Glossary


A list of glossary terms used throughout the Earthquakes@Geoscience Australia website.


A – C  | D – G | H – K | L – N | O – S | T – Z |

 

A – C

Age
Geological age of a deposit or event, defined with reference to the International Stratigraphic Chart Ages are often expressed using the units 'ka' or 'Ma'.
Age of youngest deformed deposit
Geological age of the youngest deposits that have been subject to deformation in the Neotectonic period [Neotectonics database field]
Alluvial terrace
Elongate terrace(s) usually lying parallel to and above a river channel and its floodplain. Alluvial terraces consist of a relatively level strip of land, called a "tread", separated from an adjacent floodplain, other terraces, or uplands by distinctly steeper strips of land called "risers". Alluvial terraces are remnants of earlier floodplains that existed at a time when either a stream or river was flowing at a higher elevation before its channel down-cut to create a new floodplain at a lower elevation.
Approximate location
The nearest region, city or town and country for the epicentre of a teleseismic (distant) earthquake. The nearest city, town or general locality and state for a local (Australian) earthquake.
Arrival time
The UTC time (Coordinated Universal Time) at which an earthquake wave arrives and is recorded on the seismogram at a seismic station.
Average strike
Average strike or azimuth (in degrees from north) of the surface trace of a structure. In the Neotectonics Database we express the strike of a structure using the right-hand rule, whereby an azimuthal value of between 0° and 360° is assigned, with the fault plane dipping to the right. [Neotectonics database field]
Azimuth
Bearing given in degrees clockwise from North. For example, Southwest corresponds to azimuth 225°.
Bibliographic references
Bibliographic reference(s) relating to a neotectonic feature. May contain published and unpublished information sources. References are formatted as per the Australian Journal of Earth Sciences. [Neotectonics database field]
Blind thrust fault
A thrust fault that does not rupture all the way to the ground surface. Movement along the fault produces uplift in the form of an anticlinal fold, but a clear or continuous surface rupture is not recognised. Many Quaternary blind thrust faults are thought to be present in the Murray, Gippsland and Otway basins. An example of a known blind thrust fault is the Rosedale Fault underlying the Rosedale Monocline in eastern Gippsland, Victoria.
Body wave
An earthquake wave that travels within the Earth, sometimes going through its deep interior, P and S waves are body waves.
Butterworth / Band Pass
Bandpass filters describe the upper and lower limits of desired frequency ranges. The Butterworth filter type used in seismic processing produces a ripple free signal with smooth cutoffs.
Compiler
Name and affiliation of the person responsible for compiling or most recently updating the information in a database record. [Neotectonics database field]
Confidence level
In the Neotectonics Database, we define four categories of faults (Classes A-D) based on demonstrable evidence of neotectonic movement (known or presumed to be associated with large-magnitude earthquakes). [Neotectonics database field]
Class Definitions:
A. Geologic evidence demonstrates the existence of a fault of neotectonic origin, whether the fault is exposed by mapping or inferred from liquefaction or other deformational features.
B. Geologic evidence demonstrates the existence of neotectonic deformation, but either (1) the feature might not extend deeply enough to be a potential source of significant earthquakes, or (2) the currently available geologic evidence is too strong to confidently assign the feature to Class C but not strong enough to assign it to Class A.
C. Geologic evidence is insufficient to demonstrate (1) the existence of neotectonic faulting, or (2) slip or deformation associated with the feature.
D. Geologic evidence demonstrates that the feature is not a neotectonic fault or feature; this category includes features such as joints, landslides, erosional or fluvial scarps, or other landforms resembling fault scarps but of demonstrable non-tectonic origin.

D – G

Damage radius
The "damage radius" is the average distance from the earthquake epicentre to the Modified Mercalli Intensity (MMI) VI isoseismal contour. Intensity values are a measure of the level of ground shaking at a specific location. MMI VI is the level that masonry buildings might begin to take some damage depending on the construction and local soil conditions. The isoseismal contours outline areas which experience a given level of shaking or higher and are based on reports submitted to Geoscience Australia or other agencies. The amount of shaking from an earthquake can be affected by factors such as the depth of the earthquake and the local geology. Whether a building becomes damaged or not will also depends on the quality and type of the construction. These factors are not taken into consideration in the calculation of the damage radii, so these radii are approximate and should only be taken as a very rough guide to the area that would experience damage by an earthquake.
Date compiled
The date (dd/mm/yyyy) of compilation or update of a database record. [Neotectonics database field]
Defining phases
The arrival times of defining phases (earthquake waves) are used to determine the location of an earthquake. P and S arrivals are the most common defining phases.
Depth
The depth (in kilometres) at which the fault causing the earthquake begins to rupture. This depth is expressed relative to sea-level.
Depth uncertainty
The uncertainty of the depth of the earthquake varies from about 300 metres for the best located events, to 10's of kilometres for events in most parts of the world. When depth is poorly constrained by available seismic data, the seismic analyst will set the depth at a fixed value. For example, default depths of 0 or 10 km are often used in Australian areas depending on the local earthquake activity in the area.
Dextral
See right lateral.
Dip
A numerical value between 0° and 90° representing the angle the fault plane makes with the horizontal (if known). Values of dip may reflect near-surface measurements at specific locations or generalised subsurface dip values (based on geologic cross-sections or geophysical modelling). [Neotectonics database field]
Dip direction
Direction of dip of the fault plane (if known). General down-dip direction(s) of the structure are defined by compass octants: north (N), west (W), south (S), east (E), northwest (NW), northeast (NE), southwest (SW) or southeast (SE). [Neotectonics database field]
Dip-slip fault movement
Slip (movement) that is parallel to the dip of the fault. Normal slip and reverse slip are opposite senses of dip-slip movement and describe movement of the hanging wall block down and up the plane of the fault respectively (compare strike-slip fault movement).
Displacement
Height data (in metres) representing the vertical offset between the upthrown and downthrown sides of a neotectonic feature (most often a fault, fault scarp or fold). Usually derived from digital elevation data, this value does NOT necessarily represent the true slip on a fault, and is subject to the limitations of the elevation data. [Neotectonics database field]
Distance to station
The distance (in kilometres) from the seismic station to the initial earthquake fault rupture location (epicenter or hypocentre).
Domain
A spatial grouping of neotectonic features considered to exhibit similar recurrence and behavioural characteristics. [Neotectonics database field]
Earthquake
A sudden release of stress by a fault rupturing within the Earth's continental or oceanic crust which results in a series of seismic waves that propagate within the Earth's crust, mantle and core.
Earthquake data
Earthquake data constitutes information such as earthquake latitudes, longitudes, depths and magnitudes. Comprehensive catalogues containing such data are maintained to help in understanding earthquake mechanisms.
Earthquake location - Australian Region
The geographic region defined by the box with sides 10°N, 85°E, 70°S and 150°W. All earthquakes with a magnitude of 5 and over are measured and catalogued by Geoscience Australia.
Earthquake location - Australia
The geographic region that covers Australia, excluding Australia's external territories. All earthquakes that can be located are measured and catalogued by Geoscience Australia.
Entity number
Unique identifier (database-specific) associated with each record in the database. [Neotectonics database field]
Epicentre
The point on the Earth's surface directly above where the fault rupture (which caused the earthquake) started. (i.e. directly above the earthquake's hypocentre).
Faceted spur
A planar surface that truncates a spur (narrow ridge) as a result of faulting and subsequent erosion. Also known as a 'triangular facet' or 'triangular spur'. These features are commonly regarded as neotectonic features, although the rates and actual processes of their formation are poorly understood.
Fault
A fracture or zone of fractures along which there has been displacement of the adjacent blocks relative to one another. There are three major types of faults: 'normal', 'reverse' (see also 'thrust'), and 'strike-slip'.
Fault line
Generally represents the surface trace of a fault, a fault scarp, lineament, or fold axis in the Neotectonics database.
Feature name
Name given to a feature in the Neotectonics Database. The name used in the earliest reference to the feature is generally given preference, except in cases where a more commonly accepted name is widely used in the recent literature. [Neotectonics database field]
Feature type
Type of neotectonic deformation feature that best describes the record. e.g. fault, fold, uplifted terrace, etc. [Neotectonics database field]
Felt radius
The "felt radius" is based on the average distance from the epicentre to the Modified Mercalli Intensity (MMI) III isoseismal contour. Intensity values are a measure of the level of ground shaking at a specific location. The isoseismal contours outline areas which experience a given level of shaking or higher and are based on reports submitted to Geoscience Australia or other agencies. The amount of shaking people feel from an earthquake can be affected by factors such as the depth of the earthquake and the local geology. These factors are not taken into consideration in the calculation of the felt radii, so these radii are very approximate and should only be taken as a very rough guide to the area in which people would feel an earthquake.
Filters
Devices that pass desired wave frequencies while rejecting others. Filters assist in removing noise and other unsuitable frequencies allowing easier signal processing.
Focal mechanism
The three dimensional description of the seismic waves that radiate outward from the focus (hypocentre) of an earthquake. The focal mechanism contains information on the orientation and slip on two perpendicular planes, either of which could represent the fault that ruptured to produce the earthquake. Additional information is needed to select which of the two orientations is correct.
Focus
Also known as the hypocentre, the focus of an earthquake is the point on the fault plane where rupture began. This point is defined by latitude, longitude, and depth.
Fold
Bending or curvature of a stack of originally flat and planar surfaces, such as sedimentary strata, that results in permanent deformation. Folds are commonly formed by shortening of existing layers, but may also form as a result of displacement on a non-planar fault (fault bend fold), at the tip of a propagating fault (fault propagation fold), or by differential compaction.
Footwall
The underlying side of a fault. If you walked on the fault plane, your foot would be on this wall. See also 'hanging wall'.
Gap angle
The maximum angle separating two adjacent seismic stations where the angle is measured at the epicentre of an earthquake.
Geologic setting
Generalised description of the geologic setting of the fault in terms of its regional geology and location, amount of total offset, and general age of deformed strata. [Neotectonics database field]
Geomorphic expression
Generalised description of deformational features at the surface that are related to a Neotectonic feature, such as the size, shape and morphology of scarps, modified drainage, grabens, shutter ridges and faceted spurs. [Neotectonics database field]
GMT
An acronym for Greenwich Mean Time. GMT is used as the basis for standard time throughout the world. Standard time in Australia is 8–10 hours ahead of GMT, depending on your location. The Greenwich Meridian (or prime meridian of the world) is taken as 0° longitude and it is the line from which all other lines of longitude are measured. Seismologists may refer to UTC (Universal Coordinated Time), which is synonymous with GMT.
Graben
An elongate down-dropped block bounded by normal faults on its long side.

H – K

Hanging wall
The overlying side of a fault: this is the part that 'hangs' above the fault plane. See also 'footwall'.
Historic events
Identifies the date, location, magnitude and data source for any historical earthquake(s) known to be associated with a neotectonic feature. [Neotectonics database field]
Horst
An elongate uplifted block bounded by faults on its long side.
Hypocentre
The point within the Earth where the fault rupture (which caused the earthquake) started. The hypocentre is also known as the focus of the earthquake. This point is defined by latitude, longitude, and depth.
Intensity
A measure of the level of earthquake ground shaking at a specific location. The dominant intensity system used in Australia (and in most other countries) is the Modified Mercalli Intensity (MMI) scale. The magnitude of an earthquake is related to the total energy released by the event; an earthquake has only a single magnitude value. The shaking at the Earth's surface produced by an earthquake decreases with distance from the epicentre, therefore, an earthquake can have multiple intensities.
Isoseismal map
A contour map showing the distribution of intensities for an earthquake. Isoseismal lines divide areas of equal intensity from one another on an isoseismal map.
Isoseisms (or isoseismal lines)
Lines connecting points at which the intensity for an earthquake is the same.
Ka
An abbreviation for the Latin 'kilo annum', this unit of time is equal to one thousand (1000) years. The unit is commonly used when referring to the age of a geologic unit or event with respect to the present time (e.g. the event occurred between 2 ka and 4 ka).

L – N

Largest single event displacement
This field is populated where single earthquake displacements have been identified as the result of field studies. This value may not be equivalent to the absolute maximum single event displacement along the entire length of a scarp. For example, the maximum single event displacement identified from a trench investigation might be reported, but this trench may not be located at the highest part of the scarp. [Neotectonics database field]
Last update date
The date and time of the most recent assessment of the earthquake location, magnitude, depth, etc.
Lateral fault or lateral-slip fault
A fault that slips in such a way that the two sides move laterally with respect to one another. These terms are generally synonymous with strike-slip faults. See left lateral or right lateral.
Latitude
The distance North or South from the Equator measured in degrees. Positive latitudes are North, negative are South.
Left lateral
Horizontal displacement along a fault such that, when facing the fault, the side opposite the viewer appears to have moved to the left. This term is also known as 'sinistral'.
Length
Length data measured (in kilometres) as a straight line from the most distal ends of the surface trace of a neotectonic feature. This value usually represents the length of the surface expression of a neotectonic feature (most often a fault, fault scarp or fold), and is most commonly derived from digital elevation or remotely-sensed data. [Neotectonics database field]
Lineament
A linear feature, or an alignment of surficial features that may reflect control by the underlying geology. Some lineaments are defined by alignments of vegetation, patterns in drainage systems, subtle colour changes visible on aerial photographs, or cultural features such as fence lines or power lines. Some lineaments are associated with faults.
Liquefaction
The transformation of loose sediment or soil into a fluid state as a result of increasing the pressure of the fluid in between the grains due to strong ground shaking. Liquefaction typically occurs in poorly consolidated, water-saturated sediment. Liquefaction can cause significant earthquake-related damage because structures located on ground that liquefies can collapse or sink into the ground.
Liquefaction deposit
A deposit formed when loose sediment or soil is transformed into a fluid state as a result of liquefaction. The pressures generated during large earthquakes can cause the liquefied soil (usually sand) and excess water to force its way to the surface from several metres below the ground. This is often observed as 'sand boils' also called 'sand blows' or 'sand volcanoes' (as they appear to form small volcanic craters). The phenomenon may incorporate both flow of already liquefied sand from a layer below ground, and a quicksand effect whereby upward flow of water initiates liquefaction in overlying non-liquefied sandy deposits. Another observed phenomenon is land instability—cracking and movement of the ground down slope or towards unsupported margins of rivers, streams, or the coast. The failure of ground in this manner is called 'lateral spreading', and may occur on very shallow slopes of angles of only 1–2 degrees from the horizontal.
Location
The latitude, longitude and depth of where the fault causing the earthquake begins to rupture. This three dimensional location is known as the hypocentre. The two dimensional location of latitude and longitude is known the epicentre. The latitude is the number of degrees north (+) or south (−) of the equator and varies from 0 at the equator to 90 at the poles. The longitude is the number of degrees east (+) or west (−) of the zero longitude through Greenwich. The depth is in kilometres.
Location algorithm
The method used to determine the hypocentre (latitude, longitude and depth) of an earthquake.
Location method
Identifies the method employed to locate a Neotectonic feature. Examples include the use of digital elevation data, remotely sensed imagery (including aerial photography), publications, geological maps and personal communications. [Neotectonics database field]
Location precision
A measure of the error that might be expected in the location of a point feature or an arc. Sources of error include: the resolution of original source data from which points or arcs are digitised, digitisation errors, and co-ordinate transformation errors. [Neotectonics database field]
Location remarks
Provides further details about the location of the feature. Usually describes the position of the feature with respect to known localities (e.g. towns) and cultural features (e.g. roads, railways). [Neotectonics database field]
Location uncertainty
The uncertainty in the latitude and longitude of the earthquake varies from about 100 m for the best located events, to 10's of kilometres for global events in most parts of the world.
Longitude
The distance East or West measured in degrees from the Prime Meridian running through Greenwich, London. Positive longitudes are East of Greenwich, negative longitudes are West (compare latitude. See also GMT).
Ma
An abbreviation for the Latin 'mega annum', this unit of time is equal to one million (1 000 000) years. The unit is commonly used when referring to the age of a geologic unit or event with respect to the present time (e.g. the age of the deformed rock is 10 Ma).
Magnitude
The magnitude is a way of measuring the size of an earthquake from measurements of shaking made on a seismograph. Magnitude scales are logarithmic, so a magnitude 6.0 earthquake releases about 32 times the energy of a magnitude 5.0, which in turn releases about 1000 times the energy of a magnitude 4.0. The first magnitude scale developed was the Richter or local magnitude scale. Other magnitude scales such as the surface wave, body wave, and moment magnitude scales determine the size of the earthquake using different methods. Commonly used magnitude measurements include ML, MS, mb and MW.
Magnitude (preferred)
The magnitude type deemed most appropriate for a particular earthquake. The preferred magnitude type will depend on factors such as: source—receiver distance, depth, energy release and rupture characteristics.
Magnitude author
The organisation that has calculated the magnitude displayed for this earthquake. This is usually the authoritative source for earthquakes in that region. For example, in Australia or the Australian region, magnitudes determined by the Geoscience Australia are provided. In areas outside this, magnitudes from authoritative sources such as the US Geological Survey or the Pacific Tsunami Warning Center are used.
Marine terrace
A relatively flat, horizontal or gently inclined surface of marine origin, a marine terrace is usually an old abrasion platform which has been moved beyond the influence of wave activity. Accordingly the landform lies above or below current sea level, depending on the timing of its formation.
mb (body-wave magnitude)
The magnitude of an earthquake determined by measuring the maximum amplitude of the primary wave (P-wave) on a seismogram of the event. P-waves are compressional waves that have the highest velocity of all waves generated by earthquakes.
Mainshock
The largest earthquake in a series of earthquakes that cluster, both geographically and in time. To be definitively called a mainshock, it should generally be at least half a magnitude unit larger than the next largest earthquake in the series. Otherwise, the series of earthquakes may be more accurately characterised as an earthquake swarm.
ML (local magnitude)
A numerical calculation that defines the strength (magnitude) of an earthquake based on seismograms from recording stations within a 600 km radius; also commonly known as Richter magnitude. As initially defined by Charles Richter, ML represented the largest deflection of the needle on a standard seismograph at a distance of 100 km from the epicentre of a shallow earthquake that was recorded in southern California.
Modified drainage
Drainage that has been diverted, impeded or otherwise modified by changes in the shape of the land surface. Examples related to tectonic deformation include the development of swamps or sag ponds (caused by damming of an existing drainage by faulting/folding), changes in the channel form of rivers (e.g. straight versus sinuous), and diversion of river channels.
Modified Mercalli Intensity (MMI) scale
An earthquake intensity scale originally developed by Italian seismologist Giuseppe Mercalli in 1902. The scale describes the effects of an earthquake in twelve categories from I (not felt by people) to XII (total damage) (see intensity). The version of this scale used in Australia is the same as that published for New Zealand by Eiby (1966). [Eiby, G. 1966. The Modified Mercalli Scale of earthquake intensity and its use in New Zealand. New Zealand Journal of Geology and Geophysics 9, 122–129.]
MS (surface-wave magnitude)
The magnitude of an earthquake determined from surface waves on a seismogram from a teleseismic earthquake (one located more than 20° [~2000 km] away). Surface waves are seismic waves that travel over the surface of the Earth, as opposed to those that travel through the Earth, such as P-waves and S-waves. MS magnitudes are measured from surface waves that have a period of about 20 seconds.
MW (moment magnitude)
The magnitude calculated from an earthquake's total energy (seismic moment). The seismic moment is a function of the amount of slip on a fault, the area of the fault that slips, and the average strength of the rocks that are faulted. Because MW is directly related to the energy released by an earthquake, it is a uniform means of measuring earthquake magnitude and has become the standard measure of earthquake magnitude in modern seismology.
Neotectonics
For the purposes of the Neotectonics database, neotectonics is the study of deformation features that have formed under conditions imposed by the current crustal stress field. The current stress field is considered to have established in the period 5–10 Ma.
Normal fault
A fault characterised by predominantly vertical displacement in which the hanging wall moves downward with respect to the footwall of the fault. If the fault surface is exposed, the footwall is the side onto which water would flow. Generally this type of fault is associated with tectonic extension.
Number of stations and phases
These indicate the number of seismic stations and phases (earthquake waves) that were used in determining the earthquake location. Some of these stations may have been excluded from defining the final magnitude and location of this earthquake for various accuracy reasons.

O – S

Oblique slip (also oblique fault)
Describes fault motion or faulting that has a combination of lateral and vertical slip.
Paleoseismology
The geologic study of prehistoric earthquakes.
P-wave
Primary wave. The first earthquake wave to arrive at a near seismic station. The direction of vibration of the particles in the wave is the same as the direction in which the wave travels.
Phase
A type of seismic energy (earthquake wave) distinguished by its propagation speed, period, amplitude and vibration direction. P and S waves are examples of phases.
Pre-historic events
Identifies and provides timings (or ages) of pre-historic events related to a neotectonic feature (where known). It also includes any remarks relative to these events. Data to populate this field is comparatively sparse, as it is acquired primarily through field investigation and geological dating of materials. [Neotectonics database field]
Preliminary vs final
Preliminary earthquake results are updated by Geoscience Australia Seismic Analysts at a later stage when all the data are available and can be reviewed in detail post-earthquake.
Quality assurance
This flag distinguishes between features that have been identified but not yet fully investigated, and those that have been subject to field assessment and detailed validation. A feature cannot be assigned a confidence value of A without having been field validated, as indicated by the QA flag. [Neotectonics database field]
Related earthquakes
Earthquakes that can be confidently related to the neotectonics database feature. In most instances, only the earthquakes that have generated the surface expression can be related with confidence. In some instances, the largest aftershocks related to a surface rupturing earthquake might also be included. [Neotectonics database field]
Reverse fault
A fault characterised by predominantly vertical displacement in which the hanging wall moves upward with respect to the footwall of the fault. If the fault surface is exposed, the footwall is the side onto which water would flow. If the fault has a dip angle of less than 45 degrees, it is called a thrust fault. Generally this type of fault is associated with tectonic compression.
Richter scale
Introduced in 1935 by Charles F. Richter and Beno Gutenberg, the Richter scale is based on a logarithmic expression that quantifies earthquake magnitude—typically it refers to local magnitude, but for large earthquakes, it commonly refers to surface-wave magnitude. (Large earthquakes are also commonly assigned a moment magnitude, which is based on seismic moment and is a better measure of the energy of an earthquake than are local or surface-wave magnitudes.) Since the Richter scale is logarithmic, very small earthquakes (microearthquakes) can have a negative magnitude. Although the scale has no theoretical upper limit, the practical upper limit, given the strength of materials in the crust, is just below 9 for local or surface-wave magnitudes and just below 10 for moment magnitudes. (See also ML, local magnitude.)
Right lateral
Horizontal displacement along a fault such that, when facing the fault, the side opposite the viewer appears to have moved to the right. This term is also known as dextral.
Residual (time)
The time difference between an observed and a predicted phase (earthquake wave) arrival. Predicted arrivals are determined using predefined seismic wave velocity models of the Earth.
Review process
Preliminary earthquake parameters are determined by Geoscience Australia Duty Seismologists analysing real-time data. These results are displayed as soon as possible to provide information to emergency managers and the public. These preliminary results are reviewed later, and more data added if available, to improve their accuracy.
RMS residual
The root-mean-square (RMS) travel time residual. This is displayed in seconds. This parameter provides a measure of the fit of the observed earthquake wave arrival times at various seismic stations to the arrival times predicted from the computed location of the earthquake. Smaller numbers reflect a better fit of the data. The value is dependent on the accuracy of the global or local seismic wave velocity model used to compute the earthquake location, the quality weights assigned to the arrival time data, the accuracy with which the arrival times of the seismic waves can be read from the seismogram, and the procedure used to locate the earthquake.
S-wave
Secondary wave. The second wave to arrive at seismic stations near the earthquake. The direction of vibration of the particles in the wave is at right angles (perpendicular) to the direction of travel of the wave.
Sag pond
A small body of water (pond) that occupies an enclosed depression or sag formed where recent fault movement has impounded drainage. Most common along strike-slip faults and in normal fault grabens.
Scarp
A prominent to subdued, often linear, slope or escarpment. Scarps are often produced by faulting, especially that which involves a significant amount of dip slip. However, scarps can also form as a result of stream erosion, wave erosion (e.g. lake shorelines) or landsliding. Fault scarps vertically offset the ground surface, creating portions of the same surface at different elevations on either side of the scarp.
Seismic moment
A measure of the strength of an earthquake, computed from the product of the area of fault rupture, the average amount of slip, and the shear modulus (rigidity) of the rocks offset by faulting. The moment can also be calculated from the amplitude spectra of seismic waves.
Seismic zone (or seismic belt)
A region of the Earth's crust (elongated in the case of a belt) associated with active seismicity. It may or may not be associated with particular geological structures (e.g. faults).
Seismicity
Usually defined for a specific area, the seismicity describes the distribution of earthquakes in time, geographic location, depth, and magnitude.
Seismograms
The recording made by a seismograph in response to ground motion caused by an earthquake, explosion, or other energy source. Old records were recorded mechanically on paper, but modern records are recorded digitally. The seismogram's x-axis usually represents time, while the y-axis records ground motion amplitude, velocity, or acceleration.
Seismograph
An instrument that detects, magnifies, and records earthquakes and other ground motions.
Seismometer
A seismometer is an instrument used to measure ground motion. When paired with a data recorder it is referred to as a seismograph.
Sense of movement
Sense of movement for a fault is based on the angle of dip of the fault and the relative direction of movement across the fault. Terms used to describe sense of movement include normal, reverse, strike-slip, dextral (right-lateral), sinistral (left-lateral), and oblique. [Neotectonics database field]
Shaking and damage—how we estimate
We use a modified local Richter Magnitude (ML) to calculate the magnitude for earthquakes within Australia. The magnitude can then be converted into shaking and damage estimates for the area surrounding the epicentre of the earthquake. The magnitude scale is logarithmic; an increase of 1 magnitude = 10 times the shaking.
Shutter ridge
A ridge formed by vertical, lateral or oblique displacement on a fault that crosses an area having ridge and valley topography, with the displaced part of the ridge "shutting in" the valley. Almost exclusively associated with strike-slip fault movement.
Signal to noise ratio
A ratio of the earthquake vibration to background noise. The larger the ratio the more pronounced is the signal above noise.
Significant earthquake
Any earthquake that was felt in Australia or with a magnitude of 3.5 or greater. Also, any global earthquake with a magnitude of 6 or greater, but occurring at a depth of 100 km or less.
Sinistral
See left-lateral.
Slip rate
The rate of motion obtained when amount of offset is divided by time interval. The common units of measure are mm/yr or m/ka (equivalent units). The average slip rate at a point along a fault is commonly determined from geodetic measurements, displacement of cultural features, or from offset geologic features whose age can be estimated or measured. Offset is measured parallel to the predominant slip direction or estimated from the vertical or horizontal separation of geologic features. In special cases, interval slip rates may be calculated if the times and amounts of slip of prehistoric earthquake events have been determined. This type of high-quality data is rather sparse. [Neotectonics database field]
Slip rate category
Defines one of four slip-rate categories, as determined by the compiler, or based on reported slip rates. The categories include (1) less than 0.01 mm/yr, (2) 0.01 to less than 0.1 mm/yr, (3) 0.1 to 0.2 mm/yr, and (4) greater than 0.2 mm/yr. "Comments" include a brief description of the basis for the compiler's selection, or reference to relevant published slip rates and associated documentation. Generally, two types of slip rates are reported. The first type is herein termed a "geologic slip rate" and is typically derived from the age and amount of offset of geologic features. These rates are averages of slip over several to many earthquake cycles. The second type defines an interval or "paleoseismic slip rate" that is calculated on the basis of known times and amounts of slip for two or more prehistoric earthquakes. [Neotectonics database field]
Source
Geoscience Australia sometimes chooses to use the earthquake information from other organisations. The source describes whom this is.
Solution finalised
When flagged with Yes, the earthquake data have been scrutinised by a seismic analyst who has produced the most accurate assessment of the earthquake's latitude, longitude, depth and magnitude from the currently available data.
Strike
Trend or bearing of the line marking the intersection of a fault plane (or other planar geologic feature) with a horizontal surface. Strike is always perpendicular (at a right angle) to dip. [Neotectonics database field]
Strike—slip fault
A fault in which the dominant sense of motion is horizontal, parallel to the strike of the fault. Also known as a lateral-slip fault. Motion is commonly described as left-lateral (sinistral) or right-lateral (dextral).
Strike—slip fault movement
Slip (movement) that is parallel to the trace of the fault. Two kinds of strike slip occur: right-lateral (also referred to as dextral) and left-lateral (also referred to as sinistral). Also known as lateral-slip fault movement. (Compare dip-slip fault movement.)
Surface rupture
Breakage or rupture of the ground surface along the trace of a fault, as caused by an earthquake.
Surface trace
The intersection of a fault with the surface of the Earth. It is sometimes, but not always, expressed at the surface by geomorphic features such as scarps, ridges, valleys, saddles, sag ponds, etc. Also called a fault line or fault trace.
Surface wave
An earthquake wave that travels around the surface of the Earth, rather than through its interior.
Synopsis
Contains a concise summary of information that serves as a thumb-nail sketch of what is known about a neotectonic feature. [Neotectonics database field]

T – Z

Thrust fault
A reverse fault with a dip of less than 45°, in which the hanging wall moves up relative to the footwall.
Tsunamigenic
Any earthquake determined by the Geoscience Australia Duty Seismologist to have the potential to generate a tsunami. These are generally earthquakes with a magnitude of 6.5 or greater with a depth 100 km or less, under the sea or islands or near coastlines.
Time
Also known as the origin time, this is the time at which the fault causing the earthquake began to rupture. The time of the earthquake is usually computed accurately with a small uncertainty of a few seconds or less.
Time uncertainty
The uncertainty in the time at which the earthquake happened, usually no more than a few seconds. Well located earthquakes may have an uncertainty of less than 1 second.
UTC
Coordinated Universal Time. The international basis for standard time (synonymous with GMT).
Velocity model
An approximation of the thicknesses of layers in the Earth and the speed with which earthquake waves travel through each layer. These data are used by computer programs to determine the location of earthquakes from the arrival times of earthquake waves at various seismic stations.
Waveform data
The trace of seismic waves as recorded by a seismograph. The trace consists of amplitude measurements over time which can be used by seismologists to locate and estimate the size of seismic events such as earthquakes or blasts.