Pore Fluid Pressure Imaging of the Mt. Pollino Region (Southern Italy) From Earthquake Focal Mechanisms

Focal mechanisms of selected earthquakes, recorded in the Mount Pollino region (southern Italy) from 2010 through 2014, are used to infer the pore fluid pressure at hypocenter depths. The 3-D excess pore pressure field provides evidence that the sequence occurs in a fluid-filled volume with values reaching 35 MPa. The mechanisms underlying this swarm-like sequence and the triggering of earthquakes are investigated by computing the cumulative static Coulomb stress change at hypocenter depths and analyzing the pore-pressure diffusion mechanism. The results indicate that static Coulomb stress change was lower than 0.01 MPa, which is the value generally assumed as threshold for the triggering, and seismicity distribution was actually driven by pore-pressure diffusion with relatively low diffusivity value. This latter mechanism could also explain the delayed triggering of the two larger events M-L 4.3 and M-L 5.0, respectively, that occurred about 150 days apart.

Automated summary

Focal mechanisms of selected earthquakes in the Mount Pollino region from 2010 to 2014 were used to infer pore fluid pressure at hypocenter depths, revealing a fluid-filled volume with values reaching 35 MPa. The study found that seismicity distribution was actually driven by pore-pressure diffusion mechanism with relatively low diffusivity value, which can also explain the delayed triggering of larger events.