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1.
3D P-wave Velocity Structure and Active Tectonics in the Xinfengjiang Area of Guangdong 总被引:2,自引:0,他引:2
In this paper,we determined an earthquake sequence location in the Xingfengjiang area from June,2007 to July,2014 and the 3 D P-wave velocity structure by a simultaneous inversion method. On that basis,we studied the occurrence features of active tectonics and the earthquake source mechanism. The results show that the reservoir fracture system has a tendency to increase with gradual depth from southeast to northwest,consistent with gravitational field research results. There are 4 high velocity zones( HVZ) under the depth of the 7 km-12 km crust between the Xinfengjiang Reservoir dam and Xichang District,Dongyuan. The max velocity of the biggest HVZ which is under Xichang is 6. 3 km/s. Under the reservoir dam there is a strong tectonic deformation zone,as the center exit Renzishi fault( F_2),Nanshan-Aotou faults( F_4),Heyuan fault( F_1) and Shijiao-Xingang-Baitian fault( F_5),7 earthquakes with M_L≥ 5. 0( including M 6. 1 in March,1962) occurred at the high gradient zone of the HVZ Ⅲ and HVZ Ⅳ edge which has been under the reservoir dam since 1960, with relativity energy releasing more thoroughly. Moderate seismic activity occurred at the HVZ Ⅰ edge which has been under Xichang since 2012,and is a danger zone for M5. 0 earthquakes in the future. 相似文献
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The latent impact of the Ghab pull-apart basin tectonic setting and associated deformations resulting from active tectonics on the Qastoon Dam in northern Ghab in Syria have been evaluated. This was achieved by applying an appropriate methodology essentially based on morphotectonic mapping and integrated geophysical surveys consisting of electrical resistivity profiling, vertical electrical sounding and self-potential. The integrated interpretation of the acquired morphotectonic and geophysical data allowed the detection of subsurface deformed structures, either underlying the Qastoon Dam lake floor, or close to it. It is believed that these active structures were developed through the ongoing active tectonic processes occurring in the Northern Arabian plate. The tectonic survey proved that the N66.5°E striking Wadi Al Mashta fault, extending beneath the Qastoon Dam lake floor, is one of the youngest active structures, and that the intersection of the fault with the Qastoon Dam prism is a water-leaking point. Dam supporting measures, continuous monitoring and precautious disaster management are therefore recommended to be urgently adopted and practiced. 相似文献
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利用近震层析成像方法和2003年新疆巴楚-伽师MS6.8地震走时资料反演得到了震区地下速度图像。结果表明:P波速度在地壳内5km以上表现出了较强的横向非均匀性,反映该区地表的沉积盖层介质特征;在5~22km深度内以NWW和NNE向共轭相交的高速异常带为主,周围速度相对较低。结合构造背景和震源机制解,认为这一区处于NW-SE向的右行走滑和NNE-SSW向的挤压应力双力偶作用下,使得发生的地震有一定的相似性。而NWW和NNE向非均匀性条带为应变能的积累和释放提供了基础,是这次地震发生的一个重要条件。结合宏观调查和石油资料,推断这次地震发生在塔里木盆地西部的一条NWW走向、北倾的巴什托普隐伏断裂上。 相似文献
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The Southern Granulite Terrain of India, formed through an ancient continental collision and uplift of the earth’s surface,
was accompanied by thickening of the crust. Once the active tectonism ceased, the buoyancy of these deep crustal roots must
have supported the Nilgiri and Palani-Cardamom hills. Here, the gravity field has been utilized to provide new constraints
on how the force of buoyancy maintains the state of isostasy in the Southern Granulite Terrain. Isostatic calculations show
that the seismically derived crustal thickness of 43–44 km in the Southern Granulite Terrain is on average 7–8 km more than
that required to isostatically balance the present-day topography. This difference cannot be solely explained applying a constant
shift in the mean sea level crustal thickness of 32 km. The isostatic analysis thus indicates that the current topography
of the Southern Granulite Terrain is overcompensated, and about 1.0 km of the topographic load must have been eroded from
this region without any isostatic readjustment. The observed gravity anomaly, an order of magnitude lower than that expected
(−125 mGal), however, shows that there is no such overcompensation. Thermal perturbations up to Pan-African, present-day high
mantle heat flow and low Te together negate the possible resistance of the lithosphere to rebound in response to erosional
unloading. To isostatically compensate the crustal root, compatible to seismic Moho, a band of high density (2,930 kg m−3) in the lower crust and low density (3,210 kg m−3) in the lithospheric mantle below the Southern Granulite Terrain is needed. A relatively denser crust due to two distinct
episodes of metamorphic phase transitions at 2.5 Ga and 550 Ma and highly mobilized upper mantle during Pan-African thermal
perturbation reduced significantly the root buoyancy that kept the crust pulled downward in response to the eroded topography. 相似文献
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本文首先论述了板块学说提出的过程和存在的一些不足与疑问,特别是该学说将Holmes(1948)的地幔热对流说作为驱使岩石圈板块运动的动力机制.而后又以青藏高原及邻区为例,根据区域地质、蛇绿岩和地质构造研究的成果,特别是地震测深研究的成果,详细地论证了本区不存在有大洋中脊扩张成为大洋盆地的新大洋和大洋板块简单的B型俯冲模式,但存在有海底扩张的陆间海和海洋地壳板片(蛇绿岩构造岩片)的仰冲以及大陆岩石圈板片复杂的A型俯冲新模式.新模式不是以地幔对流运动,而是以扩张分离A型俯冲的大陆岩石圈板片与软流圈之间的水平剪切相对运动机制作为它的躯动力. 相似文献
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—?We introduce a conceptual model for the in-plane physics of an earthquake fault. The model employs cellular automaton techniques to simulate tectonic loading, earthquake rupture, and strain redistribution. The impact of a hypothetical crustal elastodynamic Green's function is approximated by a long-range strain redistribution law with a r ?p dependance. We investigate the influence of the effective elastodynamic interaction range upon the dynamical behaviour of the model by conducting experiments with different values of the exponent (p). The results indicate that this model has two distinct, stable modes of behaviour. The first mode produces a characteristic earthquake distribution with moderate to large events preceeded by an interval of time in which the rate of energy release accelerates. A correlation function analysis reveals that accelerating sequences are associated with a systematic, global evolution of strain energy correlations within the system. The second stable mode produces Gutenberg-Richter statistics, with near-linear energy release and no significant global correlation evolution. A model with effectively short-range interactions preferentially displays Gutenberg-Richter behaviour. However, models with long-range interactions appear to switch between the characteristic and GR modes. As the range of elastodynamic interactions is increased, characteristic behaviour begins to dominate GR behaviour. These models demonstrate that evolution of strain energy correlations may occur within systems with a fixed elastodynamic interaction range. Supposing that similar mode-switching dynamical behaviour occurs within earthquake faults then intermediate-term forecasting of large earthquakes may be feasible for some earthquakes but not for others, in alignment with certain empirical seismological observations. Further numerical investigation of dynamical models of this type may lead to advances in earthquake forecasting research and theoretical seismology. 相似文献
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Integrated Analysis on Gravity and Magnetic Fields of the Hailar Basin, NE China: Implications for Basement Structure and Deep Tectonics 总被引:2,自引:0,他引:2
Bin Sun Liangshu Wang Ping Dong YongJing Wu Changbo Li Bo Hu Chong Wang 《Pure and Applied Geophysics》2012,169(11):2011-2029
The Hailar Basin is one of the typical basins among the NE China Basin Groups, which is situated in the east of East Asia Orogene between the Siberia Plate and the North China Plate. Based on the detailed analysis of magnetic, gravity, petrophysical, geothermal and seismological data, we separate the Gravity and Magnetic Anomalies (GMA) into four orders using Wavelet Multi-scale Decomposition (WMD). The apparent depths of causative sources were then assessed by Power Spectrum Analysis (PSA) of each order. Low-order wavelet detail anomalies were used to study the basin’s basement structure such as major faults, the basement lithology, uplifts and depressions. High-order ones were used for the inversion of Moho and Curie discontinuities using the Parker method. The results show that the Moho uplifting area of the Hailar Basin is located at the NE part of the basin, the Curie uplifting area is at the NW part, and neither of them is consistent with the basin’s sedimentary center. This indicates that the Hailar Basin may differ in basin building pattern from other middle and eastern basins of the basin groups, and the Hailar Basin might be of a passive type. When the Pacific Plate was subducting to NE China, the frontier of the plate lying on the mantle transition zone didn’t pass through the Great Khingan Mountains region, so there is not an obvious magma upwelling or lithospheric extension in the Hailar Basin area. Finally, based on the seismological data and results of WMD, a probable 2D crust model is derived from an across-basin profile using the 2D forward modeling of the Bouguer gravity anomaly. The results agree with those from seismic inversion, suggesting WMD is suitable for identifying major crustal density interfaces. 相似文献
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四川较场弧形构造与1933年叠溪地震发震构造的再讨论 总被引:5,自引:0,他引:5
较场弧形构造是四川众多弧形构造带之一。本文对该弧形构造的特征及其西冀发育的松平沟断裂的新活动性作了进一步论证,确认松平沟断裂属全新世活动断裂。该弧形构造西翼弧顶部位1933年曾发生过叠溪7.5级地城,丧人对该次地震的发震构造众说纷纭。作者通过近年来在现场的多次考察,并对该次地震的等烈度线形态,地表震害展布特征,建筑物沿松平沟断裂的左旋位错,震后持表发育的西北向地震地裂缝等现象的进一步研究认为,1933年叠溪7.5级地震的发展震构造仍为较场弧形构造西翼的松平沟断裂。 相似文献
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New insights into the spatial variability of the surface water carbon dioxide in varying sea ice conditions in the Arctic Ocean 总被引:1,自引:0,他引:1
In the summer of 2005, continuous surface water measurements of fugacity of CO2 (fCO2sw), salinity and temperature were performed onboard the IB Oden along the Northwest Passage from Cape Farwell (South Greenland) to the Chukchi Sea. The aim was to investigate the importance of sea ice and river runoff on the spatial variability of fCO2 and the sea–air CO2 fluxes in the Arctic Ocean. Additional data was obtained from measurements of total alkalinity (AT) by discrete surface water and water column sampling in the Canadian Arctic Archipelago (CAA), on the Mackenzie shelf, and in the Bering Strait. The linear relationship between AT and salinity was used to evaluate and calculate the relative fractions of sea ice melt water and river runoff along the cruise track. High-frequency fCO2sw data showed rapid changes, due to variable sea ice conditions, freshwater addition, physical upwelling and biological processes. The fCO2sw varied between 102 and 678 μatm. Under the sea ice in the CAA and the northern Chukchi Sea, fCO2sw were largely CO2 undersaturated of approximately 100 μatm lower than the atmospheric level. This suggested CO2 uptake by biological production and limited sea–air CO2 gas exchange due to the ice cover. In open areas, such as the relatively fresh water of the Mackenzie shelf and the Bering Strait, the fCO2sw values were close to the atmospheric CO2 level. Upwelling of saline and relatively warm water at the Cape Bathurst caused a dramatic fCO2sw increase of about 100 μatm relative to the values in the CAA. At the southern part of the Chukchi Peninsula we found the highest fCO2sw values and the water was CO2 supersaturated, likely due to upwelling. In the study area, the calculated sea–air CO2 flux varied between an oceanic CO2 sink of 140 mmol m−2 d−1 and an oceanic source of 18 mmol m−2 d−1. However, in the CAA and the northern Chukchi Sea, the sea ice cover prevented gas exchange, and the CO2 fluxes were probably negligible at this time of the year. Assuming that the water was exposed to the atmosphere by total melting and gas exchange would be the only process, the CO2 undersaturated water in the ice-covered areas will not have the time to reach the atmospheric CO2 value, before the formation of new sea ice. This study highlights the value of using high-frequency measurements to gain increased insight into the variable and complex conditions, encountered on the shelves in the Arctic Ocean. 相似文献
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The ultimate goal of reservoir simulation in reservoir surveillance technology is to estimate long-term production forecasting and to plan development and management of petroleum fields. However, maintaining reliable reservoir models which honour available static and dynamic data, involve inherent risks due to the uncertainties in space and time of the distribution of hydrocarbons inside reservoirs. Recent applications have shown that these uncertainties can be reduced by quantitative integration of seismic data into the reservoir modelling workflows to identify which areas and reservoir attributes of the model should be updated. This work aims using seismic data to reduce ambiguity in calibrating reservoir flow simulation model with an uncertain petro-elastic model, proposing a circular workflow of inverted seismic impedance (3D and 4D) and engineering studies, with emphasis on the interface between static and dynamic models. The main contribution is to develop an updating procedure for adjusting reservoir simulation response before using it in the production forecasting and enhance the interpretive capability of reservoir properties. Accordingly, the workflow evaluates consistency of reservoir simulation model and inverted seismic impedance, assisted by production history data, to close the loop between reservoir engineering and seismic domains. The methodology is evaluated in a complex, faulted, sandstone reservoir, the Norne benchmark field, where a significant reservoir behaviour understanding (about the static and dynamic reservoir properties) is obtained towards the quantitative integration of seismic impedance data. This leads to diagnosis of the reservoir flow simulation reliability and generation of an updated simulation model consistent with observed seismic and well production history data, as well as a calibrated petro-elastic model. Furthermore, as Norne Field is a benchmark case, this study can be considered to enrich the discussions over deterministic or probabilistic history matching studies. 相似文献
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The entrainment of bottom deposits (silt and clay) into newly formed ice was investigated in the Amderma/Vaygach flaw lead in the southwestern Kara Sea, Siberian Arctic. Fine-grained bottom deposits and sea ice sediments (SIS) were analyzed by granulometry, scanning electron microscopy and X-ray diffractometry. On average, SIS contain by a factor of four times more silt than the shelf deposits (66.7% vs. 16.3%), and the SIS clay percentage is more than three-fold of the bottom value (31.2% vs. 9.1%). Sand-sized particles are significantly less abundant in SIS compared to bottom sediment (2.1% vs. 74.6%). The preferred entrainment of silt into ice is underpinned by the enhanced silt-to-clay-ratio in SIS compared to bottom deposits. Though silt is preferably entrained into SIS, no evidence was found for preferential ice-entrainment of any silt sub-fraction (coarse, medium or fine). However, sub-angular- and angular-discoidal silt particles are favorably entrained into local sea ice. Clay mineral assemblages in SIS and shelf surface sediments match very well revealing that no individual clay mineral is preferably enriched in SIS or reduced at the bottom. The general textural, compositional and statistical match of fine-grained shelf surface deposits and SIS proves that bottom sediment is the principle source for ice-entrained material in the study area. We propose e.g. wave action and thermohaline convection to take sediment particles upward from the bottom nepheloid layer into the well-mixed 10–40 m deep water column of the Amderma/Vaygach flaw lead, and the turbulent process of suspension freezing to bring sediment particles and frazil crystals into contact, finally leading to the formation of sediment-laden ice. The role of SIS entrainment and export for local/regional shelf erosion and coastal retreat is of minor importance in the SW Kara Sea compared to other circum-Arctic shelf seas. However, the characteristic clay mineral assemblage of local SIS and bottom deposits can help identify the origin of SIS both on regional and Arctic-wide scales. 相似文献
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Toshihiro Ike Gregory F. Moore Shin'ichi Kuramoto Jin-Oh Park Yoshiyuki Kaneda Asahiko Taira 《Island Arc》2008,17(3):358-375
Abstract When seamounts and other topographic highs on an oceanic plate are subducted, they cause significant deformation of the overriding plate and may act as asperities deeper in the seismogenic zone. Kashinosaki Knoll (KK) is an isolated basement high of volcanic origin on the subducting Philippine Sea Plate that will soon be subducted at the eastern Nankai Trough. Seismic reflection imaging reveals a thick accumulation of sediments (∼1200 m) over and around the knoll. The lower portion of the sedimentary section has a package of high-amplitude, continuous reflections, interpreted as turbidites, that lap onto steep basement slopes but are parallel to the gentler basement slopes. Total sediment thickness on the western and northern slopes is approximately 40–50% more than on the summit and southeastern slopes of KK. These characteristics imply that the basal sedimentary section northwest of KK was deposited by infrequent high-energy turbidity currents, whereas the area southeast of KK was dominated by hemipelagic sedimentation over asymmetric basement relief. From the sediment structure and magnetic anomalies, we estimate that the knoll likely formed near the spreading center of the Shikoku Basin in the early Miocene. Its origin differs from that of nearby Zenisu Ridge, which is a piece of the Shikoku Basin crust uplifted along a thrust fault related to the collision of the Izu–Bonin arc and Honshu. KK has been carried into the margin of the Nankai Trough, and its high topography is deflecting Quaternary trench turbidites to the south. When KK collides with the accretionary prism in about 1 My, the associated variations in sediment type and thickness around the knoll will likely result in complex local variations in prism deformation. 相似文献
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—Tomographic maps of Lg coda Q (Q c Lg) variation are now available for nearly the entire African, Eurasian, South American, and Australian continents, as well as for the United States. Q c Lg at 1 Hz (Q 0) varies from less than 200 to more than 1000 and Q c Lg frequency dependence (<eta>) varies between 0.0 and nearly 1.0. Q 0 appears to increase in proportion to the length of time that has elapsed since the most recent major episode of tectonic or orogenic activity in any region. A plot of Q 0 versus time since that activity indicates that a single Q 0-time relation approximates most mean Q 0 values. Those that deviate most from the trend lay in Australia, the Arabian Peninsula, and the East African rift. The increase in Q 0 with time may be due to a continual increase in crustal shear wave Q (Q ) caused by the loss of crustal fluids and reduction of crustal permeability following tectonic or orogenic activity. Extrapolated values of Q c Lg at 5 Hz (using Q 0 and <eta> values measured at 1 Hz and assuming that <eta> is constant in all regions between 1 and 5 Hz) show a similar percentage-wise increase with times that has elapsed since the most recent activity. Other factors that can reduce Q 0 in continental regions include thick accumulations of sediment (especially sandstone and shale of Mesozoic age and younger), severe velocity gradients at the crust-mantle transition and, possibly, lateral variations in the depth, thickness, and severity of those gradients. Severe and large increases of Q in the mid-crust of some regions can cause relatively large values of <eta>, even if the frequency dependence of Q is small. 相似文献
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A new combined satellite-terrestrial model of the gravity field is used together with seismic data for construction of a density model of the lithosphere of the Central Tien Shan and for estimation of its isostatic balance. The Tien Shan is one of the most active intraplate orogens in the world, located about 1,500 km north of the convergence between Indian and Eurasian plate, and surrounded by stable Kazakh platform to the north and the Tarim block to the south. Although this area was extensively studied during recent decades, several principal problems, related to its structure and tectonics, remain unsolved up to now: (1) various geodynamic scenarios have been discussed so far to explain tectonic evolution, such as direct “crustal shortening,” intracontinental subduction and some others, but no definite evidence for any of them has been found. (2) Still, it is not clear why Tien Shan grows so far from the plate boundary at the Himalayan collision zone. Gravity modeling can provide valuable constraints to resolve these questions. The results of this study show that: (1) there exists a very strong deflection of the Tien Shan lithosphere from isostatic equilibrium. At the same time, the patterns of the isostatic anomalies are very different in the Western and Central Tien Shan. The latter one is characterized by much stronger variations. The best fit of the modeling results is found for the model according to which the Tarim plate partially underthrusts the Central Tien Shan; (2) negative density anomalies in the upper mantle under the central block possibly relate to magmatic underplating during the initial stage of the tectonic evolution. Therefore, the weak lithosphere could be the factor that initiates mountain building far away from the collision zone. Alternatively, this might be a gap after detachment of the eclogised lower crust and lithospheric lid, which is filled with the hot asthenospheric material. 相似文献