地震後の建物安全検査

Post-Earthquake Building Safety Inspections

After a major earthquake, hundreds of thousands of building owners, tenants, and emergency managers face a critical question: can this building be occupied? The answer determines whether people return to their homes or businesses, whether emergency responders can use a facility, and whether valuable property assets are preserved or lost to unnecessary abandonment. Post-earthquake building safety inspections are the professional process that answers this question systematically, rigorously, and consistently.

These inspections are not full engineering assessments of structural capacity — they are rapid evaluations of observable damage to determine whether immediate occupancy is safe. This distinction is important: an inspection team may determine that a building is safe to reoccupy based on a rapid assessment even when full characterization of the building's reduced seismic capacity would require months of detailed analysis.

The ATC-20 Protocol

The American standard for post-earthquake building safety evaluation is the Applied Technology Council's ATC-20 procedure, developed in the aftermath of the 1971 San Fernando earthquake and refined through subsequent events. The ATC-20 protocol is referenced or directly adopted in seismic safety regulations across the United States and in various forms internationally.

ATC-20 defines two inspection levels. The rapid evaluation is intended to be completed by a trained inspector in 15 to 20 minutes per building, primarily through exterior observation. The inspector examines the building's structural system, looks for visible evidence of damage to primary structural elements, assesses geotechnical hazards like 液状化水を含んだ緩い土壌が強い揺れによって一時的に強度を失い、液体のように振る舞う現象。建物が地面に沈下・傾斜・崩壊することがある。 or slope failure, and notes visible non-structural hazards like falling hazards and utility damage.

The inspection results in a placard posting. A green placard (Inspected) indicates the building is deemed safe for entry and occupancy. A yellow placard (Restricted Use) indicates the building may be entered and/or occupied only with restrictions specified on the placard — a specific entrance only, upper floors only, no occupancy. A red placard (Unsafe) indicates the building is not safe to enter or occupy. Red-placarded buildings may pose danger from structural failure, hazardous materials, or other conditions requiring resolution before reoccupancy.

Identifying Key Structural Vulnerabilities

Effective post-earthquake inspection requires understanding which building types and configurations are most likely to have suffered serious damage. Several building types have exhibited consistently poor earthquake performance in past events and warrant particular attention.

[[Unreinforced-masonry]] buildings — brick, adobe, or stone construction without internal reinforcing — are among the most dangerous buildings in earthquakes. These materials perform well in compression but have very little tensile or shear strength. During earthquakes, the mortar joints between masonry units fail, walls crack diagonally or topple outward, and floors and roofs they support can pancake. Post-earthquake inspection of 無補強組積造（URM）鉄筋補強のないレンガまたはブロック造の建物で、地震の揺れに極めて脆弱である。URM建物は、世界の地震死者数の大部分を占める。 buildings focuses on diagonal cracking in walls, separation between walls and floor/roof diaphragms, and any visible out-of-plane movement or bulging.

[[Soft-story]] buildings — typically multi-family residential buildings where the ground floor is open for parking or commercial use, creating a floor that is substantially weaker and more flexible than those above — have caused disproportionate casualties in earthquakes including the 1989 Loma Prieta and 1994 Northridge events. During strong shaking, the soft story deforms dramatically while upper floors remain relatively rigid, creating concentrated damage and sometimes complete collapse of the ground story. Post-earthquake inspection of soft-story buildings focuses on deformation of the first story: tilting, story shortening, buckled columns, and cracked connections.

The 耐震基準建物の最低限の耐震安全性を確保するための、設計・建設に関する法的要件の体系。大地震で新たな脆弱性が明らかになるたびに更新される。 requirements that address these vulnerabilities — reinforcement requirements for masonry, soft-story retrofit mandates — are products of lessons learned from post-earthquake damage assessments. The inspection process thus both protects current occupants and generates data that improves future codes.

Using the Building Safety Checker Tool

The Building Safety Checker tool provides guidance on interpreting visual inspection findings and understanding what damage patterns indicate about occupancy safety. By inputting observable characteristics — building type, construction era, visible damage types — the tool guides users through the decision logic that trained inspectors apply. While not a substitute for professional engineering inspection, this tool helps building owners understand what to look for and how to communicate with inspectors.

Construction era matters significantly for safety evaluation. Buildings constructed before modern seismic building codes were adopted have not been designed for earthquake loads and are statistically more likely to have suffered damage. In the United States, major improvements in seismic design requirements occurred after significant earthquakes: after the 1971 San Fernando earthquake, after the 1989 Loma Prieta earthquake, and after the 1994 Northridge earthquake. Buildings constructed before these updates and not retrofitted since operate under substantially older standards.

Organizing the Inspection Effort

After a major earthquake affecting a large metropolitan area, coordinating post-earthquake building inspections across hundreds of thousands of structures requires significant organizational infrastructure. Most major jurisdictions in earthquake-prone areas maintain pre-trained volunteer inspection cadres — licensed engineers and architects who have taken ATC-20 or equivalent training and are registered with local emergency management to be called up after major events.

California's Safety Assessment Program (SAP) is a model of this approach, maintaining a statewide roster of trained evaluators who can be deployed rapidly after major earthquakes. Similar programs exist in Japan, New Zealand, and other earthquake-prone countries. International mutual assistance — teams of trained inspectors from unaffected regions traveling to help in the disaster zone — has also been used in major events.

Inspection coordination requires managing the deployment of teams across the affected area, ensuring systematic coverage, tracking placard postings, and managing the data that flows from inspections into damage databases that feed recovery program administration. Digital tools for field data collection, including tablet-based inspection forms and GPS tagging of placard postings, have significantly improved this coordination compared to paper-based approaches.

Contested Placarding and Appeals

The building safety placard system creates significant consequences for property owners and tenants. A red placard means loss of access to the building and potential loss of rental income, business continuity, or personal possessions. Yellow placards create ambiguity and may complicate insurance claims.

Building owners have the right to request re-evaluation of placards, particularly as initial rapid assessments are replaced by more detailed engineering analyses. The appeals process involves detailed engineering assessment — typically by the owner's own structural engineer — that is reviewed by city or county engineering staff. This process protects property rights while maintaining the primacy of safety in placard decisions.

In some communities, concerns have been raised about inconsistency in placard decisions — identical damage conditions resulting in different placard colors from different inspectors. These concerns highlight the importance of training quality, clear decision protocols, and calibration exercises that align inspector judgment across different teams.

From Inspection to Recovery

Building safety inspection data feeds directly into recovery programs. Damage statistics by building type and location inform decisions about housing reconstruction programs, retrofit requirement prioritization, and land use changes that reduce future exposure. [[Loss-estimation]] methodologies use inspection-derived damage statistics to calibrate models for future events.

Insurance claims processing relies on post-earthquake inspection data — a red-placarded building creates a strong presumption of significant insured loss that streamlines claims processing. Government housing assistance programs use placard data to determine eligibility for disaster housing assistance.

The long-term policy lesson from repeated post-earthquake inspection programs is consistent: buildings that meet modern 耐震基準建物の最低限の耐震安全性を確保するための、設計・建設に関する法的要件の体系。大地震で新たな脆弱性が明らかになるたびに更新される。 seismic requirements perform dramatically better than older, unretrofitted buildings. The most effective use of post-earthquake inspection knowledge is to drive pre-earthquake investment in building retrofits that prevent damage rather than documenting it after the fact.