🤙🏼Earthquake Engineering Unit 13 – Major Earthquake Case Studies & Lessons

Key Earthquake Events

• 1906 San Francisco earthquake (magnitude 7.8) ruptured along the San Andreas Fault, causing widespread destruction and fires
• 1923 Great Kanto earthquake (magnitude 7.9) struck the Tokyo-Yokohama metropolitan area, resulting in significant damage and loss of life
• 1960 Great Chilean earthquake (magnitude 9.5) remains the largest recorded earthquake in history, triggering tsunamis and landslides
• 1964 Great Alaska earthquake (magnitude 9.2) caused extensive damage to infrastructure and generated tsunamis that affected the U.S. West Coast
• 1976 Tangshan earthquake in China (magnitude 7.6) resulted in the highest death toll of any earthquake in the 20th century
• 1985 Mexico City earthquake (magnitude 8.0) caused severe damage to buildings due to the city's unique geological conditions
• 1995 Great Hanshin earthquake (magnitude 6.9) struck the Kobe region of Japan, exposing vulnerabilities in modern urban infrastructure
• 2004 Indian Ocean earthquake and tsunami (magnitude 9.1) affected multiple countries, highlighting the need for improved early warning systems

Geological Context

• Tectonic setting plays a crucial role in determining the location and frequency of earthquakes
  • Plate boundaries, such as convergent (subduction zones), divergent (mid-ocean ridges), and transform (strike-slip faults) boundaries, are prone to seismic activity
• Local geology influences ground motion characteristics and site effects
  • Soft soil conditions can amplify seismic waves and prolong shaking duration
  • Proximity to the fault rupture can result in higher ground accelerations and more severe damage
• Seismic hazard assessment involves identifying potential seismic sources, estimating their recurrence intervals, and characterizing the expected ground motions
• Paleoseismology studies ancient earthquakes by examining geologic evidence, such as fault scarps and displaced sedimentary layers, to extend the seismic record beyond instrumental data
• Microzonation maps provide detailed information on local soil conditions and expected ground motion amplification, aiding in urban planning and seismic design

Seismic Characteristics

• Magnitude is a measure of the energy released by an earthquake, typically expressed using the moment magnitude scale (Mw)
  • Moment magnitude is based on the seismic moment, which considers the fault area, average slip, and rock rigidity
• Intensity describes the observed effects of an earthquake at a specific location, often measured using the Modified Mercalli Intensity (MMI) scale
• Ground motion parameters, such as peak ground acceleration (PGA), peak ground velocity (PGV), and spectral accelerations (SA), quantify the severity of shaking at a site
• Seismic waves, including body waves (P and S waves) and surface waves (Rayleigh and Love waves), propagate through the Earth's interior and along its surface
  • P waves are compressional waves that travel fastest and arrive first at a seismic station
  • S waves are shear waves that cause the most damage due to their higher amplitudes and longer durations
• Seismic hazard curves illustrate the probability of exceeding various ground motion levels at a specific site over a given time period
• Seismic risk assessment combines the seismic hazard with the vulnerability of structures and potential consequences to estimate the expected losses

Structural Damage Analysis

• Building typology and construction materials significantly influence the seismic performance of structures
  • Unreinforced masonry buildings are highly vulnerable to collapse due to their brittle behavior and lack of ductility
  • Non-ductile concrete frames with insufficient reinforcement and poor detailing can experience sudden failures
• Structural irregularities, such as soft stories, torsional irregularities, and vertical discontinuities, can concentrate damage and lead to localized failures
• Soil-structure interaction (SSI) effects can modify the seismic response of structures, particularly for tall buildings and those founded on soft soils
• Liquefaction, a phenomenon where saturated loose soils lose strength and behave like a liquid during strong shaking, can cause foundation failures and differential settlements
• Nonstructural components, such as facades, partitions, and mechanical systems, can pose significant hazards and contribute to economic losses
• Performance-based seismic design aims to ensure that structures meet specific performance objectives under different levels of seismic hazard
  • Performance levels can range from immediate occupancy to life safety and collapse prevention

Human and Economic Impact

• Casualties, including fatalities and injuries, are the most tragic consequence of earthquakes
  • Factors influencing casualties include building collapse, falling debris, and secondary hazards like fires and tsunamis
• Displacement of affected populations can lead to long-term social and economic challenges
  • Temporary shelters and transitional housing are often required to accommodate displaced individuals and families
• Economic losses encompass direct costs (structural and nonstructural damage) and indirect costs (business interruption, supply chain disruptions)
• Infrastructure damage, including transportation networks, utilities, and critical facilities, can hinder emergency response and recovery efforts
• Psychological trauma and mental health issues can persist long after the physical impact of the earthquake
• Disproportionate impact on vulnerable communities, such as those with lower socioeconomic status or marginalized populations, highlights the need for equitable disaster risk reduction strategies

Emergency Response Evaluation

• Rapid damage assessment is crucial for prioritizing search and rescue operations and allocating resources effectively
  • Remote sensing techniques, such as satellite imagery and unmanned aerial vehicles (UAVs), can provide valuable information for rapid damage mapping
• Search and rescue efforts focus on locating and extracting survivors trapped in collapsed structures
  • Specialized teams, including urban search and rescue (USAR) units, are trained to operate in complex and hazardous environments
• Medical response involves treating injuries, managing chronic health conditions, and preventing disease outbreaks in the aftermath of an earthquake
  • Field hospitals and mobile medical units can be deployed to provide emergency healthcare services
• Shelter and relief management ensures that affected populations have access to safe shelter, food, water, and basic necessities
  • Coordination among government agencies, NGOs, and community organizations is essential for effective relief distribution
• Communication and information management systems are vital for disseminating warnings, coordinating response efforts, and keeping the public informed
  • Social media platforms can play a significant role in crowdsourcing information and facilitating community-driven response initiatives

Engineering Lessons Learned

• Importance of seismic design codes and their regular updates based on the latest research findings and lessons learned from past earthquakes
  • Codes provide minimum requirements for the design and construction of structures to ensure life safety and reduce damage
• Need for retrofitting and strengthening of existing vulnerable buildings, particularly those built before modern seismic codes were implemented
  • Retrofit techniques can include adding shear walls, braces, or base isolation systems to improve seismic performance
• Significance of ductile detailing and capacity design principles in promoting the overall stability and integrity of structures during strong shaking
  • Ductile detailing ensures that structural elements can undergo significant deformations without losing strength
• Role of innovative technologies, such as seismic isolation and energy dissipation devices, in enhancing the seismic resilience of structures
  • Base isolation systems decouple the structure from the ground motion, reducing the seismic forces transmitted to the building
  • Energy dissipation devices, like viscous dampers or friction dampers, absorb seismic energy and limit the damage to structural elements
• Importance of geotechnical considerations, such as site-specific ground response analysis and foundation design, in mitigating seismic risks
  • Ground improvement techniques, like deep soil mixing or stone columns, can be used to stabilize weak soils and reduce liquefaction potential

Future Preparedness Strategies

• Developing and implementing risk-informed land-use planning policies to guide development away from high-seismic-hazard areas
  • Microzonation maps can inform land-use decisions and help identify areas suitable for development or requiring special design considerations
• Promoting community awareness and education programs to enhance public understanding of seismic risks and preparedness measures
  • Earthquake drills and training sessions can help individuals and communities practice response procedures and identify areas for improvement
• Investing in early warning systems that can provide seconds to minutes of advance notice before strong shaking arrives
  • Early warning systems can be used to trigger automated actions, such as shutting down critical infrastructure or broadcasting alerts to the public
• Enhancing the resilience of critical infrastructure systems, such as hospitals, schools, and lifelines (power, water, transportation), through seismic upgrades and redundancy measures
  • Resilient infrastructure can maintain functionality or recover quickly after an earthquake, reducing the overall impact on communities
• Encouraging the development and adoption of new technologies, such as advanced sensors, data analytics, and decision support tools, to improve real-time monitoring and post-earthquake assessment
  • Smart sensors and Internet of Things (IoT) devices can provide valuable data for rapid damage assessment and prioritization of response efforts
• Fostering interdisciplinary collaboration among engineers, scientists, policymakers, and communities to develop holistic and sustainable seismic resilience strategies
  • Participatory approaches that engage stakeholders throughout the planning and implementation process can lead to more effective and socially acceptable solutions