GEOLOGY

Detailed explanation-1: -During an earthquake, vibrations called seismic waves move out from the focus in all directions. Seismic waves carry the energy of an earthquake away from the focus, through Earth’s interior, and across the surface.

Detailed explanation-2: -At farther distances the amplitude of the seismic waves decreases as the energy released by the earthquake spreads throughout a larger volume of Earth. Also with increasing distance from the earthquake, the waves are separated apart in time and dispersed because P, S, and surface waves travel at different speeds.

Detailed explanation-3: -The focus is the place inside Earth’s crust where an earthquake originates. The point on the Earth’s surface directly above the focus is the epicenter. When energy is released at the focus, seismic waves travel outward from that point in all directions.

Detailed explanation-4: -The arrival times of the P-and S-waves at different seismometers are used to determine the location of the earthquake. Assuming that we know the relative speed of P-and S-waves, the time difference between the arrivals of the P-and S-waves determines the distance the earthquake is from the seismometer.

Detailed explanation-5: -As discussed in Lesson 5, earthquakes occur when elastic energy is accumulated slowly within the Earth’s crust as a result of plate motions and then released suddenly at fractures in the crust called faults. The released energy travels in the form of waves called seismic waves.