Earthquake Hazards and Plate Tectonics - Study Notes

EARTHQUAKE BASICS AND PLATE TECTONICS

  • Earth’s crust is divided into several regions called plates that carry the continents on top of them. These tectonic plates continue to move either by colliding, moving away, or sliding over or under one another.
  • Historical idea: continents were once part of a supercontinent called Pangaea, and motion has continued since it split. This ongoing movement raises questions about the effects on humans and whether earthquakes are something to be prepared for.
  • What is an earthquake? Any sudden shaking of the ground caused by the passage of seismic waves through Earth's rocks.

PLATES & BOUNDARIES

  • The earth's continents are constantly moving due to the motions of the tectonic plates.
  • Crust types:
    • Continental crust: underlying the continents.
    • Oceanic crust: underlying the oceans.
  • All plates have names, usually referring to landmasses, oceans, or regions where they are located.
  • The border between two tectonic plates is called a boundary.
  • All tectonic plates are constantly moving — very slowly — around the planet, but in many different directions. Some plates move toward each other, some are moving apart, and some slide past each other.
  • Because of these differences, tectonic plate boundaries are grouped into three main types:
    • A convergent boundary occurs where two plates are pushing toward each other.
    • A divergent boundary marks two plates that are moving apart from each other.
    • A transform boundary occurs where two plates slide past each other.

THREE MAIN TYPES OF PLATE BOUNDARIES

  • There are $3$ main boundary types: convergent, divergent, and transform.
  • Convergent boundary: two plates push toward each other.
  • Divergent boundary: two plates move apart.
  • Transform boundary: two plates slide past each other.

POTENTIAL EARTHQUAKE HAZARDS

1) Ground Shaking – refers to the vibration of the ground during an earthquake.
2) Ground Rupture – the movement of the ground along one side of a fault relative to the other side.
3) Liquefaction – occurs when seismic shaking triggers the mixing of loose materials with groundwater or soil saturated with water.
4) Earthquake-induced Landslide – occurs when the top layers of soil and rock slip on sloping ground, triggered by earthquake ground motion.
5) Tsunami – a series of waves caused by an underwater earthquake.

HOW DO WE KNOW THAT THERE’S AN UPCOMING TSUNAMI?

1) Feel the Earth’s shake
2) See the ocean drop
3) Hear an unusual roaring sound

CAN WE PRECISELY TELL A FORTHCOMING EARTHQUAKE?

  • Question: Can we precisely tell a forthcoming earthquake?
  • Answer: Seismometers help scientists estimate earthquakes.

SEISMOgraph AND SEISMOGRAPHY

  • A seismograph is an instrument used to detect and record seismic waves.
  • Seismic waves are propagating vibrations that carry energy from the source of an earthquake outward in all directions.
  • In some discussions, the term seismometer is used for the instrument that measures ground motion; seismograph records the waves.

WHAT IF WE DON’T HAVE ANY SEISMOGRAPH OR SEISMOMETER? HOW CAN WE LESSEN CASUALTIES?

  • Question: What if we don’t have any seismograph or seismometer to use? Is there anything else that we can do to lessen casualties?
  • (Note: The provided transcript poses this question but does not supply an answer. The implication is that alternative mitigation strategies are important even without instrumentation.)

HAZARD MAPPING

  • Hazard mapping is used to identify areas that sit on a particular geologic feature, such as a fault or trench.
  • Purpose: to assess and plan for earthquake risks based on geological features.