Question

objective 4: earthquakes

1. what causes an earthquake?
2. what are smaller earthquakes called that may precede and follow a major earthquake and why do they occur?
3. list and describe the motion (of the waves & the material they pass through) of the 3 types of seismic waves.
4. describe the 2 types of measurements seismologists use to describe earthquakes.
5. what are the factors caused by earthquakes that determine the amount of damage caused to buildings and other structures?
6. if you know the distance of an earthquake epicenter from the three seismic stations, how can you find the exact location of the epicenter of the earthquake?
7. list 4 dangers that are associated with earthquakes/.

Explanation:

1. Earthquakes are caused by the sudden release of energy in the Earth's crust, usually due to the movement of tectonic plates along faults.
2. Smaller earthquakes preceding a major one are called foreshocks and those following are aftershocks. Foreshocks occur as the stress - strain system adjusts before the main rupture, and aftershocks are due to the readjustment of the crust after the main shock.
3. P - waves (primary waves) are compressional waves that move in a push - pull motion through materials, traveling fastest. S - waves (secondary waves) are shear waves that move materials side - to - side and cannot travel through liquids. Surface waves move in a rolling or swaying motion along the Earth's surface and are the most destructive.
4. Seismologists use magnitude (a measure of the energy released, e.g., Richter scale or moment magnitude scale) and intensity (a measure of the effects of the earthquake at a particular location, e.g., Mercalli intensity scale).
5. Factors include the magnitude of the earthquake, the distance from the epicenter, the type of soil and rock at the site, the design and construction quality of the buildings, and the depth of the earthquake.
6. By using the distances from three seismic stations, circles are drawn around each station with radii equal to the respective distances. The intersection of these three circles gives the exact location of the epicenter.
7. Dangers include ground shaking, which can damage buildings; tsunamis, which are large ocean waves triggered by underwater earthquakes; landslides, which can be caused by the shaking; and fires, which can start due to broken gas lines or electrical problems.

Answer:

1. Sudden release of energy due to tectonic plate movement along faults.
2. Foreshocks precede, aftershocks follow. Foreshocks: stress - strain adjustment before main rupture. Aftershocks: crust readjustment after main shock.
3. P - waves: compressional, push - pull, fastest. S - waves: shear, side - to - side, can't travel through liquids. Surface waves: rolling/swaying along surface, most destructive.
4. Magnitude (e.g., Richter or moment magnitude scale) and intensity (e.g., Mercalli intensity scale).
5. Magnitude, distance from epicenter, soil/rock type, building design/construction, earthquake depth.
6. Draw circles around each of the three seismic stations with radii equal to the distances. The intersection is the epicenter.
7. Ground shaking, tsunamis, landslides, fires.