1. Some areas where earthquakes and volcanic activity often occur together are a
ID: 153209 • Letter: 1
Question
1. Some areas where earthquakes and volcanic activity often occur together are along oceanic ridges where lithospheric plates move apart. If we know the age of the crust and the distance from the ridge center, we can calculate how fast the two plates are moving away from each other. Look at the figures of oceanic ridges (spreading centers)
a. Calculate the half-spreading rate across the mid-atlantic ridge and east pacific rise. This is the rate at which one of the plates is growing.
b. Determine the full spreading rate for these same ridges. This is the rate at which the ocean basins are opening.
Mid-Atlantic Ridge East Pacific Rise sediment cover secment cove Plate #1 Plate #2- plate # 1 Plate #2 oceanic crust 2400 1800 1200 600 0 600 1200 1800 2400 distancs from ridoe (in km 2400 1800 1200 600 0 600 1200 1800 2400 distance from ridge (in km) 80 60 40 200 20 40 6080 age of crust on milions of years) 40 30 20 10 0 10 20 30 40 age of cust on milions of years)Explanation / Answer
Ans
1a) Half spreading rate is defined as ( Distance/Time ) of one side of a mid oceanic ridge. For mid atlantic ridge the distance from the ridge axis to the farthest point is 2400 km and the time period is 80Mya and the half spreading rate is 2400/80=30 km/million year or 3cm/yr and for east pacific rise the half spreading rate is 2400/40= 60km/million year or 6cm/yr. This thing also indicates that the east pacific rise is fastest spreading ridge.
b) The full spreading rate is 2 times the half sprreading rate. So for mid atlantic ridge it is 60 km/million year or 6cm/yr and for east pacific rise it is 120 km/million year or 12cm/year.
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