Hydrographic variability on a coastal shelf directly influenced by estuarine outflow

Hydrographic variability on the Alabama shelf just outside of Mobile Bay, a major source of river discharge into the Gulf of Mexico, is examined using time series of water column temperature and surface and bottom salinity from a mooring site with a depth of 20 m in conjunction with a series of across-shelf CTD surveys. The time series data show variability in a range of time scales. The density variation is affected by both salinity and temperature, with its relatively strong annual signal mostly determined by temperature and its year to year variability mostly determined by salinity. Seasonal mean structures of temperature, salinity, and density show a transition from estuarine to shelf conditions in which three regions with distinct seasonal characteristics in their horizontal and vertical gradient structures are identified. Correlation analysis with the available forcing functions demonstrates the influence of Mobile Bay on the variability at the mooring site. At low frequencies, river discharge from Mobile Bay has a varying influence on salinity, which is absent during the periods with unusually low discharge. At shorter synoptic time scales, both the estuarine response to the across-shelf wind stress and the shelf response to the along-shelf wind stress are significantly correlated with temperature/salinity variability: the former becoming important for the surface layer during winter whereas the latter for the bottom layer during both winter and summer. These forcing functions are important players in determining the estuarine-shelf exchange, which in turn is found to contribute to the shelf hydrographic structure.     

Effective periods and seismic performance of steel moment resisting frames designed for risk categories I and IV according to IBC2009

In current seismic design, structures that are essential for post‐disaster recovery, and hazardous facilities are classified as risk category IV and are designed with higher importance factors and stringent drift limits. These structures are expected to perform better in an earthquake event because a larger base shear and more stringent drift limit are used. Although this provision has been in the seismic design code over the last three decades, few studies have investigated the performance of essential structures. The aim of this study is to quantify the impact of higher importance factors and stringent drift limits on the seismic performance of steel moment resisting frames. A total of 16 steel structures are designed for Los Angeles and Seattle. Different risk categories are used for the design. The effects of the risk categories on the structural periods, and thus on the seismic force demand, are investigated. A suite of inelastic time history analyses are carried out to understand the probability of exceeding a specified limit state when the structures are subjected to different levels of earthquake events. The results show that the periods of the structures in risk category IV decrease by a factor of 0.5 to 0.8, and the strengths increase by a factor of 1.5 to 3.2. Seismic fragility analysis shows that the structures in risk category IV generally satisfy the probabilistic performance objectives. Copyright © 2014 John Wiley & Sons, Ltd.     

Why are flood and landslide victims less willing to take mitigation measures than the public?

Almost annually, natural hazards such as floods and landslides cause a great deal of financial loss and human suffering in Taiwan. In order to gain a better understanding of disaster preparedness, this paper examines several factors in relation to hazard mitigation behavior: social economic status (education, income), psychological vulnerability (sense of powerless and helpless), risk perception (perceived impact and control) and social trust. The statistical analysis reported here is based on the “2004 National Risk Perception Survey of Floods and Landslides in Taiwan”. The main findings include: (1) in comparison with general public, victims are less willing to adopt risk mitigation measures than the public, even though they perceive larger impacts, worry more about the hazard, and pay more attention to hazard information; (2) trust, risk perception and social economic status are positive predictors for mitigation intentions, whereas psychological vulnerability is a negative predictor; and (3) psychological variables are stronger predictors for mitigation intentions than that of socio-economic variables. In light of these findings, the policy implications and intervention strategy are also discussed.

Prediction of landslide occurrence based on slope-instability analysis and hydrological model simulation

Hillslope failure usually occurs as soil resistance deteriorates in the presence of the acting stress developed by a rising groundwater level during rainstorms. The present study adopted a slope-instability analysis and a hydrological model for landslide prediction during heavy rainstorms. Variation of the groundwater table on hillslope was simulated by using the hydrological model and then the temporal groundwater level at each grid was substituted into the slope-instability analysis to determine the instability of the grids in watersheds for prediction of massive landslides.Hydrological records from two landslide-prone areas in northern Taiwan were collected. Digital elevation model was adopted to obtain the geomorphologic factors required for the slope-instability analysis and the hydrological model. The spatial distribution of soil thickness required for performing the infinite slope model was estimated by using a wetness index. Results showed that the temporal variation of the percentage of unstable grids in the study watersheds basically followed the variation of rainfall hyetographs. The percentage of the unstable grids reached a maximum value when the centroid of the hyetograph passed. A comparison between the landslide records and the model analytical results revealed that a massive landslide might occur if more than 50% of the grids in the subwatershed were classified as unstable in the study areas. The predicted time and location of landslide occurrence were consistent with those obtained from field investigations. It is therefore considered promising to apply the developed analytical method for landslide warning to alleviate the loss of lives and property.     

柴达木盆地低频地震探测结晶基底的工作方法

根据地质资料,柴达木盆地的基岩（结晶基底）埋藏深度,可达十公里以上.勘探这样深的基岩,利用反射和一般折射方法是不容易得到良好的效果.1958年6月,在柴达木盆地开始试验低频地震的方法,来接收基岩面的折射波.所用检波器的谐振频率为13周/秒,放大器最低谐振频率为8周/秒.最大接收距离为100公里左右.     

Does El Niño-Southern Oscillation affect the precipitation in Korea on seasonal time scales?

A number of studies in the past two decades have attempted to find the relationship between the precipitation in Korea and the El Niño-Southern Oscillation (ENSO) on various time scales. Comprehensive analyses of station precipitation data in Korea for the 61-year period, 1954-2014, in this study show that the effects of ENSO on the seasonal precipitation in Korea are practically negligible. The correlation between summer precipitation and ENSO is insignificant regardless of the intensity, type (e.g., eastern-Pacific or central-Pacific), and stage (e.g., developing, mature, or decaying) of ENSO. Somewhat meaningful correlation between ENSO and precipitation in Korea occurs only in the ENSO-developing fall. Because summer rainfall accounts for over half of the annual total and fall is a dry season in Korea, the overall effects of ENSO on precipitation in Korea are practically nonexistent.     

On Northern Hemisphere Wave Patterns Associated with Winter Rainfall Events in China

During extended winter(November–April),43% of the intraseasonal rainfall variability in China is explained by three spatial patterns of temporally coherent rainfall.These patterns were identified with empirical orthogonal teleconnection(EOT) analysis of observed 1982–2007 pentad rainfall anomalies and connected to midlatitude disturbances.However,examination of individual strong EOT events shows that there is substantial inter-event variability in their dynamical evolution,which implies that precursor patterns found in regressions cannot serve as useful predictors.To understand the physical nature and origins of the extratropical precursors,the EOT technique is applied to six simulations of the Met Office Unified Model at horizontal resolutions of 200–40 km,with and without air–sea coupling.All simulations reproduce the observed precursor patterns in regressions,indicating robust underlying dynamical processes.Further investigation into the dynamics associated with observed patterns shows that Rossby wave dynamics can explain the large inter-event variability.The results suggest that the apparently slowly evolving or quasi-stationary waves in regression analysis are a statistical amalgamation of more rapidly propagating waves with a variety of origins and properties.     

Spatio-temporal comparisons of imposex status and tissue organotin concentration in the whelk Reishia clavigera collected along the coasts of Dapeng Bay and Daya Bay,Shenzhen, China

Organotin compounds (OTs) have caused widespread adverse effects on marine organisms. As no local restrictions on OT-based antifouling paints have been implemented in China, high concentrations of OTs still occur in coastal environments. In this study, we measured the imposex status and tissue concentrations of OTs in the whelk Reishia clavigera collected along the coast of Dapeng Bay and Daya Bay of Shenzhen, China in 2013. Our results showed that all female whelks suffered from the onset of imposex. The highest concentration of total OTs was 27,756 μg kg⁻¹ dry weight in the samples collected from Shuitousha. Triphenyltin was the most predominant residue, accounting for more than 97.8% of total OTs across all sites. Compared with the results from previous studies, the marine environment of this region is still heavily contaminated with OTs. Therefore, a tightened control is necessary to regulate the use and release of OTs in China.