Historical development of the saltmarsh at Wells,Maine

Comparisons of maps and aerial photographs dating from the late 1700s to the present document the recent development of an 8 km² saltmarsh that is situated behind a barrier spit in southern Maine. Tidal channels that were relatively narrow in 1794 became wider by 1872. The reduction of marsh bordering tidal channels is interpreted as evidence that marsh accretion could not keep pace with rising sea-level. This suggests that the rate of sea-level rise had increased, although a change in discharge or sediment load caused by extensive settlement and land clearance may also have been involved. Meander patterns of the tidal streams changed considerably throughout the time period covered by the maps, demonstrating that the streams of this marsh are more dynamic than some others that have been widely reported in the literature. These differences in stream dynamics are probably related to the differences in sedimentological structure of the marshes. Between 1872 and 1956 the barrier spit eroded on its inside (shoreward) edge, probably in response to the construction of riprapping and houses along the spit, and the subsequent reduction of overwash and aeolian transport of sediment. Modification of the tidal inlet and adjacent marsh during the 1960s, including jetty construction, dredging, and filling of portions of the marsh surface, affected the marsh only locally. One tidal stream has been migrating rapidly apparently in response to compaction of peat by dredge spoils and consequent local disruption of the marsh hydrology. Except for this migration, erosion of the marsh edge occurred immediately after the inlet modifications; planimetric changes in the marsh and its streams have been minor since then.     

历史上10年—100年尺度气候跃变的分析

利用史料重建了华北海河流域和陕西关中地区两千多年来的旱涝变化概况.采用移动符号检验法和移动T检验法分析了其中的几十和几百年尺度的跃变现象.通过比较海河、关中以及河南等地区的同期变化,区分出局地性和非局地性两类跃变事件;并通过个例分析指出了华北地区气候跃变和季风环流形势的可能联系.本文还对10~1—10~2年尺度气候跃变的发生频率和变化程度作了一般估计.     

当前反射地震学研究中的问题浅析

反射地震学作为地震学应用于国民经济建设的分支学科取得了巨大的成功。它在矿产资源勘探、工程建设与环境、自然灾害预测等各种领域发挥了不可替代的作用，特别是在能源开发中功不可殁。另一方面，反射地震学在广泛的工业应用中全面地完善和发展了地震学的理论、方法和技术。时至今日，反射地震学的发展已经从经典理论方法的研究走向更加与客观介质密切相关的深层次研究新阶段，这些问题是，反射地震学从单纯的构造研究走向地层岩性研究，与此有关的是从偏移构造成像步入层析成像、利用单波单分量数据转向应用多波多分量数据、假设地层为固体弹性介质转向双相孔隙介质、各向同性研究转向各向异性研究以及经典的一些方法技术与现代新技术同时使用等。本文对这些方面的研究现状进行概要的分析。     

中,美,日地震学文献近期引文特征分析比较

本文利用引文分析方法，对代表中、美、日地震学研究水平的《地震学报》、《美国地震学会通报》和《地震》三个核心期刊１９８８－１９９０年期间的４１０篇论文所附的７０９５篇引文的引文量、引用学科、引文来源和语种、自引、互引及引文年代进行了统计分析；此外，还探讨了中外地震学文献交流的现状和影响因素，以期对掌握地震学文献交流的规律和特征、文献的利用和管理及促进中外地震学文献的交流提供有益的启示和参考。     

14C dating and palaeoenvironment of the historic ‘little ice age’ glacier advance of Nigardsbreen Southwest Norway

Moss and grass remains associated with a well-developed in situ palaeosol buried beneath a moraine ridge in front of Nigardsbreen (Jostedalsbreen ice cap, southern Norway) have been ¹⁴C-dated. Pollen preserved with the plant remains suggests the existence of an agricultural landscape prior to the deposition of the moraine. The calibrated dates and the pollen spectra are in close accord with historically-documented evidence for the timing and palaeoenvironment of the ‘Little Ice Age’ advance of the glacier. Considerable potential is indicated for estimating the maximum ages of moraine ridges and for palaeoenvironmental reconstruction where such documentary evidence does not exist.     

走向21世纪的实用地震学

实用地震学包括地震勘探、深部地震测深、工程地基与质量勘查以及浅部地质灾害预测等，在国民经济各方面起着重要作用，特别是在我国油气资源勘探与开发中起着并将继续起着不可替代的作用．在即将迈向２１世纪的今天，我们探讨一下实用地震学未来发展的道路是很必要的．实用地震学在２１世纪仍将在地学研究和国家建设中发挥它应有的作用，而且对它的要求也将越来越高，因而它在理论和应用方面都有诸多疑难问题要研究．本文就其发展现状、未来的理论研究和新技术的应用问题做些探讨．     

1500年宜良地震地表形变带的考证

据历史记载１５００年在宜良一带发生了一次强烈地震，由前人对该次地震无较详细的现 场实地考查资料，因此对这次地震认识说法不一。１９９２年作者对该次地震进行了实地考证。发现和确认了这次地震十分丰富的地震地表形变带，现存长度达８１公里，最大左旋水平位错量９至１１米。研究结果表明该次地震的发震构造为小新街－徐家渡断裂，震级接近８级。     

Crustal transit time monitoring using PKP

The arrival time difference for the AB branch of PKP from deep Tonga earthquakes is constant over years with a standard deviation of ±0.05 seconds at seismographs located 10 to 50 km from each other. If published travel time curves are used to calculate the relative residuals of PKP the standard deviation from the constant mean is improved by approximately 0.01 seconds for AB branch data. For the BC branch, standard deviations of relative travel times of ±0.06 seconds are reduced to less than ±0.05 seconds by calculating relative residuals. We conclude that changes of crustal transit time forP-waves could be resolved, based on careful PKP arrival time measurement at two or more neighboring stations if the changes exceed 0.05 sec and last for more than one year. The conditions for achieving this result are that PKP from Tonga earthquakes is clearly recorded, and that time-keeping is accurate. The data on which these conclusions are based were obtained from the Graefenberg seismograph array, which is located in West Gemany and consists of 13 stations separated by distances of 10 km to 100 km. We propose that relative arrival times of PKP from Tonga could be used in the Mediterranean - Middle East area to search for precursory travel time changes before large earthquakes.