I'm not sure if this is the right area of the forum (it may be more Earth physics) or even the right site for this (it might be more of a geology question), but I'm wondering if someone more knowledgeable in physics could explain the physics of human caused earthquakes to me. Recently the United States Geological Survey updated its seismic activity maps to account for human activity and determined that Oklahoma has an earthquake risk profile similar to Alaska and California. Here's the map: However, Oklahoma doesn't have much of an earthquake history before 2011, when the area seems to have awakened, and fluid and steam injection has been done for decades. Oklahoma is a major center of hydraulic fracturing, which is a relatively new technology, but there doesn't seem to be similar levels of induced seismic activity elsewhere as a result of hydraulic fracturing. Could someone clarify the physics of how this process might work, and why other activities involving large amounts of mass (such as reservoirs) and energy (such as nuclear tests) don't seem to have created induced seismic activity, or at least nothing as dramatic as what's occurring in Oklahoma?