（Richter magnitude scale），亦稱地震規模（local magnitude，M_L）、又譯裡氏、黎克特製震級，是表示地震規模大小的標度。它是由觀測點處地震儀所記錄到的地震波最大振幅的常用對數演算而來。由於地震儀的位置一般並不在震央，考慮到地震波在傳播過程中的衰減以及其它干擾因素，計算時需減去觀測點所在地規模0地震所應有的振幅之對數。

發展歷史

芮氏地震規模最早是在1935年由兩位來自美國加州理工學院的地震學家芮克特（Charles Francis Richter）和古騰堡（Beno Gutenberg）共同制定的。

此標度原先僅是為了研究美國加州地區發生的地震而設計的，並用伍德-安德森扭力式地震儀（Wood-Anderson torsion seismometer）測量。芮克特設計此標度的目的是區分當時加州地區發生的大量小規模地震和少量大規模地震，而靈感則來自天文學中表示天體亮度的星等。

為了使結果不為負數，芮克特定義在距離震央100公里處之觀測點地震儀記錄到的最大水準位移為1微米（這也是伍德-安德森扭力式地震儀的最大精度）的地震作為0級地震。按照這個定義，如果距震央100公里處的伍德-安德森扭力式地震儀測得的地震波振幅為1公釐（10³微米）的話，則震級為芮氏3。芮氏地震規模並沒有規定上限或下限。現代精密的地震儀經常記錄到規模為負數的地震。

由於當初設計芮氏地震規模時所使用的伍德-安德森扭力式地震儀的限制，近震規模 M_L 若大於約6.8或觀測點距離震央超過約600公里便不適用。後來研究人員提議了一些改進，其中面波震級（M_S）和體波震級（M_b）最為常用。

缺點和改進

芮氏地震規模的主要缺陷在於它與震源的物理特性沒有直接的聯繫，並且由於「地震強度頻譜的比例定律」（The Scaling Law of Earthquake Spectra）的限制，在8.3-8.5左右會產生飽和效應，使得一些強度明顯不同的地震在用傳統方法計算後得出芮氏地震規模（如(M_S）數值卻一樣。到了21世紀初，地震學者普遍認為這些傳統的地震規模表示方法已經過時，轉而採用一種物理含義更為豐富，更能直接反應地震過程物理實質的表示方法即矩震級_W）。地震矩規模是由同屬加州理工學院的金森博雄（Hiroo Kanamori）教授於1977年提出的。該標度能更好的描述地震的物理特性，如地層錯動的大小和地震的能量等。 （Moment magnitude scale，M

地震規模與地震烈度是不同的概念。地震烈度（例如麥加利地震烈度）是表示地震破壞程度的標度，與地震區域的各種條件有關，並非地震之絕對強度。

震級與發生頻率

下表列出的是不同芮氏規模（M_L）的年均發生次數和震央地區的影響：

(數據來自美國地質調查局。需要注意的是由於地震影響還受當地地質條件等因素的影響，表中描述的是極端影響)

歷史紀錄中最強烈的地震是1960年5月22日的智利大地震，芮氏8.9（M_L），地震矩規模（M_W）9.5。

震級與能量

由於芮氏地震規模是常用對數，因此在估算能量的時候，芮氏規模每增加一，釋放的能量大約增加32倍。

下表列出的是不同級別的地震釋放的能量相當於的TNT當量：

log 能量 = 11.8 + 1.5 x 規模

log 能量 = 11.8 + 1.5 x 7.8
log 能量 = 23.5

能量 = 10^23.5 erg

則： 本次規模 7.8 地震釋放能量約為 549 顆廣島原子彈

註：(有時計算出來的「顆數」會不同，是因對爆炸當量的定義數字不同)

不容易想像其威力嗎？何不改換成其他較易理解的「單位」呢？

步槍彈：


一枚65K2步槍用彈 (

) 的能量約為 1785 J，換算為 17,850,000,000 erg。則計算後此次地震的能量約等於 17,715,841,230,000 枚

四零榴彈：


一顆四零榴彈槍用彈 (40x46 mm 榴彈) 約有 40g TNT 裝藥，換算後能量為 1,673,600,000,000 erg。

約等於 188,950,625,000 顆

手榴彈：


一顆美製 mk3 手榴彈內裝有 8 oz 的 TNT，能量換算約為 9,489,152,380,400 erg。

約等於 33,325,185,780 顆


換算成軍事武器，似乎沒照顧到那些沒入伍過，甚至入伍過但卻沒碰過這些彈藥的人喔？用這個多數人童年時都玩過的東西吧：

一根水鴛鴦約有 1 g 的黑火藥，能量約為 4,437,500,000 erg

約等於 71,262,595,160,000 根

嗯... 最近沒有童年的人似乎越來越多了，換算成這個好像又沒照顧到他們哩？而且管制越來越嚴，也不容易買到、買到也越來越沒地方可以放了... 那就換算成這個就算沒有童年的人，也應該親自接觸過；就算生活困苦或是與世俗隔離者，也應該會常在電視平面媒體上看到、各大媒體最喜歡的單位吧：



一份營養午餐約 700 KCal，換算後為 29,307,600,000,000 erg。

震度階級表

Richter magnitude scale

From Wikipedia, the free encyclopedia

The Richter magnitude scale, or more correctly local magnitude M_L scale, assigns a single number to quantify the amount of seismic energy released by an earthquake. It is a base-10 logarithmic scale obtained by calculating the logarithm of the combined horizontal amplitude of the largest displacement from zero on a Wood–Anderson torsion seismometer output. So, for example, an earthquake that measures 5.0 on the Richter scale has a shaking amplitude 10 times larger than one that measures 4.0. The effective limit of measurement for local magnitude is about M_L = 6.8.

The energy release of an earthquake, which equates to its destructive power, scales with the ³⁄₂ power of the shaking amplitude. Thus, a difference in magnitude of 1.0 is equivalent to a factor of 31.6 ((10^1.0)^{(3 / 2)}) in the energy released; a difference of magnitude of 2.0 is equivalent to a factor of 1000 ((10^2.0)^{(3 / 2)} ) in the energy released.

Development

Developed in 1935 by Charles Richter in partnership with Beno Gutenberg, both of the California Institute of Technology, the scale was originally intended to be used only in a particular study area in California, and on seismograms recorded on a particular instrument, the Wood-Anderson torsion seismometer. (Many scientists and historians feel it should be known as the Richter–Gutenberg scale, and Richter himself never attached his name to it, calling it the "earthquake magnitude scale".) Richter originally reported values to the nearest quarter of a unit, but decimal numbers were used later. His motivation for creating the local magnitude scale was to separate the vastly larger number of smaller earthquakes from the few larger earthquakes observed in California at the time.

His inspiration was the apparent magnitude scale used in astronomy to describe the brightness of stars and other celestial objects. Richter arbitrarily chose a magnitude 0 event to be an earthquake that would show a maximum combined horizontal displacement of one micrometre on a seismograph recorded using a Wood-Anderson torsion seismometer 100 kilometres (62 mi) from the earthquake epicenter. This choice was intended to prevent negative magnitudes from being assigned. However, the Richter scale has no upper or lower limit, and sensitive modern seismographs now routinely record quakes with negative magnitudes.

Because of the limitations of the Wood-Anderson torsion seismometer used to develop the scale, the original M_L cannot be calculated for events larger than about 6.8. Investigators have proposed extensions to the local magnitude scale, the most popular being the surface wave magnitude m_S and the body wave magnitude m_b. These traditional magnitude scales have largely been superseded by the implementation of methods for estimating the seismic moment and its associated moment magnitude scale.

Richter magnitudes

The Richter magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded by seismographs (adjustments are included to compensate for the variation in the distance between the various seismographs and the epicenter of the earthquake). Because of the logarithmic basis of the scale, each whole number increase in magnitude represents a tenfold increase in measured amplitude; in terms of energy, each whole number increase corresponds to an increase of about 31.6 times the amount of energy released.

Events with magnitudes of about 4.6 or greater are strong enough to be recorded by any of the seismographs in the world, given that the seismograph's sensors are not located in an earthquake's shadow.

The following describes the typical effects of earthquakes of various magnitudes near the epicenter. This table should be taken with extreme caution, since intensity and thus ground effects depend not only on the magnitude, but also on the distance to the epicenter, the depth of the earthquake's focus beneath the epicenter, and geological conditions (certain terrains can amplify seismic signals).

(Based on U.S. Geological Survey documents.)

Great earthquakes occur once a year, on average. The largest recorded earthquake was the Great Chilean Earthquake of May 22, 1960 which had a magnitude (M_W) of 9.5.

The following table lists the approximate energy equivalents in terms of TNT explosive force though note that the energy here is that of the underground energy release (ie a small atomic bomb blast will not simply cause light shaking of indoor items) rather than the overground energy release; the majority of energy transmission of an earthquake is not transmitted to and through the surface, but is instead dissipated into the crust and other subsurface structures.