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The U.S. Contribution to the International Macroseismic Scale

Description: 

The International Macroseismic Scale (IMS) working group seeks to extend the European Macroseismic Scale (EMS-98) globally. To better reflect United States (US) structure types, we have parameterized three components for the US contribution to the IMS: (1) the national building taxonomy, (2) the system to assign vulnerability classes, and (3) damage grades. We chose from commonly used US taxonomies: FEMA P-154, ATC-20, ATC-38, Hazus, and ASCE/SEI 41. We judged each option by nine desirable seismic features and whether maintenance and data-collection training programs for them exist. FEMA P-154 best satisfies our desiderata. Of particular value: its built-in fragility model helps assign vulnerability classes. A significant challenge was how to describe damage grades consistent with the IMS. A suitable system must assign a damaged building one of five damage grades. We adapted the three-level ATC-20 green-yellow-red post-earthquake safety tagging system by subdividing red (unsafe) tags into two grades depending on whether collapse occurred, and yellow (restricted use) tags into two grades depending on the extent of damage. ATC-20 rapid evaluation forms—the de facto global standard for evaluating earthquake building damage—provide all the necessary data to assign these grades. Using ATC-20 leverages an existing evaluation system to provide abundant, free, spatially located post-earthquake damage data and, thus, robust IMS intensity assignments. These country-specific details will be catalogued in a national annex to the IMS. The benefits flow both ways: loss modelers will likely estimate shaking intensity (and therefore damage) before field observations can be made. Doing so will provide US emergency managers, officials, and the public with estimates of safety and functionality of the building stock within minutes of damaging earthquakes. Using ATC-20 protocols, inspectors can help refine these intensity estimates during post-earthquake inspections. As a further benefit, similarities between US and Canadian building data and inspection systems could facilitate the extension of the US IMS contribution to Canada.

Session: Macroseismic Intensity: Past, Present and Future - I

Type: Oral

Date: 4/17/2025

Presentation Time: 02:15 PM (local time)

Presenting Author: David

Student Presenter: No

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