For decades, seismologists modeling subduction zones—regions where one tectonic plate is forced beneath another—operated under a binary assumption regarding fault behavior. Faults were thought to be either steadily creeping, safely dissipating tectonic stress, or completely locked, accumulating massive strain over centuries that would eventually be unleashed in a catastrophic, high-magnitude earthquake.
This binary model was upended in the early 2000s by the discovery of "slow slip" events, often referred to as silent earthquakes. Using newly deployed networks of high-resolution GPS stations, geologists detected anomalous data: landmasses above subduction zones were occasionally reversing their trajectory for weeks at a time, moving opposite to the direction of the subducting plate. These GPS anomalies provided the first evidence that faults can intermittently unlock and slide over a period of weeks or months. While these slow slip events do not generate seismic waves detectable by humans, they do have a measurable physical effect, causing localized, transient increases in the pressure of deep underground aquifers.
The passage indicates that 'slow slip' events cause which of the following?
- A steady accumulation of massive strain over centuries.
- Temporary elevations in the pressure of subterranean water reservoirs. (correct answer)
- Seismic waves that are easily detectable by human populations.
- The permanent locking of tectonic plates within subduction zones.
- The deployment of high-resolution GPS networks above fault lines.
Explanation: The final sentence states slow slip events cause 'localized, transient increases in the pressure of deep underground aquifers.' (B) is a precise synonymous paraphrase: 'temporary elevations' for 'transient increases' and 'subterranean water reservoirs' for 'deep underground aquifers.' (C) is a direct contradiction — the passage explicitly states these events 'do not generate seismic waves detectable by humans.' (A) describes completely locked faults, which is the opposite behavior from the intermittent unlocking that characterizes slow slip events.