Auxiliary Material for
Evolution of pore fluid pressures in a stimulated geothermal reservoir
inferred from earthquake focal mechanisms
Toshiko Terakawa
(Earthquake and Volcano Research Center, Graduate School of Environmental Studies,
Nagoya University, Nagoya 464-8601, Japan)
Geophysical Research Letters
Introduction
The material contains the tectonic stress tensor and the pore fluid pressure field in the Basel EGS
estimated in this study. The detailed results of the tectonic stress field are given in the figures
fs01.jpg and fs02.jpg. Evolution of pore fluid pressures is shown as a movie in ms01.wmv. History
of pore fluid pressure with a different friction coefficient (0.85) from the main results’ (0.6) is shown
as the figure fs03.jpg. The comparison of observed focal mechanism solutions with those expected
from the stress field is shown in the figure fs04.jpg.
1. fs01.jpg (Figure S1): The tectonic stress field in the Basel EGS. The large blue circle, green
diamond, and red triangle denote the best estimates of the maximum, intermediate, and minimum
compressive principal stresses. The azimuths (measured clockwise from the north) and plunges
for 1,  2, and  3 are 142o and 16 o, 322 o and 74 o, and 52 o and 0 o, respectively. The small
circles, diamonds, and triangles show the 67 % confidence regions.
2. fs02.jpg (Figure S2): The depth distribution of absolute stresses.
3. ms01.avi (Movie S3): Evolution of pore fluid pressures in the Basel EGS.
4. fs03.jpg (Figure S4): History of pore fluid pressure with  = 0.85 and cumulative seismic
moment at four representative locations. This is shown in the same way as in Figure 3.
5. fs04.jpg (Figure S5): Relationship between focal mechanism and pore fluid pressure in the 3-D
Mohr diagram. (a) The theoretical focal mechanisms expected from the Wallace–Bott hypothesis
and the stress field in the Basel EGS. The lower hemisphere of focal spheres is shown in the two
Mohr diagrams with respect to the strike,  L , measured from the direction of the  1 axis in the
1   2 plane. The classification of focal mechanisms is the same as that in Fig. 1b. True fault
planes are shown by thick black lines. The grey lines labeled with H1 and H3 show the
Mohr–Coulomb failure lines with a friction coefficient of 0.6 under the hydrostatic pressure Ph
and  3 , and that labeled with H2 is under the intermediate pressure between Ph and  3 . (b)
Focal mechanisms observed in Basel EGS (2–12 December 2006). The method to plot focal
spheres is the same as that in (a).