The first seismograph was invented in 132 A.D. by the Chinese astronomer and mathematician Chang Heng. He called it an “earthquake weathercock.” Each of the eight dragons had a bronze ball in its mouth. Whenever there was even a slight earth tremor, a mechanism inside the seismograph would open the mouth of one dragon.

seismic wave

P waves travel fastest and are the first to arrive from the earthquake. In S or shear waves, rock oscillates perpendicular to the direction of wave propagation. Both P and S waves travel outward from an earthquake focus inside the earth.

Earthquakes are recorded by instruments called seismographs. The recording they make is called a seismogram. The seismograph has a base that sets firmly in the ground, and a heavy weight that hangs free.

What is a geophysicist? A geophysicist is someone who studies the Earth using gravity, magnetic, electrical, and seismic methods. Research geophysicists study the internal structure and evolution of the earth, earthquakes, the ocean and other physical features using these methods.

1177 B.C.

Lay of the Land: New York 125th Street Fault – The largest fault in New York City, it extends from New Jersey to the East River, while partially running to the northern tip of Central Park and extending to Roosevelt Island.

There were five previous tornadoes in New York City on record, but none as strong as this one. The New York City borough of Staten Island has had the most tornadoes on record of any of the five boroughs, with a total of three, all since 1990.

Pacific plate’s Ring

The North American and Eurasian Plates are moving away from each other along the line of the Mid Atlantic Ridge.