The differences in travel time from the epicenter to the observatory are a measure of the distance and can be used to image both sources of earthquakes and structures within the Earth. Also, the depth of the hypocenter can be computed roughly. P-wave speed
Upper crust soils and unconsolidated sediments: 2–3 km (1.2–1.9 mi) per second
Upper crust solid rock: 3–6 km (1.9–3.7 mi) per second
Lower crust: 6–7 km (3.7–4.3 mi) per second
Deep mantle: 13 km (8.1 mi) per second. S-waves speed
Light sediments: 2–3 km (1.2–1.9 mi) per second in
Earths crust:4–5 km (2.5–3.1 mi) per second
Deep mantle: 7 km (4.3 mi) per second

Seismic wave arrival
As a consequence, the first waves of a distant earthquake arrive at an observatory via the Earths mantle. On average, the kilometer distance to the earthquake is the number of seconds between the P- and S-wave times 8. Slight deviations are caused by inhomogeneities of subsurface structure. By such analysis of seismograms, the Earths core was located in 1913 by Beno Gutenberg. S-waves and later arriving surface waves do most of the damage compared to P-waves. P-waves squeeze and expand the material in the same direction they are traveling, whereas S-waves shake the ground up and down and back and forth. Earthquake location and reporting
Earthquakes are not only categorized by their magnitude but also by the place where they occur. The world is divided into 754 Flinn–Engdahl regions (F-E regions), which are based on political and geographical boundaries as well as seismic activity.
Sympathetic ophthalmia (SO), also called spared eye injury, is a diffuse granulomatous inflammation of the uveal layer of both eyes following trauma to one eye. It can leave the affected person completely blind. Symptoms may develop from days to several years after a penetrating eye injury. It typically results from a delayed hypersensitivity reaction. Signs and symptoms
Eye floaters and loss of accommodation are among the earliest symptoms. The disease may progress to severe inflammation of the uveal layer of the eye (uveitis) with pain and sensitivity of the eyes to light. The affected eye often remains relatively painless while the inflammatory disease spreads through the uvea, where characteristic focal infiltrates in the choroid named Dalén–Fuchs nodules can be seen. The retina, however, usually remains uninvolved, although perivascular cuffing of the retinal vessels with inflammatory cells may occur. Swelling of the optic disc (papilledema), secondary glaucoma, vitiligo, and poliosis of the eyelashes may accompany SO. Pathophysiology
Sympathetic ophthalmia is currently thought to be an autoimmune inflammatory response toward ocular antigens, specifically a delayed hypersensitivity to melanin-containing structures from the outer segments of the photoreceptor layer of the retina. The immune system, which normally is not exposed to ocular proteins, is introduced to the contents of the eye following traumatic injury. Once exposed, it senses these antigens as foreign, and begins attacking them. The onset of this process can be from days to years after the inciting traumatic event. Diagnosis
Diagnosis is clinical, seeking a history of eye injury.