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GEM-USGS Project to Enhance Earthquake Load Assessments Worldwide


Sep 29, 2023

In a significant collaborative effort between the Global Earthquake Model Foundation (GEM) and the U.S. Geological Survey (USGS), funded by the U.S. Department of State (DoS) and the U.S. Department of Defense (DoD), the ASCE Earthquake Loads Overseas (AELO) project is making steady progress in providing updated global assessments of seismic actions for design.

The primary objective of the project is to create a web service capable of calculating design ground motions, both on rock and soil, in adherence to the American Society of Civil Engineers (ASCE) guidelines. These guidelines include ASCE 7-16, ASCE 41-17, ASCE 7-22, and ASCE 41-23. This web service heavily relies on the hazard models that are part of GEM’s global mosaic and the OpenQuake Engine.

The project's planned activities span four years and include various critical components:

  • Calculation of design values for peak ground acceleration (PGA), Ss, and S1 under rock site conditions, in accordance with ASCE 7-16 and ASCE 41-17.

  • Development of a web service for computing design ground motions based on ASCE 7-16 and ASCE 41-17.

  • Computation of ground motions for soil conditions across the entire spectrum, following ASCE 7-22 and ASCE 41-23, for the same 500 global locations.

  • Development of web service for computing design ground motions based on ASCE 7-22 and ASCE 41-23.

The project's accomplishments to date include the calculation of a set of Maximum Considered Earthquake (MCE) ground motions for around 500 global sites. To achieve these results, several updates and improvements were made to the GEM global seismic hazard mosaic, particularly regarding the definition of the ground-motion characterization (GMC) and the homogenisation of models (e.g. definition of the minimum magnitude).

In the first half of 2023, the project focused on developing an Application Programming Interface (API) for end-to-end calculations. This API facilitates the retrieval of probabilistic and deterministic hazard results, as well as governing ground-motion values, based on site coordinates. While the emphasis has been on the probabilistic aspect, progress is already evident in the later stages of the assessment.

With a joint effort from the USGS and GEM IT and hazard teams, the project continues to evaluate its results by comparing them with site-specific reports where significant differences are noted. This diligent approach ensures the accuracy and reliability of the earthquake load assessments.

Future work will encompass a broader spectrum of soil conditions, aligning with the updated ASCE7-22 and ASCE41-23 guidelines.

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