Answer to Question 1
Answer: First there is the crust, both continental and oceanic. This layer is composedly mostly of igneous and metamorphic rocks. It is solid except for local accumulations of magma. Next is the mantle, composed of ultramafic igneous rocks. The mantle is almost entirely solid. However, small amounts of partially molten rock are likely present at the base of the lithosphere and possibly in discontinuous zones just above the core-mantle boundary. Finally there is the core, both outer and inner. The outer core is composed of iron and nickel and is liquid melt. The inner core is very iron rich and made of an iron-nickel alloy. The inner core is solid. Refer to table 8.1
Answer to Question 2
Answer: Scientists gain knowledge about seismic waves not only from earthquakes, but from artificial explosions as well. During the 1950s and '60s, seismic stations were established around the world. Initially these seismometers were set up to measure seismic waves from underground nuclear bomb tests during the Cold War. These seismometers pick up seismic activity from explosions in rock quarries and mines, as well as human disasters such as the World Trade Center attacks.
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