概率地震危害分析(PSHA)工具

What Is Probabilistic Seismic Hazard Analysis?

概率地震危险性分析（PSHA）一种量化地震危险性的方法，综合考虑所有可能的地震震源、震级及地震动水平，以超过特定震动水平的概率来表示结果。 — Probabilistic Seismic Hazard Analysis — is the methodological framework that transforms geological knowledge about earthquake sources into quantitative estimates of ground shaking probability at specific sites. Developed by C. Allin Cornell in 1968, PSHA integrates three inputs — earthquake source characterization, ground motion prediction, and site response — into a single hazard curve that expresses the annual probability of exceeding any given level of ground shaking. PSHA output drives building codes, insurance pricing, infrastructure design standards, and land-use planning across seismically active regions worldwide.

The Four Steps of PSHA

The first step identifies and characterizes all seismic sources capable of affecting the site of interest. Sources include fault lines断层在地表的痕迹，表现为一条线状或破碎岩石带。地质学家绘制活动断层线图，以评估周边社区的地震危险性。 with known geometry and 滑动速率断层沿线位移的平均速率，通常以每年若干毫米衡量。滑动速率越高，通常意味着地震发生频率和危险性越高。, area sources representing diffuse seismicity in regions without mapped faults, and background seismicity derived from historical earthquake catalogs. Each source is assigned a magnitude-frequency distribution, typically following the 古登堡—里克特定律描述地震频率与震级之间关系的统计规律：震级每增加一个单位，地震发生频率约降为原来的十分之一。 relation, or the characteristic earthquake model for well-characterized faults.

The second step uses ground motion prediction equations (GMPEs, also called attenuation relations) to predict the probability distribution of ground shaking at the site as a function of earthquake magnitude, source-to-site distance, fault mechanism, and site conditions. Modern GMPEs are derived from large empirical databases of strong motion recordings and express not just the median expected shaking but also the uncertainty (sigma) in that prediction. The large variability in observed ground motion means that sigma terms dominate hazard at very long return periods.

The third step integrates over all possible earthquakes from all sources, weighted by their probability of occurrence, to compute the annual exceedance probability of each ground shaking level. This integration is the PSHA calculation itself and is typically performed using dedicated software packages.

The fourth step expresses results as a hazard curve — annual probability of exceedance versus 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。 or spectral acceleration — or as a hazard map showing ground shaking expected at a specific exceedance probability across a geographic area.

PSHA Software Tools

Several software packages implement PSHA calculations. OpenQuake Engine, developed by the Global Earthquake Model (GEM) Foundation, is an open-source Python-based platform used by researchers and national agencies worldwide. The USGS uses Fortran-based legacy code plus newer OpenQuake-compatible tools to produce the National Seismic Hazard Maps published approximately every six years. EZ-FRISK and R-CRISIS are commercially available tools with graphical interfaces used widely in engineering practice. All implement the same fundamental PSHA mathematics with varying capabilities for complex source geometries and large-scale probabilistic calculations.

The 地震危险性图显示在特定时间段内地震震动超过指定水平之概率的地图，供工程师、规划者和保险公司用于评估地震风险。 and Design Ground Motion

The principal product of national PSHA programs is the 地震危险性图显示在特定时间段内地震震动超过指定水平之概率的地图，供工程师、规划者和保险公司用于评估地震风险。: a gridded map showing the peak ground acceleration (or spectral acceleration) with a specified probability of exceedance in 50 years. The standard US building code design level uses 2% in 50 years (approximately a 2,475-year return period), while some codes use 10% in 50 years (475-year return period) for different performance objectives. The 地震危险性图显示在特定时间段内地震震动超过指定水平之概率的地图，供工程师、规划者和保险公司用于评估地震风险。 values feed directly into building code seismic zone designations — higher hazard zones require stronger structural systems, more detailed analysis, and more conservative design factors.

地震风险评估对特定地区或结构物的地震危险性、建筑物易损性及潜在损失进行评估的过程，综合了危险性图、建筑物清单及损失模型。 vs. PSHA

概率地震危险性分析（PSHA）一种量化地震危险性的方法，综合考虑所有可能的地震震源、震级及地震动水平，以超过特定震动水平的概率来表示结果。 produces hazard estimates (ground shaking probability); 地震风险评估对特定地区或结构物的地震危险性、建筑物易损性及潜在损失进行评估的过程，综合了危险性图、建筑物清单及损失模型。 combines hazard with exposure and vulnerability to estimate probable losses. The distinction is important: a remote area may have high seismic hazard but low risk because few people or structures are exposed. A moderately hazardous urban area may have high risk because enormous concentrations of people and infrastructure are exposed to even modest shaking. Risk assessment requires 概率地震危险性分析（PSHA）一种量化地震危险性的方法，综合考虑所有可能的地震震源、震级及地震动水平，以超过特定震动水平的概率来表示结果。 output as input but additionally requires building inventory databases, vulnerability functions描述特定类型建筑在给定震动水平下出现各种损坏状态概率的数学函数，是损失估算模型的核心要素。, and population data.

The Seismic Risk Checker Tool

The Seismic Risk Checker tool implements a simplified single-site PSHA calculation that allows users to estimate ground shaking probability at any location based on the USGS National Seismic Hazard Model. Entering a US zip code returns the 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。 at the 2%-in-50-year and 10%-in-50-year exceedance levels, along with the corresponding building code seismic design category. This helps property owners, architects, and engineers quickly assess the seismic design requirements applicable to a specific site without performing a full PSHA calculation.

Uncertainties in PSHA

PSHA quantifies both aleatory uncertainty (inherent randomness in earthquake occurrence and ground motion) and epistemic uncertainty (incomplete knowledge of source parameters). Epistemic uncertainty is handled through logic trees — weighted combinations of alternative source models, magnitude-frequency distributions, and GMPEs. A typical national PSHA logic tree may have thousands of branches representing different defensible scientific interpretations. The mean hazard curve averages over this epistemic uncertainty, while fractile curves (16th, 50th, 84th percentile) quantify the spread.

Site-Specific PSHA in Engineering Practice

Building codes provide general 地震危险性图显示在特定时间段内地震震动超过指定水平之概率的地图，供工程师、规划者和保险公司用于评估地震风险。 values that conservatively account for typical site conditions. For critical facilities — hospitals, nuclear power plants, dams, LNG terminals — site-specific PSHA is required. This analysis uses a detailed characterization of local seismic sources, site-specific velocity profiles for site amplification modeling, and GMPEs selected for regional appropriateness. Site-specific PSHA may produce hazard estimates substantially different (higher or lower) than the code map values, justifying custom structural designs and potentially significant cost differences.

The Seismic Hazard Model Update Cycle

National seismic hazard models are updated periodically as new data improves source characterization. The 2023 USGS National Seismic Hazard Model update incorporated 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。 constraints on fault slip rates, expanded fault databases including many previously unmapped blind thrust faults未延伸至地表的逆冲断层，在地面无法观察到，因而更难被发现。1994年北岭地震便发生在一条隐伏逆冲断层上。, updated GMPEs incorporating lessons from the 2010 Canterbury and 2011 Tohoku earthquakes, and improved 诱发地震活动由水力压裂、废水回注、采矿或水库蓄水等人类活动引发的地震。大多数震级较小（低于4级），但部分曾超过5.5级。 characterization in the central and eastern United States. Each update can significantly revise hazard estimates in specific regions, driving building code revisions and insurance repricing.

Summary

概率地震危险性分析（PSHA）一种量化地震危险性的方法，综合考虑所有可能的地震震源、震级及地震动水平，以超过特定震动水平的概率来表示结果。 tools transform geological and seismological data into the probabilistic ground shaking estimates that underpin all quantitative earthquake risk management. Understanding the 地震危险性图显示在特定时间段内地震震动超过指定水平之概率的地图，供工程师、规划者和保险公司用于评估地震风险。 as a probabilistic product — not a prediction — and recognizing the role of uncertainty in 地震风险评估对特定地区或结构物的地震危险性、建筑物易损性及潜在损失进行评估的过程，综合了危险性图、建筑物清单及损失模型。 allows engineers, planners, and policymakers to use these powerful tools appropriately. The Seismic Risk Checker tool provides immediate access to national PSHA results for any US location.