(Solved): The more we know about the history of a continental transform fault that lies close to heavily popu ...

The more we know about the history of a continental transform fault that lies close to heavily populated regions, the better we can prepare for its next pulse of activity. Geologists try to find out how long a continental transform fault has been active, how much it has offset features on the plates it separates, and how fast it has moved in the past. Geologists estimate that the San Andreas fault system, mapped below, has been active for about 20 million years. This exercise shows how geologic markers cut by transform faults enable us to measure the amount and rate of motion along a fault. Amount of fault movement indicated by offset bodies of Before tackling the San Andreas system, let's practice on a much simpler area. Field geologists have mapped an active continental transform fault (the red line in the figure on the next page) for several hundred klometers. A 50 -million-year-old (50-Ma) body of granite and a 30-Ma vertical dike have been offset by the fault as shown. (a) Draw arrows on opposite sides of the fault to show the direction in which the two plates moved relative to each other. (b) Measure the amount of offset of the 50-Ma granite body. \( \mathrm{km} \) (c) The geologists have proved that the faulting began almost immediately after the granite formed and continues today. Assuming that the plates moved at a constant rate for the past 50 million years, calculate the rate of offset. (d) Now do the same for the 30-Ma dike. Offset: \( \mathrm{km} \). Assuming a constant rate of movement for the past 30 million years, calculate the rate of offset. (e) Compare the two rates. Has faulting taken place at a constant rate, or has the rate increased or decreased over time? Explain in as much detail as possible.