Seismic risk assessments should be provided by a licensed civil or structural engineer with years of experience in seismic design of buildings. The engineer should also have post-earthquake reconnaissance experience and working knowledge of ASCE 31 “Seismic Evaluation of Existing Buildings” and ASCE 41 “Seismic Rehabilitation of Existing Buildings”. This ensures that the Engineer is familiar with the vulnerabilities of the type of structure and considers the workmanship of vintage buildings on their judgment.
In order to adequately address seismic loss, there are two primary items which should be addressed: Life-Safety and Loss of Real Property. Acceptable limits of risk for one do not necessarily indicate that the other is within acceptable limits. Seismic risk is comprised of three components: Hazard, Vulnerability, and Exposure. Hazards relate to the “external forces” which cause damage, such as ground shaking, liquefaction, surface fault rupture, etc. Vulnerability relates to how well the structure is designed and detailed, along with weaknesses and deficiencies in the structural systems. Exposure is the value at risk, and can be expressed in terms of occupant loading (life-safety) or building value (property loss).
Seismic risk assessments from probabilistic methods provide an estimate of damage to a building when it is subjected to earthquake ground shaking. The damage estimate, or probable maximum loss (PML) value, is expressed as a percentage of the total replacement cost of the building. These assessments are used by loan underwriters and insurance brokers to assess seismic risk. The services are usually requested by other due-diligence professionals to include as part of a more comprehensive due-diligence investigation report. The request may also come directly from building owners that want to assess and mitigate seismic risk in their investment properties. A planned seismic retrofit is generally more cost effective than repairing a damage structure after a seismic event.
The procedures underlying our assessments rely on methods developed by reputable researchers, Thiel & Zsutty. Our methods adjust with modification factors by considering a building's unique strengths and weaknesses that are essential to seismic resilience, the building's proximity to earthquake faults, and the effects of local soil conditions. Experience and engineering judgment play an important role in attempting to compare a building to other "average" buildings within a classification. Loss estimates should be modified based on positive and negative features specific to each building.
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