THEORY OF DIKE INTRUSION IN A SATURATED POROUS SOLID

A study of the pore pressure fields that develop around intruding dikes is described under the motivation that intruded geometry may be determined from pore pressures recorded in relatively remote monitoring wells. The pore pressure fields induced around cylindrical and planar intrusions are described as analogues to moving point or line dislocations within an infinite saturated porous elastic medium. The resulting transient pressure fields reduce to an equivalent steady state when viewed from the advancing front. Solutions for the moving point and line dislocations yield a dependence on common dimensionless groupings. Thus, dimensionless pressure rise accompanying intrusion, and recorded at a static location, may be uniquely referenced to the dimensionless parameters representing emplacement velocity and time. The resulting transient pressure response may be divided into two groups, representing fast and slow emplacement. Where hydraulic parameters representing the host porous medium are known a priori, both emplacement location and the cross-sectional area may be determined uniquely. For slow emplacement, the intrusion rate may also be determined; only a lower limiting intrusion rate may be discerned for fast emplacement. Field data are rare, but two intrusive events at Krafla, Iceland are examined using the proposed moving dislocation models. Predicted location and lower limiting intrusion rate of the Krafla dikes compare favorably with field observation despite more than a 9 km separation to the monitoring well.