Recent research from MS Amlin shows that insurers may be significantly underestimating earthquake risk (by up to 60% in extreme cases) because models fail to capture the effects of little-known “supershear” earthquakes.
According to the study, two-thirds of insured losses from seismic events over the past decade were caused by destructive supershear ruptures, causing losses equivalent to $13.2 billion.
The paper, published in the Journal of Disaster Risk and Resilience, warns that this blind spot poses a serious threat to capital and pricing decisions, especially in major earthquake zones such as California.
Therefore, there is an urgent need for disaster model providers and risk takers to urgently address these vulnerabilities.
When fault ruptures progress at unusual speeds, supershear earthquakes can produce shock waves comparable to jet sonic booms. These events produce strong ground motions and a “two-fist” impact from continuous seismic waves.
Supershear earthquakes can produce “unusual torsional forces” on buildings, especially taller ones, as well as stronger shaking farther away from faults, the paper said
Supershear earthquakes used to be considered rare, but now, as seismic technology improves, they are being discovered more frequently. Since 2010, approximately 36% of major strike-slip earthquakes worldwide have involved supershear ruptures.
“There’s still a lot we don’t know about supershear earthquakes, but evidence now suggests they are more common and potentially more destructive than previously understood,” said MS Amlin senior research analyst Luke Wedmore, who co-authored the study with research analyst William Sturgeon.
“The sonic booms generated by these ruptures could cause more severe and widespread damage, but this impact is significantly underestimated in models used for earthquake risk capital and pricing decisions.”
The 2025 magnitude 7.7 earthquake in Myanmar was a classic example of a supershear event, which produced a surface rupture that extended 475 kilometers, about 230 kilometers longer than expected.
This greatly increased the area subject to shaking, the newspaper said. The findings are particularly important in California, the world’s largest earthquake insurance market, where the San Andreas Fault is susceptible to supershear forces.
The 1906 San Francisco earthquake has been determined to be a supershear event, the report said.
“Given the higher shaking intensities caused by supershear earthquakes, California’s seismic risk is likely to be significantly underestimated,” Wedmore said. “California may experience its longest major earthquake drought in 1,000 years, and now is a critical time for the industry to address this blind spot.”
MS Amlin simulated the impact of supershear on representative insurance and reinsurance portfolios and found that losses increased by 5% to 10% over a 200-year return period. Using a 500-year payback period, losses jump by 30% to 60%.
Widmore urged insurers to quickly incorporate supershear risks before next-generation catastrophe models are finalized.
In the short term, the paper recommends that insurers and providers use stress testing and sensitivity scenarios to assess risk. Other recommended actions include identifying long strike-slip faults capable of supershear rupture and testing alternative vibration modes in catastrophic models.
