Seismic Risk Assesment : A Focus on Risk Mangement

                                                                                                                        Prabin Shijo Peter, Dominika Kalota, Julia Mentel

INTRODUCTION

Basic information

Earthquake risk encompasses the likelihood of both physical disruption and human or financial consequences resulting from seismic activity. It combines the potential for damage, which refers to the physical harm caused by the earthquake, with the broader concept of loss, which includes the human and financial impacts arising from that damage. Hazard, on the other hand, denotes the probable intensity of the natural effects of an earthquake, serving as a precursor to potential damage and loss. Mitigation efforts play a crucial role in reducing earthquake risk by implementing measures aimed at minimizing both the likelihood and severity of damage and loss. These measures may include structural reinforcements, early warning systems, land-use planning, and public education initiatives designed to enhance preparedness and resilience in earthquake-prone areas. Through effective mitigation strategies, communities can better safeguard lives, property, and infrastructure against the impacts of seismic events.

Overview on earthquake risk

Earthquakes bring forth various hazards, including fault rupture, ground shaking, ground failures, and water wave hazards such as tsunamis. Many buildings and structures are unable to withstand these hazards, resulting in damage. This can range from minor cracks to complete collapse. Even structures that remain intact may see their contents severely affected. This is particularly crucial for essential facilities like hospitals or emergency communication centres, where damage to contents can be devastating and restoration efforts can be costly and time-consuming.

Primary damage can lead to secondary hazards and damage, such as hazardous material releases, significant fires, or flooding. The damage results in various losses, including loss of life or injury, financial loss, and loss of functionality.

Understanding and addressing each stage of this process is crucial for effective earthquake preparedness, response, and recovery efforts. This involves measures such as implementing standards, enhancing structural resilience, creating emergency response plans.

The picture shows global seismic risk map.

Earthquake hazard

Earthquake hazards can be assessed and measured through various means. Charles F. Richter introduced the concept of earthquake magnitude with the Richter scale in 1935. Subsequently, multiple scales for magnitude and intensity have been introduced.

Intensity is also evaluated using the Modified Mercalli Intensity (MMI) scale. Engineers determine seismic intensity peak ground acceleration (PGA) and other measures.

Following significant earthquakes, maps depicting the distribution of earthquake intensity across the affected region are released.

Identifying and assessing earthquake hazards for a specific site or community is crucial in the earthquake risk management process.

World map showing USGS Magnitude 2.5+ Earthquakes for a day 21.03.2024

Earthquake damage and loss

Buildings can suffer damage in several ways during an earthquake.

Exterior walls may collapse, particularly in unreinforced buildings. This can lead to partial or total roof and floor collapse, posing significant life hazards and resulting in substantial financial losses.
Concrete columns may shear, causing the building to collapse. It is frequently observed in older, reinforced concrete frame buildings.
Concrete and masonry walls may crack, resulting in visible damage. If the cracking is severe, pieces of the wall can become loose and fall away from the structure, creating a safety hazard. This is a common occurrence in older, lightly reinforced structures.

Structural damage varies depending on the intensity of earthquake hazards and the quality of individual building design and construction. While most buildings are not expected to collapse, damage is widespread.

Damage results in loss, which can take many forms.

Life loss and injury
Major damage to property
Loss of function (hospitals, infrastructure)
Business interruption (loss of costs)

Damage to residential housing after 4.8 magnitude earthquake struck southeast France
Damage to road due to earthquake
Photo of the interior of the masonry-built hospital in Cauquenes, Chile 2010, after severe earthquake.

Mitigation basics

Damage and loss can be mitigated in many ways.

Faulting and shaking hazards are extensively mapped for example in California by the Division of Mines and Geology (USGS). Shaking intensity maps are also accessible online. It's advisable to avoid locating important facilities in areas prone to faulting or severe shaking, with remediation measures sometimes necessary for soil conditions or ground failure.

Recent advancements include techniques for soil improvement. Primary damage mitigation primarily involves structural engineers and design professionals specializing in earthquake-resistant structures.

Secondary damage requires comprehensive solutions, improved material handling, and infrastructure enhancements. Emergency response capabilities and personnel training are crucial, with earthquake insurance providing partial financial mitigation.

CASE STUDY 1: Japanese Architecture's Response to Earthquake Damage

Introduction

Japan deals with earthquakes frequently, and this presents a major challenge for its buildings. However, Japanese architecture has a rich history of finding solutions to this problem through innovation and adaptation. In this case study, we delve into how Japanese architecture addresses the challenge of earthquake damage through structural design, materials selection, and engineering practices.

The Great Kanto Earthquake of 1923 and Its Legacy

The Great Kanto Earthquake of 1923, which measured 7.9 on the Richter scale, caused significant devastation in Tokyo and its surrounding areas, having a profound impact on Japan's approach to urban development. Recognizing the critical need for robust infrastructure, Japan launched a major rehabilitation effort, with a special emphasis on engineering systems that can withstand seismic impacts. This seismic event sparked advances in structural engineering, driving Japan to the forefront of earthquake-resistant architecture. By incorporating creative design techniques and cutting-edge engineering practices, Japan is improving the seismic resilience of its built environment, assuring the safety and stability of its cities in the face of future seismic disasters.

The Great Kanto Earthquake: 100-Year Retrospective | Moody's RMS Kanto Earthquake | Volunteerism in Japan The Great Kanto Earthquake in Japan, 1923

Structural Design

Japanese architecture's reaction to earthquake damage is reflected by its unique structural design. Traditional Japanese buildings, such as temples and shrines, use "shin-ko-sho" construction, which includes lightweight timber frames and flexible connections. This design allows buildings to swing and absorb seismic energy while remaining structurally sound. In the current era, Japanese architects include seismic-resistant design ideas such as base isolation systems and dampening devices to improve buildings' capacity to endure ground shaking. For example, the Tokyo Skytree, an icon of modern Japanese design, uses a tuned mass damper to reduce the impacts of wind and earthquakes, assuring structural integrity and safety.

Things to do around the Tokyo Skytree area | The Official Tokyo Travel Guide, GO TOKYO

Materials

The key to Japan's architectural adaptability to seismic difficulties is the careful selection of building materials. Japanese architects have capitalized on the special qualities of traditional materials like paper and wood, which are known for being naturally lightweight and flexible, by drawing on centuries of tradition. These tried-and-true, well-refined materials have shown to be crucial in reducing structural damage by absorbing and dispersing the energy produced by earthquakes. The combination of steel frames and reinforced concrete has become standard in current construction methods, providing buildings with unmatched strength and durability that are essential for withstanding the powerful pressures generated during seismic occurrences. However, the quest for robustness is not static; rather, it changes in tandem with advances in material science. A new generation of seismic-resistant materials, including high-performance concrete and fibre-reinforced polymers, has been created as a result of this unrelenting innovation. These materials are designed to offer improved levels of resilience and structural integrity. By carefully integrating these cutting-edge materials into architectural plans, Japan keeps pushing the envelope in terms of building structures that are earthquake-resistant, protecting its built environment and guaranteeing the long-term security and stability of its cities.

Engineering Practices

Japanese architects and engineers employ rigorous engineering practices to ensure the seismic resilience of buildings. Prior to construction, extensive seismic analysis and computer simulations are conducted to assess a building's response to earthquakes and identify potential vulnerabilities. This allows architects to optimize structural design and incorporate appropriate seismic mitigation measures. Furthermore, strict building codes and regulations mandate seismic-resistant construction practices, ensuring that new buildings meet stringent safety standards. Additionally, proactive measures for retrofitting existing structures are implemented to improve their seismic performance, including strengthening weak structural elements and upgrading foundation support.

Conclusion

Historical Turning Point: The Great Kanto Earthquake of 1923 marked a pivotal moment in Japan's architectural history, prompting significant advancements in earthquake-resistant design and construction practices.
Continuous Evolution: Japanese architecture continues to evolve with innovative structural design, material selection, and engineering practices aimed at minimizing damage from seismic events.
Resilience Building: Japan's commitment to earthquake-resistant design sets a global benchmark, demonstrating the importance of prioritizing resilience in urban development.

CASE STUDY 2: The Christchurch Earthquake of 2011

Introduction

The Christchurch earthquake of 2011, with a magnitude of 6.3, shook the foundations of the city, causing extensive damage to buildings, infrastructure, and communities. The central business district bore the brunt of the devastation, with numerous iconic structures reduced to rubble and thousands of homes rendered uninhabitable. In the wake of this catastrophe, Christchurch faced the monumental task of rebuilding its urban landscape while simultaneously addressing the pressing need for enhanced earthquake resilience.

Earthquake in New Zealand - The Atlantic

Construction Aspects

Building Design

The seismic design of structures emerged as a paramount consideration in the reconstruction efforts in Christchurch. Architects and engineers prioritized innovative design principles aimed at enhancing buildings' ability to withstand seismic forces. This included the incorporation of base isolation systems, which decouple buildings from the ground motion during earthquakes, thereby reducing structural damage and ensuring the safety of occupants.

Materials

The choice of construction materials played a pivotal role in determining the resilience of buildings in Christchurch. Traditional materials such as timber, known for their flexibility and seismic resilience, were favored in the reconstruction efforts. Additionally, advancements in material science led to the development of new seismic-resistant materials, such as high-performance concrete and fiber-reinforced polymers, which offered enhanced strength and durability to withstand the rigors of seismic activity.

Retrofitting Measures

Retrofitting existing buildings emerged as a key strategy in bolstering the seismic resilience of Christchurch's built environment. Structural engineers implemented retrofitting measures to strengthen vulnerable structures, including the installation of steel bracing, reinforced concrete shear walls, and seismic dampers. These interventions aimed to improve the structural integrity of existing buildings, reduce the risk of collapse during earthquakes, and ensure the safety of occupants.

Conclusion

Construction Priority: Christchurch earthquake's case study emphasizes the vital role of construction practices in rebuilding urban areas post-seismic events.
Innovative Design: Prioritizing innovative building design helps enhance resilience against earthquakes and ensures safer structures for communities.
Resilient Materials: The use of resilient materials, such as timber and advanced composites, strengthens buildings and infrastructure against seismic forces.
Proactive Retrofitting: Implementing proactive retrofitting measures improves existing structures' ability to withstand earthquakes and minimizes damage.

SUMMARY

The report provides a comprehensive examination of earthquake risk management strategies, focusing on mitigation, hazard assessment, damage evaluation, and case studies of earthquake-prone regions. It begins by defining key terms such as earthquake risk, hazard, damage, loss, and mitigation, emphasizing the importance of understanding each stage of the earthquake process for effective preparedness and response. The discussion then delves into earthquake hazards, including fault rupture, ground shaking, and secondary effects like tsunamis, highlighting the necessity of assessing and measuring these hazards through various scales and techniques. The report also explores earthquake damage and loss, detailing the various ways buildings can suffer damage during earthquakes and the resulting consequences in terms of life loss, financial loss, and loss of functionality. Mitigation strategies are thoroughly examined, ranging from mapping faulting and shaking hazards to implementing structural resilience measures and enhancing emergency response capabilities. Two case studies, focusing on Japanese architecture's response to earthquake damage and the reconstruction efforts following the Christchurch earthquake of 2011, offer real-world examples of innovative design principles, material selection, and retrofitting measures aimed at enhancing seismic resilience. Throughout the report, a clear emphasis is placed on the importance of proactive measures, rigorous engineering practices, and ongoing research and technological advancements in mitigating earthquake risk and safeguarding urban populations against future seismic events.

CONCLUSIONS

Understanding Earthquake Risk: The report provides a clear understanding of earthquake risk, including hazards, damage, and loss, stressing the importance of mitigation measures.
Hazard Assessment: Various methods for assessing earthquake hazards, such as magnitude scales and intensity maps, are discussed, highlighting the need for thorough hazard evaluation.
Damage and Loss Evaluation: Different types of earthquake damage and resulting losses, including life loss, property damage, and functional impairment, are outlined, emphasizing the widespread impact of earthquakes.
Mitigation Strategies: The report explores mitigation basics, including mapping hazards and implementing structural resilience measures, underscoring the importance of proactive measures in reducing earthquake risk.
Case Studies: Case studies of Japanese architecture and the Christchurch earthquake demonstrate innovative design, material selection, and retrofitting measures, showcasing effective strategies for enhancing seismic resilience.
Engineering Practices: Rigorous engineering practices, such as seismic analysis and adherence to building codes, are highlighted as crucial for ensuring the seismic resilience of structures.