Comprehensive Notes on Earthquake Hazards, Prediction, and Tectonics

Forecasting and Minimizing Hazard

  • Earthquakes strike without warning; extensive research aimed at anticipating earthquakes
  • Focus of minimization is on forecasting and warning
  • Forecasts assist: planners considering seismic safety measures; people deciding where to live
  • Long-term forecasts do not help predict a specific earthquake; predictions have eluded us

The National Earthquake Hazard Reduction Program

  • Coordinated by USGS, universities, and others
  • Major goals:
    • Develop an understanding of the earthquake source
    • Determine earthquake potential
    • Predict effects of earthquakes
    • Apply research results

Estimating Seismic Risk

  • Hazard maps show earthquake risk
  • Indicate the probability of a particular event or the amount of shaking

Short-Term Prediction

  • Pattern and frequency of earthquakes – foreshocks
  • Deformation of ground surface – changes in land elevation
  • Seismic gaps along faults – areas that have not seen recent quakes
  • Geophysical and geochemical changes – changes in Earth’s magnetic field, groundwater levels

Banda Aceh and Sunda Megathrust (Seismic Gap and Megaquake Context)

  • Banda Aceh, Sumatra: 2004 M 9.2 earthquake on the Sunda Megathrust (Indian-Australian Plate vs Eurasian Plate)
  • 2005, M 8.6 event (aftershock sequence and major hazard context)
  • Plates involved: Indian-Australian Plate and Eurasian Plate; region includes Sumatra, Padang, Singapore
  • Relative plate motion: approximately 5.7 extcm/yr5.7\ ext{cm/yr} along the Sunda megathrust
  • Concept of seismic gaps: areas that have not experienced recent large earthquakes may be sites of future large events

The Future of Earthquake Prediction

  • Still a long way from reliably predicting earthquakes
  • Information is being collected with the aim of:
    • Consistent long-range forecasts
    • Intermediate-range forecasts
    • Short-range predictions
  • Problem: predictions released publicly before vetting could cause harm or panic

Earthquake Warning Systems

  • Plan for issuing a prediction or warning
  • Liability concerns include: false alarms, failures, and potential damage from actions taken in response

Perception of and Adjustment to the Earthquake Hazard

  • How people perceive/adjust to hazard can affect the extent of the hazard
  • Actions to reduce risk:
    • Use appropriate building materials
    • Ensure adequate insurance coverage
    • Ensure emergency and relief efforts are adequate

Perception of the Earthquake Hazard

  • Emotional and psychological distress can drive relocation
  • Past experience does not always translate into increased preparedness
  • Examples:
    • Kobe, Japan: emergency response delays in two earthquakes within two years
    • Turkey: emergency response delays in earthquakes
  • Construction issues despite high survivability standards

Community Adjustments to the Earthquake Hazard

  • Location of critical facilities should be in earthquake-safe locations
  • Need detailed microzonation maps of ground response
  • Structural protection: buildings must be designed to withstand vibrations; retrofitting old buildings may be necessary

Education and Public Awareness

  • Education through pamphlets, workshops, internet resources
  • Earthquake and tsunami drills

Insurance and Relief Measures

  • Losses from major earthquakes can be enormous
  • Improvements in insurance mechanisms
  • No federal subsidies for earthquake insurance (California has a state-subsidized program)
  • Tools for estimating potential impacts: Hazards U.S., a free software program

Personal Adjustments: Before an Earthquake

  • Evaluation by a structural engineer; home inspection to ensure structural soundness
  • Secure large objects; reinforce foundations
  • Develop a personal plan of how to react during a quake
  • Ensure supplies are on hand for emergency response

Personal Adjustments: During and After an Earthquake

  • Drop! Cover! Hold On!
  • After shaking stops, leave buildings if safe
  • Watch for fallen or falling objects; turn off the main gas line; move to an open area

Construction to Minimize Earthquake Effects

  • Visual references show various retrofitting and construction strategies
  • Notable examples include reinforced and retrofitted structures (e.g., bridges, parking structures)

Seismic Retrofitting

  • Older buildings can be strengthened via seismic retrofitting
  • Sometimes more expensive than new construction
  • Primary goal: ensure occupants survive the earthquake; damage control and property protection are secondary
  • Added materials must be compatible with existing structure

Seismic Retrofitting Strategies (Possible retrofit options)

  • Infill Walls
  • Add Braces
  • Add Buttresses
  • Add Frames (interior or exterior)
  • Completely Rebuild
  • Isolate Building
  • Common diagrams show combinations like Double Blocking, Diagonal Braces, Plywood Shear Walls, and structural connections

Examples and Case Imaging

  • Partially collapsed and fully collapsed buildings illustrate poor framing (e.g., CSUN parking structure failure)
  • Well-braced buildings exemplify effective retrofitting

Offshore and Chilean Seismology Examples

  • Offshore Bio-Bio, Chile: M 8.8 on Feb 27, 2010; depth ~35 km
  • USGS ShakeMap visualization shows near-field effects and ground shaking potential
  • Chilean earthquakes feature complex rupture and tsunami generation due to subduction processes

Haiti Earthquake (2010)

  • Magnitude: 7.0; Date/Time: Jan 12, 2010; Epicenter at near Port-au-Prince
  • Depth: ~13 km
  • Result: Massive humanitarian crisis; damages and collapsed infrastructure

Tectonics: Caribbean and North American Plates

  • Boundary region between Caribbean plate and North America plate
  • Dominated by left-lateral strike-slip motion and compression
  • Accommodates about 20 extmm/year20\ ext{mm/year} slip
  • Caribbean plate moving eastward with respect to the North American plate

Tectonics: Fault Systems in Hispaniola

  • Motion partitioned between two major east-west trending strike-slip fault systems:
    • Septentrional Fault System (northern Hispaniola)
    • Enriquillo-Plantain Garden Fault System (EPGFZ) in southern Hispaniola

Tectonics: Pacific-North American Interaction and Chilean Subduction

  • Denali-like context for Alaska and larger West Coast regions shows the importance of plate boundary processes
  • In Chile, the Nazca Plate subducts beneath the South American Plate along a gently dipping thrust fault; convergence rate around 7 cm/yr7\ \text{cm/yr} (roughly 7 meters per century)
  • Offshore rupture can be wide (exceeding 100 km) and long (nearly 500 km parallel to the coast)
  • Rupture propagates offshore and generates tsunami; ocean floor deformation drives tsunami waves

Tectonics: Sichuan and the Longmenshan Fault

  • Tectonics involve a NE-striking thrust fault on the NW margin of the Sichuan Basin
  • Movement on the Longmenshan fault (or a related fault) reflects crustal convergence: Indian Plate colliding with Eurasian Plate
  • Uplift due to continental collision formed the Himalayas, Karakoram, Pamir, and Hindu Kush ranges
  • The NW margin previously experienced destructive earthquakes; notable M7.5 event on August 25, 1933, causing significant fatalities

Eastern Sichuan, China (2008)

  • Magnitude: 7.9; Date/Time: May 12, 2008; Depth: 19 km
  • USGS ShakeMap shows broad ground shaking in the region (Yaan, Deyang, Chengdu, Leshan, etc.)
  • Ground shaking interpreted via Peak Acc and Peak Velocity values and intensity scales

Kashmir, Pakistan (2005)

  • Magnitude: 7.6; Date/Time: Oct 8, 2005; Depth: ~26 km
  • USGS ShakeMap shows strong ground shaking in Mansehra, Baramula, Abottabad, and surrounding regions
  • Intensity distribution and peak ground motion values used to assess damage patterns

Indian Subcontinent Tectonics and the Himalayas

  • Indian subcontinent moving northward at a rate of approximately 40 mm/yr40\ \text{mm/yr} (≈ 1.6 inches/yr)
  • Resulting continental collision drives uplift of the Himalayan, Karakoram, Pamir, and Hindu Kush ranges
  • Crustal shortening and thickening accommodate the convergence

Main Thrust Zone System in the Himalayas

  • Slip is accommodated by a suite of major thrust faults at the surface in the foothills and dipping northward beneath the ranges:
    • Main Frontal Thrust
    • Main Central Thrust
    • Main Boundary Thrust
    • Main Mantle Thrust

Historic Earthquakes and Rupture History (Caribbean, Chile, Sichuan, Kashmir, etc.)

  • 1751 and 1770 events in Hispaniola (Enriquillo Fault region) contributed to building codes and construction practices (e.g., use of lightweight wood; masonry restrictions) due to tsunami and heavy destruction
  • 1933 M7.5 Sichuan earthquake on the NW margin of the Sichuan Basin
  • 1960s and 1960s-1980s Chilean seismic history includes significant ruptures along the Nazca-South American boundary
  • 1945-2009 various major earthquakes have defined fault rupture areas and depths in the Pacific-North American and Caribbean regions

2010 Chilean Earthquake and Tsunami (Offshore Maulé, Bio-Bío Region)

  • Offshore M 8.8 earthquake near Maule, Chile (Feb 27, 2010)
  • Depth ~35 km
  • ShakeMap and ground shaking patterns show coastal deformation and tsunami generation

2017 Mexico Earthquake

  • M 8.1 – 87 km SW of Pijijiapan, Mexico (Sept 8, 2017)
  • Depth: ~69.7 km
  • Strongest Mexican quake in a century; notable aftershocks and regional shaking
  • Context: Cocos Plate subducting beneath the North American Plate; offshore rupture along a subduction zone
  • Earlier significant event: M 8.0 Michoacán earthquake in 1985 with ~5000 deaths

Other Notable Seismic Hazards and Visual Data

  • USGS ShakeMaps provide perceived shaking and potential damage estimates for regions like Haiti, Chile, Sichuan, Kashmir, and Mexico
  • Perceived shaking scales show translations from instrument readings to human impact levels
  • Visual maps include fault lines, plate boundaries, rupture histories, and tsunami potential

Summary of Practical Implications

  • Hazard assessment combines physics of plate tectonics, fault systems, and historical earthquake records
  • Retrofitting and land-use planning focus on reducing vulnerability of structures and critical facilities
  • Public policy must balance timely warnings with risk of false alarms and liability concerns
  • Education, insurance, and preparedness (before and after events) are central to reducing casualties and economic losses

Key Equations and Quantities (LaTeX)

  • Plate convergence rate (Chile subduction context):
    v≈7 cm/yr=7 m/ centuryv \approx 7\ \text{cm/yr} = 7\ \text{m/ century}
  • Global plate motion example (Himalayas):
    vIP−EA≈40 mm/yr=1.6 in/yrv_{IP-EA} \approx 40\ \text{mm/yr} = 1.6\text{ in/yr}
  • Slip accommodation in Caribbean-North American boundary region:
    vCar−NA≈20 mm/yrv_{Car-NA} \approx 20\ \text{mm/yr}
  • Depth and magnitude annotations (examples):
    • Haiti: M=7.0M = 7.0; depth d≈13 kmd \approx 13\ \text{km}
    • Sichuan 2008: M=7.9; d=19 kmM = 7.9; \ d = 19\ \text{km}
    • Chile 2010: M=8.8; d≈35 kmM = 8.8; \ d \approx 35\ \text{km}
  • Notation for intensity scales (example mapping):
    • Peak Acc: Peak Acc(%g)\text{Peak Acc} \left(\%g\right)
    • Peak Ground Velocity: Peak Vel(cm/s)\text{Peak Vel} (\text{cm/s})
    • Instrumental and Intensity levels: I, II-III, IV, V, VI, VII, VIII, IX, X+

References to Notable Case Studies and Visuals

  • Banda Aceh 2004–2005 sequence on the Sunda Megathrust
  • Haiti 2010 earthquake and its tectonic context in the Caribbean
  • Eastern Sichuan 2008 earthquake and the Longmenshan fault dynamics
  • Kashmir 2005 earthquake and the Enriquillo-Plantain Garden fault system
  • Maule, Chile 2010 offshore megathrust rupture and tsunami generation
  • 2017 Mexico M8.1 offshore quake and its relation to the Cocos-North American boundary