USGS issues report on seismic hazard, risk, and design for South America

Maps of South America showing 100-year earthquake shaking projections. (Public Domain)

Reston, Va. — South America is one of the most earthquake-prone regions of the world and has witnessed tremendous losses throughout recorded history. A recently released U.S. Geological Survey (USGS) report provides probabilistic tools to help engineers assess seismic hazards, risk, and building code requirements, potentially saving lives and dollars.

During the last century, earthquakes have caused billions of dollars of damage and tens of thousands of casualties across the northern and western part of the South American continent. The seismic activity in this continent is driven by the South American Subduction Zone and other complex fault interactions. Future human and financial losses can be mitigated through making informed decisions based on where future earthquakes may occur, how often they might occur, and how strong the ground will shake. Such information is the purpose of probabilistic (i.e., based on a mathematical forecast) seismic hazard models that are applied in building codes, insurance models, and public policy.

New data provides new opportunities

For the past couple of decades, the USGS has been collaborating with South American colleagues to develop models and maps to support nationwide emergency planning efforts.  While there are a number of in-country studies that have evaluated earthquake shaking hazard and risk, the coverage is hardly uniform or complete across the South American continent. This report is the first to apply standardized methodologies and tools for hazard and risk assessments, to reduce discrepancies at national borders, and to identify areas of high hazard and risk within each country. The study relies on five important datasets and methodologies:

(1) an updated USGS earthquake catalog (ComCat),

(2) models of known and mapped faults generated by USGS over the past 30 years in collaboration with scientists from South America,

(3) the latest seismic ground motion models applied in the USGS hazard maps,

(4) USGS PAGER vulnerability models (“PAGER” stands for the Prompt Assessment of Global Earthquakes for Response, and it is a system that provides fatality and economic loss impact estimates following significant earthquakes worldwide), and

(5) methods applied in U.S. building codes. This information can be used to identify areas of high hazard and to develop strategies to strengthen vulnerable buildings.

The new results indicate that over 160 million people (or about a third of the total population of South America) live in areas with significantly elevated seismic hazard, primarily within the northern and western portions of the continent where earthquakes associated with subduction and crustal faulting are most common. The risk is not uniform or limited to only coastal areas. Countries such as Venezuela, Colombia, Ecuador, and Peru face high hazard and risk; Chile also faces high hazard, but the vulnerability of buildings is much lower compared with the northern countries due to modern and stringent building codes.

A cornerstone of international collaboration

About a decade ago, scientists in South America from the Centro Regional Seismological para América del Sur requested that USGS scientists collaborate in developing shaking hazard, risk, and design maps for South America. Over the past decade several workshops and discussions with South American colleagues were held to discuss the input data and evaluate the assessments. In June 2016, the USGS and the University of Chile jointly hosted a seismic hazard planning workshop in Costa Rica in which 24 scientists from 17 countries across Latin America participated. This effort was funded by the United States Agency for International Developments Office of U.S. Foreign Disaster Assistance program which is devoted to mitigating risk in this region. The report describing the results was recently published in the journal “Bulletin of the Seismological Society of America.”

Start with science

The USGS provides science which is critical for understanding earthquake risk because communities cannot plan for earthquakes if they do not know the expected earthquake occurrence and potential shaking.  These USGS models reflect the best and most current understanding of earthquake science and engineering.

Earthquakes are a global concern; in the last decade alone, seismic events have claimed tens of thousands of lives and caused hundreds of billion dollars of economic impact. These international collaborations are an important part in making sure that everyone can benefit from the best available science. For instance, USGS scientists take the scientific expertise and experience they gain working with collaborators in South America and apply it to similar situations here in the United States. In return, scientists in other countries can benefit from the lessons learned by USGS scientists responding to domestic earthquakes.

In the United States, earthquake risk continues to grow with increased exposure of population and development in hazard-prone regions of the country. Understanding earthquake hazards is critical for informed policies, priorities, strategies, and funding decisions to protect the most at-risk communities.

Datasets and models presented in this study and the results are publicly available at https://www.sciencebase.gov/catalog/item/59aeeedee4b0e9bde133ea59.