Microstructural characterization of natural fractures and faults in the Opalinus Clay: insights from a deep drilling campaign across central northern Switzerland

Swiss Journal of Geosciences

Table 1 Inventory of macroscopic fractures per borehole

	BOZ2-1		BOZ1-1		BAC1-1		STA2-1		STA3-1		BUL1-1		MAR1-1		TRU1-1
OPA Thickness [m]	122.14		121.11		106.57		105.53		108.68		104.15		115.05		111.49
	Number	%	Number	%	Number	%	Number	%	Number	%	Number	%	Number	%	Number	%
J	0	0	0	0	1	1	0	0	0	0	0	0	1	1	0	0
TG	28	14	25	19	42	39	40	51	24	33	1	2	20	12	1	2
MirFP	84	43	62	46	31	29	19	24	11	15	18	40	52	32	45	87
FP	78	40	45	34	32	30	18	23	35	49	24	53	87	53	4	8
FZ	4		1		1		1		2		0		3		2
UF	0	0	1	1	0	0	0	0	0	0	0	0	1	1	0	0
Count	194		134		107		78		72		45		164		52
Count / core m	1.6		1.1		1.0		0.7		0.7		0.4		1.4		0.5
Veins / core m	0.23		0.21		0.39		0.38		0.22		0.01		0.17		0.01
Shear sense
Up	57	68	29	76	17	65	6	100	12	55	8	100	5	7	0	0
Down	24	29	6	16	8	31	0	0	10	45	0	0	63	89	19	95
Strike-slip	3	3	3	8	1	4	0	0	0	0	0	0	3	4	1	5
Counts	84		38		26		6		22		8		71		20

J Joint, TG Tension gash, MirFP mirror-like fault plane, FP fault plane, FZ fault zone, UF unassigned fracture, Up reverse shear sense; Down normal shear sense; Strike slip strike-slip shear sense. Faults of syn-sedimentary origin were excluded from kinematic analysis