From incipient island arc to doubly‐vergent orogen: A review of geodynamic models and sedimentary basin‐fills of southern Central America          下载免费PDF全文

Christian Brandes  Jutta Winsemann 《Island Arc》2018,27(5)

Southern Central America is a Late Mesozoic/Cenozoic island arc that evolved in response to the subduction of the Farallón Plate beneath the Caribbean Plate in the Late Cretaceous and, from the Oligocene, the Cocos and Nazca Plates. Southern Central America is one of the best studied convergent margins in the world. The aim of this paper is to review the sedimentary and structural evolution of arc‐related sedimentary basins in southern Central America, and to show how the arc developed from a pre‐extensional intra‐oceanic island arc into a doubly‐vergent, subduction orogen. The Cenozoic sedimentary history of southern Central America is placed into the plate tectonic context of existing Caribbean Plate models. From regional basin analysis, the evolution of the southern Central American island arc is subdivided into three phases: (i) non‐extensional stage during the Campanian; (ii) extensional phase during the Maastrichtian‐Oligocene with rapid basin subsidence and deposition of arc‐related, clastic sediments; and (iii) doubly‐vergent, compressional arc phase along the 280 km long southern Costa Rican arc segment related to either oblique subduction of the Nazca plate, west‐to‐east passage of the Nazca–Cocos–Caribbean triple junction, or the subduction of rough oceanic crust of the Cocos Plate. The Pleistocene subduction of the Cocos Ridge contributed to the contraction but was not the primary driver. The architecture of the arc‐related sedimentary basin‐fills has been controlled by four factors: (i) subsidence caused by tectonic mechanisms, linked to the angle and morphology of the incoming plate, as shown by the fact that subduction of aseismic ridges and slab segments with rough crust were important drivers for subduction erosion, controlling the shape of forearc and trench‐slope basins, the lifespan of sedimentary basins, and the subsidence and uplift patterns; (ii) subsidence caused by slab rollback and resulting trench retreat; (iii) eustatic sea‐level changes; and (iv) sediment dispersal systems.  相似文献   

饱和地基中空沟近场隔振的现场试验与二维半解析边界元分析          下载免费PDF全文

孙连勇  时刚  崔新壮  卢晓峰  宋洋  王兴云  甘晓丽 《世界地震工程》2020,(2):229-240

动力机器运行和车辆行驶等会产生振动污染,危及邻近建筑物安全和干扰精密仪器设备正常运行等。这些振动污染可通过在地基中设置空沟的方式来降低或消除。针对饱和地基上明置动力机器基础的环境振动影响及空沟近场隔振问题,进行了饱和地基上空沟近场隔振的现场试验,并对试验结果进行了无量纲化分析;基于饱和土半解析边界元法,分别推导了动力机器基础环境振动影响和空沟近场隔振的边界元方程;在此基础上,详细研究了空沟对动力机器基础振动影响的隔振效果,分析了空沟深度、宽度和距振源距离对其隔振效果的影响。结果表明:空沟能够有效的降低动力机器基础的环境振动影响;空沟宽度对其隔振效果影响相对较小,而空沟深度对其隔振效果影响较大,为获得较好的隔振效果,空沟深度建议取1倍Rayleigh波波长;空沟距振源距离对其隔振效果也有较大影响,距离越远则隔振效果也越好,当被保护建筑距振源较远时,建议空沟在被保护建筑附近设置。此外,在某些特殊情况下,空沟隔振系统会由于共振现象而出现隔振效果劣化的现象,在工程设计中应予以注意。  相似文献   

EFFECT OF TSUNAMIS GENERATED IN THE MANILA TRENCH ON CHINA MAINLAND          下载免费PDF全文

SHI Feng  HE Hong-lin  ZHOU Ben-gang  WEI Zhan-yu  BI Li-si 《地震地质》2018,40(3):579-589

Tsunami is one of the most devastating natural coastal disasters. Most of large tsunamis are generated by submarine earthquakes occurring in subduction zones. Tsunamis can also be triggered by volcano eruptions and large landslides. There are many records about "sea-overflow" in Chinese ancient books, which are not proved to be tsunamis. Tectonics and historical records analysis are import to forecast and prevention of tsunami. Consider the tectonic environment of the China sea, the possibility of huge damage caused by the offshore tsunami is very small. And the impact of the ocean tsunami on the Bohai sea, the Yellow sea, and the East China sea is also small. But in the South China Sea, the Manila subduction zone has been identified as a high hazardous tsunamigenic earthquake source region. No earthquake larger than M_W7.6 has been recorded in the past 100a in this region, suggesting a high probability for larger earthquakes in the future. If a tsunamigenic earthquake were to occur in this region in the near future, a tragedy with the magnitude similar to the 2004 Indian Ocean tsunami could repeat itself. In this paper, based on tectonics and historical records analysis, we have demonstrated that potential for a strong future earthquake along the Manila subduction zone is real. Using a numerical model, we have also shown that most countries in the South China Sea will be affected by the tsunamis generated by the future earthquake. For China, it implies that the maximum wave height over 4.0 meter on China mainland, especially the Pearl River Estuary. But the island, local relief maybe influence the maximum wave. But it takes nearly 3 hours to attack China mainland, if there is the operational tsunami warning system in place in this region, should be greatly reduced losses. And the simulated results are conformable to historical records. It indicates that the tsunami hazards from Manila trench to China mainland worthy of our attention and prevention.  相似文献   

Sequential radiocarbon measurement of bulk peat for high-precision dating of tsunami deposits     

《Quaternary Geochronology》2017

Dates of tsunami deposits have been used to estimate paleotsunami recurrence intervals in areas affected by these natural events. The depositional age of tsunami deposits is commonly constrained by the radiocarbon (¹⁴C) dating of sediments above and below the geological event. However, because of calibration curve fluctuations, the depositional age sometimes has a wide error range. In this study, we conducted millimeter-scale high-resolution radiocarbon measurements of tsunami deposits at Urahoro in southern Hokkaido, Japan. The site faces the Pacific Ocean along the Kuril Trench. Eight event deposits were identified within peat at this site. We took sequential measurements for ¹⁴C dating using bulk peat samples. The results were validated based on comparison with the absolute and radiometric ages of tephra layers. Dating results were further constrained by stratigraphic order using statistical methods. We constrained the depositional age of the paleotsunami deposits better using this method than we did when using conventional methods. We proposed an efficient measurement strategy with respect to the radiocarbon calibration curve. This method is also applicable for other deposits formed by any natural hazard if bulk peat is obtainable so it can contribute to better hazard assessment worldwide.  相似文献   

马尼拉俯冲带北段增生楔前缘构造变形和精细结构   总被引：1，自引：0，他引：1       下载免费PDF全文

高金尉  吴时国  姚永坚  陈传绪  宋陶然  王吉亮  孙金  张汉羽  马本俊  谢杨冰 《地球物理学报》2018,61(7):2845-2858

马尼拉俯冲带是南海的东部边界,记录了南海形成演化的关键信息,同时也是地震和海啸多发区域.本文利用过马尼拉俯冲带北段的高分辨率多道地震剖面,分析了研究区内海盆和海沟的沉积特征,精细刻画了区内增生楔前缘的构造变形、结构以及岩浆活动特征.研究区内增生楔下陆坡部分由盲冲断层、构造楔和叠瓦逆冲断层构成,逆冲断层归并于一条位于下中新统的滑脱面上,滑脱面向海方向的展布明显受到增生楔之下埋藏海山和基底隆起的影响;上陆坡的反射特征则因变形强烈和岩浆作用而难以识别;岩浆活动开始于晚中新世末期并持续至第四纪.马尼拉俯冲带北段增生楔的形成时间早于16.5 Ma,并通过前展式逆冲向南海方向扩展;马尼拉俯冲带的初始形成时间可能在晚渐新世,而此时南海海盆扩张仍在持续.南海东北缘19°N-21°N区域为南海北部陆坡向海盆的延伸,高度减薄的陆壳的俯冲造成马尼拉海沟北段几何形态明显地向东凹进.  相似文献   

太山龙泉寺舍利塔边坡地震稳定性研究          下载免费PDF全文

丁学文  李国珍  丁志平  李申  冯凯宇 《地震工程学报》2020,42(6):1632-1640,1722

为了研究太原市太山龙泉寺拟建舍利塔边坡稳定性,对所在场地及外围地形地貌、地层、地质构造、水文条件进行了调查。结合7个探井,确定了塔址所在场地的土质边坡体可能失稳的模式,进行了边坡稳定性分析、计算。结果表明,场地在自然状态下边坡稳定系数为1.37,在烈度为Ⅷ、Ⅸ度地震影响下边坡稳定系数分别为1.24、1.15。根据《建筑边坡工程技术规范》（GB50330-2013）,塔址所在边坡是稳定的,不必对边坡进行处理;其次结合3个探槽揭露,发现场地北侧基岩边坡曾发生过滑动,据其滑动面倾角、滑动量及错断地层特征,认为是一种特殊边坡变形破坏-岩体错落,为崩塌与滑坡之间的中间类型,从现存的地形地貌特征分析,现阶段错落体已趋于基本稳定状态,稳定性较好;最后给出了预防边坡滑动的建议和措施,研究结果可为其他类似边坡场地地震稳定性研究提供参考借鉴。  相似文献   

涞源龙门金多金属矿普查绿色勘查实践          下载免费PDF全文

张万河  和新  郝国利  刘成  张淼鑫  杨永超 《探矿工程》2020,47(7):73-77

河北省涞源县龙门金多金属矿普查工作,贯彻绿色勘查理念,对槽探工程、老硐清理、钻探工程按《绿色勘查指南》进行了专项设计并付诸实施。槽探工程施工挖掘的腐植土和碎石就近分开堆放并遮盖,待项目验收合格后,回填腐植土和碎石,最后平整并绿化;老硐清理出的碎石选择离硐口较近的相对平坦的地方堆放,并做好防护工作,最后覆土绿化;钻进工程采用清水和环保泥浆做冲洗液,金刚石单管和绳索取心钻进,提高了效率,减少了对地质环境的影响。机台建设占地少,施工过程中避免油污等的外溢,项目竣工验收后地貌恢复采用植草、自然恢复等绿化方法。绿色勘查充分贯彻了绿水青山就是金山银山的绿色发展理念。  相似文献   

Lithospheric flexural modelling of the seaward and trenchward of the subducting oceanic plates     

Jiangyang Zhang  Zhen Sun 《International Geology Review》2020,62(7-8):908-923

ABSTRACT

Based on a two-segment plate flexural modelling, we investigated the effective elastic thickness of global subducting oceanic lithosphere. Our results show that for the plate age of 0 to 50 Ma, the seaward effective elastic thickness T _e ^M values are located between 600 and 900°C isotherms, and do not track any isotherm, while the majority of the trenchward effective elastic thickness T _e ^m values are located between 300 and 600°C isotherms. For the plate age older than 50 Ma, T _e ^M values basically matches the 600°C isotherm with some fluctuations for the age older than 110 Ma, while T _e ^m values mainly fall between 200 and 400°C isotherms. The reduction in effective elastic thickness (T _e ^M-T _e ^m) varies from 2.6 to 30.1 km, or 11–68% of seaward T _e ^M. Thus, the absolute value of the decrease in the effective elastic thicknesses (T _e ^M-T _e ^m) increases with the plate age, while the percentage reduction in the effective elastic thickness (1-T _e ^m/T _e ^M) has no obvious relationship with the age, but more related to the curvature of bending plate. Almost all bending-related earthquakes occurred above the T _e ^M line, but many normal-faulting earthquakes are deeper than the T _e ^M-T _e ^m line, implying that the plate may still retain some thickness of an elastic property core in the areas (depth) where earthquakes occur.  相似文献   

水位变化对多空沟屏障远场隔振效果的影响研究     

李建平  张晓磊  冯世进 《岩土力学》2020,41(9):3131-3138

受季节性降雨的影响,雨季和旱季存在明显的水位波动。为分析地下水位升降对多空沟隔振效果的影响,建立了上覆单相弹性层饱和地基中空沟有限元分析模型。模型中考虑了沟中水的作用,算例分析了等沟深和不等沟深多沟屏障、沟壁倾斜多沟屏障和连续起伏地形屏障在不同水位下的远场隔振效果。计算结果与相应单相弹性地基进行对比,结果表明：土体渗透性低时,多数水位下不利于多沟屏障隔振;沟深为0.3LR（LR为R波波长）的三沟屏障通常可获得较理想的隔振效果（75%隔振率）,但屏障在隔振效果最差的共振水位(0.6LR)下,空沟须贯穿上覆干土层才可获得75%隔振率;递减沟深屏障可有效降低上覆土层共振的不利影响;沟深较浅时,沟壁倾角越大,多沟的隔振效果越好,但对较深多沟的影响小;连续起伏的地形景观可作为一种有效的绿色隔振屏障。  相似文献   

马尼拉海沟几何形态特征的构造演化意义   总被引：4，自引：0，他引：4  

陈志豪  李家彪  吴自银  吴振利  尚继宏 《海洋地质与第四纪地质》2009,(2)

通过对马尼拉海沟海底地形地貌、构造特征及其相关地震等数据资料的分析,结合俯冲带动力学数值模拟成果,尤其是Schellart等的模式,详细讨论了马尼拉海沟几何形态、海沟南北段俯冲角度突变等构造特征。分析认为,南海中代表古扩张脊的黄岩海山链的俯冲挤入对马尼拉俯冲带的几何形态没有造成较大的影响,其几何形态较符合中等长度(2000～3000km)的海沟模型。由海沟后退和板片反转引起的平行于马尼拉海沟方向的地幔流加剧了海沟南北段俯冲角度的突变。  相似文献