18. How are earthquake locations determined? __________________________________

Question

18. How are earthquake locations determined? __________________________________ _____________________________________________________________. What realistic assumptions are made in determining their location? ______________________________ _________________________________________________________ _____________________ What is the difference between the earthquake focus and the epicenter? _________________________________________________________________________________.

19. BELOW, draw a cross section through Earth, with the North Geographic Pole up. Draw the configuration of the magnetic field flux lines in a normal polarity configuration. 20. What is the geomagnetic polarity time scale? _______________________________________ ____________________________________________________________________________________.

21. In the context of plate tectonics, continents have different kinds of margins. What is a passive margin, and provide an example. _______________________________________ ________________________________________________________________________________. Would you expect much seismicity in a passive margin setting? Why or why not? _____________________________________________________________________________

22. In what kind of plate tectonic setting did the March, 2011, Japan earthquake take place? ___________________________________________________________________________.

Explanation / Answer

Seismologist determined the location of earthquakes by using elastic waves (P and S waves). The difference of arrival of P and S waves is used to calculate the exact distance of the earthquake location.

The focus is a point within the subsurface, where the earthquake originates and produces seismic waves. A point on the surface which is perpendicular to focus is called epicenter. Earthquake originates at the focus and come out from the epicenter.

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