Earth Quakes Flashcards
What is the difference between the hypocenter and the epicenter of an earthquake?
The hypocenter (focus) is the point within the Earth where the rupture begins, while the epicenter is the point on the surface directly above it.
How do intensity and magnitude differ in describing an earthquake?
Intensity measures ground shaking and damage at specific locations, whereas magnitude quantifies the energy released at the source, using data from seismic records.
What happens when earthquake magnitude increases by 2 units?
The seismic wave amplitude increases about 10-fold (roughly 100-fold overall for 2 units) and the energy released increases roughly 30–32 times per unit, resulting in around 1,000 times more energy for a 2-unit jump.
How does earthquake frequency relate to magnitude?
Larger magnitude earthquakes occur less frequently, while smaller ones are much more common.
What are the main types of seismic waves?
Seismic waves include body waves (P and S waves) that travel through the interior and surface waves (Rayleigh and Love waves) that travel along the Earth’s surface.
What are the characteristics of P waves?
P waves are compressional waves that are the fastest, arriving first at a seismic station, and can travel through solids, liquids, and gases.
How do S waves differ from P waves?
S waves are shear waves that arrive after P waves, travel only through solids, and typically have a larger amplitude.
Why are surface waves particularly destructive?
Surface waves have the slowest velocity but the highest amplitude, causing extensive ground shaking and damage near the surface.
What does the elastic rebound theory explain?
It explains that strain energy builds in rocks until they reach their elastic limit, after which they rupture suddenly, releasing stored energy as an earthquake.
How are earthquakes recorded?
Seismographs record the motion of seismic waves, and the resulting records—seismograms—help determine the earthquake’s location, magnitude, and fault type.
How is the epicenter of an earthquake determined?
By using the time difference between P and S wave arrivals at multiple stations and applying triangulation with travel-time curves.
What are foreshocks and aftershocks?
Foreshocks are smaller quakes that sometimes occur before a mainshock, while aftershocks follow the main event, gradually decreasing in magnitude and frequency.
How do megathrust earthquakes generate tsunamis?
They occur at subduction zones where enormous thrust faults rupture, causing significant vertical displacement of the seafloor that displaces large volumes of water, triggering tsunamis.
What are some challenges in predicting earthquakes?
Predicting the exact time of earthquakes is difficult; however, long-range forecasts use seismic gaps, strain estimates from plate movements, and paleoseismology to assess risk.
Where do most earthquakes occur globally?
Earthquakes are concentrated along plate boundaries, particularly in earthquake belts like the Pacific “Ring of Fire” where subduction, transform, and convergent boundaries exist.
