理解ShakeMap:实时烈度

What Is a ShakeMap?

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。 is a product of 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 regional 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。 partnerships that converts raw seismometer recordings into a spatially continuous map of ground shaking intensity. Within minutes of a significant earthquake, ShakeMap delivers color-coded maps showing where shaking was strongest, providing emergency managers, utilities, insurers, and individuals with rapid situational awareness. Understanding how to read these maps and what their values represent is an essential skill in earthquake-prone regions.

From Seismic Stations to Spatial Maps

When an earthquake occurs, seismometers at dozens to hundreds of stations record ground motion simultaneously. ShakeMap ingests these recordings and extracts peak ground acceleration, peak ground velocity, and spectral acceleration values at each station. Because stations are sparsely distributed relative to the affected area, the software uses ground motion prediction equations to interpolate values across the gaps between stations. The result is a smooth, continuous surface that estimates shaking intensity at every point within the affected region.

The Role of Site Amplification

Raw interpolation would be inadequate because soil conditions dramatically influence local shaking. 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。 can multiply shaking intensity by a factor of five or more compared to bedrock. ShakeMap incorporates Vs30 data — the average shear-wave velocity in the upper 30 meters of soil — to adjust estimates at each interpolated grid point. In urban areas where detailed Vs30 maps exist, this correction significantly improves accuracy. Where site data is sparse, the adjustment relies on topographic proxies developed through regional calibration.

Reading the Color Scale

ShakeMap uses a standard color palette mapped to instrumental intensity values, which correlate with the 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. Green tones represent weak shaking (MMI I–III), yellow represents light to moderate (MMI IV–V), orange represents strong (MMI VI–VII), red represents very strong to violent (MMI VIII–IX), and purple represents extreme to catastrophic (MMI X–XII). The boundaries between colors are not precise lines — shaking transitions gradually, and the color at any location represents the statistical best estimate given available data.

Peak Ground Acceleration and Velocity

ShakeMap reports ground motion in physically meaningful units. 峰值地面加速度（PGA）地震期间地面运动的最大加速度，以重力加速度（g）为单位测量。是地震工程中结构设计的关键参数。 is expressed as a percentage of g (gravitational acceleration). Human perception begins around 0.5%g; structural damage begins around 10%g for poorly built structures; engineered buildings designed to modern codes may sustain damage at 50%g or more depending on duration. Peak ground velocity (cm/s) better captures the damage potential for flexible structures because it relates directly to spectral displacement demands.

The Distance-from-Epicenter Relationship

A key use of ShakeMap is understanding how shaking attenuates with distance. Use the Distance from Epicenter tool alongside a ShakeMap to quantify how far different intensity zones extend from 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。. As a general rule, strong shaking (MMI VII+) is concentrated within tens of kilometers of the rupture for M 6.0 events but can extend hundreds of kilometers for M 8.0+ megathrust earthquakes. Rupture directivity — the direction in which the fault rupture propagates — creates asymmetric patterns where shaking is stronger in the direction of rupture propagation.

Uncertainty and Data Density

ShakeMap includes an uncertainty layer showing where estimates are most and least reliable. Areas with dense station coverage have lower uncertainty, while remote areas rely more on model predictions. Immediately after a large event, the ShakeMap is provisional — it may be updated multiple times as additional station data is processed, “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。 reports are integrated, and moment tensor solutions refine the source model. Always note the version timestamp when using ShakeMap for post-event analysis.

Did You Feel It Integration

Citizen intensity reports from the “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 feed directly into ShakeMap as additional data points. Each report provides an estimated 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。 at a geocoded location, supplementing instrumental data particularly in areas with few sensors. During the 2011 Virginia earthquake, which occurred far from densely instrumented regions, DYFI reports were essential to mapping the broad felt area. The system has collected tens of millions of responses since its launch, creating a historical archive of felt reports for thousands of events.

Applications in Emergency Response

Emergency managers rely on ShakeMap as a primary situational awareness tool in the first hours after a major earthquake. FEMA's HAZUS loss estimation software ingests ShakeMap data to produce rapid estimates of casualties, displaced households, and infrastructure damage. These estimates guide decisions about where to concentrate 搜救（SAR）地震后有组织地开展定位并救出被困于倒塌建筑物中幸存者的行动。震后头72小时是发现生还者的关键窗口期。 resources and how large a response effort will be required. Utilities use ShakeMap to prioritize inspection routes for gas and water pipeline systems.

Operational ShakeAlert Integration

In regions covered by ShakeAlert预警系统由美国地质调查局及多所大学合作运营的美国地震预警系统，覆盖美国西海岸（加利福尼亚州、俄勒冈州、华盛顿州），通过无线紧急警报发送提醒。, ShakeMap output becomes available within one to three minutes of an earthquake, faster than the several minutes historically required. The speed improvement comes from pre-event parameter estimates transmitted by ShakeAlert's real-time source characterization, which gives ShakeMap a head start before station recordings are fully processed. This rapid availability is critical for the first wave of emergency response decisions.

Reading Scenario ShakeMaps

Beyond real-time events, the USGS publishes scenario ShakeMaps for hypothetical future earthquakes on known faults. These scenario products show what shaking would look like if a given fault segment ruptured with a specified magnitude. Urban planners, building departments, and emergency planners use scenario ShakeMaps to evaluate infrastructure vulnerability and develop response plans before a disaster occurs. California's HayWired scenario, for example, modeled a M 7.0 earthquake on the Hayward Fault and generated ShakeMap products that revealed catastrophic expected shaking in the East Bay.

Summary

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。 translates the abstract numbers of seismology into spatial context that operators, responders, and communities can act upon. By understanding the color scale, recognizing uncertainty zones, appreciating the role of 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。, and knowing how to supplement maps with the Distance from Epicenter tool, you gain a clearer picture of the real geographic footprint of any earthquake.