The graph shows the vertical acceleration of the ground from

The graph shows the vertical acceleration of the ground from the 1994 Northridge earthquake in Los Angeles, as measured by a seismograph. (Here t represents the time in seconds.)

(a) At what time t did the earthquake first make noticeable movements of the earth?
t = sec

(b) At what time t did the earthquake seem to end?
t = sec

(c) At what time t was the maximum intensity of the earthquake reached?
t = sec

Solution

a) the earthquake first make noticeable movements of the earth at
t = 5 sec

b) The earthquake seem to end at
t = 30 sec

c)    the maximum intensity of the earthquake reached at

t = 16 . 5 sec