On January 17, 1994 a magnitude 6.9 earthquake near Northridge, California released energy equivalent to almost 2 billion kilograms of high explosive. The earthquake killed 51 people, caused over $20 billion in damage, and raised the Santa Susana Mountains north of Los Angeles by 70 centimeters. It also created seismic waves that ricocheted throughout Earth's interior and were recorded at geophysical observatories around the world. The paths of some of those seismic waves and the ground motion that they caused are shown in this poster. Seismologists use these recordings to explore the Earth's deep interior.
- Seismic waves propogate outwards from an earthquake in all directions.
- Seismologists use the recordings of the ground motion caused by these waves to explore the Earth's deep interior.
- We do not see shear (S) waves passing through the outer core. Because liquids can not be sheared, we infer that the outer core is molten.
- We do, however, see S waves as they go through the inner core. Because the inner core transmits shear energy, we assume it is solid.
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