Aftershocks posing a risk to residential structures following an earthquake
In the aftermath of the magnitude 5.9 earthquake that struck Victoria's north-east on September 22, over 150 aftershocks with a magnitude greater than 1.0 have been recorded by Geoscience Australia. This seismic activity has caused concern for homeowners, particularly those living in older or heritage properties.
The Risks to Victorian Homes
Victorian homes, with their masonry structures and intricate details, are more susceptible to damage during earthquakes. Properties built with bricks, blocks, or concrete are more likely to crack or move than timber houses. Additionally, houses with old-style clay piping may be vulnerable to damage due to seismic activity.
Common Signs of Earthquake Damage
Homeowners should be aware of the signs of earthquake damage. These may include jammed doors or windows, uneven floorboards, unstable stairs, subsidence or sinking in the front or backyard, and damage to exposed beams. Cracking to plasterboard or masonry elements is also a potential sign of earthquake damage. Displaced rainwater structures, such as guttering, downpipes, and roof tiles, can lead to leaks in the roof due to earthquake damage.
The Role of a Building Inspector
A qualified building inspector can determine whether the damage is major or minor and may recommend additional specialists, such as an engineer, to provide advice on how to rectify it. The inspector conducts a visual inspection of the property, observes the exterior and interior of the roof, external and internal walls, floors, ceilings, driveway, fences, subfloor, and the yard. They photograph and write down details about the location and nature of any obvious defects, advise the homeowner on why a defect should be fixed, and recommend the types of tradesmen or specialists that can repair the issue.
Strategies for Seismic Protection
Protecting older or heritage Victorian homes from structural damage due to aftershocks and future earthquakes involves several steps that balance preservation with seismic resilience.
Seismic Assessment
Start by conducting a thorough seismic assessment of the home to identify potential vulnerabilities. This involves evaluating the foundation, walls, roof, and any other structural elements that could be affected by earthquakes.
Foundation Strengthening
Ensure the foundation is strong and secure. This might involve installing new footings, reinforcing existing ones, or using techniques like micropiling to stabilize the soil beneath the foundation.
Wall Reinforcement
Use materials like carbon fiber strips similar to those in StablWall to reinforce walls. Carbon fiber is lightweight yet incredibly strong, making it an effective material for preventing wall cracks and bowing under seismic stress. Alternatively, consider using cob or rammed earth techniques for new repairs or additions, as these materials are naturally resistant to seismic activity.
Roof and Ceiling Supports
Ensure the roof is securely fastened to the walls using appropriate fasteners to prevent collapse during earthquakes. Strengthen ceiling structures to support the weight of the roof and any additional loads.
Seismic Isolation Systems
Consider installing seismic isolation systems, such as bearings, which can reduce the impact of earthquakes on the structure by decoupling it from the ground motion.
Secure Heavy Objects
Ensure that heavy objects such as bookshelves and appliances are securely fastened to walls to prevent them from falling and causing injury or damage.
Insurance and Planning
Purchase earthquake insurance to protect against financial losses. Earthquake coverage is not typically included in standard home insurance policies, so it's crucial to add it if available.
Special Considerations for Heritage Homes
When making any repairs or reinforcements, ensure that the original architectural features of the heritage home are preserved. This might involve using traditional materials and techniques where possible. Engage with architectural historians and structural engineers experienced in working with heritage buildings to ensure that any modifications are sympathetic to the original design.
By taking these steps, older or heritage Victorian homes can be better protected against the structural damage caused by aftershocks and future earthquakes while preserving their historical integrity. Homeowners and landlords can prepare for unexpected natural events such as earthquakes by ensuring they have adequate home buildings and contents insurance.
[1] StablWall: https://www.stabwall.com.au/ [2] Seismic Isolation Systems: https://www.seismicisolation.com/ [3] Earthquake Insurance: https://www.apia.com.au/home-insurance/earthquake-insurance [4] Carbon Fiber Strips: https://www.seismic-rehab.com/ [5] Cob and Rammed Earth Techniques: https://www.greenbuildingadvisor.com/article/rammed-earth-foundations-and-walls
- To strengthen the seismic resilience of older or heritage Victorian homes, homeowners may consider reinforcing walls with materials like carbon fiber strips or employing cob or rammed earth techniques for repairs or additions, as these materials naturally resist seismic activity.
- In addition to reinforcing their homes, homeowners should consider purchasing earthquake insurance to protect against financial losses, as this coverage is not typically included in standard home insurance policies.
