Seismic hazard maps may overestimate earthquake intensity

Seismic hazard maps may overestimate earthquake intensity
by Clarence Oxford
Los Angeles CA (SPX) May 03, 2024

A study conducted by researchers from Northwestern University has revealed a discrepancy in seismic hazard maps, which are instrumental in guiding the construction of earthquake-resistant structures. The researchers noted that these maps generally forecast higher levels of seismic activity than what has historically been observed.

Seismic hazard maps, which have been used for nearly five decades, are designed to predict the intensity of future earthquakes to help engineer safer buildings. However, the rarity of significant earthquakes in many regions has made it difficult to assess the accuracy of these maps.

The Northwestern team, led by geophysicist Leah Salditch, analyzed historical shaking data from past earthquakes using resources like the California Historical Intensity Mapping Project (CHIMP). This project incorporates data from seismometers and historical accounts, providing a rich picture of the earthquake's impact on human-made structures.

"We found a puzzling problem," Salditch commented. "Hazard maps for California as well as Japan, Italy, Nepal, and France all seemed to overpredict the historically observed earthquake shaking intensities."

The investigation into the causes of this overprediction led the team to identify issues with the conversion equations used to relate predicted seismic activity on hazard maps to actual recorded data. This problem was not with the hazard maps themselves but with how the predictions were quantified and compared with empirical data.

"The problem isn't the maps but in the conversion," explained Norman Abrahamson, a coauthor from the University of California, Berkeley. "Changing the conversion solves most of the misfit between the maps and data. Moreover, a better description of the ground shaking should make things even stronger."

This discovery underscores the complexity of predicting earthquake impacts and the need for continuous refinement of the tools used to estimate seismic risks. As researchers improve these models, they contribute to safer building practices, which are essential for minimizing earthquake-related fatalities and damage.

The findings from this study are set to be published in the journal Science Advances on May 1.

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