High-frequency earthquakes at White Island volcano, New Zealand: insights into the shallow structure of a volcano-hydrothermal system

Volcano-tectonic earthquakes at White Island are concentrated in a single seismically active zone, southeast of the active vents and at depths of less than 1 km. A few deeper earthquakes also occur beneath the active vents. A composite focal mechanism indicates that the stress regime in the shallow seismic zone is N-S extensional. Shallow seismicity occurs within the main volume of the volcano-hydrothermal system that underlies the Main Crater floor, and we interpret this as a region where the rocks have been weakened by past magmatic intrusions, elevated pore fluid pressure and physico-chemical effects of acid volcanic fluids, thereby allowing preferential seismic failure. Brittle seismic failure within this region requires a temperature less than about 400 °C, and implies high horizontal temperature gradients close to the active craters and fumaroles. Spasmodic bursts events are also a result of brittle failure, but occur close to zones of significant permeability in response to changes in local fluid pressure.     

7th Annual Report on the International Status of Engineering Geology—Year 2001: Encompassing hydrogeology, environmental geology and the applied geosciences

The year was marked by noteworthy advances in multinational consortia of commercial firms and of forward-looking universities. Again, the tenor of the practice of Engineering Geology has picked up. Not to be in the vanguard does indeed mean that one languishes in the dust raised by those on the move. Engineering geologists must understand an infinity of challenges stemming from land development, environmental protection and cleanup and resource development. This is a profession in which age can bring wisdom and increased competence.Most practitioners were busy in 2001; more than 80% of ASFE member companies report that business has increased or stayed the same for the past 6 months. Sixty percent of practitioners expect that their 2002 revenues will be stable or increase for Year 2002.     

Dynamics of Wood Transport in Streams: A Flume Experiment

The influence of woody debris on channel morphology and aquatic habitat has been recognized for many years. Unlike sediment, however, little is known about how wood moves through river systems. We examined some dynamics of wood transport in streams through a series of flume experiments and observed three distinct wood transport regimes: uncongested, congested and semi-congested. During uncongested transport, logs move without piece-to-piece interactions and generally occupy less than 10 per cent of the channel area. In congested transport, the logs move together as a single mass and occupy more than 33 per cent of the channel area. Semi-congested transport is intermediate between these two transport regimes. The type of transport regime was most sensitive to changes in a dimensionless input rate, defined as the ratio of log volume delivered to the channel per second (Q_log) to discharge (Q_W); this ratio varied between 0·015 for uncongested transport and 0·20 for congested transport. Depositional fabrics within stable log jams varied by transport type, with deposits derived from uncongested and semi-congested transport regimes having a higher proportion of pieces orientated normal to flow than those from congested transport. Because wood input rates are higher and channel dimensions decrease relative to piece size in low-order channels, we expect congested transport will be more common in low-order streams while uncongested transport will dominate higher-order streams. Single flotation models can be used to model the stability of individual pieces, especially in higher-order channels, but are insufficient for modelling the more complex intractions that occur in lower-order streams. © 1997 John Wiley & Sons, Ltd.     

Decreases in turbidity during neap tides initiate late winter blooms of Eucampia zodiacus in a macrotidal embayment

Eucampia zodiacus Ehrenberg is harmful, as it causes reduction in the quality of the aquacultured Porphyra thalli owing to nutrient depletions during dense blooms in the late winter in the macrotidal Ariake Sea, Japan. To understand the mechanism of bloom development, changes in the abundance of E. zodiacus during a bloom were investigated along vessel transects from February to April 2012. In addition, marine environmental variables were continuously monitored by the Ariake Sea Monitoring Tower, which revealed that turbidity periodically decreased during neap tides. During the 16 February neap tide, a high Secchi depth (4.3 m) was recorded at offshore stations and the Z _1% depth, at which the light intensity attenuates to 1 % of that at the sea surface, exceeded the water depth. On 16 February, the abundance of E. zodiacus was 52–732 cells mL^?1, peaking at 7.0 m depth offshore. Subsequently, abundance increased at all stations. During the 22 February spring tide, abundance became vertically uniform. On 19 March, abundance at the tower reached 3758 cells mL^?1 at the surface. We conclude that an improvement in light conditions in the deeper layer triggered the bloom, although the size and the duration of the bloom were determined by nutrient availability. Thus, decreases in turbidity during neap tides and subsequent strong vertical mixing during spring tides may be instrumental in the population dynamics of the large diatom E. zodiacus in macrotidal environments.     

Study on Paleoearthquakes of the Eastern Liupanshan Piedmont Fault Zone

Based on trench excavation and detailed field investigation, the authors have ascertained that 6 paleoearthquake events have occurred in the Haizixia area of the Eastern Liupanshan Piedmont fault zone since 46Ka B.P. The recurrence time of 6 events were about 15000a, 20250a, 14750a, 12150a, 8550a and 4000a B.P., respectively, the recurrence intervals were about 15000a, 5500a, 2600a, 3600a and 4550a, respectively. According to M-D empirical relations, the vertical dislocation of events 1 and 2 corresponded to the dislocation of the earthquake with M8.0; the vertical dislocation of events 3-6, was corresponded to the dislocation of earthquakes with M6.5~7.5.     

Damage sequence and safety margin assessment of expansion joints by shake table testing

The performance of nonstructural components has attracted attention, and previous large earthquakes have resulted in widespread damage to expansion joints. In contrast to the main structural components, for which ductility beyond the design tolerance is ensured, the safety margin of nonstructural components classified as the product of mechanical engineering, such as expansion joints, is uncertain. This paper investigates the damage sequence and safety margin of expansion joints through shake table testing. The expansion joints were installed to connect 2 rigid steel frames with short and long natural periods. Four commonly used types, high-performance and standard-performance floor and wall expansion joints, were tested. Seven damage patterns of the 4 expansion joints were observed, and most of the damage patterns were considered displacement dependent. The damage mechanisms and relative displacements at the moment of damage were identified by using strain gauges attached near collision and damage locations. The high-performance expansion joints showed only minor damage beyond the design motion range, whereas the standard-performance expansion joints exhibited minor damage below the design motion range and failure at the design motion range or slightly beyond. For each damage state, repair information was obtained through a questionnaire to an expansion joint manufacturer, and the sum of the initial cost and repair cost for high-performance and standard-performance expansion joints was compared. The results will be useful for the selection of expansion joints in the design process.     

强震区轻骨料混凝土桥梁地震响应研究

为研究轻骨料混凝土桥梁的地震响应,以一座强震区典型连续梁桥为研究对象,在考虑轻骨料混凝土材料特性基础上建立桥梁结构有限元分析模型,采用非线性动力时程分析法进行结构地震响应分析,研究轻骨料混凝土材料布设位置对桥梁结构动力特性和地震响应的影响,并从内力和位移响应方面与普通混凝土桥梁进行对比。结果表明:与普通混凝土桥梁相比,仅上部结构或仅下部结构采用轻骨料混凝土对降低桥墩内力并不明显,而全桥采用轻骨料混凝土能够显著降低桥墩内力。轻骨料混凝土桥梁与普通混凝土桥梁地震内力和位移响应变化趋势不同,桥墩塑性发展程度和时间存在差异。采用轻骨料混凝土桥梁方案时,应综合考虑结构质量、刚度分布及材料塑性特性与普通混凝土桥梁的不同,合理确定抗震设计方案。     

渔港防台风等级评估研究 ——以霞关一级渔港为例

文章通过对历史上影响苍南近岸海域的24场风暴潮过程进行分析筛选,确定1323“菲特”为最危险台风路径基础,设计了8~17级的间距为22.5 km的18条构造台风路径,采用FVCOM浪、潮、流耦合模式分别计算潮位场、流场和浪场分布,通过分析渔港岸线是否淹没、锚泊地是否船只走锚、防波堤防浪能力3个指标确定单项防台评估能力,按“就低不就高”的原则最终确定霞关一级渔港的防台风等级为9级,并且渔船锚泊是渔港的薄弱环节,最后结合研究过程中发现的问题,提出渔港防台风建议。     

基于遥感的江苏省区域建设用海集约利用现状评价

区域建设用海是海域使用的一种重要方式。文章以土地与海域集约利用评价为参照,从"投入—产出"的角度出发构建了区域建设用海集约利用评价指标体系,利用遥感解译方法从2017年高分影像中提取并计算了江苏省12个区域建设用海的主要评价指标值,应用TOPSIS模型评价了江苏省沿海已建项目的集约用海现状。研究表明:①江苏省区域建设用海开发利用程度较低,53.2%的土地处于未利用状态,农渔业为面积占比最小的用地类型,江苏省对第二、第三产业的发展更为重视。②已有的开发活动中,人工设施面积较小,建筑与道路等面积占比远小于生态面积,区域生态健康状况良好。③根据指标计算,江苏省区域建设用海集约利用评价得分集中在0.4～0.6,集约利用程度整体较低,不同项目集约化利用程度差异较小,主要原因在于项目投资强度两极分化,道路等基础设施不够完善等。④从不同用海类型来看,交通运输用海集约利用程度最高,其用海结构布局最适宜,效率最高。文章所建指标具有指向性,应用TOPSIS模型进行无须赋予权重,因此更能客观真实地反映江苏省区域建设用海的集约利用情况。     

Circulation patterns in the lower Arctic Ocean derived from geochemical data

Climatological water-mass structures were identified in the Arctic Ocean using the geochemical dataset in the Hydrochemical Atlas of the Arctic Ocean (HAAC) as well as data on a geochemically conserved parameter, PO₄*, based on phosphate and dissolved oxygen. In the upper ocean above a depth of 500 m, the HAAC was found to reliably depict the boundary between Pacific-Origin Water (P-Water) and Atlantic-Origin Water (A-Water), which is aligned 135°E–45°W near the surface but rotates counterclockwise with depth. Thus, the Arctic and Atlantic oceans exchange high-silicate P-Water and low-silicate A-Water. The PO₄* field in the lower ocean below a depth of 1500 m was analyzed statistically, and the results indicated that the Eurasian Basin receives low-PO₄* Nordic Seas Deep Water, which flows along the bottom from the Greenland Sea. The routes from the upper ocean to the lower ocean were determined. Only the southern portion of the Canada Basin, which receives water from the Chukchi and Beaufort Seas, has high PO₄* levels; the rest of the Amerasian Basin receives low-PO₄* water from the Laptev Sea and/or the Barents Sea. The Eurasian Basin receives moderate levels of PO₄* from the Fram Strait and from the intermediate layer. The intermediate-layer water gradually travels up from the lower ocean and returns to the Atlantic, entraining the subsurface portion. It is likely that high-PO₄* water occasionally flows down from the upper ocean along Greenland, making the Eurasian Basin heterogeneous.