SCEC Award Number 17245 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title Does effective stress have reduced sensitivity to pore pressure at seismogenic depths within Southern California?
Investigator(s)
Name Organization
Patrick Fulton Texas A&M University Hiroko Kitajima Texas A&M University
Other Participants
SCEC Priorities 1c, 3f, 2c SCEC Groups FARM, SDOT
Report Due Date 11/30/2018 Date Report Submitted 12/12/2019
Project Abstract
 In the study supported by this award, we studied the sensitivity of rocks to pore pressure. Based on limited extant laboratory data and theoretical considerations, we hypothesized that the effective stress controlling brittle deformation and rock failure at seismogenic depths within the San Andreas Fault system is considerably less sensitive to pore pressure than commonly assumed. By reanalyzing existing experimental rock deformation data and conducting a series of new experiments, we evaluated rock sensitivity to pore pressure in terms of deformation and frictional shear failure. The results show that indeed that sandstones and granite have less sensitivity to pore pressure than commonly assumed, and that pore pressure sensitivity can rapidly change in response to earthquake damage. These findings provide insight into properties and processes which can affect the stress state and susceptibility of earthquakes on faults within Southern California and how they may respond to sudden transients. Additional ongoing experiments are planned to supplement these results and support publications within the next year.
Intellectual Merit These results reveal that sandstones and granite have less sensitivity to pore pressure than commonly assumed, and that pore pressure sensitivity can rapidly change in response to earthquake damage. These findings provide insight into properties and processes which can affect the stress state and susceptibility of earthquakes on faults within Southern California and how they may respond to sudden transients.
Broader Impacts This work supported female graduate student Szu-Ting Kuo. It also facilitated collaboration across rock mechanics and hydrogeologic fields and between two early-career faculty researchers. It promoted the development of novel experimental strategies to measure poroelastic properties and coupled hydrologic and mechanical behavior. The results provide insights into conditions and processes which may play an important role in earthquakes and aftershocks.
Exemplary Figure Figure 6. Results of drained isotropic deformation experiments show that rock's are not as sensitive to pore pressure than assumed by simple effective stress relations for volumetric deformation.

Panel A shows data for loading and unloading conditions with Pp held at 5 MPa. The resulting Kb measurements are shown in panel B, and panel C shows calculated values of alpha or Biot coefficient which defines how sensitive rock's are to pore pressure.

Similar results are found for both volumetric strain and frictional failure through new experiments of reanalysis of legacy data.