Richter magnitude scale and energy equivalents in terms of TNT explosive force

 

The following table lists the approximate energy equivalents in terms of TNT explosive force – though note that the earthquake energy is released underground rather than overground.[21] Most energy from an earthquake is not transmitted to and through the surface; instead, it dissipates into the crust and other subsurface structures. In contrast, a small atomic bomb blast (see nuclear weapon yield) will not, it will simply cause light shaking of indoor items, since its energy is released above ground.

Approximate magnitude Approximate TNT equivalent for
seismic energy yield
Joule equivalent Example
0.0 15 g 63 kJ
0.2 30 g 130 kJ Large hand grenade
1.5 2.7 kg 11 MJ Seismic impact of typical small construction blast
2.1 21 kg 89 MJ West fertilizer plant explosion
3.0 480 kg 2.0 GJ Oklahoma City bombing, 1995
3.5 2.7 metric tons 11 GJ PEPCON fuel plant explosion, Henderson, Nevada, 1988
3.87 9.5 metric tons 40 GJ Explosion at Chernobyl nuclear power plant, 1986
3.91 11 metric tons 46 GJ Massive Ordnance Air Blast bomb
6.0 15 kilotons 63 TJ Approximate yield of the Little Boy atomic bomb dropped on Hiroshima (~16 kt)
7.9 10.7 megatons 45 PJ Tunguska event
8.35 50 megatons 210 PJ Tsar Bomba—Largest thermonuclear weapon ever tested. Most of the energy was dissipated in the atmosphere. The seismic shock was estimated at 5.0–5.2
9.15 800 megatons 3.3 EJ Toba eruption 75,000 years ago; among the largest known volcanic events.
13.0 100 teratons 420 ZJ Yucatán Peninsula impact (creating Chicxulub crater) 65 Ma ago (108 megatons; over 4×1029 ergs = 400 ZJ).

Magnitude empirical formulae

These formulae are an alternative method to calculate Richter magnitude instead of using Richter correlation tables based on Richter standard seismic event (M_\mathrm{L}=0, A=0.001mm, D=100 km).

The Lillie empirical formula:

tnt

Where:

  • A is the amplitude (maximum ground displacement) of the P-wave, in micrometers, measured at 0.8 Hz.
  • \Delta is the epicentral distance, in km.

For distance less than 200 km:

M_\mathrm{L} = \log_{10} A + 1.6\log_{10} D - 0.15

For distance between 200 km and 600 km:

M_\mathrm{L} = \log_{10} A + 3.0\log_{10} D - 3.38

where A is seismograph signal amplitude in mm, D distance in km.

The Bisztricsany (1958) empirical formula for epicentral distances between 4˚ to 160˚:

M_\mathrm{L} = 2.92 + 2.25 \log_{10} (\tau) - 0.001 \Delta^{\circ}

Where:

  • M_\mathrm{L} is magnitude (mainly in the range of 5 to 8)
  • \tau is the duration of the surface wave in seconds
  • \Delta is the epicentral distance in degrees.

The Tsumura empirical formula:

M_\mathrm{L} = -2.53 + 2.85 \log_{10} (F-P) + 0.0014 \Delta^{\circ}

Where:

  • M_\mathrm{L} is the magnitude (mainly in the range of 3 to 5).
  • F-P is the total duration of oscillation in seconds.
  • \Delta is the epicentral distance in kilometers.

The Tsuboi, University of Tokyo, empirical formula:

M_\mathrm{L} = \log_{10}A + 1.73\log_{10}\Delta - 0.83

Where:

  • M_\mathrm{L} is the magnitude.
  • A is the amplitude in um.
  • \Delta is the epicentral distance in kilometers.
Source :

Wikipedia

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