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| Question | Answer |
| How are earthquakes distributed around the globe? | 85-90% occur at plate margins = interplate earthquakes 10-15% occur in the interior of plates = intraplate earthquakes |
| What is the tectonic collision zone and why is it special? | It is a zone that extends from the western Mediterranean to Indonesia Most earthquakes killing 100,000+ occur here due to: High frequency of earthquakes Mountainous topography Human vulnerability (Arabian Plate, Eurasian Plate, Indo-australian Plate) |
| Distinguish between the epicentre and the hypocentre | Hypocentre: point at which energy is released Epicentre: surface point directly above the hypocentre |
| Birelfy outline the Elastic Rebound Theory | There is a continuous slow build up of elastic energy as plates attempt to drift pass each other, getting stuck on rocks. When the imposed stresses exceed the strengths of the fault, the rock fractures and portions around the rock 'spring' back, relieving displacement. |
| Describe a Normal fault | Divergent fault/Extensional Zone/Constructive plate boundary two plates pull away from each other earthquake foci tend to be shallow and often associated with magmatic activity |
| Describe a Reverse Fault | Compressional Zone/Collisional/Destructive plate boundary/Convergent plates move into each other |
| Describe a Strik-Slip Fault | Transform/Conservative plate boundary plates slide past each other laterally |
| What is meant by the Benioff Zone | The Benioff zone is the active seismic zone in subduction region |
| What are the different types of waves and why are they different? | Body Waves: p-waves and s-waves Surface Waves : Love and rayleigh waves they travel at different speeds different amplitudes which cause different levels of damage |
| Distinguish between the two types of body waves | P-waves: pass through Earth's liquid outer core faster compressional S-waves: cannot pass through core 50% of speed of p-waves transverse (right angles to travel direction) |
| Distinguish between the two types of surface waves | Rayleigh Wave: up/down and side to side movement slow confined to the surface Love wave: Horizontally polarised faster than Rayleigh waves confined to the surface |
| Why is the s-p interval useful? | the gap on seismographs between p- and s-waves tells seismologists how far away the earthquake was |
| Distinguish between earthquake intensity and magnitude | Intensity: measure of the shaking created y the earthquake (indicates damage) Magnitude: A measured value of the earthquake size by measuring energy release, ground motion and area of fault |
| How is the Richter-magnitude scale calculated | amplitude of seismic waves on seismographs corrected for distance from the focus the magnitude on the Richter scale is directly related to the amount of energy released |
| How is the moment-magnitude scale calculated? | seismic moment = rock strength x area of fault that moved during the earthquake x average slip |
| Distinguish between the Richter Scale and the Moment-magnitude Scale | Richter Scale: calculated from amplitude, corrected for distance takes seconds to calculate less accurate Moment-magnitude scale: calculated from area, slip and rock strength takes hours to calculate more accurate |
| List the secondary hazards caused by earthquakes | Building and structural collapse Landslides Liquefaction Tsunamis Fire Fore-/Aftershocks |
| What is meant by the resonant/natural frequency of buildings | Atoms are in constant vibration. The natural frequency is the rate at which a structure 'likes' to vibrate If a seismic wave frequency is close to the natural frequency it can greatly amplify the shaking of a building/structure |
| What are the benefits of living close to a volcano? | Tourism Argiculture (fertile soil) Geothermal Energy Products (construction materials, abrasive and cleaning agents) |
| What are factors influencing the degree of hazard? | Distance from volcano Velocity of eruption products Temperature of eruption products Length of warning Frequency of occurrence |
| What are factors influencing the degree of social factors? | Nature & degree of hazard Extent of resultant death/injury Reactions of community leaders to hazard and aftermath Individual perception of risk |
| Where are the three places volcanoes occur | Divergent boundaries Destructive plate boundary Intra-plate hotspots |
| Distinguish between lava and magma | Magma: (partially) molten rock from mantel beneath the surface Lava: erupted magma |
| What does magma consist of? | Liquid portion Solid portion made of minerals crystallized in the melt Solid Rock (xenoliths/inclusions) Dissolved gases (volatiles) |
| What factors affect the viscosity of magma? | Silica content: the more the more viscous Temperature: high temperature=low viscosity |
| What are common properties of basaltic magma? | -relatively low silica content (<45-55%) -high eruption temperature (1050-1200°C) -low volatile content -low viscosity -low explosivity -bubbles form but insufficient gas to cause explosion -mostly generate lava flows |
| What are common properties of magma at compressional zones | Andesetic and Rhyolitic: -relatively high silica content -med. to low temperature (650-1000°C) -high volatile content -lots of dissolved gases (mostly water from dissolved crustal material) -very explosive -high viscosity |
| List all the volcanic phenomena | Tephra Volcanic Gases Pyroclastic Flow Lahar Lava flow Tsunamis |
| What is meant by Tephra, Lahar and pyroclastic flows | Tephra: fragments of volcanic rock blasted into the air or carrid upwards by hot gases (blocks, ash, bomb, Pele's hair) Pyroclastic flows: high density mixtures of hot gases, ashes, cinders, rocks (temp. inside flow usualy 200-700°C) Lahar: hyperconcentrated volcanic mud-flows, high density flow (up to 75% solids), very erosive |
| How can one measure volcanic explosivity? | The Volcanic Explosivity Index is a scale which measures: -volume of products -eruption cloud height -qualitative observations |
| What is risk assessment and how is it carried out? | risk assessment: the quantitative or qualitative valuation of the significance of risk risk = probability of occurrence x expected loss |
| Define mass-wasting | Down slope movement of rock or regolith near Earth's surface mainly due to force of gravity |
| Define regolith | Unconsolidated rock debris, including the basal soil horizons, overlying bedrock |
| What are the three types of materials involved in mass-wasting | Earth (less coarse than debris) Debris (mixture of sand, cobbles, boulders, silt and clay) Rock (can be broken with a hammer) |
| What are the three types of movement involved in mass-wasting | Fall Slide Flow |
| What is meant by Talus? | Accumulation of fallen material at cliff base |
| Distinguish between slurry flows and granular flows | Slurry flows (20-40% water present) Granular flows (0-20 water present) |
| Distinguish between solifluction, debris flows and mud flows | All type of slurry flows Solifluction: 1cm/year Debris Flows: 1m/yr to 100m/hr Mud flows: >1km/hr |
| What is meant by shear strength and shear stress | Shear Strength are the forces holding the slope in place (frictional resistance, cohesion among particles making the up the object) Shear Stress are the forces pulling the slope downwards |
| What are the two factors affecting slope stability? | Gravity Water (incl. fluid pressure) |
| How is the safety factor calculated? | Fs=(Shear Strength)/(Shear Stress) Fs < 1 = slop actively unstable 1.0 < Fs < 1.3 = conditionally unstable Fs > 1.3 = slope is stable |
| What is meant by the Angle of Repose? | Steepest angle at which a pile of unconsolidated grains remains stable, controlled by the frictional contact between the grains (for dry material usually 30-37°) |
| How does liquefaction occur? | Occurs when lose sediment is oversaturated with water to such extent that grain to grain contact is lsot |
| List the major triggers of mass-wasting events | Earthquakes Heavy Rainfall Sudden Snowmelt Volcanic Eruptions through explosion, melting of glacier, draining or crater lake or minor earthquakes caused |
| List the minor triggers of mass-wasting events | Slope modification Undercutting Fire Added mass Minor Shocks (trucks, trees blowing in wind, human-made explosions) |
| What can be done to reduce deaths related to mass-wasting events | i) Areas prone to such hazards can be recognised with some geological knowledge ii)slopes can be stabilised or avoided iii) warning systems can be put in place that minimise the hazard |
| List the short-term prediction issues of mass-wasting | -earthquake and volcano prediction issues -constant attention to slopes needed -able to give out warnings of susceptible areas but which out of million slopes will be affected |
| List mass-wasting engineering mitigation techniques | Shotcrete/Concrte/Metal Mesh Retaining walls Debris chutes (channel flows) Rockfall sheds Drainage pipes in slope Over-steepened slops could be graded |
| How do water waves propagate? | Deep-water theory: D>~/2 Shallow-water theory: D<~/20 (D = water depth; ~ = water wavelength) |
| How does one calculate the celerity of a shallow-water wave? | celerity = speed = root of (g x D) (g = gravity; D = water depth) |
| What technology has been developed to help tsunami warnings? | Deep-ocean Assessment and Reporting of Tsunamis (DART) consists of: seafloor bottom pressure recording system (notices tsunamis as small as 1cm) Moored surface buoy (for real-time communications) |
| What is meant drawback? | The sudden withdrawal of the water line from the shore line. This is the trough of the tsunami reaching the shore. Does not always happen. |
| Define run-up | Difference between elevation of maximum tsunami penetration (inundation line) and sea-level at time of tsunami. |
| Where is wave energy concentrated? | Headlands and Bays |
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