Estimador de PGA

Estimate Peak Ground Acceleration at your location for a given earthquake scenario.

Calculation

¿Qué es la aceleración máxima del suelo (PGA)?

La Aceleración Máxima del Suelo (PGA) es la aceleración máxima experimentada en la superficie terrestre durante un terremoto, medida como una fracción de la aceleración gravitacional (g = 9,81 m/s²). Es uno de los parámetros más importantes en ingeniería sísmica porque se relaciona directamente con las fuerzas que los edificios e infraestructura deben soportar. Una PGA de 0,1g significa que el suelo aceleró al 10% de la gravedad — suficiente para sentirse con fuerza y causar daños menores. A 0,5g, la aceleración es la mitad de la gravedad y el daño estructural a edificios bien diseñados se vuelve probable. La PGA más alta registrada fue 2,7g durante el terremoto de Tōhoku de 2011 en Japón.

Las Ecuaciones de Predicción del Movimiento del Suelo (GMPEs), también llamadas relaciones de atenuación, son modelos empíricos que estiman la PGA basándose en la magnitud del terremoto, la distancia a la falla, la profundidad y las condiciones del sitio. Esta herramienta utiliza una GMPE simplificada para proporcionar estimaciones educativas. El análisis profesional de peligro sísmico emplea múltiples GMPEs y tiene en cuenta la incertidumbre mediante árboles lógicos. Las condiciones del sitio importan significativamente — los suelos blandos pueden amplificar la PGA de 2 a 3 veces comparado con la roca madre, un fenómeno capturado por factores de amplificación del sitio definidos en códigos de construcción como ASCE 7 y Eurocódigo 8.

PGA y diseño estructural

Los códigos de construcción especifican valores de PGA de diseño: las estructuras deben resistir cierto nivel de aceleración del suelo sin colapsar. En zonas de alta sismicidad, esto es típicamente 0,3-0,4g.
La PGA por sí sola no describe completamente la severidad del movimiento del suelo — la duración y el contenido de frecuencia también importan. Un pulso breve de PGA alta puede ser menos dañino que sacudidas moderadas prolongadas.
La clasificación del sitio (A a F en ASCE 7) afecta el espectro de diseño: los sitios de suelo blando (Clase D/E) requieren fuerzas de diseño más altas debido a efectos de amplificación.
Los mapas de peligro sísmico, como los producidos por USGS y GSHAP, muestran los valores de PGA con un 10% de probabilidad de excedencia en 50 años — la referencia estándar para los códigos de construcción.

Usos comunes

Estimar el nivel de sacudida del suelo en una ubicación específica para un escenario hipotético de terremoto.
Comprender cómo la distancia y las condiciones del suelo afectan la aceleración del suelo.
Comparar la PGA estimada con los requisitos de los códigos de construcción para evaluar el daño potencial.
Demostraciones educativas de la atenuación sísmica y los efectos de amplificación del sitio.

How to Use

1
Define the Earthquake Scenario
Enter the earthquake magnitude (Mw), epicenter coordinates, and focal depth. For site-specific design purposes, you may also use a return period (e.g., 475-year) to retrieve the probabilistic PGA from the USGS seismic hazard map.
2
Specify Your Site Location and Soil Class
Enter your coordinates and select your site soil class (A through F per ASCE 7 / Eurocode 8). Site class D (stiff soil, Vs30 = 180–360 m/s) is the reference class; softer soils amplify PGA, harder rock reduces it.
3
Review the PGA Estimate and Design Implications
Read your estimated PGA in g-units and its corresponding approximate MMI intensity. The tool notes the relevant building code seismic design category (SDC) for US locations and the equivalent Eurocode 8 PGA design value.

About

Peak Ground Acceleration emerged as the primary seismic engineering parameter in the 1950s–60s when strong-motion accelerographs first became widely deployed following the 1940 El Centro earthquake (which produced the first complete accelerogram used in engineering, with PGA = 0.33g). PGA's appeal lies in its direct measurement from instruments, its physical intuition (how hard the ground shakes), and its correlation with observations from historical earthquakes. The USGS National Seismic Hazard Maps, first produced in the 1970s and updated through PSHA methodology, express seismic hazard primarily as PGA at specific probability levels.

However, PGA has known limitations as a sole damage predictor. It reflects high-frequency energy that governs rigid structural response but may not capture the damage potential for taller, more flexible structures sensitive to long-period energy. The 1985 Mexico City earthquake illustrated this dramatically: soft sediment resonance amplified long-period (2 second) waves while PGA on those same sediments was not extreme, yet mid-rise (8–15 story) buildings resonating at the site's natural period collapsed while shorter and taller buildings survived. This observation drove the adoption of design response spectra and, more recently, spectral acceleration at specific periods (Sa(1.0s), Sa(0.2s)) as primary design parameters in modern codes.

The emergence of broadband seismic networks and dense strong-motion arrays has dramatically expanded the observational database underpinning PGA prediction models. The Next Generation Attenuation (NGA) project, coordinated by PEER (Pacific Earthquake Engineering Research Center), compiled an international database of over 21,000 ground motion records from 600+ earthquakes to develop the NGA-West2 model suite—five independent GMPEs now used as the foundation of USGS hazard maps and incorporated into building codes in the US and internationally. These models explicitly account for magnitude, distance, depth, style of faulting, hanging wall effects, basin depth, and Vs30, providing PGA predictions with quantified uncertainty at any site worldwide.

FAQ

¿Qué es la aceleración máxima del suelo (PGA)?

Peak Ground Acceleration (PGA) is the maximum acceleration experienced by the ground surface during an earthquake, measured in units of gravitational acceleration (g, approximately 9.81 m/s²) or as a percentage of g (%g). PGA is the most widely used parameter for characterizing seismic hazard in building codes because it correlates reasonably well with damage to short-period structures such as low-rise buildings. A PGA of 0.05g is typically the threshold for human perception; 0.1g can cause non-structural damage; 0.3g represents severe shaking that damages poorly designed structures; and PGA values exceeding 1.0g have been recorded near fault ruptures (1.8g was recorded in the 1994 Northridge earthquake). PGA is measured by accelerographs (strong motion seismometers) rather than standard seismographs.

How does PGA relate to structural damage?

PGA is most relevant for predicting damage to stiff, low-period structures. For flexible structures (tall buildings, bridges) with natural periods greater than 0.5–1.0 seconds, spectral acceleration at the structure's period is a more accurate damage predictor than PGA. This is why modern building codes use design response spectra rather than PGA alone: the spectrum describes the maximum acceleration experienced by oscillators of different natural periods during the earthquake, capturing the full range of structural response. PGA corresponds approximately to the spectral acceleration at zero period (a completely rigid structure). The correlation between PGA and Modified Mercalli Intensity is approximate: MMI VI ≈ 0.06–0.10g PGA; MMI VII ≈ 0.10–0.18g; MMI VIII ≈ 0.18–0.34g.

What is Vs30 and why does it matter for PGA?

Vs30 is the time-averaged shear-wave velocity of the top 30 meters of soil, calculated as 30 meters divided by the summed travel time of shear waves through each layer. It is the internationally standardized proxy for site characterization in seismic hazard analysis and building codes (ASCE 7, Eurocode 8, Japanese seismic code). Higher Vs30 indicates stiffer, harder ground that amplifies shaking less. ASCE 7 site classes range from A (hard rock, Vs30 > 1,500 m/s) through F (potentially liquefiable soils). A change from rock (Site Class B, Vs30 ~760 m/s) to soft soil (Site Class E, Vs30 < 180 m/s) can amplify PGA by a factor of 3–5 at low spectral periods, with even larger amplification at mid-periods (0.1–0.5 s) relevant to 2–5 story buildings.

What is the difference between PGA, PGV, and PGD?

PGA (Peak Ground Acceleration), PGV (Peak Ground Velocity), and PGD (Peak Ground Displacement) are the three fundamental ground motion intensity measures derived from accelerograph recordings. PGA is the maximum of the acceleration time history and governs response of stiff, low-period structures. PGV—obtained by integrating the acceleration record—correlates best with damage to medium-period structures (0.5–2.0 s) such as mid-rise buildings and bridges, and is considered by many researchers to be the best single predictor of overall structural damage. PGD—the double integral of acceleration—governs response of long-period structures, buried pipelines, and dams, where absolute displacement matters. Modern ground motion attenuation models (Next Generation Attenuation, NGA-West2) simultaneously predict PGA, PGV, and spectral accelerations.

How do engineers use PGA in building design?

Engineers use probabilistic seismic hazard analysis (PSHA) to determine design PGA values at specified return periods. The ASCE 7-22 standard uses Risk-Targeted Maximum Considered Earthquake (MCER) maps, which represent ground motions with a 1% probability of collapse in 50 years for a code-conforming building (approximately a 5,000-year return period). The design-level ground motion is two-thirds of MCER. Site-specific hazard analysis, required for critical or large structures, integrates contributions from all potential earthquake sources (faults and distributed seismicity) to produce a hazard curve—the annual probability of exceeding different PGA levels. The design spectrum is then constructed from uniform hazard spectra, and dynamic analysis of the structural model under ground motions scaled to the design spectrum is used to verify code compliance.