里氏量表解释:历史、公式和局限性

Charles Richter and the Birth of Earthquake Measurement

In 1935, a young seismologist at the California Institute of Technology named Charles Francis Richter had a practical problem. The seismological laboratory received reports of dozens of earthquakes each week from stations across Southern California, but there was no standard way to compare their sizes. Some quakes were clearly larger than others, but no one had a number for "how much larger."

Richter, working with his colleague Beno Gutenberg, devised an elegant solution. He would use the maximum amplitude recorded on a 地震仪用于探测并记录地震波引起的地面运动的仪器。现代数字地震仪可探测到小于一纳米的位移。 of a standard type — the Wood-Anderson torsion seismometer — and adjust for the distance between the station and the earthquake. The result was a dimensionless number he initially called the "magnitude" scale but which the world came to call the Richter scale. His 1935 paper established the framework that all subsequent magnitude scales would build upon, and 地震记录图地震仪记录的输出结果，以时间为函数显示地面运动情况。地震学家通过分析地震记录图来确定地震的震级、深度和位置。 analysis became the foundation of earthquake measurement worldwide.

How the Richter Scale Works: The Logarithmic Formula

The original 里氏震级查尔斯·里克特于1935年提出的最初对数震级标度，用于测量地方性地震的震级。如今已在很大程度上被矩震级取代，但媒体报道中仍常被提及。, technically known as local magnitude (ML), is defined by a deceptively simple formula. Richter took the logarithm (base 10) of the maximum wave amplitude measured in micrometres on a standard seismograph at 100 kilometres distance and called that the magnitude. For stations at different distances, he applied correction factors derived from tables of how amplitude decreases with distance in Southern California.

The logarithmic nature has a critical practical implication: each whole number increase in magnitude corresponds to a tenfold increase in the amplitude of shaking recorded on the seismograph. In terms of actual energy released, the relationship is steeper — each magnitude unit represents approximately 31.6 times more energy. A 震级量化地震所释放总能量的单一数值。震级每增加一个整数单位，释放的能量约增加31.6倍。 7.0 earthquake therefore releases about 31.6 times more energy than a 6.0, and about 1,000 times more than a 5.0.

Limitations of the Richter Scale for Large Earthquakes

The original Richter scale worked well for moderate earthquakes in Southern California, the region for which it was calibrated. When seismologists tried to apply it to large earthquakes elsewhere, problems emerged. The most serious was "saturation" — for very large earthquakes, different magnitude scales give inconsistent readings that fail to grow appropriately with earthquake size.

The 地方性震级（ML）最初的里氏震级，通过距震中600公里以内伍德-安德森地震仪记录的最大振幅计算得出，仅适用于地方性浅源地震。 scale saturates because it is based on high-frequency waves recorded on a particular type of instrument. For great earthquakes with magnitude above about 6.5 to 7.0, the energy is mostly carried at very long periods — slow, sweeping motions of the ground that the original Wood-Anderson seismometer could not capture well. This is why scientists noticed that the Richter scale gave similar values for the 1960 Chile earthquake and the 1964 Alaska earthquake, even though both events were clearly "off the charts" in terms of destruction. Those two events are now known to have had moments equivalent to approximately magnitude 9.5 and 9.2, respectively.

Why Scientists Switched to Moment Magnitude

The 矩震级衡量地震规模的现代标准（Mw），基于地震矩——即断层面积、平均滑动量与岩石刚度的乘积。对任何规模的地震都能给出准确结果。 scale (Mw), developed by Thomas Hanks and Hiroo Kanamori in 1979, solved the saturation problem by measuring something physically meaningful: the seismic moment of the earthquake. Seismic moment is the product of three quantities — the rigidity of the rock, the area of the fault that ruptured, and the average amount of slip. This can be calculated from 地震记录图地震仪记录的输出结果，以时间为函数显示地面运动情况。地震学家通过分析地震记录图来确定地震的震级、深度和位置。 analysis at very long periods, using 宽频带地震仪能够在0.001至50赫兹的宽频率范围内记录地震波的地震仪，是现代全球地震观测网络中的主要仪器。s that record the full spectrum of ground motion.

Because seismic moment scales with the true physical size of the earthquake without saturating, Mw gives consistent and physically meaningful values for all earthquake sizes. The formula relating Mw to seismic moment is logarithmic, and Richter himself calibrated the original scale so that for moderate earthquakes the values agree closely. This means you can often see ML and Mw values that are nearly identical for moderate quakes, which eases the transition.

Common Misconceptions About the Richter Scale

Several persistent misconceptions surround the Richter scale. The most common is that it is the scale scientists use today — it is not. The 美国地质调查局（USGS）负责监测地震、运营国家地震信息中心并向全球发布实时地震数据的美国政府主要机构。 and virtually all major seismological agencies worldwide now report moment magnitude (Mw), yet news media continue to say "on the Richter scale" as if that were the current standard. The mistake is understandable because for most newsworthy earthquakes in the magnitude 5–7 range, Mw and ML give very similar numbers.

Another misconception is that there is a maximum value for the scale. There is no theoretical ceiling. Richter himself noted that the scale was open-ended at both ends. Similarly, there is no minimum — seismologists routinely detect and catalogue micro-earthquakes at negative magnitudes. The practical limits are set by what instruments can detect and what physics can produce.

A third misconception is that each magnitude step is "10 times more destructive." This confuses amplitude (which does increase tenfold per step) with energy (which increases 31.6-fold per step) with actual damage (which depends on depth, distance, soil, and construction quality in complex ways).

Richter Scale in Media: Why It Persists

Despite being scientifically superseded, the "Richter scale" name continues to dominate media coverage of earthquakes for several reasons. It is short, simple, and familiar — a single word that any headline can carry. The phrase entered popular culture deeply during the mid-20th century when Richter himself was a prominent public scientist who gave numerous interviews and was telegenic in explaining earthquakes to the public.

The persistence also reflects the close numerical agreement between scales for the moderate earthquakes that most news stories cover. When a reporter writes "magnitude 5.8 on the Richter scale," the actual moment magnitude is likely 5.8 or very close to it. The scientific inaccuracy rarely produces a misleading number in those cases. Seismologists have largely accepted that the battle to retire the term from popular usage is unwinnable, even as they continue to use 矩震级衡量地震规模的现代标准（Mw），基于地震矩——即断层面积、平均滑动量与岩石刚度的乘积。对任何规模的地震都能给出准确结果。 exclusively in research and official communications.