Internal architecture and mobility of tidal sand ridges in the East China Sea     

Zhenxia Liu  Serge Berné  Yoshiki Saito  Hua Yu  Alain Trentesaux  Katsuto Uehara  Ping Yin  J. Paul Liu  Chaoxing Li  Guanghai Hu  Xiangqin Wang 《Continental Shelf Research》2007

On the basis of bathymetric and seismic data and data from piston cores collected by the Chinese–French marine geology and geophysics investigation of 1996, we discuss the internal architecture and mobility of tidal sand ridges in the East China Sea (ECS). We characterized the sand ridges on the middle to outer shelf of the ECS as tide-dominated sand ridges with southwest dipping beds, indicating that the regional net sediment transport is toward the southwest. As the sand ridges gradually migrate toward the southwest, new sand ridges are continually replacing old ones, and several generations of sand ridges have developed in the study area.  相似文献   

VHF radar observations of surface currents off the northern Opal coast in the eastern English Channel     

Alexei Sentchev  Max Yaremchuk 《Continental Shelf Research》2007

Two very high-frequency radars (VHFR) operating on the Opal coast of eastern English Channel provided a nearly continuous 35-day long dataset of surface currents over a 500 km² area at 0.6–1.8 km resolution. Argo drifter tracking and CTD soundings complemented the VHFR observations, which extended approximately 25 km offshore. The radar data resolve three basic modes of the surface velocity variation in the area, that are driven by tides, winds and freshwater fluxes associated with seasonal river discharge. The first mode, accounting for 90% of variability, is characterized by an along-shore flow pattern, whereas the second and third modes exhibit cross-shore, and eddy-like structures in the current velocity field. All the three modes show the dominant semi-diurnal variability and low-frequency modulation by the neap-spring tidal cycle. Although tidal forcing provides the major contribution to variability of local currents, baroclinicity plays an important role in shaping the 3D velocity field averaged over the tidal cycle and may strongly affect tracer dynamics on larger time scales. An empirical orthogonal function (EOF) decomposition and a spectral rotary analysis of the VHFR data reveal a discontinuity in the velocity field occurring approximately 10 km offshore which was caused by the reversal in the sign of rotation of the current vector. This feature of local circulation is responsible for surface current convergence on ebb, divergence on flood and strong oscillatory vertical motion. Spectral analysis of the observed currents and the results of the Agro drifter tracking indicate that the line of convergence approximately follows the 30-m isobath. The most pronounced feature of the radar-derived residual circulation is the along-coast intensification of surface currents with velocity magnitude of 0.25 m/s typical for the Regions of Freshwater Influence (ROFI). The analysis has provided a useful, exploratory examination of surface currents, suggesting that the circulation off the Opal coast is governed by ROFI dynamics on the hypertidal background.  相似文献   

Tide-induced groundwater head fluctuation in coastal multi-layered aquifer systems with a submarine outlet-capping     

Qiaona Guo  Hailong Li  Michel C. Boufadel  Yuqiang Xia  Guohui Li 《Advances in water resources》2007

This paper considered the tide-induced head fluctuations in two coastal multi-layered aquifer systems. Model I comprises two semi-permeable layers and a confined aquifer between them. Model II is a four-layered aquifer system including an unconfined aquifer, an upper semi-permeable layer, a confined aquifer and a lower semi-permeable layer. In each model, the submarine outlet of the confined aquifer is covered with a skin layer (“outlet-capping”). Analytical solutions of the two models are derived. In both models, leakages of the semi-permeable layers decrease the tidal head fluctuations. The outlet-capping reduces the aquifer’s head fluctuation by a constant factor and shifts the phase by a positive constant. The solution to Model II explains the inconsistency between the relatively small lag time and the strong amplitude damping effect of the tidal head fluctuations reported by Trefry and Johnston [Ground Water 1998;36:427–33] near the Port Adelaide River, Australia.  相似文献   

1997年以来巴颜喀拉块体周缘强震之间的黏弹性触发研究   总被引：2，自引：5，他引：2       下载免费PDF全文

程佳  刘杰  甘卫军  余怀忠 《地球物理学报》2011,54(8):1997-2010

本文利用考虑黏弹性地壳结构和精确震源参数的震后形变模型,计算了玛尼、昆仑山口西、汶川地震所形成的同震和震后形变场的变化过程与特征,结果显示玛尼地震的震后形变场有利于昆仑山口西地震的能量积累,玛尼地震与昆仑山口西地震的震后形变场对汶川地震的作用不明显,而这三次地震总的震后形变场在玉树断裂带附近形成了一个明显带有左旋性质的...  相似文献   

潮坪风暴沉积特征及其研究意义   总被引：18，自引：0，他引：18  

胡明毅  贺萍 《地球科学进展》2002,17(3):391-395

风暴沉积是20世纪70年代后期才指提出的一个重要概念，被认为是沉积学理论的一次重大突破。但是以往的研究多集中在对浅海陆棚区风暴沉积的研究，而对近岸地带潮坪风暴沉积的研究则比较薄弱。系统总结了近20年来国内外对现代潮坪风暴沉积研究的成果，同时介绍了在古代地层中首次识别出的潮坪风暴岩沉积特征，最后指出了潮坪风暴沉积的研究意义。  相似文献   

关于Coulomb应力变化/扰动作用下的Dieterich余震触发机制的广义解          下载免费PDF全文

仲秋  史保平 《地球物理学报》2013,56(5):1526-1537

基于单自由度弹簧-滑块模型,滑移速率和状态相依赖的摩擦关系可用于对断层内部地震成核和断层失稳过程的定量化描述.Dieterich(1994)余震触发理论模型首次给出中强震后区域应力场受到静态应力扰动后所导致的区域地震活动性的时空变化特征,近期研究也表明Dieterich理论模型可进一步推广至依赖时间的地震预测模型的建立.本文从简单直观的断层群体化概念模型出发,推导出了包括静态剪应力和正应力扰动作用下广义Dieterich解.同Dieterich经典解相比,广义Coulomb应力变化:ΔCFF^G=Δτ－(μ₀－α)Δσ取代了Dieterich方程中原有的剪切应力扰动Δτ.从而表明余震发生率R同作用于断层上的正应力的变化(扰动)有着密切的相关性.进一步,我们讨论了传统Coulomb应力变化(扰动)模型在地震预测过程中可能存在的局限性.以1976年M_S7.8唐山大地震的主余震序列为例,采用本文中得到的结果,并结合视时窗分段方法,拟合了该地区地震活动性的时间演化过程.结果表明,除Coulomb应力变化(扰动)的影响外,主震前后加载于断层上的剪应力速率变化可对早期余震发生率产生很大影响.  相似文献   

2013年芦山M_S7.0地震的震前及临震应变异常   总被引：2，自引：0，他引：2       下载免费PDF全文

池顺良  刘琦  池毅  邓涛  廖成旺  阳光  张贵萍  陈洁 《地震学报》2013,35(3):296-303

距离芦山地震震中70 km的姑咱地震台YRY四分量钻孔应变仪2013年4月16—19日记录到8次幅度达到十倍固体潮幅的张性应变阶跃, 这在该仪器6年多运行期间尚属首次. 这些应变异常与芦山地震在时间、 空间上相关; 应变异常的主压应力方向与震前宝兴水压致裂地应力测量主压应力方向相近, 并与震前5个月中长达3个月的应变异常主压应力方向一致; 应变阶跃起始与远震震波同时到达. 综上认为, 4月16—19日的应变异常有可能是芦山地震发震断裂在破裂错动前地层蠕滑的反映.   相似文献   

Richardson number profiles in laboratory experiments applied to shallow seas     

John A. T. Bye 《地球物理与天体物理流体动力学》2013,107(1-4):135-166

Abstract

A unified analysis is given of the critical conditions for the onset of stratification due to either a vertical or a horizontal buoyancy flux, with tidal or wind stirring.

The critical conditions for the onset of stratification with a horizontal buoyancy flux are found to be of the form of ratios of the tidal slope, or wind setup, to the equivalent surface slope due to the lateral density gradient. These ratios, which are easily determined from sea data, indicate that the profiles of critical flux Richardson Number, averaged over the stirring cycle, are similar to those inferred from the laboratory experiments of Hopfinger and Linden (1982) in which there is zero mean shear turbulence with a stabilising buoyancy flux, and also that the efficiency for the conversion of kinetic energy to potential energy for tidal stirring is similar to that for wind stirring.

The observed much greater efficiency for wind stirring, compared with tidal stirring with a vertical buoyancy flux, is also consistent with the existence of flux Richardson Number profiles in the sea similar to those occurring in the corresponding laboratory experiments. Using the solution of the turbulent kinetic energy equation for the water column, the relative importance of the production of turbulent kinetic energy, and its diffusion by turbulence are assessed, and the critical conditions for the onset of stratification with a vertical buoyancy flux are shown to reduce the classical Simpson—Hunter form.  相似文献   

库仑应力变化及其在地震学中的应用研究进展          下载免费PDF全文

刘方斌  王爱国  冀战波 《地震工程学报》2013,35(3):647-655

首先介绍了库仑应力的定义及其物理含义。阐述了库仑应力在强震对余震的触发作用、强震对后续地震序列的触发、应力影区对地震的抑制作用、地震活动性分析以及相关软件的应用等五个方面的应用研究进展。最后探讨了库仑应力在地震学应用中存在的不足与前景。  相似文献   

Seismogenic Tectonics and Dynamics of the 2011 Ms5.9 Yingjiang Earthquake in Yunnan,China     

SUN Yao  AN Meijian  FENG Mei  LONG Changxing  YANG Zhenyu 《《地质学报》英文版》2014,88(2):468-482

In the southern South–North Seismic Zone, China, seismic activity in the Yingjiang area of western Yunnan increased from December 2010, and eventually a destructive earthquake of Ms5.9 occurred near Yingjiang town on 10 March 2011. The focal mechanism and hypocenter location of the mainshock suggest that the Dayingjiang Fault was the site of the mainshock rupture. However, most of foreshocks and all aftershocks recorded by a portable seismic array located close to the mainshock occurred along the N–S-striking Sudian Fault, indicating that this fault had an important influence on these shocks. Coulomb stress calculations show that three strong(magnitude ≥5.0) earthquakes that occurred in the study region in 2008 increased the coulomb stress along the plane parallel to the Dayingjiang Fault. This supports the Dayingjiang Fault, and not the Sudian Fault, as the seismogenic fault of the 2011 Ms5.9 Yingjiang earthquake. The strong earthquakes in 2008 also increased the Coulomb stress at depths of ≤5 km along the entire Sudian Fault, and by doing so increased the shallow seismic activity along the fault. This explains why the foreshocks and aftershocks of the 2011 Yingjiang earthquake were located mostly on the Sudian Fault where it cuts the shallow crust. The earthquakes at the intersection of the Sudian and Dayingjiang faults are distributed mainly along a belt that dips to the southeast at ~40°, suggesting that the Dayingjiang Fault in the mainshock area also dips to the southeast at ~40°.  相似文献