East Antarctic sources of extensive Lower–Middle Ordovician turbidites in the Lachlan Orogen,southern Tasmanides,eastern Australia     

R. A. Glen  I. C. W. Fitzsimons  W. L. Griffin  A. Saeed 《Australian Journal of Earth Sciences》2017,64(2):143-224

Lower to upper Middle Ordovician quartz-rich turbidites form the bedrock of the Lachlan Orogen in the southern Tasmanides of eastern Australia and occupy a present-day deformed volume of ～2–3 million km³. We have used U–Pb and Hf-isotope analyses of detrital zircons in biostratigraphically constrained turbiditic sandstones from three separate terranes of the Lachlan Orogen to investigate possible source regions and to compare similarities and differences in zircon populations. Comparison with shallow-water Lower Ordovician sandstones deposited on the subsiding margin of the Gondwana craton suggests different source regions, with Grenvillian zircons in shelf sandstones derived from the Musgrave Province in central Australia, and Panafrican sources in shelf sandstones possibly locally derived. All Ordovician turbiditic sandstone samples in the Lachlan Orogen are dominated by ca 490–620 Ma (late Panafrican) and ca 950–1120 Ma (late Grenvillian) zircons that are sourced mainly from East Antarctica. Subtle differences between samples point to different sources. In particular, the age consistency of late Panafrican zircon data from the most inboard of our terranes (Castlemaine Group, Bendigo Terrane) suggests they may have emanated directly from late Grenvillian East Antarctic belts, such as in Dronning Maud Land and subglacial extensions that were reworked in the late Panafrican. Changes in zircon data in the more outboard Hermidale and Albury-Bega terranes are more consistent with derivation from the youngest of four sedimentary sequences of the Ross Orogen of Antarctica (Cambrian–Ordovician upper Byrd Group, Liv Group and correlatives referred to here as sequence 4) and/or from the same mixture of sources that supplied that sequence. These sources include uncommon ca 650 Ma rift volcanics, late Panafrican Ross arc volcanics, now largely eroded, and some <545 Ma Granite Harbour Intrusives, representing the roots of the Ross Orogen continental-margin arc. Unlike farther north, Granite Harbour Intrusives between the Queen Maud and Pensacola mountains of the southern Ross Orogen contain late Grenvillian zircon xenocrysts (derived from underlying relatively juvenile basement), as well as late Panafrican magmatic zircons, and are thus able to supply sequence 4 and the Lachlan Ordovician turbidites with both these populations. Other zircons and detrital muscovites in the Lachlan Ordovician turbidites were derived from relatively juvenile inland Antarctic sources external to the orogen (e.g. Dronning Maud Land, Sør Rondane and a possible extension of the Pinjarra Orogen) either directly or recycled through older sedimentary sequences 2 (Beardmore and Skelton groups) and 3 (e.g. Hannah Ridge Formation) in the Ross Orogen. Shallow-water, forearc basin sequence 4 sediments (or their sources) fed turbidity currents into outboard, deeper-water parts of the forearc basin and led to deposition of the Ordovician turbidites ～2500–3400 km to the north in backarc-basin settings of the Lachlan Orogen.  相似文献   

Applying ultrasonic waves to evaluate the volumetric block proportion of bimrocks     

Saeed Mahdevari  Parviz Maarefvand 《Arabian Journal of Geosciences》2017,10(9):204

As a result of civilization, a lot of underground and surface structures have been constructed on or within complex rocks such as mélange and lahars. There are many engineering problems related to this group of rocks called block-in-matrix rocks (bimrock). In the literature, the more important parameter controlling the geomechanical characteristics of bimrocks is volumetric block proportion (VBP), and there is much uncertainty related to estimated VBP applying sieve or image analysis. So, in this research, to develop a relation between the VBP and ultrasonic wave velocities and find how the fractal dimension and maximum block size affect the P and S wave velocities, 90 large-scale cubic samples were fabricated and the P and S wave velocities were measured in three perpendicular directions inside the physical samples. The fabricated samples were almost isotropic, and there was a direct relation between ultrasonic wave velocities and VBP. The difference between the evaluated VBP and the real one was in the range of ?10 to +15% when the real VBP was equal or less than 60% and up to +25% when the real VBP was equal to 75%. In general, the fractal dimension had an indirect relation with ultrasonic velocities and there was no dominant trend for ultrasonic wave velocity variation versus the maximum block size.  相似文献   

Hazard risk assessment of landslide-prone sub-Himalayan region by employing geospatial modeling approach     

Saleem  Javeria  Ahmad  Sheikh Saeed  Butt  Amna 《Natural Hazards》2020,102(3):1497-1514

Natural Hazards - Ecological processes such as landslide disaster are primarily impacted by both geological and land use activities happening at different spatiotemporal scale. They specifically...  相似文献   

Forensic isotope analysis to refine a hydrologic conceptual model     

Bassett RL  Steinwand A  Jorat S  Petersen C  Jackson R 《Ground water》2008,46(3):372-383

Water resources in the arid southwestern United States are frequently the subject of conflict from competing private and public interests. Legal remedies may remove impasses, but the technical analysis of the problem often determines the future success of legal solutions. In Owens Valley, California, the source of water for the Los Angeles Aqueduct (LAA) is flow diverted from the Owens River and its tributaries and ground water from valley aquifers. Future management of ground water delivered to the LAA needs technical support regarding quantity available, interconnection of shallow and confined aquifers, impact on local springs, and rate of recharge. Ground water flow models and ground water composition are tools already in use, but these have large uncertainty for local interpretations. This study conducted targeted sampling of springs and wells to evaluate the hydrologic system to corroborate conceptual and numerical models. The effort included measurement of intrinsic isotopic composition at key locations in the aquifers. The stable isotopic data of boron (delta(11)B), sulfur (delta(34)S), oxygen (delta(18)O), hydrogen (delta D), and tritium ((3)H) supported by basic chemical data provided rules for characterizing the upper and the lower aquifer system, confirmed the interpretation of ground water flow near faults and flow barriers, and detected hydraulic connections between the LAA and the perennial springs at key locations along the unlined reach of the LAA. This study exemplifies the use of forensic isotopic approaches as independent checks on the consistency of interpretations of conceptual models of a ground water system and the numerical hydrologic simulations.  相似文献   

Spatio-temporal variation of transition probability of bursting events over the ripples at the bed of open channel   总被引：2，自引：1，他引：1  

Saeed Jafari Mianaei  Ali Reza Keshavarzi 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(2):257-264

In this study, the turbulent flow structure over the ripples at the bed of open channel was investigated experimentally. An analysis of bursting process was used to recognize the susceptible regions for sediment entrainment and deposition over the ripples. Two artificial ripples were built according to the ripples, formed by nature. Three different configurations of ripples were used by changing the wavelength. According to analysis of bursting event it was found that at the stoss side of ripples, quadrants (II) and (IV) were dominant to the quadrants (I) and (III) and at the lee side of the ripple it was vice versa. Also the transition probabilities of the bursting events were determined. The results showed that stable organizations of each class of the events had highest transition probabilities whereas cross organizations had lowest transition probabilities. Additionally, an effort was made to find the average inclination angle of the bursting events in quadrants (II) and (IV). The results showed that the mean angle of events in quadrants (II) and (IV) increases at the downstream of stoss side to the crest in each experimental test. Also, at the lee side where the sediment particles were deposited, the inclination angles had the highest values.  相似文献   

Research Note: A unifying framework for the widely used stabilization of potential field inverse problems     

Saeed Vatankhah  Rosemary Anne Renaut  Shuang Liu 《Geophysical Prospecting》2020,68(4):1416-1421

We present a brief review of the widely used and well-known stabilizers in the inversion of potential field data. These include stabilizers that use L₂, L₁ and L₀ norms of the model parameters and the gradients of the model parameters. These stabilizers may all be realized in a common setting using two general forms with different weighting functions. Moreover, we show that this unifying framework encompasses the use of additional stabilizations which are not common for potential field inversion.  相似文献   

Time-history responses on the surface by regularly distributed enormous embedded cavities:Incident SH-waves          下载免费PDF全文

Mehdi Panji  Saeed Mojtabazadeh Hasanlouyi 《地震科学（英文版）》2018,31(3):137-153

The time-history responses of the surface were obtained for a linear elastic half-plane including regularly distributed enormous embedded circular cavities subjected to propagating obliquely incident plane SH-waves. An advanced numerical approach named half-plane time-domain boundary element method(BEM), which only located the meshes around the cavities, was used to create the model. By establishing the modified boundary integral equation(BIE)independently for each cavity and forming the matrices, the final coupled equation was solved step-by-step in the timedomain to obtain the boundary values. The responses were developed for a half-plane with 512 cavities. The amplification patterns were also obtained to illustrate the frequencydomain responses for some cases. According to the results,the presence of enormous cavities affects the scattering and diffraction of the waves arrived to the surface. The introduced method can be recommended for geotechnical/mechanical engineers to model structures in the fields of earthquake engineering and composite materials.  相似文献   

A Geographic Information System‐based site selection experience for the construction of a geomagnetic observatory in Kerman Province,Iran          下载免费PDF全文

Marjan Izadi Yazdanabadi  Azadeh Hojat  Hojjatollah Ranjbar  Saeed Karimi Nasab 《Geophysical Prospecting》2017,65(Z1):237-245

In recent years, the necessity of constructing new geomagnetic observatories in Iran has been discussed from various aspects. Improper site selection of such important data centres can significantly affect the quality of their recorded data. In this research, site selection studies were performed to find the most favourable location to construct a geomagnetic observatory in Kerman Province, southeast of Iran. Having defined 11 site selection criteria for geomagnetic observatories, all the data layers were prepared for the whole province. After detection of seven promising regions using analytical hierarchy process and fuzzy logic method in geographical information system, Technique for Order of Preference by Similarity to Ideal Solution was used for ranking of the suitable areas. The most favourable region was finally detected southwest of Kerman Province, located between the cities of Baft and Sirjan. Detailed land surveys can be focused in this region to decide on the optimum area for the construction of the geomagnetic observatory.  相似文献   

Seismic expression and inferred depositional environments of Plio-Pleistocene sedimentary sequences in the southwestern Caspian Sea   总被引：1，自引：1，他引：0  

Mohsen?Kalani  Saeed?KhodabakhshEmail author  Changiz?Amirbehboudi 《Geo-Marine Letters》2008,28(1):31-41

Eight seismic profiles from the southwestern Caspian Sea were analyzed to establish the sedimentary environments and depositional history in the South Caspian Basin since Pliocene times. Based on reflection terminations, nine sequence boundaries (S1 to S9) were identified and traced across the study area. Consequently, nine depositional sequences (S1–S9) were defined on the basis of seismic facies analysis. The results suggest a transition from non-marine sedimentation in the Lower Pliocene to marine-dominated conditions in the Upper Pliocene (S1–S4). Marine conditions then continued to the present time; however, several sea-level changes led to the formation of sequences S5 to S9. Although no local sea-level curve is available due to a lack of well data, there is good agreement between the seismic stratigraphy of the study area and a published regional sea-level curve.  相似文献   

Normalized residual displacement spectra for post-mainshock assessment of structures subjected to aftershocks     

Amiri  Saeed  Garakaninezhad  Alireza  Bojórquez  Edén 《地震工程与工程振动(英文版)》2021,20(2):403-421

Residual displacement, as a significant measure of structural inelasticity, is effectively used in post-earthquake seismic assessment of structures. This demand can be considered for seismic evaluation of structures under multiple earthquakes. This study introduces a simple and novel index to predict the residual displacement of mainshock-damaged structures against subsequent aftershock. The proposed index is defined as a ratio between residual displacement of damaged structures against aftershock and peak inelastic displacement of intact structures under mainshock. In this study, constantstrength spectra based on the index are developed considering the effects of important structural characteristics and also significant seismic parameters. Moreover, analytical equations are presented to predict the proposed index for bi-linear single-degree-of-freedom(SDOF) systems considering both the effects of positive and negative polarities of aftershock. Furthermore, an equation is suggested to estimate the peak inelastic displacement of intact systems under mainshock, which is required to compute the index.  相似文献