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Seismic Damageability Reports

Seismic Damageability Reports and Probable Maximum Loss Reports are terms that are used interchangeably in the engineering due diligence field. In both instances, engineers are engaged to quantify the amount of seismic risk associated with a building. Most engineers prepare reports according to ASTM E 2026-2007 guidelines.  

While Probable Maximum Loss (PML) is by far the more commonly used term in the industry, many engineers have favored Seismic Damageability Report, as the term PML can have several meanings. Consequently, ASTM has issued a guideline document that attempts to standardize the terminology used for seismic loss reports.

Many engineers, including my firm (Partner Engineering and Science), provide “Scenario Loss” estimates to clients. The Scenario Upper Loss (SUL) is the scenario loss that has a 10% probability of exceedance due to the specified earthquake scenario, and the Scenario Expected Loss (SEL) is the expected loss value due to the specified earthquake scenario. Therefore, the SUL represents an upper loss estimate, and the SEL represents an average or expected estimate. 

Clients should be careful when ordering Seismic Damageability Reports (or PMLs) as there are some firms that use significantly different methods for calculation of the SEL and SUL.   My recommendation when ordering a report is to make sure of the following:       

1)      The firm should have a registered engineer on staff;

2)      Ask the firm to follow ASTM E2026-2007 and, if being done for lenders ASTM E2557-2007;

3)      Request that the firm show their math on the calculations.

Whether you call it a Probable Maximum Loss Report or a Seismic Damageability Report, in the end, the name does not matter; as long as the assessment is done by a quality engineer and performed consistently and transparently, the lender can use this tool to measure their seismic risk.