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Earthquakes-Pt.2

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Earthquakes-Pt.2 Earthquake Processes (mechanisms/causes) Effects of earthquakes (damage) Earthquake risk and prediction Responses to earthquake hazards – PowerPoint PPT presentation

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Title: Earthquakes-Pt.2


1
Earthquakes-Pt.2
  • Earthquake Processes (mechanisms/causes)
  • Effects of earthquakes (damage)
  • Earthquake risk and prediction
  • Responses to earthquake hazards

2
Earthquake Processes
  • Earthquake Cycle Elastic Rebound
  • Dilatancy-Diffusion Model
  • Fault-valve mechanism
  • Roles of fluid pressure

3
Earthquakes Cycle
  • Elastic Rebound Model
  • Four Stages
  • Long period of inactivity (following a major
    earthquake)
  • increased seismicity elastic strain accumulates,
    approaches, locally exceeds rock strength
  • Foreshocks (hours or days before next large
    earthquake)
  • Major earthquake, aftershocks (few minutes,
    months, to a yr)

4
Elastic Rebound Model
5
Elastic Rebound
6
Dilatancy-Diffusion Model/Fault Valve Mechanism
7
Earthquakes Caused by Human Activity
  • Reservoir-induced seismicity (e.g., Hoover Dam)
  • Deep waste disposal (e.g., Rocky Mtn, arsenal)
  • Nuclear explosions
  • Shallow focus only

8
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9
Effects of earthquakes
  • Ground shaking and rupture
  • Liquifaction
  • Landslides
  • Fires
  • Tsunamis
  • Regional changes in land elevation

10
Earthquake Damage
  • Buildings Swaying, Pancaking
  • Broken pipelines (gas, water) electrical lines
  • Fires explosions (from pipelines storage
    tanks)
  • Shearing subsidence of sand fills
  • Quicksand, sand boils, sand volcanoes
  • Quickclays
  • Landslides

11
Earthquake Damage San Francisco, 1989
12
Pancaked building
Mexico City earthquake, 1985
13
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14
Origins of Tsunamis (seismic sea waves)
  • Sudden vertical displacement of seafloor (from
    dip-slip fault)
  • Momentary drop in local sea level
  • Water rushes into depression, but overcorrects,
    locally raising the sea level
  • Sea level locally oscillates before stabilizing
  • Oscillations are transmitted as long, low seismic
    sea waves

15
Sudden vertical displacement of seafloor (from
dip-slip fault)
Momentary drop in local sea level
Water rushes into depression, but overcorrects,
locally raising the sea level
Sea level locally oscillates before
stabilizing Oscillations are transmitted as long,
low seismic sea waves
16
Characteristics of Tsunamis
  • Long wavelengths (up to 100 km)
  • Low wave height in open ocean (lt 0.5 m)
  • Velocities up to 700 km/hr in deep water
  • As tsunami waves enter shallow coastal water
  • Speed decreases
  • Water withdraws from shore before tsunami hits
  • Water rises up, successive tsunami waves hit
  • First wave is not necessarily the largest
  • Waves sweep inland, like a flood front rather
    than an ocean wave
  • Tsunami waves range up to several tens of meters
    high
  • Most damaging are from nearby sources with little
    warning

17
Tsunami Warning System
18
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19
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20
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21
Mercalli Intensity (damage) map and peak ground
acceleration map for the 1994 Northridge, CA
earthquake (M 6.7) X- shows location of
epicenter
X
22
Earthquake Risk and Prediction
  • Short-term prediction
  • Long-term prediction
  • Estimation of seismic risk
  • seismic hazard maps
  • probability of events
  • Conditional probabilities for future earthquakes

23
Short-Term Prediction
  • Pre-seismic uplift/subsidence
  • Seismic Gaps
  • Anomalous animal behavior

24
Longer-Term Prediction
  • ???

25
Idealized diagram of an Earthquake warning system
26
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27
Relationships between recurrence interval, slip
rate and earthquake magnitudes
28
Response/Prediction Options
29
Response to Earthquake Hazards
  • Earthquake hazard-reduction programs
  • Earthquakes and critical facilities
  • Societal adjustments to earthquakes
  • structural protection
  • land-use planning
  • increased insurance and relief measures
  • earthquake warning systems
  • perception of earthquake hazard

30
Learning objectives
  • Understand the relationship of earthquakes to
    faulting
  • Familiarization with earthquake wave (energy)
    terminology
  • Understand the concept of earthquake magnitude
    (and its calculation)
  • How seismic risk is estimated
  • Familiarization with the major effects of
    earthquakes
  • The prediction of earthquakes
  • Mitigation of earthquake damage

31
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