Earthquake duration magnitude
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The concept of Earthquake Duration Magnitude – originally proposed by E. Bisztricsany in 1958 using surface waves only - is based on the realization that on a recorded earthquake
seismogram A seismogram is a graph output by a seismograph. It is a record of the ground motion at a measuring station as a function of time. Seismograms typically record motions in three cartesian axes (x, y, and z), with the z axis perpendicular to the ...
, the total length of the seismic wavetrain – sometimes referred to as the CODA – reflects its size. Thus larger earthquakes give longer seismograms s well as stronger seismic wavesthan small ones. The seismic wave interval measured on the time axis of an earthquake record - starting with the first
seismic wave A seismic wave is a wave of acoustic energy that travels through the Earth. It can result from an earthquake, volcanic eruption, magma movement, a large landslide, and a large man-made explosion that produces low-frequency acoustic energy ...
onset until the wavetrain
amplitude The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of am ...
diminishes to at least 10% of its maximum recorded value - is referred to as "earthquake duration". It is this concept that Bisztricsany first used to develop his Earthquake Duration Magnitude Scale employing surface wave durations.


Earthquake Duration Magnitude () development

In 1965, Solovev proposed the use of total
duration Duration may refer to: * The amount of time elapsed between two events * Duration (music) – an amount of time or a particular time interval, often cited as one of the fundamental aspects of music * Duration (philosophy) – a theory of time and ...
instead of the duration of surface waves. In 1972, Lee et al. used coda duration for the first time to estimate Richter magnitude of local
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n earthquakes. Based on their study, they suggested that it is appropriate to estimate the magnitude of local earthquakes using signal duration. More recently, the development in
instrumentation Instrumentation a collective term for measuring instruments that are used for indicating, measuring and recording physical quantities. The term has its origins in the art and science of scientific instrument-making. Instrumentation can refer to ...
led to the use of signal duration to estimate the coda magnitude () for earthquakes recorded on short-period vertical seismographs. Numerous studies determined the relation between coda duration and magnitude for different regions of the World. According to a recent study by Mandal et al. (2004), previous studies showed that duration magnitude estimation is quite stable for local earthquakes ranging from magnitude 0.0 to 5.0.


empirical relationships

In two most recent investigations using statistically stable samples for
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earthquakes (approximately 100,000 events over the period 1981–2002 in the Richter local [] magnitude range of 3.5–5.8) and for Indian earthquakes exemplified by an aftershock sequence of 121 events with (surface wave magnitude) > 4.0 in 2001 in the
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area of northwestern India, the latest ''empirically'' derived equations for determinations are published: M_d = 2.49*log_ (T) - 2.31 + (Station\ correction\ factor) (Castello et al., 2007) M_d = 0.08*log_ (T)^2 + 1.7*log_ (T) - 0.87 (Mandal et al., 2004) Where is coda duration magnitude, and ''T'' is the coda duration in seconds.


from

Although conversions between empirically derived "sensitive" seismic parameters such as earthquake magnitude scales is mathematically cautioned as well as physically limited, some seismologists such as Brumbaugh have nevertheless attempted to produce a relationship linking to for a rather small sample of 17 events in Arizona: M_L = 0.936 * M_d - 0.16 \pm 0.22


References

{{Seismic scales Seismic magnitude scales