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Earth Hazards Midter
| Question | Answer |
|---|---|
| What is a natural hazard? | Naturally occurring events that operate at high energy over short periods in restricted areas and can cause damage. |
| What is a natural disaster? | When a natural hazard causes destruction and negative impacts on ecosystems. |
| What defines a great natural disaster? | So overwhelming that international assistance is required; kills thousands and displaces hundreds of thousands. |
| Are natural hazards inevitable? Are natural disasters inevitable? | Natural hazards are inevitable, but natural disasters are not. |
| How can we reduce disaster risk? | Through planning and mitigation. |
| What is the magnitude-frequency relationship? | Large-magnitude events are much less common than small-magnitude events. |
| What is a recurrence interval? | The average time between similar-sized events. |
| Who proposed seafloor spreading? | Harry Hess. |
| How is seafloor spreading proven? | Using paleomagnetism. |
| Why does basalt record Earth's magnetic field? | It contains magnetite that aligns with Earth's magnetic field when molten. |
| What are magnetic stripes? | Preserved polarity reversals in oceanic crust showing symmetrical patterns. |
| How do rock ages change moving away from ocean ridges? | They increase symmetrically on both sides. |
| What is a divergent Plate Boundary? | Two plates moving away from each other. |
| What are two types of divergent boundaries? | Continental and oceanic. |
| What is a convergent plate boundary? | Two plates moving toward each other. |
| What are three types of convergent boundaries? | Ocean–continent, ocean–ocean, continent–continent. |
| What happens to lithosphere at convergent boundaries? | Destruction/recycling. |
| What is a transform boundary? | Two plates sliding past each other. |
| What earthquakes occur at transform boundaries? | Shallow earthquakes (often destructive). |
| What is stress? | Force applied to an object. |
| What is strain? | Rock deformation due to stress. |
| What are three types of stress? | Tension, compression, shear. |
| Difference between ductile and brittle deformation? | Ductile = bending; brittle = breaking. |
| What causes normal faults? | Tension (pulling). |
| Motion of hanging wall in normal fault? | Moves down. |
| What causes reverse/thrust faults? | Compression (pushing). |
| What causes strike-slip faults? | Shear stress (horizontal movement). |
| Example of strike-slip faults? | San Andreas Fault. |
| What is the hypocenter? | Point underground where rupture starts. |
| What is the epicenter? | Surface point directly above the focus. |
| What is elastic rebound theory? | Rocks deform, then snap back during an earthquake. |
| Two main types of seismic waves? | Body waves and surface waves. |
| What are P-waves? | Fastest compressional waves. |
| What are S-waves? | Slower shear waves. |
| What are two type of surface waves? | Love waves and Rayleigh waves. |
| Which waves cause the most damage? | Surface waves. |
| How are earthquakes located? | Using time differences between P and S wave arrivals. |
| Why are multiple stations required? | To determine direction and exact location. |
| What type of particle motion do Love waves produce? | Side-to-side horizontal motion (snake-like movement). |
| What type of particle motion do Rayleigh waves produce? | Rayleigh waves move particles in a rolling, ocean-wave–like motion. |
| What does magnitude measure? | Energy released. |
| What scale replaced the Richter scale? | Moment Magnitude Scale (Mw). |
| Why is Moment Magnitude better? | Works worldwide and measures total energy released. |
| What does MMI (Modified Mercalli Intensity) measure? | Ground shaking and damage (subjective). |
| What controls building period? | Height, materials, and geology. |
| What is resonance? | When seismic wave period matches building period → amplified motion. |
| What is acceleration? | Change of velocity over time. |
| What is gravity in m/s²? | 9.8 m/s² (1.0 g). |
| At what acceleration do weak buildings fail? | 0.1 g. |
| What controls explosivity? | Temperature, gas content, silica content. |
| High silica magma = ? | High viscosity → explosive eruptions. |
| Low silica magma = ? | Low viscosity → effusive eruptions. |
| Characteristics of shield volcanoes? | Broad, basaltic, effusive, low viscosity. |
| Characteristics of composite (stratovolcanoes)? | Tall, layered, explosive, high viscosity. |
| What is tephra? | Volcanic debris ejected into the air. |
| What are pyroclastic flows? | Hot, fast-moving volcanic avalanches. |
| What is a lahar? | Hot, fast-moving volcanic avalanches. |
| What are travel-time curves, and how are they used to locate earthquakes? | Travel-time curves show how long seismic waves take to travel different distances through Earth and are used to determine the distance from a seismic station to an earthquake by comparing the arrival times of P-waves and S-waves. |
| Motion of hanging wall in reverse fault? | Moves up. |
| How do you identify a left-lateral strike-slip fault? | When standing on one side of the fault, the opposite side appears to move to the left. |
| How do you identify a right-lateral strike-slip fault? | When standing on one side of the fault, the opposite side appears to move to the right. |
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