地震如何测量:震级 vs 烈度

Magnitude: Measuring Energy at the Source

When scientists report that an earthquake had 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。 of 6.5, they are describing a single property of the earthquake itself — the total energy released at the source. Magnitude is calculated from measurements made by 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。 instruments around the world, and it does not change depending on where you are. A magnitude 6.5 event in California is the same magnitude whether measured in Sacramento or Stockholm.

The most widely used magnitude scale today is 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 (abbreviated Mw), which measures the total "seismic moment" of an earthquake: the product of the fault area that ruptured, the average distance the fault slipped, and the rigidity of the rock. Scientists prefer it because it does not saturate at high values the way earlier scales did, making it reliable for earthquakes of all sizes. Use the Earthquake Energy Calculator to explore how different magnitudes translate to energy released and shaking radius.

Intensity: Measuring Effects at Your Location

地震烈度根据对人员、建筑物和自然环境的观测影响，衡量特定地点震动强度的指标，随距震中距离增大而降低。 answers a completely different question: how hard did the ground shake at this particular spot? The same earthquake can produce very different intensities at different locations. At the 震中地震发生在地下的震源正上方对应的地表位置，新闻报道中通常将其作为地震发生的位置。, intensity may reach the highest levels on the scale. A hundred kilometres away, it might be much gentler. And in some distant city, sensitive people might barely feel it — or not feel it at all.

The standard measure of intensity in the United States is the Modified 修订麦加利烈度一种12级标度（I—XII），用于衡量地震在某一特定地点造成的可观察影响，从无法察觉（I级）到全面毁坏（XII级）。与震级不同，烈度会随距离变化。 scale (MMI), which uses Roman numerals from I to XII. MMI I means the quake was not felt at all; MMI V is felt by nearly everyone and may rattle windows; MMI VII causes significant damage to poorly built structures; MMI XII represents total destruction of virtually all buildings. Intensity data is collected by the USGS “你感觉到了吗？”（DYFI）美国地质调查局的一项计划，收集震后公众的烈度报告，形成基于公众参与的烈度分布图，任何感受到地震的人都可以提交报告。 system, which aggregates thousands of reports from members of the public within minutes of any significant quake.

Why the Same Earthquake Has Different Intensities

Three main factors explain why intensity varies so widely. First, distance from the epicenter: shaking energy spreads out as waves travel, so intensity naturally decreases with distance. Second, 场地放大效应（土壤放大）软弱土壤或沉积层放大地震波而引起的震动强度增大现象。建在软土上的建筑物所承受的震动强度可达基岩上建筑物的2至10倍。: soft sediments like bay mud, alluvial fans, and reclaimed land amplify shaking far more than hard bedrock. Certain areas of San Francisco built on former bay fill experienced intensities far higher than nearby bedrock neighbourhoods during the 1989 Loma Prieta earthquake, even though they were about the same distance from the epicenter. Third, building quality and local construction practices profoundly affect how much damage occurs at any intensity level.

Depth also matters. A shallow earthquake 10 kilometres deep will produce much more intense shaking at the surface directly above it than an identical-magnitude earthquake 100 kilometres down, because the energy has less distance to travel and spread out before reaching the surface.

The Logarithmic Nature of Earthquake Scales

One of the most commonly misunderstood aspects of earthquake measurement is that magnitude scales are logarithmic. Each whole-number step on the moment magnitude scale represents approximately 31.6 times more energy released. A magnitude 7.0 earthquake releases about 31.6 times more energy than a magnitude 6.0, and about 1,000 times more energy than a magnitude 5.0.

This means that while a magnitude 5.0 might feel significant to someone in its path, a magnitude 8.0 in the same region would release roughly one million times more energy. 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。, which most people have heard of, was also logarithmic in this way, and its legacy continues to shape how the public thinks about earthquake sizes even though scientists now 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。 for nearly all reporting.

How Scientists Calculate Magnitude and Intensity

Magnitude is calculated by analysing the 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。 — the record of ground motion recorded by 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。. Different magnitude formulas use different parts of the seismogram. Local magnitude (ML, the original Richter scale) uses the amplitude of the largest wave on a standard instrument. Surface wave magnitude uses the amplitude of surface waves at a period of about 20 seconds. Moment magnitude is derived from the long-period part of the seismogram and is increasingly calculated in near-real-time through automated systems.

Intensity is determined either by field surveys in the aftermath of a quake — where engineers and geologists inspect damage and interview residents — or increasingly through crowdsourced data from websites like USGS Did You Feel It?, which aggregates self-reported observations from tens of thousands of people. Modern 震度速报图（ShakeMap）美国地质调查局在地震发生后发布的成果，展示地面震动强度的分布情况，综合了地震仪数据、地震动模型以及“你感觉到了吗？”的报告。 products combine instrumental data with these reports and soil models to produce colour-coded maps of intensity within minutes.

Reading Earthquake Reports: A Practical Guide

When you see an earthquake reported in the news, here is how to interpret the key numbers. The magnitude tells you how large the event was at the source. A magnitude below 3.0 is usually imperceptible to humans. Magnitude 3–4 is felt by some people near the epicenter. Magnitude 5 can cause minor damage. Magnitude 6 is capable of significant damage. Magnitude 7 is a major earthquake. Magnitude 8 and above is a great earthquake that can affect entire countries.

The depth tells you how far below the surface the rupture began. Shallow earthquakes (less than 70 km) generally cause more surface shaking per unit of magnitude than deep ones. The intensity at your location depends on all these factors combined. If you felt an earthquake, reporting your experience through “你感觉到了吗？”（DYFI）美国地质调查局的一项计划，收集震后公众的烈度报告，形成基于公众参与的烈度分布图，任何感受到地震的人都可以提交报告。 helps scientists refine intensity maps and better understand ground shaking in your area.