A recent study led by researchers at the University of California, Berkeley, has found that earthquake hazard maps in the United States may overpredict shaking for certain types of earthquakes. The researchers analyzed data from 181 earthquakes that occurred in California and found that for events known as "slow earthquakes", the maps predicted shaking that was up to six times higher than what was actually observed.

The study's findings could have implications for seismic safety in California and other regions prone to slow earthquakes. If hazard maps overpredict shaking, it could lead to buildings being designed to withstand stronger earthquakes than necessary, which would increase costs and potentially make buildings less safe.

Slow earthquakes are a relatively new type of earthquake that has been identified in recent years. They are characterized by slow slip along a fault, which can last for days or even weeks. Slow earthquakes release less energy than regular earthquakes, but they can still cause significant shaking, especially in areas close to the fault.

The researchers believe that the discrepancy between predicted and observed shaking for slow earthquakes is due to the way that hazard maps are currently calculated. Hazard maps are typically based on data from regular earthquakes, which have different properties than slow earthquakes. As a result, the maps may not accurately predict the shaking that will occur during slow earthquakes.

The researchers recommend that hazard maps be revised to take into account the unique characteristics of slow earthquakes. This would help to ensure that buildings are designed to withstand the shaking that is actually likely to occur, and it would also reduce the costs associated with seismic safety.

The study's findings were published in the journal Geophysical Research Letters.