M A S T E R P A G E
Seismic SeaWaves
Energy Analysis
(key)
2.4j
1. What is the average sea floor area that moves in an earthquake that results in a seismic sea wave?
A = 20,000 km
2
2. Knowing that the average ocean depth (h) is 3.8 km, what volume (V) of water is moved in the disturbance that
causes a seismic sea wave?
Volume of seawater: V = Ah = (20,000 km
2
)(3.8 km) = 7.6 x 10
4
km
3
= 76,000 km
3. This volume of ocean water has a certain mass. Knowing the density (D) of ocean water to be 1.03 kg/m
3
,
calculate the mass (m) of the water moved by the quake. To convert km
3
to m
3
, multiply by 10 m
3
/km
3
.
Density of seawater: D = 1.03 x 10
3
kg/m
3
Mass of seawater lifted:
m = DV = (1.03 x 10
3
kg/m
3
)(7.6 x 10
4
km
3
) = (1.03 x 10
3
kg/m
3
) (7.6 x 10
4
km
3
) (10
9
m
3
/km
3
)
7.8 x 10
16
kg or 78 trillion metric tons
(
note
:
1 km
3
= 1 x 10
9
m
3
)
4. To lift that mass of ocean water requires a force that is at least equal to water’s weight. Using 9.8 ms
2
as the
acceleration due to gravity (g), calculate the force (F) needed to lift that much ocean water.
Acceleration due to gravity: g = 9.8 m/s
2
Force due to gravity or weight of seawater:
F = mg = (7.8 x 10
16
kg)(9.8 m/s
2
) = 7.6 x 10
17
Newtons
A G U
/
F E M A
123
S
E I S M I C
S
L E U T H S
