Fractures from a 500 m deep hole in the Red River fault zone were analyzed using an ultrasonic borehole televiewer. Four hundred and eighty individual fractures were identified between 19 m and 465 m depth. Fracture frequency had no apparent relation to the major stratigraphic units and did not change systematically with depth. Fracture orientation, however, did change with stratigraphic position.

The DOSECC Cajon Pass well is located 4 km NE of the San Andreas fault in a region that includes a diversity of secondary structures. Active faults close to the well are subparallel to the right‐lateral San Andreas fault but exhibit left‐lateral and normal slip. The stress orientation measured in the well is not consistent with right‐lateral slip on the San Andreas fault or the stresses inferred from focal mechanisms of earthquakes within 10 km of the fault, but may drive the E‐striking, slightly normal, left‐lateral Cleghorn fault, the closest active fault to the well. If the in‐situ stress is everywhere consistent with the highly variable styles of active secondary faulting like the Cleghorn, the orientation of stresses along the San Andreas fault may be quite variable.

The Yongping well was drilled for earthquake research in a seismically active area of northwestern Yunnan Province.Major active faults in the area include NW-trending normal and rightlateral faults and NE-trendincf normal and left lateral faults.Analysis of the horizontal slip component on the major faults indicates that the area is undergoing WNW extension and that the maximum horizontal compressive stress is oriented NNE.This is in good agreement with recent geodetic measurements.The well was drilled to a depth of 500 m in an alkali syenite intrusive.Two hundred fifty-three fractures were identified on borehole televiewer logs.Fracture frequency does not show a systematic trend with depth.Fracture orientations are similar to those found in the Xiaguan hole, although there is a larger degree of scatter.Northwest-striking fractures are roughly parallel to the major NW-trending faults and NE-striking fractures are roughly parallel to the NE-trending faults.

This report describes the testing and calibration of the electronic pressure gauges and transducers used in the hydraulic fracturing experiment at Cajon Pass, California.Four electronic gauges were connected in parallel to a pressure manifold and tested in the range from atmospheric pressure to 10,000 psi.Two of the gauges had quartz pressure transducers with quartz temperature transducers for temperature compensation.They were certified by Terratek Systems as being traceable to The National Bureau of Standards (NBS).The other two gauges consisted of bonded semiconductor strain gauge transducers.After adjusting the readings for barometric pressure, the two quartz gauges agreed with each other to within 6.4 psi in 10,000 which was within the manufacturer's specifications.One of these gauges was used as a standard to calibrate the two strain gauge transducers.The results of these calibrations are presented along with recommendations for interpretation of pressure data, a description of the operating principle, and suggestions for future calibration procedures.

An array of five wells was drilled in Mesozoic granitic rock for hydrological and geophisical investigations at Hi Vista, California.A 592 m-deep well is located in the center of the array and four 183 m-deep wells were drilled 14 m from it in each of the cardinal directions.Two hundred seventy-seven fractures were seen in televiewer logs of the deep well and three significant fracture sets were identified; a north-striking high-angle set, a northeast-striking high-angle set, and a low-angle set that dips to the west-southwest.Each of the shallow wells contained some fractures within these sets; however the distributions of fracture orientations varied from well to well.These different fracture orientations may help to explain why water levels between wells vary by as much as 50 m.When these fracture distributions are compared with those from three other deep holes in crystalline rock at Black Butte, Crystallaire, and Cajon Pass, a regional trend can be identified.Each of the wells has significant clustering associated with it.Two of the clusters identified at Hi Vista are well defined in more than one deep hole.Fracture frequency at Hi Vista increases with depth; that at Cajon Pass decreases with depth; and the fracture frequencies at Black Butte and Crystallaire show no strong systematic trend with depth.

Fractures from a 500 m-deep hole in the Red River fault zone were analyzed using an ultrasonic borehole televiewer.Four hundred eighty individual fractures were identified between 19 m and 465 m depth.Fracture frequency had no apparent relation to the major stratigraphic units and did not change systematically with depth.Fracture orientation, however, did change with stratigraphic position.The borehole intersected 14 m of Cenozoic deposits, 363 m of lower Ordovician clastic sediments, and 106 m of older ultramafic intrusions.The clastic sequence was encountered again at a depth of 484 m, suggesting a large fault displacement.Fractures in the top 162 m of the sedimentary section appear randomly distributed.Below that depth, they are steeply dipping with northerly and northwesterly strikes, parallel to the major active faults in the region.Fractures in the ultramafic section strike roughly eastwest and are steeply dipping.These orientations are confined to the ultramafic section and are parallel to an older, inactive regional fault set.

Four borehole televiewer logs were run in the Cajon Pass well, covering the test interval from 6250 ft to 6935 ft (1905 to 2114 m).The best image resolution was in the interval from 6711 to 6935 ft (2046 to 2114 m) where the drill bit size was 6-1/2 inches (16.5 cm).Above that section, the bit size was 8-1/2 inches (21.6 cm), and the tool was poorly centralized, resulting in lower resolution.Depth uncertainties were checked and adjusted using the drillers depths for the bottom of the casing at 6000 ft (1829 m), the hole size change at 6711 ft (2046 m), and fractures that correlated with those on the core at 6748 ft and 6515 ft (2057 and 1986 m).Few natural fractures were visible on the televiewer logs and most of them had low to moderate dips.Most fractures on the core were closed or filled, causing them to be more difficult to detect on the televiewer logs.The filling material was chlorite and a white fibrose zeolite (?).One fracture offset a gneissic layer 25 mm in a reverse sense.Twenty-one borehole breakouts were logged for a total of 127 ft (39 m).The average orientation of the breakouts was NSW and the standard deviation was 11 degrees.Hydraulic fractures produced during in-situ stress measurements are visible on the logs and confirm that the maximum horizontal compressive stress is perpendicular to the breakout direction.This maximum stress is parallel to the average trend of the Cleghorn fault and is consistent with a normal component of movement on it.This direction however, is rotated 35 degrees clockwise from that reported in the section from 6000 to 6250 ft (1829 to 1905 m).Further drilling and logging is needed to determine whether this direction continues with depth or is just a localized phenomenon.

Hydraulic fracturing stress measurements were performed in a 500 m-deep well at Yongping in western Yunnan, a region of high seismicity and active normal and strike-slip faulting.The well was drilled in an alkali syenite intrusion.Five methods were used to determine the instantaneous shut-in pressure.These were:(1) the inflection point method (IP), (2) the dP/dT vs Pressure method, (3) a nonlinear regression method for isolating the negative exponential part of the decay curve (NLR), ( 4) minimal flowrate pumping pressure (LF), and (5) flow-rate vs pressure (FR).These methods were compared and upper and lower bounds were placed on the value of Shmin.The criterion for chosing or rejecting a method was its internal consitency and its consistency compared to other methods.The most successful methods was the inflection point method, which is the most subjective and the nonlinear regression method which is relatively objective.Rubber impressions of the test intervals were taken after the tests.These provided evidence that hydraulic fractures had been created, although clear breakdown pressures were not always seen during the tests.Because of poorly controlled pumping rates, fracture reopening pressures were hard to pick accurately and are presented as ranges of possible values.These ranges yielded uncertainties for the value of the maximum horizontal stress that varied from 7% up to 40%.The vertical stress is intermediate in value between the maximum and minimum horizontal stress, indicating a strike-slip stress regime.Orientations of hydraulic fractures are consistent with a maximum horizontal stress of direction of N20-40E.

Ten hydraulic fracturing stress measurements were performed in an 800 m-deep well at Jianchuan in western Yunnan, China.The minimum horizontal principal stress shows a generally linear increase with depth and the gradient is not as high as that of the theoretical vertical stress calculated from the overburden.Above 450 m most of the Shmin values are greater than or equal to Sv. Below 450 m most of them are less than or equal to Sv, indicating a transition between a thrust and strike-slip stress regime.Assuming a frictional coefficient of between 0.6 and 1.0, the rocks do not appear to be close to failure in either a thrust-faulting or strike-slip mode.Borehole breakouts were encountered from about 200 m to the bottom of the hole.Their orientations are somewhat scattered at shallow depths and become better defined below 600 m.The average SHmax direction from the breakouts is N15E, which is consistent with the horizontal slip component on major faults in the region.The orientations of six hydraulically induced fractures were determined from impression packers and they are roughly consistent with the breakout directions.The dispersion in breakout and hydraulic fracture orientation is thought to be related to local conditions, such as gravitational loading due to topography.

Yucca Mountain, located at the southwest corner of the Nevada Test Site in southern Nevada, is being investigated as a potential site for the storage of high-level radioactive waste. Sequences of ash-flow tuff like those at Yucca Mountain potentially could provide multiple geologic barriers against the release of nuclear waste, assuming that the geologic and hydrogeologic setting of the site are favorable. This report describes the geology of the Yucca Mountain site and presents preliminary conclusions on the basis of work in progress. Chapters are devoted to: geomorphology; stratigraphy; tectonic and volcanic framework of the candidate area; structural geology of the site and the site vicinity; seismicity of the candidate area and site; long-term regional stability with respect to tectonic and geological processes; and subsurface drilling and mining.