理解矩震级标度

What Seismic Moment Tells Us About Earthquakes

To understand 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, you must first understand seismic moment — the physical quantity it measures. Seismic moment (M0) is the most fundamental description of earthquake size, rooted directly in the mechanics of fault rupture rather than in any instrumental quirk. It captures three essential physical properties of an earthquake: how large an area of the fault ruptured, how far the two sides of the fault slipped past each other, and how rigid the rock surrounding the fault is.

The intuition is straightforward. Imagine tearing a piece of paper. The larger the tear, the further the paper has separated, and the stiffer the paper, the more energy was released. 地震矩衡量地震释放总能量的指标，由断层面积、平均位移量与岩石的剪切模量相乘计算得出，是矩震级的计算基础。 works exactly the same way. A great earthquake like the 2011 Tohoku event ruptured a fault area roughly 500 kilometres long and 200 kilometres wide, with average slip of perhaps 20 metres, in very rigid oceanic crust — yielding a seismic moment so enormous it dwarfs nearly all other recorded earthquakes.

The Formula: Fault Area x Slip x Rock Rigidity

The seismic moment is defined as M0 = μ × A × d, where μ (mu) is the rigidity of the rock (typically around 30 GPa for crustal rock), A is the area of the 断层破裂地震期间岩石沿断层发生破裂，将储存的弹性能量以地震波形式释放的过程。破裂长度小到数米（小地震），大到超过1,000公里（大地震）。 surface, and d is the average displacement (slip) across that surface. All three quantities must be measured or estimated from seismological data, geodetic measurements, or field observations.

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。 (Mw) is then derived from seismic moment using a formula established by Hanks and Kanamori (1979): Mw = (2/3) × log10(M0) − 10.7, where M0 is in dyne-centimetres. This formula is deliberately scaled so that Mw values align closely with the 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。 for moderate earthquakes, providing continuity with the historical record. The logarithm compresses the enormous range of seismic moments — spanning more than 20 orders of magnitude from micro-earthquakes to mega-quakes — into the familiar 0–10+ 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。 range.

Advantages Over Richter Scale and Other Scales

The primary advantage of Mw over the 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。 and other earlier scales is that it does not saturate. Earlier scales were based on specific wave types or frequency ranges that become insensitive at large earthquake sizes. The original Richter local magnitude saturates around M 6.5–7.0; surface wave magnitude saturates around 8.0–8.5. Moment magnitude, anchored in the true physical size of the earthquake, keeps growing for the largest events ever recorded.

Mw is also physically meaningful in a way earlier scales were not. Because it is derived from seismic moment, it can be independently verified by multiple methods: long-period seismogram analysis, field measurements of fault slip, 干涉合成孔径雷达（InSAR）通过对比地震前后拍摄的雷达图像，以厘米级精度测量地表形变的卫星雷达技术，可揭示断层的滑动模式。 satellite geodesy measurements of ground deformation, and GPS geodesy (GPS大地测量利用全球定位系统接收机以毫米级精度测量构造板块运动和地壳变形的方法，可揭示地震之间断层上应变积累的过程。) that tracks how the ground moves before and after the event. The convergence of these independent estimates gives scientists high confidence in Mw values for well-studied earthquakes.

Another practical advantage: Mw is defined globally and does not depend on local calibration curves. The 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。 was calibrated specifically for Southern California. When seismologists tried to apply it elsewhere, they needed correction factors. Mw requires only the seismic moment, which can be estimated from any well-calibrated global 地震观测网由若干地震台站协同组成、持续监测地震活动的系统。全球地震台网（GSN）拥有150多个台站，提供全球范围的观测覆盖。.

How Seismologists Calculate Mw in Real Time

Modern seismological agencies estimate moment magnitude by analysing the long-period content of seismograms recorded on 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。 networks around the world. When a significant earthquake occurs, automated systems at 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 national agencies like Japan's JMA ingest data from dozens or hundreds of stations simultaneously.

The key step is determining the seismic moment tensor — a mathematical representation of the earthquake's focal mechanism that encodes the orientation of the fault, the direction of slip, and the seismic moment. Automated algorithms can produce an initial moment tensor solution and a preliminary Mw estimate within minutes of a major event, good enough for tsunami warning systems and initial response decisions. A more precise solution is refined over hours to days as more data are processed.

For very recent earthquakes, the first reports may cite a slightly different value than the final Mw. This is normal and reflects the iterative nature of the process. Initial estimates from body-wave analysis may differ slightly from the final centroid moment tensor solution, but for earthquakes above about magnitude 5.0 the differences are usually small.

Notable Earthquakes on the Moment Magnitude Scale

The moment magnitude scale's ability to handle extreme events is best illustrated by the largest earthquakes ever recorded. The 1960 Valdivia, Chile earthquake holds the record at Mw 9.5 — a rupture that broke approximately 1,000 kilometres of the subduction zone boundary between the Nazca and South American plates. The seismic moment of this single event was so large that it represents a substantial fraction of all the energy released by earthquakes worldwide in the entire 20th century.

The 1964 Alaska Good Friday earthquake (Mw 9.2) remains the second-largest in the instrumental record, followed by the 2004 Indian Ocean earthquake (Mw 9.1–9.3) and the 2011 Tohoku, Japan earthquake (Mw 9.0–9.1). At the other end of the scale, modern high-sensitivity networks can detect earthquakes with negative magnitudes — tiny events releasing less energy than a firecracker. The Mw scale thus spans an enormous dynamic range with a single consistent formula, a feat that no earlier magnitude scale could match.