Coda magnitude scale

The Coda magnitude scale or Abklingmagnitude (M _d , of English duration magnitude ) is a method for measuring earthquake - magnitudes based on surface waves. It is based on the measurement of the period of time in which the signal on the seismogram is lost in the background noise after the arrival of the surface wave ( wave coda ). The method was developed in 1958 by Ede Bisztricsany . It is not dependent on the often limited dynamic range of most seismometers and offers a quick and easy method for measuring especially local, strong tremors. The calculation is dependent on constants that depend on the local conditions.

So is a dimensionless number that Bisztricsany for the measurement of near-surface earthquakes using Wiechert seismographs in the measuring station in Budapest by the expression ${\displaystyle M_{\mathrm {d} }}$

${\displaystyle M_{\mathrm {d} }=2{,}12\cdot \log _{10}\left(F-eL\right)+0{,}0065\cdot \Delta +2{,}66}$

defined the relationship while for deep earthquakes

${\displaystyle M_{\mathrm {d} }=1{,}58\cdot \log _{10}\left(F-eL\right)+0{,}002\cdot \Delta +0{,}0007\cdot h+4{,}02}$

applies.

${\displaystyle F}$and are the end and the beginning of the recorded surface waves in minutes and the distance of the measurement from the epicenter in degrees. The magnitude is then equivalent to the conventional magnitude measured in the Prague station . In the case of small values ​​of , the relevant section of the equation can be neglected, so that the distance to the epicenter does not have to be determined in the event of earthquakes close to the location of the measurement. ${\displaystyle eL}$ ${\displaystyle \Delta }$ ${\displaystyle M_{\mathrm {d} }}$ ${\displaystyle \Delta }$

In general, the formula for deriving the coda magnitude can be written as follows:

${\displaystyle M_{\mathrm {d} }=a+b\cdot \log _{10}\left(F-eL\right)-c\cdot \Delta }$

wherein on the variables described above addition , and are empirical constants. ${\displaystyle a}$ ${\displaystyle b}$ ${\displaystyle c}$

application

The method was quickly adopted by seismologists and similar determinations of the coda magnitude have been developed for many stations on all continents. An example for the acceptance of the method is the determination of the coda magnitude on the Kii peninsula in central Japan by K. Tsumura in 1967. He provided the equation valid for this area

${\displaystyle M_{\mathrm {d} }=2{,}85\cdot \log _{10}\left(F-P\right)+0{,}0014\cdot \Delta -2{,}53}$

on. and are the end and the beginning of the recorded surface waves in minutes, and are again the distance of the measurement from the epicenter in degrees. ${\displaystyle F}$ ${\displaystyle P}$ ${\displaystyle \Delta }$

An example from the recent past is the determination of the coda magnitude for the stations in Ulaanbaatar and Chowd ( Altai Mountains ) in Mongolia . The same abbreviations as above resulted for the station of Ulan Bator

${\displaystyle M_{\mathrm {d} }=-2{,}1478+2{,}2797\cdot \log _{10}\left(F-P\right)+0{,}0004\cdot \Delta }$

and was for Hovd

${\displaystyle M_{\mathrm {d} }=-2{,}1764+1{,}9969\cdot \log _{10}\left(F-P\right)+0{,}001\cdot \Delta }$

certainly.

Individual evidence

1. ↑ Magnitude based on duration. Manual of Seismological Observatory Practice, 1979 ( Memento of the original from July 23, 2008 in the Internet Archive ) Info: The archive link was automatically inserted and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  
2. ↑ ^{a b} Dashdondog Mungunsuren, Munkhuu Ulziibat, Antoine Schlupp, Jean-Louis Plantet and Marc Nicolas: Estimating Magnitude of Local Earthquakes from Signal Duration. 50th anniversary earthquake conference commemorating the 1957 Gobi-Altay earthquake, July 25 - August 8, 2007, pp. 149 - 154, Ulaanbaatar (pdf)  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective . Please check the link according to the instructions and then remove this notice.