An earthquake is defined as a tremor below the surface of the earth which causes_______.
A. Shaking of the crust
B. Shaking of the sea
C.Shaking of the mountain
D.None of these

Hint: An Earthquake arises generally below the Earth's surface. It sometimes results in a permanent change of level at the surface of the earth.

Complete answer:
-The location where an earthquake starts up is called the epicenter. It is often felt near the center. However, the vibrations from an earthquake can however be felt and distinguished thousands of miles away from the epicenter.
-Most earthquakes arise along the edge of the oceanic and continental plates.
-When tectonic plates move, it results in movements at the faults. An earthquake is the abrupt movement of Earth along its fault line.
Looking at the above options:
Option a: An earthquake is an instant vibration of the earth's crust. Earthquakes are usually caused when underground rocks abruptly break along a fault. This sudden discharge of energy causes the seismic waves that make the ground shake. This option is correct.
Option b: The shaking of the sea does not take place below the Earth's surface. If that happens, then it is Tsunami. Hence, this option is incorrect.
Option c: Earthquake is not the result of shaking of the mountain. Hence, this option is incorrect.
Option d: This option is incorrect and stands irrelevant.

Hence, the correct option is a.

Note: -A seismograph is a device which is used to observe and record earthquakes.
-The Richter scale measures the largest amplitude but other magnitude plates measure several parts of the earthquake. -The USGS presently reported that the earthquake magnitudes using the Moment Magnitude scale. An earthquake is caused by a sudden slip on a fault.