地震简问简答/How much energy is released in an earthquake?

译文

问题：地震中将会释放多少能量？

回答：地震中释放的总能量包括使岩石产生新裂痕的能量，摩擦生热消耗的能量以及地层中弹性辐射出的能量。在这三者中，唯一可以被测量到的是通过地层辐射出的能量，可以由地震仪记录下来。正是这部分能量使建筑物发生摇动。

辐射能量可用多种方法获得。历史上，首先依靠经验（观察）估计出震级Ms，然后通过里氏公式（log Es = 4.8 + 1.5Ms）得出辐射能量。里氏公式中，Es是地震能量，单位是焦耳。有了现代化测量仪器之后，可以直接由震波图测出能量Es（单位：焦耳)，然后通过公式，Me = (2/3) log Es -2.9，算出能量级别Me。没有能量级别Me数据时，可以根据经验在地震力矩Mo（单位：牛顿-米，即焦耳）的基础上估算出辐射能量。测得地震力矩后Mo，通过公式Mw = (2/3) log Mo–6.0 转换为矩震级Mw，然后再通过里氏公式用Mw代替Ms算出辐射能量。

[注意，由于Me和Mw测量的是不同的物理量级，它们在数值上不一定对等。Mw是从低频位移谱上得到的一个级别数，而Me是从较高频的速度谱上得到的级别数。 Mw衡量的是割裂区域和断层平均滑动， Me衡量的则是地震产生的震动.]

地震等级和地震能量对照表（焦耳和吨TNT当量）

等级， Me衡量的能量Es， Ms/Mw衡量的能量Es，吨TNT当量，等量原子弹（颗数）

4 0.22E+11 0.63E+11 15. 0.00

5 0.71E+12 0.20E+13 475. 0.02

6 0.22E+14 0.63E+14 15023. 0.79

7 0.71E+15 0.20E+16 475063. 25.0

8 0.22E+17 0.63E+17 15022833. 790.6

9 0.71E+18 0.20E+19 475063712. 25,003.3

当能量单位用焦耳表示，可以对比TNT爆炸当量。一吨TNT具有4.2*10E09 焦耳的能量。

当量原子弹颗数和地震级别对照表

“1945年7月16日在美国新墨西哥州的阿拉莫戈多市爆破的第一颗原子弹，即A弹，产生了相当于19，000短吨（17，000公吨）TNT爆破的能量。” 引自《世界百科全书》，芝加哥菲尔德企业1975年版第843页。

原文

Q: How much energy is released in an earthquake?

A: The total energy from an earthquake includes energy required to create new cracks in rock, energy dissipated as heat through friction, and energy elastically radiated through the earth. Of these, the only quantity that can be measured is that which is radiated through the earth. It is the radiated energy that shakes buildings and is recorded by seismographs.

The radiated energy can be obtained in various ways. Historically, the radiated energy was estimated empirically (from observations) from magnitude Ms through the Richter formula, log Es = 4.8 + 1.5Ms, where Es is seismic energy in Joules. In this formula, magnitude is measured first, after which the formula is used to obtain Es. With modern instrumentation, energy can be measured directly from velocity seismograms and converted to a magnitude. If Es is energy in joules, the energy magnitude Me is obtained by Me = (2/3) log Es -2.9. If Me is not available, the seismic moment Mo of an earthquake can provide an empirical estimate of radiated energy. After Mo is measured, it is converted to a moment magnitude Mw by Mw = (2/3) log Mo – 6.0 where Mo is in Newton-meters (Joules). Mw is then used as the magnitude in the Richter formula to obtain an estimate of radiated energy.

[Note that Me and Mw do not necessarily have the same numerical value because they measure different physical quantities. Mw is a magnitude that is derived from low-frequency displacement spectra whereas Me is measured from higher frequency velocity spectra. Mw is a measure of the area of rupture and the average slip across the fault, whereas is Me is a measure of the shaking from an earthquake.]

Magnitudes and corresponding energy (Joules and tons of TNT) Magnitude Es (from Me) Es (from Ms or Mw) Tons of TNT Nuclear Bomb Equivalence (# of bombs)