Title: Earthquakes-Pt.2
1Earthquakes-Pt.2
- Earthquake Processes (mechanisms/causes)
- Effects of earthquakes (damage)
- Earthquake risk and prediction
- Responses to earthquake hazards
2Earthquake Processes
- Earthquake Cycle Elastic Rebound
- Dilatancy-Diffusion Model
- Fault-valve mechanism
- Roles of fluid pressure
3Earthquakes 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)
4Elastic Rebound Model
5Elastic Rebound
6Dilatancy-Diffusion Model/Fault Valve Mechanism
7Earthquakes Caused by Human Activity
- Reservoir-induced seismicity (e.g., Hoover Dam)
- Deep waste disposal (e.g., Rocky Mtn, arsenal)
- Nuclear explosions
- Shallow focus only
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9Effects of earthquakes
- Ground shaking and rupture
- Liquifaction
- Landslides
- Fires
- Tsunamis
- Regional changes in land elevation
10Earthquake 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
11Earthquake Damage San Francisco, 1989
12Pancaked building
Mexico City earthquake, 1985
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14Origins 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
15Sudden 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
16Characteristics 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
17Tsunami Warning System
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21Mercalli Intensity (damage) map and peak ground
acceleration map for the 1994 Northridge, CA
earthquake (M 6.7) X- shows location of
epicenter
X
22Earthquake Risk and Prediction
- Short-term prediction
- Long-term prediction
- Estimation of seismic risk
- seismic hazard maps
- probability of events
- Conditional probabilities for future earthquakes
23Short-Term Prediction
- Pre-seismic uplift/subsidence
- Seismic Gaps
- Anomalous animal behavior
24Longer-Term Prediction
25Idealized diagram of an Earthquake warning system
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27Relationships between recurrence interval, slip
rate and earthquake magnitudes
28Response/Prediction Options
29Response 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
30Learning 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
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