Planet earth is a living entity that is constantly moving. Many forces impact the earth’s movement; however, ground force is primarily impacted by what’s happening deep within the earth’s core and the tectonic plates that cover the earth’s surface like a crust.
The seven major and eight minor tectonic plates are like giant slabs, joining together like a jigsaw, constantly moving and shifting. While tectonic plate theory is considered a complex and debatable topic among physicists, broadly speaking when tectonic plates move relative to each other, the resulting force creates intense seismic movement, which is more commonly referred to as an earthquake.
An earthquake can occur anywhere on the earth’s surface, but certain areas are more prone than others, particularly those located on a plate boundary. The Pacific plate is considered the largest and fastest moving tectonic plate and forms part of the infamous Pacific Ring of Fire, a very large seismically active basin in the Pacific region that spans across the west coast of the Americas and along the east coasts of Russia, Japan and Indonesia and down to New Zealand. This intense seismic area is where approximately 81 per cent of the world’s largest earthquakes occur and a key reason why Japan and New Zealand are considered earthquake hotspots.
The severity of an earthquake is measured by its intensity and magnitude; intensity is based on effects from the ground shaking while magnitude is related to the amount of seismic energy released at the earthquake’s epicentre. To put the forces into context, Australian Geoscience compares the energy from a magnitude 8.6 earthquake as being equivalent to 10,000 atomic bombs. In the Asia Pacific region, one of the most devastating seismic events was the 9.0 magnitude earthquake that hit Great Tohoku, Japan on 11 March 2011. This catastrophic event was the fourth largest earthquake in the world since modern record-keeping began in 1900, and was responsible for more than 22,000 deaths and a $235 billion damage bill. While the 2010 and 2011 earthquakes that struck Christchurch, New Zealand weren’t as large as the event in Japan, they caused widespread devastation throughout the Canterbury region with thousands of homeowners impacted by soil liquefaction and building foundation damage.
Australia is relatively protected from such major events; it doesn’t sit on a tectonic plate boundary. However, while significant earthquakes are relatively rare in the country, they can occur. On average, there are 100 earthquakes of magnitude 3 or more in Australia each year. While they are unlikely to cause damage, it’s important for Australia to be aware of the risks and potential damage an earthquake can cause, particularly if it occurs in a metropolitan area. For example, Australia’s largest earthquake was a 6.6 magnitude quake that occurred on 22 January 1988 at Tennant Creek, Northern Territory. However, as it occurred in a remote area, it caused minimal damage and injuries unlike the smaller 5.6 magnitude Newcastle earthquake that occurred on 28 December 1989 which was responsible for 13 deaths and caused billions of dollars in damage.
Geoscience Australia provides a comprehensive overview of the earthquake risks in Australia to help build greater resilience in the event of an earthquake and foster a greater understanding around the hazards and vulnerabilities they can cause to our built environment. The government organisation actively monitors, analyses and reports on Australian seismic events and encourages people to report local tremors through its online ‘felt’ report.
The extent of earthquake damage will depend on many factors but generally, the bigger, closer and shallower the earthquake, the stronger the shaking will be, and the more damage is likely to occur. Factors that can impact the remediation process include the proximity to the earthquake source, the magnitude and duration of the quake, the engineering behind affected structures and neighbouring buildings, the condition of the ground the structure is sitting on and the degree of soil liquefaction. Liquefaction occurs when the structure of a loose, saturated sand breaks down due to a rapidly applied loading. In an earthquake, this results in an increase in pore water pressure, thereby softening the soil deposit. When the ground has liquefied, building subsidence is common as foundations or footings are no longer supported, often sinking into the weakened ground.
Australian engineers have learnt a lot from the earthquakes in Japan and New Zealand, including how to strengthen the soils and remediate damaged structures. Mainmark has invested heavily in research and development initiatives to help promote earthquake resilience through testing its ground improvement and foundation re-levelling technologies. Its team of technical and specialist earthquake engineers are experts when it comes to innovative ground improvement solutions, such as JOG Computer-Controlled Grouting and their Terefirm® Resin Injection technique.
Following the Christchurch earthquakes, Mainmark developed its Ground Improvement and Liquefaction Mitigation solution, now known as Terefirm, which has been formally recognised as a geotechnical innovation after nearly four years in development and extensive trials and testing in the Christchurch Red Zone. This led to Resin Injection being included in MBIE Module 5: Ground improvement of soils prone to liquefaction. The internationally peer reviewed report for our Resin Injection Ground Improvement Research Trials is available for review on the New Zealand Geotechnical Society website.
With ongoing research, trials and testing, Mainmark is setting the groundwork for future innovation, using its proven technologies to remediate ever taller and larger structures. Mainmark offers viable and proven alternatives to traditional, invasive concrete piling and underpinning. Mainmark’s injection technologies can significantly reduce remediation costs by doing less with more, and incredibly the most significant outcome of all is the ability to remediate existing structures using solutions that are applied directly beneath a damaged building.
For more information and advice about our range of earthquake remediation solutions, contact Mainmark on 1800 623 312 in Australia, 0800 873 835 in New Zealand or visit our website.
By Theo Hnat
Theo Hnat is a R&D and Technical Manager at Mainmark. Based in New Zealand, Theo’s responsibilities include research in new technologies in ground improvement and liquefaction mitigation, structural risk assessment of existing structures, design, and analysis.