Earthquakes and Plate Tectonics

• Earthquake warnings occur immediately after an earthquake starts, helping people evacuate from dangerous areas, while earthquake predictions advise evacuation before an earthquake begins.
• Plate tectonics are the main geologic processes associated with earthquakes.
• Tectonic plate motions, especially at plate boundaries, cause stress in the Earth's crust, leading to earthquakes.
• The collision of the plate containing the India subcontinent with the plate containing Asia to form the Himalaya Mountains is an example of a convergent boundary.
• Brittle, rigid, or nonelastic rocks tend to break easily and do not store up stresses.
• Most faults in the United States are associated with mountains.
• A sudden release of built-up stress from locked faults causes measurable earthquakes.

Differences Between P and S Waves

• P waves arrive at a seismic station before S waves.
• Wavelengths of P waves are shorter than those of S waves.
• S waves are stronger in amplitude than P waves.
• S waves cannot travel through liquids, whereas P waves can.
• S waves cannot pass through the Earth's outer core, but P waves can.
• A minimum of three seismic stations are needed to pinpoint the epicenter of an earthquake.
• A magnitude 3.5 earthquake releases about 31.6 times more energy than a magnitude 2.5 earthquake.
• In developing countries, non-earthquake-resistant building construction is the primary factor leading to deaths during an earthquake, secondary effects aside.
• Earthquake prediction is unreliable for San Francisco because earthquakes do not occur on a regular schedule, and observational data is limited to less than 200 years.
• Understanding earthquakes helps minimize hazards by encouraging building in less prone areas and developing better prediction methods.
• The best earthquake warning systems can only give up to a minute of warning, making a one-hour notice untrue.
• Strain is the change in shape of an object due to stress.
• Rocks that are elastic and store energy are more seismically dangerous than brittle rocks
• A single fault can have multiple strikes and dips along its length.
• Faults are classified by how blocks of rock move relative to each other, not by geologic age.
• Seismic gaps can be caused by locked faults.
• Earthquakes do not occur deeper than 670 km (420 miles) below the surface.
• The Richter scale measures the energy released by an earthquake, not how it feels or the damage it causes.
• The destructiveness of an earthquake depends on its magnitude, the depth of the focus, distance from populated areas, building quality, soil and rock formations, and duration.
• Wealthier nations are generally better equipped to protect their citizens from natural disasters.