An abrupt movement of geological materials downhill in response to gravity. It can be triggered by an earthquake or other natural causes. |
Landslide |
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The location of a point north or south of the equator.It is shown on a map or globe as east-west lines parallel to the equator. |
Latitude |
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A strike-slip fault on which the displacement of the far block is to the left when viewed from either side. |
Left-lateral fault: (sinistral) |
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The process in which a granular solid (soil) takes on the characteristics of a liquid as a result of an increase in pore pressure and a reduction in stress. In other words, solid ground loses cohesion and starts flowing like a liquid. |
Liquefaction |
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Physical character of rocks. |
Lithology |
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The outer, rigid shell of the Earth above the asthenosphere. It contains the crust, continents, and plates. |
Lithosphere |
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Earthquake with its focus within a tectonic plate. Eastern Canadian earthquakes are of this type. |
Intraplate earthquake |
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A surface wave which travels through the continental crust. This wave type is the one which causes damage during large Eastern Canadian earthquakes. |
Lg Wave |
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The location of a point east or west of the prime meridian. It is shown on a map or globe as north-south lines left and right of the prime meridian, which passes through Greenwich, England. |
Longitude |
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A major type of surface wave having a horizontal motion that is shear or transverse to the direction of propagation (travel). |
Love wave |
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Any layer in the Earth in which seismic wave velocities are lower than in the layers above and below. |
Low-velocity zone |
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It is a measure of the amount of energy released during an earthquake. It may be expressed using the Richter scale. |
Magnitude |
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The largest earthquake in a "cluster" of earthquakes. These are sometimes preceded by "foreshocks", and generally followed by aftershocks. |
Mainshock |
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An earthquake having a magnitude of 7 to 7.99 on the Richter scale. |
Major Earthquake |
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The main bulk of the Earth, between the crust and the core, ranging from depths of about 40 to 3470 kilometres. It is composed of dense silicate rocks and divided into a number of concentric shells. Under Eastern Canada, it can be found at around 40 km depth. |
Mantle (of Earth) |
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The area of strong shaking and significant damage in an earthquake. |
Meizoseismal region |
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An earthquake having a magnitude of 2 or less on the Richter scale. |
Microearthquake |
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Chain of islands above a subduction zone (e.g., Japan, Aleutians). |
Island arc |
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A more or less continuous motion in the Earth that is unrelated to an earthquake and that has a period of 1.0 to 9.0 seconds. It is caused by a variety of natural and artificial agents. |
Microseism |
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The division of a town or county into smaller areas according to their variation in seismic hazard. |
Microzonation |
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An earthquake having a magnitude of 5 to 6 on the Richter scale. |
Moderate earthquake |
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The Mercalli scale rates the intensity of shaking from an earthquake. The ratings vary from I (felt only under especially favourable circumstances) to XII (total destruction). |
Modified Mercalli Intensity Scale |
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The boundary surface or sharp seismic-velocity discontinuity that separates the Earth's crust from the underlying mantle. Under Eastern Canada, it can be found at around 40 km depth. |
Mohorovicic discontinuity (the Moho): |
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A measure of earthquake size related to the leverage of the forces (couples) across the area of the fault slip. The rigidity of the rock times the area of faulting times the amount of slip. Dimensions are dyne-cm (or Newton-metres). |
Moment (of earthquakes): |
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Magnitude of an earthquake estimated by using the seismic moment. |
Moment magnitude (MW) |
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A dip-slip fault in which the rock above the fault plane has moved downward with respect to the rock below. |
Normal fault |
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The slip on the fault has components both along the dip and along the strike of the fault. |
Oblique faulting |
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The exact time at which an earthquake occurred. |
Origin time |
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A line connecting points on the Earth's surface at which earthquake intensity is the same. It is usually a closed curve around the epicentre. |
Isoseismal Line |
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The way in which the lithosphere 'floats' on the asthenosphere. |
Isostasy |
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An abrupt movement of geological materials downhill in response to gravity. It can be triggered by an earthquake or other natural causes. |
Landslide |
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The location of a point north or south of the equator.It is shown on a map or globe as east-west lines parallel to the equator. |
Latitude |
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A strike-slip fault on which the displacement of the far block is to the left when viewed from either side. |
Left-lateral fault: (sinistral) |
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The process in which a granular solid (soil) takes on the characteristics of a liquid as a result of an increase in pore pressure and a reduction in stress. In other words, solid ground loses cohesion and starts flowing like a liquid. |
Liquefaction |
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Physical character of rocks. |
Lithology |
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The outer, rigid shell of the Earth above the asthenosphere. It contains the crust, continents, and plates. |
Lithosphere |
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Outer liquid shell of the Earth's core, probably iron with some oxygen; inner radius, 1221 kilometres, outer radius, 3480 kilometres. |
Outer core |
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The odds that the size of a future earthquake will exceed some specified value. |
Probability of exceedence of a given earthquake size |
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The geological period covering about 2 million years ago to the present. |
Quaternary |
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Also called primary, longitudinal, irrotational, push, pressure, dilatational, compressional, or push-pull wave. They are the fastest body waves and arrive at stations before the S waves, or secondary waves. |
P wave |
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The study of ancient (prehistoric) earthquakes from their geological evidences. |
Paleoseismology |
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Continental margin formed during initial rifting apart of continents to form an ocean; frequently has thick sedimentary deposits. |
Passive margin |
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The time interval between successive crests in a sinusoidal wave train; it is the inverse of the frequency of a cyclic event. |
Period (wave) |
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The onset of a displacement or oscillation on a seismogram, indicating the arrival of a different type of seismic wave. |
Phase: (seismic) |
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The crust and upper mantle of the earth are made up of about a dozen large plates and several smaller ones that are constantly moving. The movements are very slow -only a few centimetres per year. Where the plates rub against one another, strain builds up, especially at the edges. |
Plates and plate tectonics |
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A change in the geological or geophysical conditions that is a forerunner to earthquake generation on a fault. It cannot reliably be recognized as such beforehand. |
Precursor |
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The forecasting in time, place, and magnitude of an earthquake; the forecasting of strong ground motions. |
Prediction (of earthquakes) |
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The number of cases that meet a given description divided by the total number of (equally likely) cases possible. |
Probability |
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A type of surface wave having a retrograde elliptical motion at the Earth's surface. These are the slowest, but often the largest and most destructive, of the wave types caused by an earthquake. |
Rayleigh wave |
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It is a measure of intensity of shaking from an earthquake. This scale was replaced by the Mercalli intensity scale. |
Rossi-Forel Intensity Scale: |
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The elevation of the water level above the immediate tide level when a tsunami runs up onto the coastal land. |
Runup height |
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Also called shear, secondary, rotational, tangential, equivoluminal, distortional, transverse, or shake wave. These waves carry energy through the Earth in very complex patterns of transverse (crosswise) waves. |
S wave |
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These waves move more slowly than P waves, but in an earthquake they are usually bigger. |
S wave |
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A narrow geological depression found in strike-slip fault zones. Those that contain water are called sag ponds. |
Sag (fault) |
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A cliff or steep slope formed by displacement of the ground surface. |
Scarp (fault) |
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A free or standing wave oscillation of the surface of water in an enclosed basin, that is initiated by local atmospheric changes, tidal currents, or earthquakes. Similar to water sloshing in a bathtub. |
Seiche |
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Of or having to do with earthquakes. |
Seismic |
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An elongated earthquake zone, for example, circum-Pacific, Mediterranean, Rocky Mountain. |
Seismic belt |
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About 60% of the world's earthquakes occur in the ______ |
Circum-Pacific seismic belt |
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They are usually felt as a rolling or rocking motion and, in the case of major earthquakes, can be seen as they approach. |
Rayleigh wave |
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A surface or thin layer within the Earth across which P-wave and/or S-wave velocities change rapidly. |
Seismic discontinuity |
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An area in an earthquake-prone region where there is a below-average release of seismic energy. |
Seismic gap |
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A tsunami generated by an undersea earthquake. |
Seismic Sea Wave |
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They are vibrations generated by sudden movements of rock. After earthquakes occur, they propagate from the hypocentre to the surface of the Earth. |
Seismic Wave |
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A region in which earthquakes are known to occur. |
Seismic Zone |
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The occurrence of earthquakes in space and time. |
Seismicity: |
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Recording of ground motions made by a seismograph. |
Seismogram |
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A very sensitive instrument used to record and measure earthquakes. |
Seismograph |
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A scientist who studies earthquakes, seismic sources, and wave propagation through the Earth. |
Seismologist |
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The study of earthquakes, seismic sources, and wave propagation through the Earth. |
Seismology |
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The approximate length of time between earthquakes in a specific seismically active area. |
Recurrence Interval |
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The sensor part of the seismograph, usually a suspended pendulum. |
Seismometer |
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The instrumental aspects of seismology. |
Seismometry |
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A simple seismograph recording on a plate without time marks. |
Seismoscope |
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The study of earthquakes and their relationships with faults. |
Seismotectonics |
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The area on the Earth's surface protected from seismic wave arrivals. |
Shadow zone |
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The comparison between the amplitude of the seismic signal and the amplitude of noise caused by seismic unrest and (or) the seismic instruments. |
Signal-to-noise ratio |
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The relative motion of one face of a fault relative to the other. |
Slip (fault) |
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Growth in the amplitude of earthquakes when seismic waves pass from rock into less rigid material such as soil. |
Soil amplification |
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The layout of seismometer or geophone groups from which data from a single shot (the explosive charge) are recorded simultaneously. |
Spread |
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To bounce back from a surface that represents an acoustic impedance contrast. |
Reflect |
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To bend or change direction due to an acoustic impedance contrast. |
Refract |
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The rock above the fault plane (the "hanging"wall) moves up and over the rock below ("foot" wall). |
Reverse faulting |
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Region where the crust has split apart, usually marked by a rift valley (e.g., East African Rift, Rhine Graben). |
Rift |
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A strike-slip fault on which the displacement of the far block is to the right when viewed from either side. The Queen Charlotte fault is one of this type of fault. |
Right-lateral fault: (dextral) |
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An index of the resistance of an elastic body to shear. The ratio of the shearing stress to the amount of angular rotation it produces in a rock sample. |
Rigidity |
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The probabilistic risk is the odds of an earthquake occurring and causing damage within a given time interval and region. |
Risk (seismic) |
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The geometrical deformation or change in shape of a body. The change in an angle, length, area, or volume divided by the original value. |
Strain (elastic) |
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Earthquakes resulting from sudden release of energy stored by major deformation of the Earth. |
Tectonic earthquakes |
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An earthquake that is distant (usually more than 20 degrees) from the recording station. |
Teleseism |
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A reverse fault in which the upper rocks above the fault plane move up and over the lower rocks at an angle of 30 ° or less so that older strata are placed over younger. |
Thrust fault |
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Construction of the image of velocity variations inside the Earth from measurements of seismic waves at the surface. |
Tomography |
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A strike-slip fault connecting the ends of an offset in a midoceanic ridge, an island arc, or an arcridge chain. Pairs of plates slide past each other along these. |
Transform fault |
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The time required for a wave train to travel from its source to the point of observation. |
Travel time |
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A graph of travel time versus distance for the arrival of seismic waves from distant events. Each type of seismic wave has its own curve. |
Travel-time curve |
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Long, narrow arcuate depression in the seabed which results from the bending of the lithospheric plate as it descends into the mantle at a subduction zone. |
Trench |
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The point where three plates meet. |
Triple junction |
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A series of huge ocean waves caused by a rapid, large-scale disturbance of the sea water, such as a major earthquake beneath the seabed that causes large vertical movements. |
Tsunami |
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The sudden reduction of stress across the fault plane during rupture. |
Stress (drop) |
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Loosely arranged, not cemented together, so particles separate easily. |
Unconsolidated |
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UTC |
Coordinated Universal Time |
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The time scale based on the atomic second but corrected every now and again to keep it in approximate sync with the earth's rotation. |
UTC |
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A material which can behave as an elastic solid on a short time scale and as a viscous fluid on a long time scale. |
Viscoelastic material |
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An opening in the crust that has allowed magma to reach the surface. |
Volcano |
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Geological process which involved the eruption of molten rock. |
Volcanism |
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Imaginary surface or line that joins points at which the waves from a source are in phase (e.g., all at a maximum or all at a minimum). |
Wavefront |
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The distance between two successive crests or troughs of a wave. |
Wavelength |
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A measure of the forces acting on a body in units of force per unit area. |
Stress (elastic) |
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The line of intersection between the fault plane and the surface of the Earth. Its orientation is expressed as the angle west or east of true north. |
Strike of fault |
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A fault whose relative displacement is purely horizontal. |
Strike-slip fault |
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The shaking of the ground near an earthquake source made up of potentially damaging seismic waves of various types. |
Strong ground motion |
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A region where the earth's plates collide, with one plate sliding beneath the other. The world's largest earthquakes occur along this type of plate boundary. |
Subduction Zone |
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Waves that move over the surface of the Earth. Rayleigh and Love waves are examples. |
Surface Waves |
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Magnitude of an earthquake estimated from measurements of the amplitude of surface waves. |
Surface-wave magnitude: MS |
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A series of minor earthquakes, none of which may be identified as the main shock, occurring in a limited area and time. |
Swarm: (or Earthquake swarm) |
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The geometrical deformation or change in shape of a body. The change in an angle, length, area, or volume divided by the original value. |
Strain (elastic) |
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Earthquakes resulting from sudden release of energy stored by major deformation of the Earth. |
Tectonic earthquakes |
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An earthquake that is distant (usually more than 20 degrees) from the recording station. |
Teleseism |
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A reverse fault in which the upper rocks above the fault plane move up and over the lower rocks at an angle of 30 ° or less so that older strata are placed over younger. |
Thrust fault |
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Construction of the image of velocity variations inside the Earth from measurements of seismic waves at the surface. |
Tomography |
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A strike-slip fault connecting the ends of an offset in a midoceanic ridge, an island arc, or an arcridge chain. Pairs of plates slide past each other along these. |
Transform fault |
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The time required for a wave train to travel from its source to the point of observation. |
Travel time |
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A graph of travel time versus distance for the arrival of seismic waves from distant events. Each type of seismic wave has its own curve. |
Travel-time curve |
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Long, narrow arcuate depression in the seabed which results from the bending of the lithospheric plate as it descends into the mantle at a subduction zone. |
Trench |
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The point where three plates meet. |
Triple junction |
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A series of huge ocean waves caused by a rapid, large-scale disturbance of the sea water, such as a major earthquake beneath the seabed that causes large vertical movements. |
Tsunami |
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The sudden reduction of stress across the fault plane during rupture. |
Stress (drop) |
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Loosely arranged, not cemented together, so particles separate easily. |
Unconsolidated |
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UTC |
Coordinated Universal Time |
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The time scale based on the atomic second but corrected every now and again to keep it in approximate sync with the earth's rotation. |
UTC |
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A material which can behave as an elastic solid on a short time scale and as a viscous fluid on a long time scale. |
Viscoelastic material |
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An opening in the crust that has allowed magma to reach the surface. |
Volcano |
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Geological process which involved the eruption of molten rock. |
Volcanism |
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Imaginary surface or line that joins points at which the waves from a source are in phase (e.g., all at a maximum or all at a minimum). |
Wavefront |
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The distance between two successive crests or troughs of a wave. |
Wavelength |
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In the Philippines, the intensity of an earthquake is determined using the _____ |
PHIVOLCS Earthquake Intensity Scale (PEIS) |
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Types of Earthquakes |
Tectonic Earthquakes Volcanic Earthquakes Man-made Earthquakes |
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A measure of the forces acting on a body in units of force per unit area. |
Stress (elastic) |
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Produced by sudden movement along faults and plate boundaries. |
Tectonic earthquakes |
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Induced by rising lava or magma beneath active volcanoes. |
Volcanic earthquakes |
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Induced by mining and extraction of natural resources from the ground and other human activities like, large dam and building construction, atomic explosions, etc. |
Man-made earthquakes |
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The line of intersection between the fault plane and the surface of the Earth. Its orientation is expressed as the angle west or east of true north. |
Strike of fault |
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A fault whose relative displacement is purely horizontal. |
Strike-slip fault |
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The shaking of the ground near an earthquake source made up of potentially damaging seismic waves of various types. |
Strong ground motion |
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A region where the earth's plates collide, with one plate sliding beneath the other. The world's largest earthquakes occur along this type of plate boundary. |
Subduction Zone |
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Waves that move over the surface of the Earth. Rayleigh and Love waves are examples. |
Surface Waves |
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Magnitude of an earthquake estimated from measurements of the amplitude of surface waves. |
Surface-wave magnitude: MS |
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A series of minor earthquakes, none of which may be identified as the main shock, occurring in a limited area and time. |
Swarm: (or Earthquake swarm) |
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The geometrical deformation or change in shape of a body. The change in an angle, length, area, or volume divided by the original value. |
Strain (elastic) |
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Earthquakes resulting from sudden release of energy stored by major deformation of the Earth. |
Tectonic earthquakes |
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An earthquake that is distant (usually more than 20 degrees) from the recording station. |
Teleseism |
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A reverse fault in which the upper rocks above the fault plane move up and over the lower rocks at an angle of 30 ° or less so that older strata are placed over younger. |
Thrust fault |
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Construction of the image of velocity variations inside the Earth from measurements of seismic waves at the surface. |
Tomography |
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A strike-slip fault connecting the ends of an offset in a midoceanic ridge, an island arc, or an arcridge chain. Pairs of plates slide past each other along these. |
Transform fault |
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The time required for a wave train to travel from its source to the point of observation. |
Travel time |
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A graph of travel time versus distance for the arrival of seismic waves from distant events. Each type of seismic wave has its own curve. |
Travel-time curve |
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Long, narrow arcuate depression in the seabed which results from the bending of the lithospheric plate as it descends into the mantle at a subduction zone. |
Trench |
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The point where three plates meet. |
Triple junction |
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A series of huge ocean waves caused by a rapid, large-scale disturbance of the sea water, such as a major earthquake beneath the seabed that causes large vertical movements. |
Tsunami |
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The sudden reduction of stress across the fault plane during rupture. |
Stress (drop) |
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Loosely arranged, not cemented together, so particles separate easily. |
Unconsolidated |
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UTC |
Coordinated Universal Time |
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The time scale based on the atomic second but corrected every now and again to keep it in approximate sync with the earth's rotation. |
UTC |
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A material which can behave as an elastic solid on a short time scale and as a viscous fluid on a long time scale. |
Viscoelastic material |
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An opening in the crust that has allowed magma to reach the surface. |
Volcano |
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Geological process which involved the eruption of molten rock. |
Volcanism |
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Imaginary surface or line that joins points at which the waves from a source are in phase (e.g., all at a maximum or all at a minimum). |
Wavefront |
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The distance between two successive crests or troughs of a wave. |
Wavelength |
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In the Philippines, the intensity of an earthquake is determined using the _____ |
PHIVOLCS Earthquake Intensity Scale (PEIS) |
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Types of Earthquakes |
Tectonic Earthquakes Volcanic Earthquakes Man-made Earthquakes |
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A measure of the forces acting on a body in units of force per unit area. |
Stress (elastic) |
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Produced by sudden movement along faults and plate boundaries. |
Tectonic earthquakes |
|
|
Induced by rising lava or magma beneath active volcanoes. |
Volcanic earthquakes |
|
|
Induced by mining and extraction of natural resources from the ground and other human activities like, large dam and building construction, atomic explosions, etc. |
Man-made earthquakes |
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The line of intersection between the fault plane and the surface of the Earth. Its orientation is expressed as the angle west or east of true north. |
Strike of fault |
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A fault whose relative displacement is purely horizontal. |
Strike-slip fault |
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|
The shaking of the ground near an earthquake source made up of potentially damaging seismic waves of various types. |
Strong ground motion |
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|
A region where the earth's plates collide, with one plate sliding beneath the other. The world's largest earthquakes occur along this type of plate boundary. |
Subduction Zone |
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Waves that move over the surface of the Earth. Rayleigh and Love waves are examples. |
Surface Waves |
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Magnitude of an earthquake estimated from measurements of the amplitude of surface waves. |
Surface-wave magnitude: MS |
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A series of minor earthquakes, none of which may be identified as the main shock, occurring in a limited area and time. |
Swarm: (or Earthquake swarm) |
