Question

If the San Andreas Fault moves 200 cm (2 meters) per big earthquake, and plate movement is xx cm/yr (see question above), how many years of plate motions must accumulate to produce one big earthquake? This is the recurrence interval for earthquakes of this size.

a. 4 years
b. 20 years
c. 80 years
d. 200 years

Answer 1

To produce a big earthquake with 200 cm of displacement, it would take 40 years at a plate movement rate of 5 cm/year.

Step-by-step explanation:

To compute the number of years of plate motions that must accumulate to produce one big earthquake, one must first know the rate of plate motion and the magnitude of displacement during such an earthquake. According to the question, each big earthquake results in 200 cm (or 2 meters) of displacement along the San Andreas Fault. Given that the plate movement associated with the fault is about 5 cm/year, we can calculate the number of years required to build up enough strain to produce a 2-meter slip.

The calculation is as follows:

Amount of movement per earthquake = 200 cm

Annual plate movement = 5 cm/year

Years needed to accumulate 200 cm = 200 cm ÷ 5 cm/year

Years needed = 40 years

Answer 2

Option C

80 years

Step-by-step explanation:

From Scientific records, the rate of movement of the plate is 0.025 meters

Since the fault moves at the rate of 2 meters per year, to obtain the number of years it will takes to produce an earth quake, we will have to divide the rate of movement of the fault by the rate of movement of the plate.

Number of years for earthquake =
`(2)/(0.025)`= 80 years.

Hence, it will take 80 years to produce one big earthquake.