Earthquake Resistance Standards

The earthquake resistance standards are technical requirements ensuring buildings remain safe during earthquakes. Established by the Building Standards Act and enforced by the Ministry of Construction, these standards have evolved over time.

The original standard, used from 1950 until May 31, 1981, required buildings to withstand seismic intensity of upper 5 without collapsing and to be livable after repairs if damaged. Following the 1978 Miyagi Earthquake, this standard was significantly revised. From June 1, 1981, the new standard mandated that building frames should not be damaged in earthquakes of seismic intensity upper 5 and should not collapse in upper 6 to 7 earthquakes, which occur once every few hundred years.

Since then, the Building Standards Act has undergone several revisions, notably after the Great Hanshin Earthquake in 1995 and the Chuetsu Earthquake in 2004. Buildings constructed or verified after June 1, 1981 must meet the new standards and are considered to have a certain level of seismic performance. Those built after June 1, 2000 have enhanced seismic performance.

There is also an “earthquake resistance standard certification of compliance,” issued by registered architects or designated evaluation organizations. Properties with this certification can enjoy several benefits:

1. 1. Tax reductions for housing loans.
2. 2. Reduced registration and license tax at purchase.
3. 3. Lower real estate acquisition tax at purchase.
4. 4. A maximum 50% reduction in fixed property tax for one year.
5. 5. A 10% reduction in earthquake insurance premiums.

While buildings meeting the new standards are more resilient to earthquakes compared to older structures, no building can be guaranteed to be completely earthquake-proof. Therefore, it is essential to gather information beyond just earthquake resistance standards when seeking a truly safe home.

Seismic Performance Level

The Housing Performance Indication System, introduced in 2000, evaluates the seismic performance level of buildings, indicating their resistance to collapse during earthquakes. The levels are defined as follows:

• Level 1: Comparable to Building Standards Act compliant buildings.
• Level 2: Can withstand earthquakes 1.25 times stronger than Level 1.
• Level 3: Can survive earthquakes 1.5 times stronger than Level 1.

Buildings with a seismic performance level of 2 or above are generally safer during earthquakes. Additionally, discounts on earthquake insurance premiums may apply based on the building's seismic performance level.

Wall Quantities, Metals, and Foundations

In Japan, various standards and criteria serve as indicators of a building's seismic performance. Key factors influencing this performance include wall quantities, materials (such as metals), and foundation types.

Buildings with numerous well-balanced bearing walls are more resistant to earthquakes. Reinforcement metals can enhance the strength of joints in wooden constructions. The foundation plays a critical role in seismic performance; for example:

• Continuous Footing: A foundation made of continuous concrete strips around the building to provide support.
• Mat Foundation: A steel-reinforced concrete slab (about 150mm thick) that covers the entire floor area in addition to continuous footing. This design improves integration and enhances seismic performance by distributing loads more evenly.

The significant revision of the Building Standards Act on June 1, 2000, introduced provisions for the allocation balance of bearing walls and specified metal types for joints. Consequently, buildings constructed or verified after this date are considered to have superior seismic performance compared to those built prior.

Structural Types

Buildings can be categorized into several structural types based on the materials used:

• Wooden Structure: Built primarily from wood.
• RC (Reinforced Concrete) Structure: Composed of reinforcing steel frames encased in cement.
• S (Steel) Structure: Utilizes steel frames for pillars and beams.
• SRC (Steel Reinforced Concrete) Structure: Combines the strengths of RC and S structures, featuring reinforcing steel at the core of reinforced concrete. This type is commonly used in high-rise buildings due to its superior seismic performance.

There are also two main ways to combine structural materials:

• Rigid Frame Structure: Supports the building's weight using pillars and beams.
• Box Frame Structure: Relies on walls for support, requiring more bearing walls. This design typically results in smaller windows and less flexibility for renovations, but the solid walls enhance earthquake resistance.

Construction Methods

Recent advancements in construction technologies focus on seismic isolation, control, and damping, moving beyond mere quake-proofing to enhance safety during earthquakes. Since the 1995 Great Hanshin Earthquake, significant developments have been made in ensuring building safety.

A quake-proof structure is designed to withstand the forces exerted during an earthquake. However, even such structures can experience falling furniture and shattered glass during severe quakes. In contrast, seismic control structures incorporate dampers that absorb vibrations, preventing deformation. These dampers can be categorized as:

• Wall-type Dampers: Integrated into walls to absorb energy.
• Brace-type Dampers: Installed as braces within the framework.
• Cylinder-type Dampers: Utilize cylindrical shapes to dissipate energy.

Seismically isolated structures use laminated rubber bearings placed between the ground and the building to mitigate vibrations. This technology reduces the energy transferred to the building, enhancing safety. Modern super high-rise buildings often employ hybrid structures that combine various seismic control and isolation techniques, including:

• Active Vibration Control: Utilizes IT to manage vibrations actively.
• Damping Technologies: Involves additional mass on rooftops or upper floors to act as dampers.

These innovations collectively improve a building's resilience against seismic events, ensuring greater safety for occupants and minimizing potential damage.

Ground Conditions

While building technologies enhance earthquake resilience, weak ground can still lead to significant damage during a major earthquake. The Great East Japan Earthquake highlighted this issue, as liquefaction caused buildings and roads to subside and tilt, affecting essential lifelines like water pipes. Liquefaction occurs under specific conditions: soft sandy ground, a shallow groundwater level, and a prolonged, strong earthquake.

To mitigate damage, it's crucial to understand the ground conditions where a building is located. Areas with older diluvium formations are less likely to amplify seismic energy, resulting in reduced damage risk. Conversely, newer alluvium formations can amplify energy and increase the likelihood of liquefaction. For detailed information on liquefaction and other natural hazards, hazard maps provided by local prefectures can be consulted.

Area Risks

In Tokyo, the risk of building collapse due to earthquakes is assessed based on building types and ground classifications. These assessments are publicly available and include general risk levels that account for both collapse and conflagration risks (the risk of fire spreading). Factors such as building structure and spacing influence conflagration risk. When searching for real estate, it’s essential to consider that fires can cause substantial damage during an earthquake.

For more information on liquefaction potential in Tokyo, refer to the following link:

Liquefaction Potential Map of Tokyo