郯庐断裂带赤山段中晚更新世之交的史前地震遗迹

赤山地处安徽省泗县东北部,为郯庐断裂带西支断裂通过处。以往研究认为,郯庐断裂带赤山段第四纪以来有较为明显的活动。此次在垂直于赤山段开挖的多个探槽中均揭露出史前地震遗迹(多期逆断型崩积楔),具体表现为断层上盘砖红色上白垩统砂岩或黄白色中更新统砾石层向东叠置于褐黄色中、上更新统黏土之上。在楔状体根部均发现向NW陡倾的断裂,陡立的断面向上转变为缓倾的上翻垮落面。多条探槽揭示的断裂点的连线总体呈NNE走向,断裂通过处的上盘后缘大部分残留了凸起地貌,部分EW向冲沟被断裂右旋扭错。多条探槽两壁都一致显示出从西向东的推挤垮塌痕迹。其中Tc1～Tc4表现为砖红色砂岩(K₂)逆冲垮落于黄褐色含铁锰结核黏土(Q_p2-3)之上,Tc5则表现为红砂岩(K₂)和黄白色砾石层(Q_p2)逆冲垮塌于上述的黏土之上。在几个探槽的逆断型崩积楔上均揭示出此段曾有多次逆断型崩积事件发生,个别探槽揭露楔体较少,可能与其所处的位置、揭露深度和剥蚀残存的高度有关。对开挖探槽及光释光测年结果的详细分析初步得出,郯庐断裂带赤山段在中、晚更新世之交曾多次发生大规模逆断型黏滑事件,即曾多次发生史前大地震。     

Decadal variability of chlorophyll a in the South China Sea: a possible mechanism

Four climatologies on a monthly scale (January, April, May and November) of chlorophyll a within the South China Sea (SCS) were calculated using a Coastal Zone Color Scanner (CZCS) (1979-1983) and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) (1998-2002). We analyzed decadal variability of chlorophyll a by comparing the products of the two observation periods. The relationships of variability in chlorophyll a with sea surface wind speed (SSW), sea surface temperature (SST), wind stress (WS), and mixed layer depth (MLD) were determined. The results indicate that there is obvious chlorophyll a decadal variability in the SCS. The decadal chlorophyll a presents distinct seasonal variability in characteristics, which may be as a result of various different dynamic processes. The negative chlorophyll a concentration anomaly in January was associated with the warming of SST and a shallower MLD. Generally, there were higher chlorophyll a concentrations in spring during the SeaWiFS period compared with the CZCS period. However, the chlorophyll a concentration exhibits some regional differences during this season, leading to an explanation being difficult. The deepened MLD may have contributed to the positive chlorophyll a concentration anomalies from the northwestern Luzon Island to the northeastern region of Vietnam during April and May. The increases of chlorophyll a concentration in northwestern Borneo during May may be because the stronger SSW and higher WS produce a deeper mixed layer and convective mixing, leading to high levels of nutrient concentrations. The higher chlorophyll a off southeastern Vietnam may be associated with the advective transport of the colder water extending from the Karimata Strait to southeastern Vietnam.     

Low-frequency variations in primary production in the Oman upwelling zone associated with monsoon winds

Thirteen-year satellite-derived data are used to investigate the temporal variability of net primary production (NPP) in the Oman upwelling zone and its potential forcing mechanisms. The NPP in the Oman upwelling zone is characterized by an abnormal decrease during El Ni o events. Such an NPP decrease may be related to El Ni o-driven anomalous summertime weak wind. During the summer following El Ni o, the anomalous northeasterly wind forced by southwest Indian Ocean warming weakens the southwest monsoon and warms the Arabian Sea. The abnormal wind weakens the coastal Ekman transport, offshore Ekman pumping and horizontal advection, resulting in reduced upward nutrient supply to the euphotic zone. A slightly declining trend in NPP after 2000 associated with a gradual decrease in surface monsoon winds is discussed.     

Interannual and interdecadal variability of East Asian monsoon and its relation to oceanic processes: a review

A key component of the East Asian climate system is seasonally varying monsoon wind. Its interannual and interdecadal variability, as well as underlying oceanic processes, is the subject of a recent project completed by the Chinese Academy of Sciences. A series of research progress in the areas of monsoon winds, ocean responses, upwelling and productivity has been made and reviewed by this paper.     

陕西蓝田新街仰韶遗址史前地震遗迹的发现和初析

蓝田新街仰韶遗址在抢救性发掘中揭露出疑似自然变形现象.地震和考古人员共同进行现场分析,认为该遗址存在史前地震遗迹,表现为文化层被错动、砂土混杂掠裹和砂土液化,变形条带呈现近南北向和东西向延伸.初步研究结果表明,研究部位在仰韶文化期后曾遭受地震变形作用.     

浅谈快捷建库与数据处理系统的功能设计

介绍了快捷建库与数据处理系统涉及的内容和研究开发的技术路线,并对该系统的各项模块功能进行了详细的阐述,提出了基于ArcGIS平台实现系统各功能模块的理论可行性综合功能的操作方法。     

基于Wigner-Ville分布的地磁前兆异常提取方法及其在川滇地区的应用

为了能够从强背景场中提取较弱的震磁信息,采用平滑伪Wigner-Ville 分布方法对川滇地区的地磁场Z分量数据开展时频分析。通过研究Z分量滤波后主要周期为2~6 h部分中的不同周期分量变化,发现其中2.4h的周期分量受到外源场影响较大,而4.4h的周期分量在多次显著地震前均出现明显的高值异常。     

江淮地区地震考古的新发现

对江淮地区近期发掘的四个考古遗址进行了地震考古研究,发现了丰富的构造变形现象,包括古地震事件。其中固镇小李家遗址的汉代砖室墓变形具有统一的方向性,显示受区域NE-SW向构造应力作用形成,与强烈地震的快速变形无关;合肥乱墩子遗址的多数竖穴土坑墓存在不规则变形,但M66的压扭变形可能受郯庐断裂右旋走滑活动牵引形成,也与地震力作用无关。在和县大城子遗址和马鞍山申东遗址发现古地震遗迹,主要为地震裂缝、文化层位错及褶曲。在和县大城子遗址通过文化层中木炭的AMS14C测年确定出西周中晚期的一次古地震事件（2 580±30)~(2 760±30） a BP;在马鞍山申东遗址通过文化层考古断代及地震裂缝与文化层的切割关系识别出一次古地震事件亦发生于西周中晚期。最后综合本次研究与前人对江淮地区西周时期的古地震研究成果,初步认为西周中晚期江淮地区处于中强地震活跃期。     

2012年江苏高邮、宝应交界MS4.9地震发震断层参数测定

基于一维单侧有限移动震源模式,根据地震波传播过程中的多普勒效应,分别利用P波和S波拐角频率的方位变化,反演2012年7月20日江苏高邮、宝应交界MS4.9地震的发震断层面参数。P波和S波拐角频率的反演结果一致显示:本次地震的断层面破裂方向为232°左右,破裂面呈NE-SW向;地震马赫数v/c为0.2左右,平均破裂速度小于S波速度,破裂长度较短,为0.2~0.3km左右。破裂面方位与震源机制解、宏观烈度调查和余震精定位的研究结果具有一致性,结合震区周边的地质构造背景,分析认为滁河断裂很可能是高邮、宝应交界MS4.9地震的发震构造。     

郯庐断裂带重岗山—王迁段晚更新世以来的活动习性

活动断裂最新错动与地震事件的关系是重要的基础研究课题。文中选定郯庐断裂带泗洪县重岗山—王迁段,开挖大型探槽,识别编录晚第四纪以来变形和史前地震事件,分析其活动期次和特性。结果表明,郯庐断裂带重岗山—王迁段晚第四纪以来曾发生强烈的挤压逆冲活动,在重岗山表现为晚白垩世砖红色砂岩向西高角度逆冲于晚更新世黄褐色黏土之上,在王迁则表现为黄白色上新世砂岩向西逆覆于晚第四纪沉积之上,且存在部分张裂现象。通过14C测年分析,得到重岗山—王迁段的2次古地震事件,其年代依次为(11 755±45)~(10 525±45)a BP与(10 135±50)a BP。郯庐断裂带重岗山—王迁段晚更新世以来逆冲活动强烈,而且一直持续到全新世初期。