Celia Tiemi Onishi

Deformation history of tectonic melange and its relationship to the underplating process and relative plate motion: An example from the deeply buried Shimanto Belt, SW Japan

Map to microscopic-scale structural analysis of the Hanazono Assemblage of the Shimanto Belt in SW Japan, an excellent example of a deeply buried accretionary complex, indicates a detailed process from underthrusting to underplating. The earliest underthursting process is recorded in fabric of melange, which has deformed by shear along the decollement, characterized by thinning strain due to extensional breakage of blocks of sandstone and exotic materials, such as basalt and pelagic sediments of oceanic affinities. The deformation mechanism for melange formation for domain I is plastic flow, concordant with metamorphic grade, which is higher than that of domain II. The deformation mechanism for domain II is predominantly pressure solution partly with grain-scale brittle breakage for the less metamorphosed part of the Hanazono Assemblage. The posterior underplating process recorded is contraction and thickening due to thrust stacking and folding. Locations of the folds developed beneath thrusts are emphasized because they are a line of evidence of thickening. The main deformation mechanism of the second stage is plastic flow for domain I and cataclasis for domain II. The cataclasis in domain II may be a result of change in strain rate and seems to be related to seismicity at the time of underplating. Kinematics deduced from fabric analysis of the earliest deformed melange indicates a good consistency with a relative plate motion between the Eurasian and oceanic plates that is estimated from a hot spot reference plate circuit model by Engebretson et al. [1985], while that of the subsequent thrusting is not. This fact suggests that strain partitioning in association with oblique subduction of oceanic plate was minimum during subduction. Another possibility for strain partitioning is the requirement of coupling between plates that are recorded by the deformation mechanisms.

Feature Detection, Characterization and Confirmation Methodology: Final Report

LBNL-1358E Feature Detection, Characterization and Confirmation Methodology F inal Report Kenzi Karasaki, John Apps, Christine Doughty, Hope Gwatney, Celia Tiemi Onishi, Robert Trautz, and Chin-Fu Tsang Earth Sciences Division March 2007 NUMO-LBNL Collaborative Research Project Report This work was supported by the U.S. Department of Energy under Contract DE-AC02-05CH11231.

Geologic Investigation of a Potential Site for a Next-Generation Reactor Neutrino Oscillation Experiment -- Diablo Canyon, San Luis Obispo County, CA

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 Poissons 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.

Summary of Test Results for Daya Bay Rock Samples

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, and a calculation of the mean atomic weight.

Visualization of rock textures using a laser scanning microscope: fluorescent images

走査型レーザー顕微鏡 (laser scanning microscope, LSM)では, 岩石鉱物の透過および反射像を定量的に解析することができる(澤口・清水, 2002)ほか, レーザー照射で励起される蛍光を分光フィルターを通して検出することにより, 走査型の蛍光顕微鏡として用いることもできる(第1図). ここでは, レーザー顕微鏡 FLUOVIEW (オリンパス光学工業(株))を用いた蛍光観察の例を紹介する. 岩石では堆積物に含まれる有機物に自家蛍光が見られるほか, 火山ガラスや斑晶, 鉱物脈などに含まれる微量の不純物も蛍光中心となる. 蛍光試薬によって生体物質を標識することにより, さらに生体鉱物化作用や続成過程についての情報を得ることができる. また, 蛍光樹脂を岩石に浸透させることにより, 間隙構造を可視化することができる.