Earth Science Exam: Review Part 1

Seismology

• Focus: The point within the Earth where an earthquake originates, also known as the hypocenter.
• Epicenter: The point on the Earth's surface directly above the focus, where the effects of the earthquake are typically strongest.
• Comparison: Both terms refer to locations related to the origin of an earthquake, but the focus is a subsurface point and the epicenter is a surface point.

Triangulation in Seismology

• Method: Triangulation is used to determine the location of a point by forming triangles to it from known points.
• Process:
  • Record seismic waves using seismographs at different locations.
  • Measure the time difference between the arrivals of P and S waves at each seismograph.
  • Calculate the distance from the seismograph to the epicenter using the time difference.
  • Draw circles on a map around each seismograph station with radii equal to the calculated distances.
  • The point where the circles intersect is the earthquake's epicenter.

Types of Seismic Waves

• P Waves (Primary Waves):
  • Travel fastest and are the first to be detected by seismographs.
  • Move through solids, liquids, and gases.
  • Cause particles to compress and expand in the direction of wave propagation (longitudinal motion).
• S Waves (Secondary Waves):
  • Slower than P waves and arrive after them.
  • Can only move through solids.
  • Cause particles to move perpendicular to the direction of wave propagation (transverse motion).
• Long Waves (Surface Waves):
  • Travel along the Earth's surface and are slower than both P and S waves.
  • Cause the most damage during an earthquake due to their high amplitude and complex motion.
  • Can be further divided into Love waves (horizontal transverse motion) and Rayleigh waves (rolling motion).

Tsunami Formation

• Causes:
  • Underwater earthquakes
  • Volcanic eruptions
  • Landslides
  • Meteorite impacts
• Process: Displaced water forms waves that travel across the ocean at high speeds, increasing in height and causing destruction upon reaching shallow coastal areas.

S Wave Path

• Generation: S waves originate at the earthquake focus and travel outward.
• Propagation: S waves move through the Earth's crust and mantle in a transverse motion.
• Interaction: S waves can only move through solid materials, not liquids or gases, and are reflected or converted into other types of waves when they encounter the Earth's outer core.
• Refraction and Reflection: S waves can be refracted or reflected depending on the density and composition of the materials they encounter, creating a shadow zone.

Liquefaction

• Definition: Liquefaction is a phenomenon where saturated soil temporarily loses its strength and stiffness in response to an applied stress, such as the shaking from an earthquake.
• Process:
  • Saturated soil
  • Seismic shaking increases water pressure within the soil
  • Loss of strength and cohesion between soil particles
  • Soil behaves like a liquid
• Implications: Ground instability, surface deformation, landslides, and lifeline disruptions.

Magnitude and Intensity

• Magnitude: Measures the energy released during an earthquake, quantifying its size and strength.
• Measurement: Richter Scale and Moment Magnitude Scale (Mw)
• Intensity: Measures the effects of an earthquake at different locations on the Earth's surface, describing the severity of shaking and damage experienced.
• Scales: Modified Mercalli Intensity (MMI) scale

Rock Formation

• Metamorphic Rocks:
  • Formation: Transformation of pre-existing rocks due to high pressure, high temperature, and/or chemically active fluids.
  • Characteristics: Foliated or banded texture, or non-foliated if formed under conditions of minimal deformation.
• Sedimentary Rocks:
  • Formation: Accumulation and lithification of sediments.
  • Characteristics: Layered appearance, may contain fossils, can be clastic, chemical, or organic.
• Igneous Rocks:
  • Formation: Cooling and solidification of molten rock material.
  • Characteristics: Classified based on texture and mineral composition, can be intrusive or extrusive.
• Comparison: Origin, formation environment, textures, and contrast between processes.

Law of Superposition

• Definition: In an undisturbed sequence of sedimentary rocks, the oldest layers are at the bottom, and the layers become progressively younger toward the top.
• Application: Relative age dating of rocks, stratigraphic analysis, identifying sequence of events, fossil correlation, and geological features.

Radioactive Decay

• Definition: The process by which an unstable atomic nucleus loses energy by emitting radiation.
• Types:
  • Alpha decay
  • Beta decay
  • Gamma decay
  • Electron capture
• Half-life: The time it takes for half of the atoms in a sample to decay.
• Decay chains: Series of decays until a stable, non-radioactive isotope is formed.