Earthquake duration magnitude
Encyclopedia
The concept of Earthquake Duration Magnitude - originally proposed by Bisztricsany in 1958 using surface wave
s only - is based on the realization that on a recorded earthquake seismogram
the total length of the seismic wavetrain - sometimes referred to as the CODA - reflects its size. Thus larger earthquakes give longer seismograms [as well as stronger seismic waves] than small ones. The seismic wave interval measured on the time axis of an earthquake record - starting with the first seismic wave
onset until the wavetrain amplitude
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.
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 California
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
led to the use of signal duration to estimate the coda magnitude (Md) 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 Md 0.0 to 5.0.
earthquakes [approximately 100,000 events over the period 1981-2002 in the Richter local [ML] magnitude range of 3.5-5.8] and for India
n earthquakes examplified by an aftershock
sequence of 121 events with Ms (surface wave magnitude) > 4.0 in 2001 in the Bhuj
area of northwestern India , the latest empirically derived equation
s for Md determinations are published:
( Castello et al., 2007)
( Mandal et al., 2004)
Surface wave
In physics, a surface wave is a mechanical wave that propagates along the interface between differing media, usually two fluids with different densities. A surface wave can also be an electromagnetic wave guided by a refractive index gradient...
s only - is based on the realization that on a recorded earthquake seismogram
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 , with the z axis perpendicular to the Earth's surface and the x- and y- axes parallel to the surface...
the total length of the seismic wavetrain - sometimes referred to as the CODA - reflects its size. Thus larger earthquakes give longer seismograms [as well as stronger seismic waves] than small ones. The seismic wave interval measured on the time axis of an earthquake record - starting with the first seismic wave
Seismic wave
Seismic waves are waves of energy that travel through the earth, and are a result of an earthquake, explosion, or a volcano that imparts low-frequency acoustic energy. Many other natural and anthropogenic sources create low amplitude waves commonly referred to as ambient vibrations. Seismic waves...
onset until the wavetrain amplitude
Amplitude
Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation...
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 [Md] Development
In 1965, Solovev proposed the use of total durationTime
Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....
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 California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
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
Instrumentation is defined as the art and science of measurement and control of process variables within a production, or manufacturing area....
led to the use of signal duration to estimate the coda magnitude (Md) 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 Md 0.0 to 5.0.
Md Empirical Relationships
In two most recent investigations using statistically stable samples for ItalianItaly
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
earthquakes [approximately 100,000 events over the period 1981-2002 in the Richter local [ML] magnitude range of 3.5-5.8] and for India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
n earthquakes examplified by an aftershock
Aftershock
An aftershock is a smaller earthquake that occurs after a previous large earthquake, in the same area of the main shock. If an aftershock is larger than the main shock, the aftershock is redesignated as the main shock and the original main shock is redesignated as a foreshock...
sequence of 121 events with Ms (surface wave magnitude) > 4.0 in 2001 in the Bhuj
Bhuj
Bhuj is a city and a municipality in Kachchh district in the state of Gujarat, India.-History:It was established by Rao Hamirji in 1510 and was made the state capital by Rao Khengarji I in 1549. Its foundation stone as state capital laid formally on Vikram Samvat 1604 Maagha 5th...
area of northwestern India , the latest empirically derived equation
Equation
An equation is a mathematical statement that asserts the equality of two expressions. In modern notation, this is written by placing the expressions on either side of an equals sign , for examplex + 3 = 5\,asserts that x+3 is equal to 5...
s for Md determinations are published:
( Castello et al., 2007) ( Mandal et al., 2004)ML from Md
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 ML to Md for a rather small sample of 17 events in Arizona: