Earthquakes

Study Guide: Earthquakes

Overview of Earthquakes

  • Definition: Natural events caused by the rapid release of energy in the Earth's crust.

  • Frequency: Over 1 million detectable earthquakes occur each year.

Earthquake Geography

  • Regions of Activity: Japan Sea, Pacific Ocean, and volcanic arcs.

  • Crust Types: Continental & Oceanic Crust.

  • Earth’s Layers: Contribute to tectonic activity.

Earthquake Mechanism

  • Cause: Rapid energy release due to tectonic forces.

  • Process: Rocks bend elastically until they break, producing vibrations.

Impacts of Earthquakes

  • Most earthquakes are small; significant earthquakes can lead to destruction and fatalities.

  • Historical Toll: 3.5 million deaths recorded in the past 2,000 years.

  • Hundreds of significant earthquakes occur annually.

Role of Seismologists

  • Study causes, effects, and potential damage from earthquakes.

  • Engage in earthquake prediction (both long-term and short-term).

Types of Faults

  1. Normal Fault: Hanging wall moves down due to extensional forces.

  2. Reverse Fault: Hanging wall moves up due to compressional forces.

  3. Thrust Fault: A low-angle reverse fault associated with mountain formations.

  4. Strike-Slip Fault: Horizontal movement with no vertical motion.

Seismic Waves

  • Body Waves: Travel through Earth's interior (includes P-waves and S-waves).

  • Surface Waves: Travel along the surface (includes R-waves and L-waves).

Measuring Earthquakes

  • Seismographs: Instruments that record ground motion.

  • Seismogram: Data recording from seismographs, depicting wave behavior and arrival times.

  • Magnitude and Intensity: Intensity relates to observed damage; Magnitude relates to energy released.

Tsunamis

  • Definition: Harbor waves resulting from underwater displacements due to earthquakes.

  • Detection: Increasing need for early-warning systems to save lives.

Earthquake Prediction

  • Long-term predictions: Possible.

  • Short-term predictions: Currently unreliable.

Identifying Recent Faults

  • Historical records and geological dating estimate recurrence intervals of faulting activity.