article_snippet.sent: The fluid pressure in the pores and fractures of the rocks is called the 'pore pressure.' the 'pore pressure acts against the weight of the rock and the forces holding the rock together.
article_snippet.sent: If the pore pressures are low - especially compared to the forces holding the rock together - then only the imbalance of natural in situ earth stresses will cause an occasional earthquake.
article_snippet.sent: If, however, pore pressures increase, then it would take less of an imbalance of in situ stresses to cause an earthquake.
article_snippet.sent: This type of failure is called shear failure.
article_snippet.sent: Injecting fluids into the subsurface is one way of increasing the pore pressure and causing faults and fractures to 'fail' more easily.
highlights_snippet.sent: Some were caused by injection of wastewater which can activate faults .
  