Sunday, November 24, 2019

How much energy does an earthquake release?

When an earthquake occurs, stress accumulated in solid rock is suddenly released along fault lines. The energy released when the rocks break along the fault is converted into seismic waves that radiate from the origin.
How much energy is involved largely depends on the magnitude of the quake: larger quakes release much, much more energy than smaller quakes. The Richter magnitude scale was devised by Charles F. Richter in 1935 to classify local earthquakes in southern California, but has evolved into the most common parameter to describe the size of the quake and hence, its energy and potential of destructive power.
It is logarithmic, meaning that an increase of 1 corresponds to a 10-fold increase in the amplitude of the seismic waves generated, which shake the ground. It can also be used to estimate the released energy of a quake, following the Gutenberg-Richter magnitude-energy relation:
log E = 1.5×R + 4.8
or equivalently:
E = 101.5×R + 4.8
The relationship also involves that an increase of 1 in magnitude results in an approx. 30-fold increase in energy.

Seismic energy by magnitude compared:

Magnitude Energy in joules (J) Wh TNT equiv. Notes
-2.0 63 0.0000175 KWh near 0 1 kg dropped 6.30 m
-1.0 2000 0.00056 KWh 0.5 g of TNT 100 kg person jumps down 2 m
0.0 6.3 x 104 0.0175 KWh 15 g of TNT 60W light bulb turned on for 17 mins
1.0 2.0 x 106 0.56 KWh 0.5 kg of TNT 60W light bulb turned on for 9 hrs
2.0 6.3 x 107 17.5 KWh 15 kg of TNT Only felt nearby
60W light bulb turned on for 12 days
3.0 2.0 x 109 556 KWh 0.5 tons of TNT Energy from 50 liters of petrol
4.0 6.3 x 1010 17.5 MWh 15 tons of TNT Annual energy consumption of 4 average UK households (US: 1.5)
Often felt up to 10s of km distance
5.0 2.0 x 1012 556 MWh 500 tons of TNT Energy from 50,000 liters of petrol
Annual energy consumption of 47 average US households
6.0 6.3 x 1013 17.5 GWh 15 kilotons of TNT 1945 Hiroshima bomb
Annual energy consumption of 1500 average US households
7.0 2.0 x 1015 556 GWh 500 kilotons of TNT Annual energy consumption of 47,000 average US households
8.0 6.3 x 1016 17.5 TWh 15 million tons of TNT 1–2 earthquakes this size each year
Total annual energy use of Cuba
9.0 2.0 x 1018 556 TWh 500 million tons of TNT Total annual energy use of UK

Some facts about earthquake energy:

  • A single magnitude 8+ quake typically releases more energy than all other earthquakes combined during the same year (if no other quakes of similar magnitude occur).
  • Magnitude 9+ quakes occur only every few years to decades on average, but account for significant part of the total seismic energy released during whole centuries.
  • The largest recorded earthquake in history was the so-called "Great Chilean Earthquake" or "Valdivia Earthquake" which occurred on May 22, 1960 near Valdivia, in southern Chile. It had a magnitude of 9.5, which is also near the largest theoretically possible value. It accounts for about 30% of the total seismic energy released on earth during the last 100 years.
For example, the 14th November 2019 7/0R in Indonesia, released energy as follows:

Date & time: Thursday, 14 November 2019 16:17 UTC
Magnitude: 7.0
Depth: 27.0 km
Epicenter latitude / longitude: 1.6°N / 126.36°E (Indonesia)
Nearest volcano: Todoko-Ranu (127 km)
Primary data source: GFZ
Estimated released energy: 2*10^15 J (554 GWh / 4.8*10^5 tons of TNT / 29.8 atomic bombs equivalent)

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