Earthquake Risks and Hazards

Earthquake Risks

• Earthquakes cannot be reliably predicted, but scientists can identify areas most prone to them for long-term planning.
• Earthquakes result from stress buildup and release along active plate boundaries.
• Rock blocks can move horizontally or vertically past each other.
• Earthquakes occur at depths ranging from Earth's surface to over 600 km.

Measuring Earthquakes

• Richter magnitude scale measures the energy of the largest seismic waves.
• Moment magnitude scale measures the total energy released by an earthquake using newer technologies for more accurate measurements.
• The Richter scale is usually applied first, followed by the moment magnitude scale.
• The Modified Mercalli scale evaluates earthquake intensity based on resulting damage.
• Earthquake damage depends on earthquake strength, surface materials, structure design, and distance to the epicenter.

Earthquake Hazards

• Earthquake hazards are factors determining the severity of earthquake damage.
• Structural failure includes collapsing buildings, such as "pancaking" (collapse from top down) and collapses due to building height.
• Liquefaction is when shaking causes wet soil to act like liquid, leading to buildings sinking and collapsing.

Tsunamis

• Tsunamis are large ocean waves generated by vertical seafloor motion during an earthquake.
• Underwater earthquakes can cause tsunamis.
• Areas with higher earthquake frequency and past activity are at greater risk.

Volcanoes

• Volcanoes form at active plate boundaries, including convergent and divergent boundaries, and at hot spots away from plate boundaries.

Major Volcanic Belts

• The Ring of Fire is an area of earthquake and volcanic activity around the Pacific Ocean.
• The Alpide Belt includes mountain ranges extending to the Mediterranean and Atlantic, containing volcanoes like Mount Etna and Mount Vesuvius.
• Both belts are associated with convergent plate boundaries.
• Not all volcanoes form near plate boundaries; some are located at hot spots, such as the Hawaiian Islands.

Hot Spots

• Hot spots are areas thought to be unusually hot at the boundary between Earth's mantle and core.
• Loihi is a relatively young, active volcano discovered in 1970, investigated after a swarm of earthquakes.
• A swarm is a term for a large amount of earthquake activity.

Volcanic Hazards

• Lava flows are slow-moving, rarely deadly but still damaging, melting everything in their path and solidifying into thick rock layers.
• Mudflows (lahars) form when volcanic thermal energy melts snow and ice, mixing water with mud and ash.
• Volcanic ash emitted during explosive eruptions can disrupt air traffic, with deposits as thin as 1 cm capable of causing engine failure.
• Volcanic gases include water vapor, carbon dioxide, and sulfur dioxide. Water vapor is harmless; sulfur dioxide irritates skin and eyes; carbon dioxide can be deadly.
• Landslides are rapid downhill movements of soil, loose rocks, and boulders during eruptions; shaking weakens rocks.
• Pyroclastic flows are fast-moving avalanches of hot gas, ash, and rock from explosive volcanoes, traveling over 100 km/h with temperatures over 1000°C.

Volcanic Risk and Prediction

• The U.S. has 169 potentially active volcanoes, mostly in the Ring of Fire.
• Scientists monitor earthquake activity, volcano tilt, gas emissions, lava samples, thermal changes, and past eruptive history to predict eruptions.

Severe Weather

• Severe weather includes hurricanes, tornadoes, and floods.

Costs and Effects

• Severe weather causes billions in damage and threatens numerous lives.

Hurricanes

• The Saffir-Simpson Hurricane Scale measures hurricane intensity.
• Hurricane damage extent depends on hurricane strength and coastal area characteristics.
• Hurricanes cause damage through wind, waves, rain, storm surge, and tornadoes.
• Storm surge is water blown outward from the hurricane's center, causing coastal flooding.
• Storm surge moves sand, floods coastal areas, damages buildings, property, and ecosystems

Tornadoes

• The Enhanced Fujita Scale measures tornado damage intensity.
• EF-0 tornadoes cause light damage such as breaking tree branches and damaging billboards.
• EF-1 to EF-4 tornadoes tear roofs from homes, derail trains, and throw vehicles.
• EF-5 tornadoes demolish concrete and steel buildings and pull bark from trees.

Floods and Droughts

• Floods and droughts are effects of severe weather.
• Floods occur when large water volumes overflow boundaries.
• Droughts are extended periods of below-average rainfall, causing heat waves.

Factors Causing Floods

• Snowmelt
• Dam failure
• Local or regional heavy precipitation
• Volcanic eruptions
• Urbanization