In the Central Valley of California there has been considerable subsidence f the land surface over the last 50 years. This subsidence has occurred because: Question 40 options: a) Development and subsequent overburden from buildings led to compaction of the sediment below. b) Groundwater was recharged at a faster rate than it was extracted in an unconfined aquifer leading to compaction of the sediment and permanent loss of pore space. c) Earthquake shaking in California was a cause of the sudden compaction of the ground. d) Groundwater was withdrawn at a faster rate than it was recharged in an unconfined aquifer leading to compaction of the sediment and permanent loss of pore space. e) Compaction occurred due to an extend drought and will rebound once it is over.he presence or absence of water in a landslide area is important because: Question 44 options: a) Water can act as a lubricant on a failure surface b) Water adds weight to the mass above the failure surface, helping hold the mass in place by increasing friction. c) Water adds weight to the mass above the failure surface, increasing the shearing force pushing material along the failure plane. d) Water erodes the slide