Naturally propped fractures caused by quartz cementation preserve oil reservoirs in basement rocks     

Mas'ud Baba  John Parnell  Stephen A. Bowden 《地学学报》2019,31(4):343-347

Much silica precipitation in oil reservoirs occurred in the presence of hydrocarbons, evidenced by the entrapment of oil fluid inclusions in quartz. Also, silica in sedimentary basins is commonly precipitated at oil‐window temperatures. This spatial and temporal relationship between oil and quartz precipitation aids the entry of oil into fractured reservoirs, including fractured basement. Where quartz is precipitated as fracture linings, the fractures are propped open by bridging quartz crystals, creating high fracture porosity and permeability. Evidence from fossil fractured reservoirs shows a large proportion of oil residue is in such propped open fractures.  相似文献   

BSRs and Associated Reflections as an Indicator of Gas Hydrate and Free Gas Accumulation: An Example of Accretionary Prism and Forearc Basin System along the Nankai Trough, off Central Japan   总被引：1，自引：0，他引：1  

Kei Baba  Yasuhiro Yamada 《Resource Geology》2004,54(1):11-24

Abstract. Multi-channel seismic data obtained from the Nankai accretionary prism and forearc basin system has been studied to elucidate the migration and accumulation process of gas to the BGHS and examine the distribution pattern of BSRs and characteristic reflections associated with them.
BSRs are distributed widely in the Nankai accretionary prism and associated forearc basins (33,000 km²) and 90 % of them have migration and recycling origins. The widest distribution of the BSRs can be seen at the prism. A correlation between the BSR distributions and prism size shows that the BSRs tend to be more well-developed in a prism of large size. This suggests that a large prism may produce much amount of gas-bearing fluids that migrate to the BGHS and form the BSRs (tectonic control), hi the forearc basins, the BSRs are identified at topographic highs, anticlines and basin margins (structural control).
The upward migration of gas-bearing fluids is carried out through permeable sand layers and as a result, the distribution of BSRs is confined to alternating beds of sand and mud facies (sedimentary control). However, if there is enough time for upward migration and accumulation of gas to the BGHS, the BSRs can be generated widely in low-permeable mud facies (time control).
Those results imply that structural, tectonic, sedimentary and time controls are primary factors to decide the distribution of BSRs in the Nankai Trough area.  相似文献   

Electrical Structure in Marine Tectonic Settings     

Kiyoshi Baba 《Surveys in Geophysics》2005,26(6):701-731

This review paper presents recent research on electrical conductivity structure in various marine tectonic settings. In at least three areas, marine electromagnetic studies for structural exploration have increasingly progressed: (1) data accumulations, (2) technical advances both for hardware and software, and (3) interpretations based on multidisciplinary approaches. The mid-ocean ridge system is the best-studied tectonic setting. Recent works have revealed evidence of conductive zones of hydrothermal circulation and axial magma chambers in the crust and partial melt zones of the mid-ocean ridge basalt source in the mantle. The role of water or dissolved hydrogen and its redistribution at mid-ocean ridges is emphasized for the conductivity pattern of the oceanic lithosphere and asthenosphere. Regions of mantle upwelling (hotspot or plume) and downwelling (subducting slab) are attracting attention. Evidence of heterogeneity exists not only in the crust and the upper mantle, but also in the mantle transition zone. Electrical conductive zones frequently overlap seismic low-velocity zones, but discrepancies are also apparent. Some studies have compared conductivity models with the results of seismic and other studies to investigate the physical properties or processes. A new laboratory-based conductivity model for matured oceanic lithosphere and asthenosphere is proposed. It takes account of both the water distribution in the mantle as well as the thermal structure. It explains observed conductivity patterns in the depth range of 60–200 km.  相似文献   

High precision slip distribution of the 1944 Tonankai earthquake inferred from tsunami waveforms: Possible slip on a splay fault     

Toshitaka Baba  Phil R. Cummins  Takane Hori  Yoshiyuki Kaneda 《Tectonophysics》2006,426(1-2):119

Inversion of tsunami waveforms is a well-established technique for estimating the slip distributions of subduction zone earthquakes, with some of the most detailed results having been obtained for earthquakes in the Nankai Trough, SW Japan. The present study, although it uses a method and tsunami waveform data set almost identical to previous study, aims to improve on previous work by using a more precise specification of initial conditions for the calculation of tsunami Green's functions. Specifically, we incorporated four improvements in the present study: (1) we used a realistic plate model based only on seismic survey results, and assumed it to be the fault plane of the 1944 Tonankai earthquake; (2) the smallest subfaults consistent with the long wavelength approximation were used in the tsunami inversion analysis; (3) we included the effect of horizontal displacement of the ocean bottom on tsunami generation; and (4) we performed a checkerboard resolution test. As obtained in previous studies, a zone of high slip (> 2.0 m) was resolved off the Shima Peninsula. However, the more precise calculation of tsunami Green's functions has revealed additional detail that was not evident in previous studies, which we demonstrate is resolvable and correlates with the position of known faults in the accretionary prism. While there was little or no slip near the trench axis in the eastern part of the rupture zone, there was up to 1.5 m of slip resolved within 30 km of the trough axis in the western part, along the coast of the Kii Peninsula. This troughward slip zone coincides with the position of a large splay fault mapped in multichannel reflection surveys. Furthermore, it is also clear that the upper edge of the Enshu fault off Shima and Atsumi peninsulas is consistent with the up-dip limit of slip in the eastern part of our model. We tested the possibility that slip occurred on the former splay fault instead of on the plate interface during the 1944 Tonankai earthquake, and find that slip on this splay fault is also consistent with the data, although we cannot distinguish whether slip was dominant on the splay fault or on the plate interface. We further suggest that the position of the Enshu fault may be determined by the subduction of topographic highs, and that such faults may have an important influence on the up-dip rupture limit of the 1944 Tonankai and, potentially, other subduction zone earthquakes.  相似文献   

Chemical composition of primary cosmic rays with energies from 10 to 10 eV     

Y. Shirasaki  F. Kakimoto  S. Ogio  N. Gironda  M. Takeda  T. Kaneko  H. Yoshii  T. Baba  S. Sano  K. Nishi  N. Tajima  Y. Yamada  S. Shimoda  H. Nakatani  E. Gotoh  K. Murakami  Y. Toyoda  Y. Matsubara  Y. Mizumoto  W. Velasquez  A. Velarde  P. Miranda 《Astroparticle Physics》2001,15(4):118-381

The chemical composition of primary cosmic rays with energies from 10¹⁵ to 10^16.5 eV, so called “knee” region, is examined. We have observed the time structures of air Čerenkov light associated with air showers at Mt. Chacaltaya, Bolivia, since 1995. The distribution of a parameter that characterizes the observed time structures is compared with that calculated with a Monte Carlo technique for various chemical compositions. Then the energy dependence of the average logarithmic mass numbers ln A of the primary cosmic rays is determined. The present result at 10^15.3 eV is almost consistent with the result of JACEE (A12) and shows gradual increase in ln A as a function of the primary energy (A24 at 10¹⁶ eV). Form the comparison of the observational results with several theoretical models, we conclude that the supernova explosion of massive stars is a plausible candidate for the origin of cosmic rays around the “knee” region.  相似文献   

New age constraints on counter-clockwise rotation of NE Japan     

Ayumi K. Baba  Takaaki Matsuda  Tetsumaru Itaya  Yutaka Wada  Noriyuki Hori  Masahiko Yokoyama  Nobuaki Eto  Rieko Kamei  Haider Zaman  Tesfaye Kidane  Yo-Ichiro Otofuji 《Geophysical Journal International》2007,171(3):1325-1341

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Near-field tsunami amplification factors in the Kii Peninsula,Japan for Dense Oceanfloor Network for Earthquakes and Tsunamis (DONET)     

Toshitaka Baba  Narumi Takahashi  Yoshiyuki Kaneda 《Marine Geophysical Researches》2014,35(3):319-325

We investigated the correlation between coastal and offshore tsunami heights by using data from the Dense Oceanfloor Network for Earthquakes and Tsunamis (DONET) observational array of ocean-bottom pressure gauges in the Nankai trough off the Kii Peninsula, Japan. For near-field earthquakes, hydrostatic pressure changes may not accurately indicate sea surface fluctuations, because ocean-bottom pressure gauges are simultaneously displaced by crustal deformation due to faulting. To avoid this problem, we focused on the average waveform of the absolute value of the hydrostatic pressure changes recorded at all the DONET stations during a tsunami. We conducted a Monte Carlo tsunami simulation that revealed a clear relationship between the average waveforms of DONET and tsunami heights at the coast. This result indicates the possibility of accurate real-time prediction of tsunamis by use of arrays of ocean-bottom pressure gauges.  相似文献   

The spatial impact of the relocation of a section of the Zaria-Kano road: a study of change and development in rural Zaria     

A.T. Salau  J.M. Baba 《Applied geography (Sevenoaks, England)》1984,4(4):283-292

The exact role of the transport sector in the development process is still a subject of controversy. Most studies have involved a narrow cost-benefit analysis done on the basis of road usage. However, a better understanding of the complex forces engendered by the introduction of roads into an area, or their improvement, can only be found on both macro- and micro-analytical levels.This study examines the effect of road improvement on its immediate locality. It focuses specifically on the short-term impact of road relocation within the rural area in relation to the following questions: what happens when a trunk road is opened through a hitherto isolated rural area? What happens when there is a permanent diversion of traffic on a transport route, especially with reference to human settlements, socioeconomic activities and community welfare?The study reveals that a locational change of transport route immediately created two distinct zones. The first was a zone of decaying or contracting opportunities along the old route, and then a zone of expanding opportunities along the new route. The implication of this is that the benefits of improved transport routes on the immediate locality may not necessarily be beneficial to all residents.  相似文献   

Observations of Tsunami Impact on the Coast of Kerala,India     

N. P. Kurian  T. N. Prakash  M. Baba  N. Nirupama 《Marine Geodesy》2013,36(2):135-145

The tsunami generated by the December 2004 Sumatra-Andaman earthquake had a devastating effect on some parts of Kerala coast, which is a coast located in southwest India. Results of post-tsunami field surveys carried out to understand the changes in coastal morphology and sediment characteristics in the worst affected Kayamkulam region of Kerala coast are documented in this study. Analysis of offshore bathymetric data indicates the shifting of depth contours towards shore, indicating erosion of sediments and deepening of innershelf due to the tsunami. Depth measurement along the backwater (T-S canal) in the hinterland region indicates siltation due to the inundation of the canal.  相似文献   

Coastal flooding due to synoptic scale,meso-scale and remote forcings     

N. P. Kurian  N. Nirupama  M. Baba  K. V. Thomas 《Natural Hazards》2009,48(2):259-273

Coastal flooding occurs due to storm surges generated by tropical and extra-tropical cyclones on the globe. The meteorological forcing fields for the generation of storm surges are the tangential surface wind stress on the ocean surface and the normal atmospheric pressure gradients associated with the weather systems. The large scale forcing from the cyclones is referred to as the synoptic scale and storm surge prediction from synoptic scale forcing is well developed and is reasonably satisfactory around the world. However, coastal flooding also occurs from weather systems, with forcing on a meso-scale and also from remote forcing. It is proposed here that the term “Storm surge” be used to only refer to coastal flooding from synoptic scale forcing and the terminology “Rissaga” be used for coastal flooding from meso-scale forcing. For flooding due to remote forcing, a new term “Kallakkadal” is proposed.  相似文献