When we think of an earthquake, we think of building toppling, huge cracks opening up in earth,and so on.What is there to be "measured?"
Well,an earthquake is a trembling or vibration of the earth's surface.And it is these vibration that are measured.The cause of a earthquake usually a "fault" in the rocks of earth crust, a break along which one rock mass has rubbed on another with great force and in the rocks.This vibrations may travel thousand of miles, which is why an earthquake in Tokyo can be detected and measured in England.
Earthquake vibration consist of three or more types of wave motion, which travel at
different speed through the earth's rocky crust.the waves move in different directions.The
primary waves vibrate length wise;the secondary waves crosswise;and the long waves travel
around the earth surface.The long waves moves more slowly,but they have larger motion and
cause all the damage that can be seen by man.
Instrument called seismographs placed in different parts of the record vibrations every
day in the year,for the earth crust is never still.the record sheets of two or more seismographs help seismologists to see where the quake took place.
A seismograph is delicately hung weight,which remains still when an earthquake shakes the surrounding parts of the instrument.in other words this weight,is a chart.As the chart moves,a record is made on it by by the weight.
Record sheets indicates the time the wave arrives,the force of their motion and can even
indicate the direction from which the waves comes
Well,an earthquake is a trembling or vibration of the earth's surface.And it is these vibration that are measured.The cause of a earthquake usually a "fault" in the rocks of earth crust, a break along which one rock mass has rubbed on another with great force and in the rocks.This vibrations may travel thousand of miles, which is why an earthquake in Tokyo can be detected and measured in England.
Earthquake vibration consist of three or more types of wave motion, which travel at
different speed through the earth's rocky crust.the waves move in different directions.The
primary waves vibrate length wise;the secondary waves crosswise;and the long waves travel
around the earth surface.The long waves moves more slowly,but they have larger motion and
cause all the damage that can be seen by man.
Instrument called seismographs placed in different parts of the record vibrations every
day in the year,for the earth crust is never still.the record sheets of two or more seismographs help seismologists to see where the quake took place.
A seismograph is delicately hung weight,which remains still when an earthquake shakes the surrounding parts of the instrument.in other words this weight,is a chart.As the chart moves,a record is made on it by by the weight.
Record sheets indicates the time the wave arrives,the force of their motion and can even
indicate the direction from which the waves comes
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