Summary

With funding from NSF, USGS and other sponsors, the Southern California Earthquake Center transitioned to become the Statewide California Earthquake Center (SCEC) in 2024. This created exciting research and collaboration opportunities that span the entire transform plate boundary, encompassing the Pacific and North American Plates from western Nevada to Baja California and Cape Mendocino.

SCEC, USGS, CGS, NASA, LLNL, CIG, and other academic partners hosted the California Community Earth Models for Seismic Hazard Assessments Workshop online on March 4–5, 2024, with more than 200 participants over two days. The workshop aimed to foster collaboration and establish a strong community around developing and maintaining community Earth models for California. These models describe the state of the Earth’s crust and upper mantle, including features like faults, elastic properties, and stress, which are crucial for understanding earthquake processes. The workshop emphasized the importance of “community” in these models, meaning they are publicly accessible and regularly updated through ongoing collaboration with the scientific community. Community Earth Models (CEMs) are critical inputs for various earthquake hazard assessment studies. Several organizations, such as the Statewide California Earthquake Center (SCEC), the U.S. Geological Survey (USGS), and the Cascadia Regional Earthquake Science Center (CRESCENT), are creating models that cover various regions of California. This workshop marks a crucial step toward building a collaborative and sustainable framework for developing and utilizing community Earth models for the entire state of California.

WORKSHOP OBJECTIVES. The workshop objectives were to

1. Form a collaborative community by bringing together researchers and stakeholders interested in developing and updating Earth models for California.
2. Promote sustainability to ensure the long-term development and maintenance of these models.
3. Embrace multiscale approaches by considering Earth models at different scales for a comprehensive understanding.
4. Assess existing models by evaluating the spatial coverage to identify gaps and regions where models could be merged.
5. Define short and long-term goals to outline priorities and milestones for future development.

WORKSHOP REPORT. The workshop report summarizes key points from the presentations and discussions. It highlights three use cases driving the development of community Earth models, presents an inventory of existing community Earth models in California, summarizes techniques for integrating and merging models, discusses potential connections with the Cascadia Region Earthquake Science Center (CRESCENT), and explores the concept of “community” in community Earth models.

KEY POINTS & RECOMMENDATIONS. Below are the key points from the workshop presentations and discussions. See the workshop report for detailed recommendations and outcomes.

• Making community Earth models accessible to users from a variety of technical backgrounds and disciplines is critical. This could be achieved by standardizing metadata, using standard scientific data formats, and providing standard interfaces for accessing each type of Earth model.
• The long-term sustainability of community Earth models requires a community of core developers and contributors with well-defined workflows to incorporate contributions into the models with appropriate attribution.
• The earthquake science community would benefit from consistent definitions of the state of the crust and upper mantle across the various types of community Earth models, extending the spatial coverage, reconciling discrepancies, and developing alternatives consistent with diverse constraints.
• Propagating uncertainty through user applications requires quantitative assessments of epistemic uncertainty and aleatory variability for Earth models, which are lacking for most existing models. These assessments can help prioritize regions for improvement based on uncertainty and seismic hazard and risk.
• Coordination among organizations working on community Earth models across the western United States will improve user accessibility and facilitate the advancement of earthquake science.