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1.
R.N. Hey F. Martinez S. Diniega D.F. Naar J. Francheteau R. Armijo M. Constantin J.P. Cogné J. Girardeau R. Hekinian R. Searle 《Marine Geophysical Researches》2002,23(1):1-12
Several mechanisms have been proposed to account for the rotation of the nearly north-south abyssal hill fabric formed on the East Pacific Rise north of the Easter Microplate to the nearly east-west trends in the northern microplate interior. Proposed mechanisms include rigid microplate rotation, transform fault – parallel shear, and bookshelf faulting during the transfer of lithosphere from the Nazca Plate to the microplate. We used a submersible magnetometer on a NAUTILE dive program to measure the magnetic vector rotation of a pillow basalt and dike spur near Pito Deep, the present location of the tip of the propagating rift system that created the microplate. Our results, although too limited to draw strong conclusions from, suggest clockwise rotations of the seafloor magnetic vectors inconsistent with the transform-parallel shear model, and larger than can be explained solely by rigid microplate rotation. 相似文献
2.
R. Hekinian J. Francheteau R. Armijo J. P. Cogn M. Constantin J. Girardeau R. Hey D. F. Naar R. Searle 《Journal of Volcanology and Geothermal Research》1996,72(3-4)
Submersible investigations along the East Rift segments, the Pito Deep and the Terevaka transform fault of the Easter microplate eastern boundary, and on a thrust-fault area of the Nazca Plate collected a variety of basalts and dolerites. The volcanics consist essentially of depleted (N-MORB), transitional (T-MORB) and enriched (E-MORB) basalts with low (0.01−0.1, < 0.7), intermediate (0.12–0.25, 0.7–1.2) and high (> 0.25, > 1.2–2) K/Ti and(La/Sm)N ratios, respectively. The Fe-Ti-rich ferrobasalt encountered among the N-MORBs are found on the Pito Deep Central volcano, on the Terevaka intra-transform ridge, on the ancient (< 2.5 Ma) Easter microplate (called EMP, comprising the East Rift Inner pseudofaults and Pito Deep west walls) and on thrust-fault crusts. The most enriched (T- and E-MORB) volcanics occur along the East Rift at 25 °50′–27 °S (called 26 °S East Rift) and on the Pito seamount located near the tip of the East Rift at 23 °00′–23 °40′S (called 23 °S East Rift). The diversity in incompatible element ratios of the basalts in relation to their structural setting suggests that the volcanics are derived from a similar heterogenous mantle which underwent variable degrees of partial melting and magma mixing. In addition the Pito seamount volcanics have undergone less crystal fractionation (< 20%) than the lavas from the other Easter microplate structures (up to 35–45%). The tectonic segmentation of the East Rift observed between 23 and 27 °S corresponds to petrological discontinuities related to Mg# variations and mantle melting conditions. The highest Mg# (> 61) are found on topographic highs (2000–2300 m) and lower values (Mg# < 56) at the extremities of the East Rift segments (2500–5600 m depths). The deepest area (5600 m) along the East Rift is located at 23 °S and coincides with a Central volcano constructed on the floor of the Pito Deep. Three major compositional variabilities of the volcanics are observed along the East Rift segments studied: (1) the 26 °S East Rift segment where the volcanics have intermediate Na8 (2.5–2.8%) and Fe8 (8.5–11%) contents; (2) the 23 °S East Rift segment (comprising Pito seamount and Pito Deep Central volcano) which shows the highest (2.9–3.4%) values of Na8 and a low (8–9%) Fe8 content; and (3) the 25 °S (at 24 °50′–26 °10′S) and the 24 °S (at 24 °10′–25 °S) East Rift segments where most of the volcanics have low to intermediate Na8 (2.6–2.0%) and a high range of Fe8 (9–13%) contents. When modeling mantle melting conditions, we observed a relative increase in the extent of partial melting and decreasing melting pressure. These localized trends are in agreement with a 3-D type diapiric upwelling in the sense postulated by Niu and Batiza (1993). Diapiric mantle upwelling and melting localized underneath the 26, 25 and 23 °S (Pito seamount and Central volcano) East Rift segments are responsable for the differences observed in the volcanics. The extent of partial melting varies from 14 to 19% in the lithosphere between 18 and 40 km deep as inferred from the calculated initial (Po=16kbar) and final melting (Pf=7kbar) pressures along the various East Rift segments. The lowest range of partial melting (14–16%) is confined to the volcanics from 23 °S East Rift segment including the Pito seamount and the Central volcano. The Thrust-fault area, and the Terevaka intra-transform show comparable mantle melting regimes to the 25 and 26 °S East Rift segments. The older lithosphere of the EMP interior is believed to have been the site of high partial melting (17–20%) confined to the deeper melting area (29–50 km). This increase in melting with increasing pressure is similar to the conditions encountered underneath the South East Pacific Rise (13–20 °S). 相似文献
3.
Rolando R. Garcia Susan Solomon Raymond G. Roble David W. Rusch 《Planetary and Space Science》1984,32(4):411-423
A two-dimensional numerical model with coupled photochemistry and dynamics has been used to investigate the response of the middle atmosphere (16–116 km) to changes in solar activity over the 11-year solar cycle. Model inputs that vary with solar cycle include solar radiation, cosmic ray and auroral ionization rates and the flux of NOx at the model's upper boundary.In this study, the results of model runs for solar cycle minimum and maximum conditions are compared. In the stratosphere, using currently accepted estimates of changes in solar radiation at wavelengths longer than 180 nm, only small responses in ozone, temperature and zonal winds are obtained. On the other hand, changes at shorter wavelengths, and the effects of particle precipitation, lead to large variations in the abundances of trace species in the thermosphere and upper mesosphere. In particular, very large abundances of NOx are produced above 90 km by auroral particle precipitation. Considerable amounts of NOx are transported subsequently to the stratosphere by the global mean meridional circulation. It is shown that this excess NOx can lead to significant decreases in ozone concentrations at high latitudes and that it may explain observations of nitrate deposition in Antarctic snow. 相似文献
4.
Keisuke ISHIDA Shigeyuki SUZUKI Carla DIMALANTA Graciano YUMUL JR. Karlo QUEA?O Decibel FAUSTINO-ESLAVA Edanjarlo MARQUEZ Noelynna RAMOS Rolando PE?A 《地球学报》2012,33(S1):29-31
The basement of the Philippine Mobile Belt (PMB) is mainly composed of ophiolites that are mostly overlain by Paleogene to Miocene turbidites in central Luzon. To clarify the geological development of the PMB with respect to the initial stage of the arc volcanism (eg. Yumul et al., 2003, 2008; Dimalanta and Yumul, 2003; Suzuki et al., 2011), radiolarian dating was examined in siliceous sediments associated with the ophiolites and turbidites. The samples were collected from sites identified with the Zambales and Montalban ophiolites, basic tuff phyllites in NW Din-galan, and their overlying formations. 相似文献
5.
Conventionally, evaluation of liquefaction potential of loose saturated cohesionless deposits as specified in Japanese design codes employs peak ground acceleration (PGA). However, recent large-scale earthquakes in Japan revealed that liquefaction at some sites did not occur even though large PGAs were recorded at or near these sites. As an alternative approach, an evaluation procedure based on peak ground motion parameters, i.e. incorporating both PGA and the peak ground velocity (PGV), is proposed. By performing parametric studies using one-dimensional seismic response analysis and formulating regression models, seismic-induced shear stresses within the deposit are expressed in terms of peak ground motion parameters at the surface, and these are used to calculate the factor of safety against liquefaction. Application to case histories in Japan indicates that the proposed two-parameter equation can adequately account for the occurrence and non-occurrence of liquefaction at various sites as compared to the conventional PGA-based approach. Moreover, analyses of several strong motion records at various sites show that liquefaction may occur when PGA≥150 gal and PGV≥20 kine, indicating that these values can serve as thresholds in assessing the possible occurrence of liquefaction. 相似文献
6.
Noel Perez Rolando Cardenas Osmel Martin Reinaldo Rojas 《Astrophysics and Space Science》2013,343(1):7-10
We do a preliminary modelling of the photosynthetic rates of phytoplankton at the very beginning of the Paleogene, just after the impact of the Chicxulub asteroid, which decisively contributed to the last known mass extinction of the Phanerozoic eon. We assume the worst possible scenario from the photobiological point of view: an already clear atmosphere with no ozone, as the timescale for soot and dust settling (years) is smaller than that of the full ozone regeneration (decades). Even in these conditions we show that most phytoplankton species would have had reasonable potential for photosynthesis in all the three main optical ocean water types. This modelling could help explain why the recovery of phytoplankton was relatively rapid after the huge environmental stress of that asteroid impact. In a more general scope, it also reminds us of the great resilience of the unicellular biosphere against huge environmental perturbations. 相似文献
7.
Lenin Campozano Daniel Mendoza Giovanny Mosquera Kenneth Palacio-Baus Rolando Célleri Patricio Crespo 《水文研究》2020,34(11):2302-2312
The problem of discharge forecasting using precipitation as input is still very active in Hydrology, and has a plethora of approaches to its solution. But, when the objective is to simulate discharge values without considering the phenomenology behind the processes involved, Artificial Neural Networks, ANN give good results. However, the question of how the black box internally solve this problem remains open. In this research, the classical rainfall-runoff problem is approached considering that the total discharge is a sum of components of the hydrological system, which from the ANN perspective is translated to the sum of three signals related to the fast, middle and slow flow. Thus, the present study has two aims (a) to study the time-frequency representation of discharge by an ANN hydrologic model and (b) to study the capabilities of ANN to additively decompose total river discharge. This study adds knowledge to the open problem of the physical interpretability of black-box models, which remains very limited. The results show that total discharge is adequately simulated in the time frequency domain, although less power spectrum is evident during the rainy seasons in the ANN model, due to fast flow underestimation. The wavelet spectrum of discharge represents well the slow, middle and fast flow components of the system with transit times of 256, 12–64 and 2–12 days, respectively. Interestingly, these transit times are remarkably similar to those of the soil water reservoirs of the studied system, a small headwater catchment in the tropical Andes. This result needs further research because it opens the possibility of determining MMT on a fraction of the cost of isotopic based methods. The cross-power spectrum indicates that the error in the simulated discharge is more related to the misrepresentation of the fast and the middle flow components, despite limitations in the recharge period of the slow flow component. With respect to the representation of individual signals of the slow, middle and fast flows components, the three neurons were uncapable to individually represent such flows. However, the combination of pairs of these signals resemble the dynamics and the spectral content of the aforementioned flows signals. These results show some evidence that signal processing techniques may be used to infer information about the hydrological functioning of a basin. 相似文献
8.
9.
The development and evolution of the persistent counterclockwise circulation in Suo-Nada have been studied in detail using
a three-dimensional numerical model. The realistic circulation has been reproduced from the monthly climatological fields
of salinity, temperature along the open boundary, wind, heat flux and buoyancy input from twenty-two major rivers surrounding
the basin. The seasonal variation of fresh-water discharge from the rivers proved to be the most important forcing mechanism
driving the circulation. The expansion and contraction of coastal low salinity water well corresponded with the development
of counterclockwise circulation from spring to summer and dissipation from autumn to winter. The circulation was found to
be vertically homogenous and quasi-barotropic. However, confined along the coastal zone is an estuarine flow (i.e., oppositely
directed currents in the upper and lower layers) whose horizontal dimension conforms to the period of maximum buoyancy flux
from the rivers. This indicates that the flow pattern in Suo-Nada can be separated into two distinct regions where the relative
dominance of estuarine circulation plays a significant role. Furthermore, the monthly water exchange capacity for autonomous
purification of the basin has been evaluated from the average residence time of conservative material based on the calculated
current field. It is demonstrated that the kinetic energy of the basin is directly responsible in promoting water exchange
in Suo-Nada.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
10.
Rolando S. Balotro Atsuhiko Isobe Manabu Shimizu Atsushi Kaneda Takatoshi Takeuchi Hidetaka Takeoka 《Journal of Oceanography》2002,58(6):759-773
An attempt was made to reproduce the circulation pattern in Suo-Nada, Japan during spring and summer season in order to elucidate
the water exchange mechanism in the basin. Two hydrographic surveys at the end of each season were conducted covering the
entire Suo-Nada area. A three-dimensional hydrodynamic Princeton Ocean Model (POM) was used to compute the current resulting
from the observed density and wind field. During spring, a very pronounced counter clockwise gyre is situated near the opening
of the basin. This is replaced by a clockwise circulation which seemed to occupy the whole domain during summer. Within each
season, however, the vertical distribution of current does not show any remarkable differences, indicating the dominance of
horizontal current and a very weak estuarine flow. These observational and numerical results were used to estimate the remnant
function and the corresponding average residence time of permanently dissolved matter (PDM) and transformable matter (TM).
The results revealed a small difference in the average residence times of materials within each season but a large seasonal
variability between spring and summer. Furthermore, calculations based on climatological density fields have indicated a similar
trend of variation between the seasonal values of average residence times.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献