Verificador de Risco Sísmico

Check the seismic risk level for any location based on historical earthquake data and geological features.

Assessment

Como Funciona a Avaliação de Risco Sísmico

A avaliação de risco sísmico avalia a probabilidade e a gravidade potencial da vibração de terremoto em um local específico. As pontuações de risco são calculadas analisando dados históricos de terremotos dentro de um raio definido, considerando fatores como frequência de terremotos, magnitude máxima observada, proximidade a linhas de falha ativas e o contexto tectônico da região. Áreas próximas a limites de placas — particularmente zonas de subducção e falhas transformantes — tendem a ter risco sísmico significativamente maior.

A pontuação de risco produzida por esta ferramenta é baseada em um raio de busca de 250 km ao redor das coordenadas fornecidas. Ela leva em conta tanto o número de eventos sísmicos registrados quanto suas magnitudes, ponderando terremotos maiores mais fortemente porque um único evento M7,0 libera aproximadamente 31,6 vezes mais energia do que um evento M6,0. Esta relação exponencial, governada pela fórmula magnitude-energia de Gutenberg-Richter, significa que regiões com mesmo poucos grandes terremotos históricos podem ter pontuações de risco desproporcionalmente altas.

Conceitos-chave em Risco Sísmico

Perigo sísmico vs. risco sísmico: o perigo descreve a probabilidade de vibração; o risco também leva em conta a exposição e vulnerabilidade de pessoas e estruturas.
A lei de Gutenberg-Richter descreve a relação estatística entre magnitude e frequência de terremotos — terremotos menores ocorrem com muito mais frequência do que os grandes.
A Análise Probabilística de Perigo Sísmico (PSHA) é o método formal de engenharia usado para estimar probabilidades de excedência de movimento do solo em um determinado período de tempo.
As condições locais do solo podem amplificar ondas sísmicas, o que significa que dois locais à mesma distância de uma falha podem experimentar intensidades de vibração muito diferentes.

Usos Comuns

Avaliar a exposição a terremotos antes de comprar um imóvel ou mudar para uma nova área.
Entender o contexto sísmico de uma região para fins educacionais ou de pesquisa.
Comparar o risco sísmico relativo entre diferentes cidades ou países.
Apoiar o planejamento de preparação para emergências identificando zonas de alto risco.

How to Use

1
Enter Your Location
Type your city name or coordinates into the location field. The tool uses USGS seismic hazard data to identify your tectonic setting.
2
Review Your Risk Level
See your Peak Ground Acceleration (PGA) percentile and the historic seismicity of your region. Risk levels follow the USGS National Seismic Hazard Model classification.
3
Explore Mitigation Advice
Read the site-specific recommendations for your risk tier, covering building codes, retrofitting priorities, and preparedness actions.

About

Seismic risk assessment quantifies the likelihood and potential consequences of earthquake shaking at a specific location. Unlike a simple map of past earthquakes, a seismic risk calculation integrates probabilistic hazard models, local soil conditions, and the characteristics of structures in the area to produce actionable risk tiers. The foundational concept is the return period: a 475-year return period corresponds to a 10% probability of exceedance in 50 years, the standard design basis for most building codes worldwide. Higher return periods (e.g., 2,475 years, or 2% in 50 years) are used for critical facilities such as hospitals and nuclear plants.

The tectonic setting of a location drives its baseline hazard. Subduction zones—where one oceanic plate descends beneath another—produce the largest earthquakes on Earth, including the 2011 Tohoku M9.1 and 1964 Alaska M9.2 events. Transform faults like the San Andreas slip horizontally and generate frequent moderate-to-large earthquakes. Rift zones such as the East African Rift and the Basin and Range Province in the western US produce extensional faulting. Intraplate regions far from active plate boundaries can still experience significant earthquakes driven by ancient fault systems reactivated by residual tectonic stresses or fluid injection.

Soil amplification profoundly modifies ground shaking intensity at the surface. Soft sediments—lake beds, river deltas, reclaimed land—amplify shaking and extend its duration compared to bedrock sites. The 1985 Mexico City earthquake dramatically illustrated this: distant soft lacustrine sediments beneath the city resonated at the dominant period of the seismic waves, causing collapse of mid-rise buildings 350 km from the epicenter. Site class characterization using shear-wave velocity (Vs30) is now standard in hazard assessments and underlies the site amplification factors in modern building codes.

FAQ

What does seismic risk level mean?

Seismic risk level expresses the probability that ground shaking of a given intensity will be exceeded at a location within a specific time period, typically 50 years. It combines seismic hazard (the physical shaking) with exposure and vulnerability. A 'High' risk level generally corresponds to regions within 50 km of active fault systems or areas that experienced Modified Mercalli Intensity VII or greater in the historical record. Risk is distinct from hazard: two areas can share the same ground motion but differ greatly in risk if one has older, unreinforced masonry buildings.

How is seismic risk calculated?

Seismic risk calculations integrate three components: hazard models derived from fault geometries and historical seismicity catalogs, exposure inventories of buildings and population, and vulnerability functions describing how structures respond to shaking. National hazard maps published by agencies such as the USGS and GEM (Global Earthquake Model) provide probabilistic ground motion values at defined return periods (e.g., 475-year, 2,475-year). These values, combined with local site amplification from soil type, produce site-specific hazard estimates.

Which regions have the highest seismic risk?

The highest seismic risk zones lie along the Pacific Ring of Fire, a 40,000-km arc encircling the Pacific Ocean where roughly 90% of the world's earthquakes occur. Key high-risk regions include the Cascadia subduction zone (Pacific Northwest USA), Japan, the Himalayan collision zone (India, Nepal, Pakistan), the Anatolian fault system (Turkey), and the San Andreas fault system (California). The Mediterranean-Himalayan seismic belt accounts for most of the remaining global seismicity. Stable continental interiors (cratons) generally carry low risk, though intraplate earthquakes such as the 1811–1812 New Madrid sequence demonstrate that zero-risk regions do not exist.

Does building type affect my seismic risk?

Yes, building type is one of the most significant modifiers of seismic risk at the site level. Unreinforced masonry (URM) buildings are highly vulnerable because masonry has low tensile strength and crumbles under lateral shaking forces. Wood-frame light construction performs relatively well due to inherent flexibility. Modern reinforced concrete or steel moment-frame buildings designed to current seismic codes (IBC, Eurocode 8, Japanese BCP) incorporate ductile detailing that dissipates energy without catastrophic collapse. Post-1994 (Northridge) and post-1995 (Kobe) building codes introduced significantly stricter requirements in the US and Japan respectively.

How often should I reassess my seismic risk?

Seismic hazard maps are updated periodically as new fault data, paleoseismic studies, and seismicity catalogs become available. The USGS updates its National Seismic Hazard Maps approximately every 6 years; the most recent edition incorporates data from the 2019 Ridgecrest earthquake sequence. For individual property owners, reassessment is warranted after any nearby major earthquake, after structural modifications to your building, or when purchasing a new property. Local governments update seismic microzonation maps (accounting for soil amplification) on similar cycles, and checking your municipality's current zoning maps provides the most site-specific guidance available.