Celia Onishi

ABSTRACT We have conducted field investigations of the Wildcat fault in Strawberry Canyon in the East Bay Hills of Berkeley, California, including a literature survey, aerial-photographic—based geomorphological study, geologic mapping, geophysical surveys, trenching, and borehole drilling and hydraulic testing. A geologic model was constructed, which became the basis of the hydrologic model. We outline the effort of constructing the geohydrologic model of the Strawberry Canyon area. We also created an East Canyon sub-model, which is a part of the Strawberry Canyon area. These models were constructed using Petrasim commercial software, which is a pre- and post- processor for TOUGH2, a non-isothermal multiphase flow and transport simulator. One of our goals is to understand the role of the Wildcat fault in controlling the natural-state groundwater flow. Another goal is that with limited data in numbers and areal extent, we evaluate the viability of modeling a relatively complex geologic area in hopes of to building a model that is valid for a scale larger than the observation. We performed both manual and automated inversion analyses and produced reasonable matches between the observed head data and model predictions. By varying the structure of the Wildcat fault, the base-case representation, which includes a high permeability damage zone and a low permeability fault core, best matches the observed head data. Using the sub-model, we conducted two-phase non-isothermal simulations utilizing the pressure and temperature data from the boreholes. We also used the information obtained from pump tests including permeability anisotropy of the fault plane. After parameter searches, we were able to match the head and temperature profiles along boreholes relatively well. We then used the best matching models to predict the observed rate of head decline during a dry period and found that anisotropic fault zone with 5 % porosity predicts the rate of decline reasonably well. There is a potential that the rate of decline may be useful to estimate the parameters downstream where there are no boreholes for observation/testing.

Brittle deformation in granite can generate a fracture system with different patterns. Detailed fracture analyses at both macroscopic and microscopic scales, together with physical property data from a drill-core, are used to classify the effects of reverse fault deformation in four domains: (1) undeformed granite, (2) fractured granite with cataclastic seams, (3) fractured granite from the damage zone, and (4) foliated cataclasite from the core of the fault. Intact samples from two orthogonal directions, horizontal (H) and vertical (V), from the four domains indicate a developing fracture anisotropy toward the fault, which is highly developed in the damage zone. As a specific illustration of this phenomenon, resin impregnation, using a confocal laser scanning microscope (CLSM) technique is applied to visualize the fracture anisotropy developed in the Toki Granite, Japan. As a result, microcrack networks have been observed to develop in H sections and elongate open cracks in V secti...

The permeability of rocks is sensitive to pore structures. In fault zones where brittle deformation dominates, connectivity of cracks is perhaps the most important factor to control the fluid permeability. The relationship between microstructure, porosity-pore structures and permeability were investigated, using drill core samples from the Toki Granite in Gifu Prefecture, Central Japan. Core samples taken from a borehole penetrating a fault strand of the Tsukiyoshi Fault at the depth of 700 m were used for analysis and measurements. The Toki Granite shows textural variations. For example, away from the fault zone, the granite is fresh, massive biotite granite. Toward the fault the granitic texture is largely destroyed, reflecting deformation due to fault movement, with extensive fracturing and development of calcite veins. The central part of the fault zone constitutes foliated ultra-cataclasites with a fine grained matrix. Microstructural observations indicate that fragmentation of crystals is the cause of grain size reduction in the fault zone and anisotropy in micro-crack development. The effective porosity of bulk samples measured by Helium pycnometer varies from 0.54% for unaltered fresh granite to over 5.4% for foliated cataclasite from the central part of the fault zone. The pore structures of the granite samples were visualized by the Laser Scanning Microscope (LSM). The samples were impregnated with low viscosity fluorescent resin under vacuum condition, and then observed by the LSM. Quasi 3-D images of pore structures were constructed from optical slices (confocal images) of thick sections. Micro-cracks in granites were successfully filled with the fluorescent resin. Micro-cracks were mainly observed at grain boundaries, and the intra and inter granular fractures. Permeability measurements were performed by a High Pressure Temperature (HPT) gas apparatus using the pore oscillation technique. Confining pressure was increased and then decreased in the range of 25- 200 MPa, with pore pressure kept around 20 MPa. Preliminary results indicate relatively high permeability for undeformed biotite granite, about 10-16m2 at the initial confining pressure (Pc=30MPa), and with a gradual decrease to 10-17m2 at the highest Pc(=198MPa). The fractured sample with cataclastic seams has lower permeability (in the order of 10-17 to 10-18m2) possibly due to crack sealing by hydrothermal activities.

Change in physical properties of granite is strongly affected by brittle deformation. Fractures are the main flow paths for the migration of contaminant materials and change in hydraulic properties of rock mass. Anisotropy of pore structure and permeability were studied using drill core of Toki Granite affected by a reverse fault -Tsukiyoshi Fault Zone (TFZ). The effect of deformation due to faulting is primarily observed on the micro-crack development.Based on fracture frequency distributions logged in the borehole, representative samples of variably deformed granite were selected to show the change in deformation and the control of structures on porosity, pore structure and permeability with depth toward the TFZ. Two fault zones were recognized in the borehole by examination of core and detailed structural analysis using BTV data. Movement indicators (mineral lineations) along fault planes and overall fracture orientations are consistent with regional structures. XRD analysis indicates hydrothermal activities along fault zones. Porosity of granite range from 0.54% to over 5.42%. The pore structure was visualized by a method assisted by a Laser Scanning Confocal Microscope where 3D images of pore structure were reconstructed from impregnated coupons. Micro-cracks were mainly observed at grain boundaries, cutting feldspars and biotite crystals in fresh granite and fracture zone. In the fault zone where the deformation is characterized by grain size reduction, the resin is seen to fill the fault matrix in a diffuse pattern. Crack density increases toward the fault zone where the cracks are highly oriented parallel to the TFZ.Permeability measurements were performed by a High Pressure-Temperature gas apparatus. In this method pore oscillation is applied with nitrogen gas as a pore fluid. Confining pressure was increased and then decreased in the range of 10-200MPa.The pore pressure was kept constant at 20MPa during oscillation method for Pc higher than 30MPa.Preliminary results indicate permeability of fresh granite about 10-15m2 at the initial confining pressure is higher than the fractured sample with chlorite veins of 10-18m2.Permeability of gouge in proximity to the Tsukiyoshi Fault core is 10-13m2. Result on permeability from two different directions show a decrease in permeability by a factor of one to two orders of magnitude in direction parallel to the TFZ.

A tectonic mélange of the ancient accretionary prism of the Shimanto Belt, Japan is investigated to understand a plate boundary process, especially of seismogenic zone in subduction zone. We analyzed deformation fabric, magnetic fabrics, deformation mechanisms and their thermal condition by using vitrinite reflectance. The investigated Mugi mélange is located in western Shikoku. In the Mugi mélange, systematic fabrics such

Fault zone hydrology, a key issue for many different geological disciplines, has in recent years been the subject of increasing interdisciplinary effort. However, a comprehensive literature survey reveals that there has been very limited work published on the subject of fault zone hydrology. The majority of the work is based on surface studies and core analyses. Only few borehole based

In our analog study of fault hydrology, we use an interdisciplinary approach to investigate fault geology and its effects on regional hydrology. The study area is along the Wildcat Fault, a right-lateral strike-slip fault that is a splay of the Hayward Fault, which extends along the west side of the Berkeley Hills, California. Geologic mapping suggests that the Wildcat Fault here mainly separates the Miocene Claremont Formation composed of shale and cherts, and the Miocene-Pliocene Orinda Formation/San Pablo Group, composed of conglomerate, sandstone, and siltstone. We excavated several trenches to expose bedrock; we acquired seismic reflection and electrical resistivity data and three vertical boreholes and one inclined borehole cored across the Wildcat Fault. Trenching and coring indicate that the geology is more complex than the surface mapping indicates, especially along the contact between the Claremont Formation and Orinda Formation/San Pablo Group. In trench exposures, we map...

In order to develop hydrologic characterization technology of fault zones, it is desirable to clarify the relationship between the geologic structure and hydrologic properties of fault zones. To this end, we are performing surface-based geologic and trench investigations, geophysical surveys and borehole-based hydrologic investigations along the Wildcat fault in Berkeley,California to investigate the effect of fault zone structure on regional

A series of analytical tests was conducted on a suite of granitic rock samples from the Daya Bay region of southeast China. The objective of these analyses was to determine key rock properties that would affect the suitability of this location for the siting of a neutrino oscillation experiment. This report contains the results of chemical analyses, rock property measurements,

Through an extensive literature survey we find that there is very limited amount of work on fault zone hydrology, particularly in the field using borehole testing. The common elements of a fault include a core, and damage zones. The core usually acts as a barrier to the flow across it, whereas the damage zone controls the flow either parallel to the strike or dip of a fault. In most of cases the damage zone isthe one that is controlling the flow in the fault zone and the surroundings. The permeability of damage zone is in the range of two to three orders of magnitude higher than the protolith. The fault core can have permeability up to seven orders of magnitude lower than the damage zone. The fault types (normal, reverse, and strike-slip) by themselves do not appear to be a clear classifier of the hydrology of fault zones. However, there still remains a possibility that other additional geologic attributes and scaling relationships can be used to predict or bracket the range of hydrologic behavior of fault zones. AMT (Audio frequency Magneto Telluric) and seismic reflection techniques are often used to locate faults. Geochemical signatures and temperature distributions are often used to identify flow domains and/or directions. ALSM (Airborne Laser Swath Mapping) or LIDAR (Light Detection and Ranging) method may prove to be a powerful tool for identifying lineaments in place of the traditional photogrammetry. Nonetheless not much work has been done to characterize the hydrologic properties of faults by directly testing them using pump tests. There are some uncertainties involved in analyzing pressure transients of pump tests: both low permeability and high permeability faults exhibit similar pressure responses. A physically based conceptual and numerical model is presented for simulating fluid and heat flow and solute transport through fractured fault zones using a multiple-continuum medium approach. Data from the Horonobe URL site are analyzed to demonstrate the proposed approach and to examine the flow direction and magnitude on both sides of a suspected fault. We describe a strategy for effective characterization of fault zone hydrology. We recommend conducting a long term pump test followed by a long term buildup test. We do not recommend isolating the borehole into too many intervals. We do recommend ensuring durability and redundancy for long term monitoring.

This report provides information on the geology and selected physical and mechanical properties of surface rocks collected at Diablo Canyon, San Luis Obispo County, California as part of the design and engineering studies towards a future reactor neutrino oscillation experiment. The main objective of this neutrino project is to study the process of neutrino flavor transformation--or neutrino oscillation--by measuring neutrinos produced in the fission reactions of a nuclear power plant. Diablo Canyon was selected as a candidate site because it allows the detectors to be situated underground in a tunnel close to the source of neutrinos (i.e., at a distance of several hundred meters from the nuclear power plant) while having suitable topography for shielding against cosmic rays. The detectors have to be located underground to minimize the cosmic ray-related background noise that can mimic the signal of reactor neutrino interactions in the detector. Three Pliocene-Miocene marine sedimentary units dominate the geology of Diablo Canyon: the Pismo Formation, the Monterey Formation, and the Obispo Formation. The area is tectonically active, located east of the active Hosgri Fault and in the southern limb of the northwest trending Pismo Syncline. Most of the potential tunnel for the neutrino detector lies within the Obispo Formation. Review of previous geologic studies, observations from a field visit, and selected physical and mechanical properties of rock samples collected from the site provided baseline geological information used in developing a preliminary estimate for tunneling construction cost. Gamma-ray spectrometric results indicate low levels of radioactivity for uranium, thorium, and potassium. Grain density, bulk density, and porosity values for these rock samples range from 2.37 to 2.86 g/cc, 1.41 to 2.57 g/cc, and 1.94 to 68.5% respectively. Point load, unconfined compressive strength, and ultrasonic velocity tests were conducted to determine rock mechanical and acoustic properties. The rock strength values range from 23 to 219 MPa and the Poisson's ratio from 0.1 to 0.38. Potential geologic hazards in the Diablo Canyon area were identified and described to provide an overall picture of processes that may affect tunnel construction activities.