Risk management lessons to learn from earthquake disasters in 2024

In early 2024, powerful earthquakes struck Japan and Taiwan.

While improved resilience and preparedness reduced human casualties and damage compared with past events, the earthquakes still resulted in significant fatalities, buildings destroyed and power failures affecting tens of thousands of homers.

In Japan, most failures were in liquefaction-prone areas, while in Taiwan, soft-story collapse was the primary cause.

These issues highlight the ongoing need to undertake seismic risk assessments, retrofit vulnerable buildings and update construction practices and codes.

Noto earthquake aftermath

On New Year’s Day 2024, a 7.5-magnitude earthquake struck Japan’s Noto peninsula at a depth of 10 kilometres, causing severe shaking, liquefaction and landslides. The shallow epicentre produced peak ground accelerations (PGAs) of up to 1.2g (gravitational acceleration; 9.81 m/s2), comparable to those felt during the 2011 Tohoku earthquake.

Over 102,000 structures were damaged in Japan’s Ishikawa Prefecture, including the complete or partial collapse of 23,700 buildings. The event resulted in 245 deaths and over 1,300 injuries, primarily from collapsed buildings.

The Cabinet Office of Japan estimated economic losses at up to 2.6 trillion yen (US $17.6 billion), while insured losses are estimated at up to 870 billion yen (US $5.5 billion).

Despite frequent seismic activity, Japan experiences fewer earthquake casualties than many other countries due to its strict building codes, which are continuously updated after major seismic events.

“Collapses were mainly seen in older structures, those with irregular designs or those with inadequate seismic detailing, particularly in liquefaction zones.”

Established after the 1923 Yokohama earthquake, these codes mandate stringent seismic design and retrofitting. The 1995 Kobe and 2011 Tohoku earthquakes prompted further improvements to the Building Standard Law, enhancing seismic resilience.

In response to the 1995 Kobe earthquake, Japan also implemented an early warning system and conducts regular earthquake drills to improve public preparedness and response.

Modern Japanese buildings, utilising reinforced concrete, steel, seismic dampers and base isolation, generally withstood the earthquake well, showing minimal structural damage.

Collapses were mainly seen in older structures, those with irregular designs or those with inadequate seismic detailing, particularly in liquefaction zones. Notably, some newly constructed wooden buildings also failed, suggesting a need for further revisions to the Building Standard Law.

“Despite improvements in building design and preparedness in recent decades, the Noto earthquake highlights the need for further hazard assessment and mitigation.”

Liquefaction and landslides were widespread, causing significant damage. Around 30% of buildings in areas affected by liquefaction experienced differential settlement, tilting and collapse due to soil-bearing capacity loss. Earthquake-triggered landslides worsened the destruction, blocking key roads and hindering rescue and relief efforts.

The earthquake also severely affected infrastructure, damaging 120 kilometers of roads. Power plants, including nuclear facilities, were closely monitored and experienced minor damage and temporary shutdowns, but overall, the power infrastructure performed satisfactorily. Internet access and data centres faced temporary outages, but redundancy and swift responses from service providers quickly restored connectivity.

Despite improvements in building design and preparedness in recent decades, the Noto earthquake highlights the need for further hazard assessment and mitigation.

This includes better understanding of liquefaction and landslide susceptibility, improving critical infrastructure resilience, promoting earthquake insurance, prioritising seismic retrofitting, and investigating the seismic performance of new and existing buildings.

Taiwan shaken by biggest earthquake in 25 years

A powerful 7.4-magnitude earthquake struck eastern Taiwan on April 3, 2024, 18 kilometres southwest of the city of Hualien at a depth of 34.8 kilometres. The relatively shallow depth produced intense shaking, with a highest PGA of 0.55 g near the epicentre.

Taiwan’s Land Management Agency reported 848 cases of damaged structures, 42 of which were listed as “code red.” The disaster resulted in 18 deaths and over 1,100 injuries. Economic losses were estimated at US $28 billion, with insured losses likely between US $0.5 billion and $1 billion.

The dramatic contrast in the number of collapsed buildings and fatalities between the 1999 Chi-Chi event in Taiwan and recent earthquakes highlights the significant improvements in seismic resilience in the past three decades.

After the 1999 earthquake, Taiwan introduced stringent construction standards, and poor construction practices were curbed.

“The Hualien earthquake once again highlighted the vulnerability of soft-story buildings”

Recognising that improving building codes alone is insufficient, Taiwan also implemented programmes to assess and retrofit structures. For example, after many schools were damaged or destroyed in the Chi-Chi earthquake, US $4 billion was allocated from 2009 to 2022 to upgrade the seismic capacity of 10,000 schools.

Additionally, private buildings underwent screenings and mandatory seismic assessments, with the government providing retrofit guidance and subsidies for high-risk buildings.

Despite these retrofit efforts, some buildings remain at high risk of seismic damage. The Hualien earthquake once again highlighted the vulnerability of soft-story buildings — multi-story structures with open spaces lacking structural walls, common in buildings with carports or commercial spaces on the first floor.

Soft-story collapses in the recent event occurred on high-rise reinforced concrete structures. These buildings became common in cities following Taiwan’s 1984 “Open Space” policy, which permitted vertical construction in congested cities if the street-level story was open.

“This common vulnerability across continents stresses the ongoing need for comprehensive seismic risk assessments”

This design results in low stiffness on the first floor, causing earthquake-induced drifts to concentrate there, creating significant stresses and potential failure. Typically, the upper part of the building, which remains relatively intact, collapses onto the soft story, as seen in recent Hualien incidents.

Soft-story buildings are an issue not only in Taiwan but also in other seismically active regions such as California. For example, the 1989 Loma Prieta earthquake in Northern California caused many failures of soft-story multi-residential buildings with carports on the ground floor.

This common vulnerability across continents stresses the ongoing need for comprehensive seismic risk assessments, as well as updating construction practices and codes.

In addition, it highlights the importance of a comprehensive risk evaluation performed by teams of experienced engineers, who not only can assess the risk but can also provide viable retrofit strategies for a vast array of structures.