OS51A-0174
Observations of stress orientation and magnitudes near the Chelungpu fault in TCDP hole-A
Borehole breakout and tensile fractures show the stress direction variations influenced by the Chelungpu fault. The breakout azimuth changes at the depth 1111m at the fault with the direction of maximum horizontal compressive stress (SHMax) changing by 83º. Leak-off test experiments determined the magnitudes of horizontal minimum stresses (Shmin) to be 20 MPa at this depth. The comprehensive suite of geophysical logs were collected in hole-A provided additional parameters to constrain the state of borehole after the Chi-Chi earthquake. Through modeling we attempt to estimate stress magnitudes before the earthquake and stress evolution on the fault during the earthquake. Simulation results show that at the depth of 1111 m, the magnitude of the maximum horizontal stress (SHMax) before and after the earthquake changed from 45 MPa to 20 MPa, which is smaller than the value of Shmin estimated from Leak-off test (LOT) on site. It suggests the exchanges of axes for the maximum and minimum stress directions after the earthquake. The Shmin data over the entire depth range shows a change of the stress regime from transitional reverse faulting to strike-slip faulting. This agrees with the observations of most of the strike-slip focal mechanisms of the aftershocks in the northern portion of the fault after the earthquake.
OS51A-0175
Prediction of magnitude of minimum horizontal stress from extended leak-off test conducted by the riser vessel CHIKYU
By means of introduction of the drilling vessel gCHIKYUh, riser drilling operations using mud fluid will be carried out in NanTroSEIZE Stage 2 for the first time as an oceanic scientific-drilling. For determining drilling operation parameter such as a mud density, a downhole experiment, leak-off test (LOT) or extended leak-off test (XLOT), is going to be implemented next to casing and cementing at each casing shoe during the drilling process. Data of the downhole experiment aimed for operation can also be used for an important scientific application to obtain in-situ stress information which is necessary for various cases of scientific drillings such as seismogenic zone drillings etc. In order to examine feasibility of the application of the LOT or XLOT data, we analyzed an example of XLOT conducted by the riser vessel CHIKYU during its Shimokita shakedown cruise, 2006; and then estimated magnitude of minimum principal stress in horizontal plane, Shmin. Moreover, we will propose the test procedures to possibly improve the quality of stress result from the applications of LOT or XLOT. The XLOT of Shimokita cruise was conducted under following conditions; 1180 m water depth, 525 mbsf (meter below seafloor) depth, 1030 kg/m3 fluid density (seawater) and 80 litter/min injection flow-rate. Estimated magnitude of the Shmin is equal to 18.3 MPa based on the assumption that fracture closure pressure balances with the minimum principal stress perpendicular to the fracture plane. For comparison, the vertical stress magnitude at the depth was estimated from density profile of core samples retrieved from the same borehole; and was equal to 20 MPa approximately. These two values can be considered to be not disagreement. Therefore, we can say that the XLOT data is valuable and practical for estimating the magnitude of minimum horizontal stress. From the viewpoint of determining stress magnitude, the XLOT is more essential rather than the LOT because it might be hardly to obtain reliable Shmin magnitude only by leak-off pressure which is exclusive stress-related parameter obtained from the latter. In addition, implementation of the LOT/XLOT multi-cycles (3 cycles) is preferable if possible. The first cycle with a lower maximum injection pressure is for knowing permeable property of the formation and for examining whether there is pre-existing fracture(s). The second cycle is a normal XLOT; and the third one is the repeat of the second one for confirm the pressure values obtained from the XLOTs.
OS51A-0176
The CoreWall Project: An Update for 2007
The CoreWall Suite is a NSF-supported collaborative development for a real-time core description (Corelyzer), stratigraphic correlation (Correlater), and data visualization (CoreNavigator) software to be used by the marine, terrestrial and Antarctic science communities. The overall goal of the Corewall software development is to bring portable cross-platform tools to the broader drilling and coring communities to expand and enhance data visualization and enhance collaborative integration of multiple datasets. The CoreWall Project is now in its second year and significant progress has been made on all 3 software components. Corelyzer has undergone 2 field deployments and testing by ANDRILL program in 2006 (and again in Fall 2007) and by ICDP's SAFOD project (summer 2007). In addition, Corewall group and ICDP are working together so that the core description (DIS) system can expose DIS core data directly into Corelyzer seamlessly and be available to future ICDP and IODP-Mission Specific Platform expeditions. Educators have also taken note of the software's ease of use and strong visualization capabilities to begin exploring curriculum projects with Corelyzer software. To ensure that the software development is integrated with other community IT activities the development of the U.S. IODP-Phase 2 Scientific Ocean Drilling Vessel (SODV), a Steering Committee was constituted. It is composed of key U.S. IODP and related database (e.g., CHRONOS, SedDB) developers and users as well as representatives of other core-based enterprises (e.g., ANDRILL, ICDP, LacCore). Corelyzer (CoreWall's main visual core description tool) software displays digital core images from one or more cores along with discrete data streams (eg. physical properties, downhole logs) and nested images (eg. thin sections, fossils) to provide a robust approach to the description of sediment cores. Corelyzer's digital image handling allows the cores to be viewed from micron to km scale determined by the image resolution along a sliding plane, effectively making it a "digital microscope". Detailed features such as lithologic variation, macroscopic grain size variation, bioturbation intensity, chemical composition and micropaleontology are easier to interpret and annotate. Significant new capabilities have been added to allow for importing multiple images and data types, sharing/exporting Corelyzer "work sessions" for multiple users, enhanced annotations, as well as support for other activities like examining clasts, and sample requests. The new Correlator software, the updated version of Splicer/Sagan software used by ODP for over 10 years, has been ported into a single new analysis tool that will work across multiple platforms and interact seamlessly with both JANUS (ODP's relational database), CHRONOS, PetDB, SedDB, dbSEABED and other databases. This functionality will result in a CoreWall Suite module that can be used and distributed anywhere for stratigraphic and age correlation tasks. CoreNavigator, a spatial data discovery tool, has taken on a virtual Globe interface that allows users to enter Corelyzer from a geographic-visual standpoint. http://www.corewall.org/
OS51A-0177
AURORA BOREALIS - Icebreaker, Drilling Platform and Multi-Purpose Research Vessel
In spite of the critical role of the Arctic Ocean in climate evolution, it is the only sub-basin of the world's oceans that has essentially not been sampled by the drill ships of the Deep-Sea Drilling Project (DSDP) or the Ocean Drilling Program (ODP), and its long-term environmental history and tectonic structure is therefore poorly known. Exceptions are the ODP Leg 151 and the more recent very successful ACEX-expedition of the Integrated Ocean Drilling Program (IODP). This lack of data represents one of the largest gaps of information in modern Earth Science. Therefore, the new research icebreaker AURORA BOREALIS will be equipped with drilling facilities to fulfil the needs of the IODP for a -Mission-Specific Platform- to drill in deep, permanently ice-covered ocean basins. This icebreaker must be also powerful enough to maintain station against the drifting sea-ice cover and will have to be equipped with a dynamic positioning system. This new icebreaker would be conceived as an optimized science platform from the keel up and will allow conducting long, international and interdisciplinary expeditions into the central Arctic Ocean during all seasons of the year. In a long-term perspective the AURORA BOREALIS will also be used to address Antarctic research targets, both in its mode as a regular research vessel as well as a polar drill ship. The construction of AURORA BOREALIS requires several new technical implementations, such as advanced dynamic positioning and deep-sea drilling under a closed sea-ice cover and two moon pools (7 x 7 m), and will provide an extended technical potential and knowledge for marine technology. The scientific and technical details will be presented. http://www.eri-aurora-borealis.eu
OS51A-0178
Determination of Volcanostratigraphy of ODP/IODP Hole 1256D: Qualitative and Quantitative Core-Log Integration
The objective of this study is to use electrofacies analysis to construct a less biased volcanostratigraphy of Ocean Drilling Program (ODP)/Integrated Ocean Drilling Project (IODP) Hole 1256D, the first complete penetration of upper oceanic crust. An accurate knowledge of the volcanostratigraphy is vital to understand processes of crustal construction, submarine magmatism, and to estimate chemical exchange with seawater. However, this is often not achieved due to very low core recovery rate in most basement holes. Detailed electrofacies analyses of Formation MicroScanner (FMS) images together with other wire line logs made it possible to investigate lithology types in volcanic and plutonic sections in ODP/IODP Hole 1256D where core recovery rates averaged 36 % and 16%, respectively. The electrofacies analyses in this study overcome previous issues, such as distinction of pillows and different degrees of brreciation, with more detailed lithologic classifications. Relocating recovered core pieces to in situ intervals provides verification of the classifications. We propose ten lithologic types for the new, qualitative volcanostraitgraphy model of Hole 1256D. Three major lithology types in the volcanic section are Massive Flows (22%), Physically Altered Flows (23 %), and Fragmented Intervals (13 %). These flows characterize fast-spreading oceanic crust formation. Subordinate intervals are classified as Possible Pillows (1.36 %), which are localized within a 100 m interval. Electrofacies analyses indicate that the boundary between the extrusive and intrusive (the lower boundary of the Transition Zone) is located at 1064 mbsf. Subvertical contacts in dikes are typically observed every 1 ~ 2 m with breciated regions around the contacts. This volcanostratigraphy model represents that the first, intact vertical section through fast-spreading oceanic crusts. Together with the observation about surface lava morphology at the other East Pacific Rise site, the volcanostratigraphy in this study documents on- and off-axis lava deposition. Additionally, we carried out artificial neural network analyses of the lithologic types using multiple parameters from the logging data to evaluate a less subjective, quantitatively determined volcanostratigraphy. This quantitative volcanostratigraphy agrees well with the qualitative lithologic subdivisions below the lower part of Sheet and Massive flows (~ 950 mbsf), whereas it primarily depicts gradual changes in porosity from one formation to the other in the upper part of the hole instead of differentiating lithologic types as in the qualitative model.