Earthquakes and Tsunamis PDF

Earthquakes and Tsunami Introduction to Natural Hazards ESCI-1000...

Earthquakes and Tsunami Introduction to Natural Hazards ESCI-1000 Dr. Neil J. Porter The course syllabus is the intellectual property of Dr. Neil J. Porter. Distribution or publication of this material in whole or in part is illegal, under the Canadian Copyright Act, RSC 1985  Earthquakes and Tsunami Overview 3.0 Introduction to Earthquakes 3.1 The Earthquake Process 3.2 Fault Movements 3.3 Seismic Waves 3.4 The Earthquake Cycle 3.5 Geographic Regions 3.6 The Effects of Earthquakes 3.7 Human Interactions 3.8 Forecast and Predictions 3.9 Minimizing the Earthquake Hazard 3.10 Tsunami 3.11 You can’t fix crazy  Earthquakes and Tsunami 3.0 Introduction to Earthquakes 20th century - 2 million people have died from earthquakes, fires, tsunami and landslides. Consequences depends on magnitude, depth, distance from populated places, Earth’s materials and construction methods. Damaging earthquakes may occur decades or centuries apart. In Canada – nearly 1400 earthquakes occur per year.  Earthquakes and Tsunami 3.0 Introduction to Earthquakes: The Toll of Earthquakes The consequences of an earthquake depend on: 1. Magnitude 2. Depth 3. Direction of fault rupture 4. Distance from populated areas 5. Nature of the local earth materials 6. Engineering and construction practices Differences in some of these factors explain why a M 7.0 earthquake in Haiti (2010) killed ~ 240,000 people but a M 6.9 earthquake in California (1989) killed less than 70. Difference is building codes  Earthquakes and Tsunami 3.0 Introduction to Earthquakes: The Toll of Earthquakes Result from the rupture of rocks along a fault Energy is released in the form of seismic waves Mapped according to the epicentre  The focus is directly below the epicentre  Depth of focus Measured by seismographs Compared based on: Magnitude Intensity  Earthquakes and Tsunami 3.0 Introduction to Earthquakes: The Toll of Earthquakes The scale is logarithmic and based on powers of ten: Ground motion for a M 3 is 10 times that of a M 2. Amount of energy released for a M 3 is 32 times that of a M 2  Earthquakes and Tsunami 3.1 The Earthquake Process: Earthquake Intensity Measured by the Modified Mercalli Intensity Scale The scale is qualitative based on damage to the structures and people's perceptions Modified Mercalli Intensity maps show where the damage and perceived shaking is most severe Data is now collected using the Internet. Shake maps use seismograph data to show areas of intense shaking.  Earthquakes and Tsunami 3.1 The Earthquake Process: Earthquake Intensity  Earthquakes and Tsunami 3.2 Fault Movements: Fault Types Earthquakes occur along faults Weakness in Earth’s crust Places where rocks are broken and displaced Strike slip faults 1. displacements are horizontal 2. Dip- slip faults displacements are vertical Footwall Block below the fault plane Miner would stand here Hanging wall Block above the fault plane Hang a lantern here  Earthquakes and Tsunami 3.2 Fault Movements: Fault Types Strike slip faults/ Transform – horizontal movement eg. San Andreas fault evidence: cracks on the surface rivers move buildings move  Earthquakes and Tsunami 3.2 Fault Movements: Fault Types Dip-slip faults: vertical Thrusts or reverse fault: Hanging wall goes up relative to footwall Due to crustal shortening Slope (dip) of fault is not steep Normal Fault Hanging wall goes down relative to footwall Due to crustal stretching  Earthquakes and Tsunami is dangerous because no cracks appear on the surface 3.2 Fault Movements: Fault Types eg. St. Lawrence in Canada Blind faults caused because:  Mountain building processes  Blind or buried faults do not reach the surface  Difficult to evaluate earthquake risk  Earthquakes and Tsunami 3.2 Fault Movements: Fault Activity Active faults - movement during the past 11,600 years Potentially active faults - movement during the past 2.6 million years inactive faults - no movement during the past 2.6 million years tectonic creep occurs when movement along a fault is so gradual that earthquakes are not felt Can slowly damage infrastructure  Earthquakes and Tsunami 3.3 Seismic Waves Seismic Wave: A wave produced by a sudden displacement of rocks along a fault; seismic waves move through or along the surface of the Earth. Two types of body waves – P waves and S waves P waves: Primary waves appear first in the sesmic graphs S waves: Secondary waves appear second in a sesmic graph.  Earthquakes and Tsunami 3.3 Seismic Waves P-Waves, primary, or compressional waves 1. Faster than S waves 2. reach the sesmic station first 3. They can travel through a solid liquid or a gas  Earthquakes and Tsunami 3.3 Seismic Waves Whipping motion S-Waves, secondary or shear waves 1. Move slower with an up and down motion 2. they can only travel through solids  Earthquakes and Tsunami 3.3 Seismic Waves Surface Waves Travel along Earth’s surface horizontally and vertically and can produce rolling motion Move more slowly than body waves Are responsible for damage near the epicenter Two types: love waves - cause horizontal shaking Rayleigh waves - rolling waves, elliptical motion  Earthquakes 3.3 Seismic Waves At least 3 stations are needed to find exact epicenter. Distance to epicenter can be found by comparing travel times of the waves using triangulation The place where all three circles intersect is the epicenter. Focal Depth influences amount of shaking due to attenuation  Earthquakes and Tsunami 3.3 Seismic Waves Geologist study the bending or refraction and reflection of P- and S-waves to help understand Earth's interior. This indicates boundaries between layers of different densities called discontinuities. Secondary waves can't reach the liquid outer cores  Earthquakes and Tsunami 3.4 The Earthquake Cycle Inactive period where stress builds in the fault Period of small earthquakes where the stress begins to release, causing strain Three or four stages: 1. Long period of inactivity 2. Accumulated elastic strain produces small earthquakes 3. Foreshocks Hours or days before large earthquake May not occur 4. Mainshock Major earthquake Includes aftershocks: few minutes to a year after  Earthquakes and Tsunami 3.5 Geographic Regions: Plate Boundary Earthquakes About 80% of all earthquakes occur in the circum-Pacific belt.  Earthquakes and Tsunami 3.6 The Effects of Earthquakes Shaking is not the only cause of death and damage. Primary effects of earthquakes: shaking and surface rupture. Secondary effects: liquefaction, changes in land level, landslides, fire, tsunami and disease.  Earthquakes and Tsunami 3.6 The Effects of Earthquakes: Primary Effects Ground rupture: Displacement along the fault causes cracks in surface. primary: racetrack damage  Earthquakes and Tsunami 3.6 The Effects of Earthquakes: Primary Effects in San fransico Shaking: Causes damage to buildings, bridges, dams, tunnels, pipelines, etc. Measured as ground acceleration. Buildings may be damaged due to resonance Matching of vibrational frequencies between ground and building  Earthquakes and Tsunami 3.6 The Effects of Earthquakes: Primary Effects Shaking Depth of focus Deeper earthquakes produce less shaking than shallow earthquakes. Direction of epicenter Path of the rupture can focus earthquake energy. Materials Waves are fast in bedrock and slow in more unconsolidated materials. Waves are more amplified in unconsolidated materials.  Earthquakes and Tsunami 3.6 The Effects of Earthquakes: Secondary Effects Liquification A near-surface layer of water-saturated sand changes rapidly from a solid to a liquid Causes buildings to “float” in earth Common in M 5.5 earthquakes in younger sediments After shaking stops, ground re-compacts and becomes solid  Earthquakes and Tsunami 3.6 The Effects of Earthquakes: Secondary Effects Liquification  Earthquakes and Tsunami 3.6 The Effects of Earthquakes: Secondary Effects Fire is more of a threat than the earthquake itself Shaking and surface displacements Cause power and gas lines to break and ignite Knock over appliances, such as gas water heaters, and leaks ignite Threat even greater due to Damaged firefighting equipment Blocked streets and bridges Broken essential water mains  Earthquakes and Tsunami 3.6 The Effects of Earthquakes: Secondary Effects Tsumami – Earthquakes on the seafloor can generate deathly waves, such as the ones that hit the Japanese coast in 2011. For a tsunami to occur it must be a vertical plate that is moved  Earthquakes and Tsunami 3.6 The Effects of Earthquakes: Secondary Effects Changes in land level - can result in building and road collapse.  Earthquakes and Tsunami 3.6 The Effects of Earthquakes: Secondary Effects Disease: Loss of sanitation and housing Contaminated water supplies Disruption of public health services Disturbance of the natural environment Rupture of sewer and water lines Water polluted  Earthquakes and Tsunami 3.7 Human Interactions: Earthquakes Caused by Humans Nuclear explosions can cause a shock across the earth and can cause an earthquake of magnitude 3-4 Loading Earth’s crust, as in building a dam and reservoir. Mining can also cause earthquakes; the extraction of some minerals Oil extractions can cause an earthquake of magnitude 2-3 Liquid waste disposals deep in the earth can create pressure on faults. Nuclear explosions can cause the release of stress along existing faults.  Earthquakes and Tsunami 3.8 Earthquake Forecasts and Predictions: Short Term you can't predict earthquakes you can only forecast it 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 and groundwater levels  Earthquakes and Tsunami 3.8 Earthquake Forecasts and Predictions: Animal Behaviour The belief that animals can predict earthquakes has been around for centuries Showing signs of nervousness or restlessness Many studies done in Japan and China However, animals react to many things “The psychological focusing effect” No substantial evidence  Earthquakes and Tsunami 3.9 Minimizing the Earthquake Hazard: Earthquake Warnings 3 types of plates: convergent plates cause intermediate to deep eathquakes divergent plates cause shallow earthquakes transform okates cause shalllow to intermediate earthquakes Seismic risk maps help geologists in determining the likelihood and potential severity of future earthquakes based on the intensity of past earthquakes. Hazard maps show earthquake risk. Plan for issuing a prediction or warning Earthquake warning systems  Earthquakes and Tsunami 3.9 Minimizing the Earthquake Hazard: Community Preparations Critical facilities must be located in earthquake safe locations. Requires detailed maps of ground response. Buildings must be designed to withstand vibrations. Retrofitting old buildings may be necessary. People must be prepared through education. Insurance must be made available.  Earthquakes and Tsunami Japan has the cest earthquakes preparation 3.9 Minimizing the Earthquake Hazard: Community Preparations  Earthquakes and Tsunami 3.9 Minimizing the Earthquake Hazard: Personal Preparations Before the shaking starts Secure large objects, reinforce foundations Could increase probability you and your property survive Probably most important preparation During the shaking Do not panic! When the shaking stops Leave the building Watch for fallen or falling objects Turn off main gas line Move to an open area  Earthquakes and Tsunami 3.10 Tsunami A tsunami is a series of waves caused by the displacement of a large volume of water. Triggered by: Large earthquakes that cause uplift or subsidence of the seafloor Underwater landslides Volcano flank collapse Submarine volcanic explosion Asteroids Can produce mega tsunami 30-50 meters high  Earthquakes and Tsunami 3.10 Tsunami: Earthquake–Triggered Tsunamis move rapidly in the deep ocean (700 km/h) Tsunami nears land, Depth of ocean decreases, slowing tsunami waves to 45 km/h More water piles up, increasing amplitude and frequency Tsunami moves inland, destroying everything in its path Can be metres to tens of metres high Trough may arrive first, exposing the seafloor Run up - furthest horizontal and vertical distance of the largest wave More waves likely to follow  Earthquakes and Tsunami 3.10 Tsunami: Earthquake–Triggered Occurred on March 11, 2011, killing ~ 16,000 people Pacific Ocean bottom vertically displaced as much as 9 m (~30 ft) Source was a M 9.0 earthquake beneath the seafloor Subduction zone east of Honshu Island The direct damage from the earthquake and tsunami was U.S. $250 billion Most expensive natural disaster in histoey  Global Tsunami Hazard Most earthquakes occur arounf the ring of fire and the Indian Ocean  Earthquakes and Tsunami 3.10 Tsunami: Effects of Tsunamis Primary effects are related to flooding and erosion Shorten the coastline Debris erodes the landscape and damages structures Diminish with distance from the coast Deaths from both drowning and the force of impact of the water Secondary effects Fires Contaminated water supplies Disease  Earthquakes and Tsunami 3.10 Tsunami: Minimizing the Tsunami Hazard Detection and warning Monitor earthquake zones Tsunami warning system Seismographs to detect earthquakes Tidal gauges to determine sea level changes Buoy sensors to detect tsunami in open ocean Information is relayed by satellite to give arrival time estimates Warning sirens are used to warn public  Earthquakes and Tsunami 3.10 Tsunami: Perception and Personal Adjustment to the Tsunami Hazard Actions to take in a warning If you feel a strong earthquake, leave the beach and low-lying coastal areas immediately. If the ocean recedes, run from the beach for higher ground. Do not assume that all locations are safe because of an absence of dangerous waves elsewhere. The time between waves can be up to an hour. Stay out of dangerous areas until a notice that all is clear is given. A number of strategies for minimizing tsunami hazard Detection and warning Structural Control Tsunami runup maps Land use Probability analysis Education Tsunami-ready status