Final answer:
Transform fault boundaries involve horizontal sliding of tectonic plates past each other, as seen with the San Andreas Fault, where the Pacific and North American plates move sideways. Earthquake patterns can suggest whether transform motion has always been present. Based on the movement rate of 5 cm/year, significant slippage is expected to accumulate over time, leading to earthquakes.
Step-by-step explanation:
Transform Fault Boundaries Movement
Transform fault boundaries are places where tectonic plates slide horizontally past each other. This lateral movement is different from the vertical motion we see at convergent and divergent boundaries. At transform fault boundaries, crust is neither produced nor destroyed. Instead, the plates grind against each other in a lateral motion. A well-known example of a transform plate boundary is the San Andreas Fault in California, which forms the boundary between the Pacific Plate and the North American Plate. These two plates move sideways relative to one another, with the Pacific Plate moving northwest and the North American Plate moving southeast.
The San Andreas Fault has a long history of earthquakes due to the stress that accumulates as the plates slide past each other. A significant earthquake occurred in Parkfield on a regular basis, roughly every 25 years, moving an average of 1 meter each time. In contrast, in the Los Angeles area, the average interval between major earthquakes is longer, about 150 years, with more significant average motion of about 7 meters each time. The continual movement along the fault suggests that stresses are constantly building, leading to occasional sudden releases of energy, which we experience as earthquakes.
To answer the question regarding the earthquake and volcanic activities indicating whether the San Andreas Fault always had transform motion, we can look at geological evidence. There are patterns of older geological features and rock types on either side of the fault that do not align, indicating that the fault has not always been a pure strike-slip, or transform, boundary. This suggests a complex history that may have involved different types of plate motions over geological time frames.
Regarding the amount of slippage along the San Andreas Fault, based on the annual movement rate of about 5 cm/year, and considering the time elapsed since the last significant earthquake event, we can calculate the expected displacement. For instance, if the plates are moving at 5 cm/year and the last major slip was in 1857, by 2017 (a span of 160 years), we would expect around 8 meters of slippage to have accumulated (160 years x 5 cm/year).