Determining Q of near-surface materials from Rayleigh waves

High-frequency (≥2 Hz) Rayleigh wave phase velocities can be inverted to shear (S)-wave velocities for a layered earth model up to 30 m below the ground surface in many settings. Given S-wave velocity (V_S), compressional (P)-wave velocity (V_P), and Rayleigh wave phase velocities, it is feasible to solve for P-wave quality factor Q_P and S-wave quality factor Q_S in a layered earth model by inverting Rayleigh wave attenuation coefficients. Model results demonstrate the plausibility of inverting Q_S from Rayleigh wave attenuation coefficients. Contributions to the Rayleigh wave attenuation coefficients from Q_P cannot be ignored when Vs/V_P reaches 0.45, which is not uncommon in near-surface settings. It is possible to invert Q_P from Rayleigh wave attenuation coefficients in some geological setting, a concept that differs from the common perception that Rayleigh wave attenuation coefficients are always far less sensitive to Q_P than to Q_S. Sixty-channel surface wave data were acquired in an Arizona desert. For a 10-layer model with a thickness of over 20 m, the data were first inverted to obtain S-wave velocities by the multichannel analysis of surface waves (MASW) method and then quality factors were determined by inverting attenuation coefficients.     

Effect of spatial variability of cross‐correlated soil properties on bearing capacity of strip footing

Geotechnical engineering problems are characterized by many sources of uncertainty. Some of these sources are connected to the uncertainties of soil properties involved in the analysis. In this paper, a numerical procedure for a probabilistic analysis that considers the spatial variability of cross‐correlated soil properties is presented and applied to study the bearing capacity of spatially random soil with different autocorrelation distances in the vertical and horizontal directions. The approach integrates a commercial finite difference method and random field theory into the framework of a probabilistic analysis. Two‐dimensional cross‐correlated non‐Gaussian random fields are generated based on a Karhunen–Loève expansion in a manner consistent with a specified marginal distribution function, an autocorrelation function, and cross‐correlation coefficients. A Monte Carlo simulation is then used to determine the statistical response based on the random fields. A series of analyses was performed to study the effects of uncertainty due to the spatial heterogeneity on the bearing capacity of a rough strip footing. The simulations provide insight into the application of uncertainty treatment to geotechnical problems and show the importance of the spatial variability of soil properties with regard to the outcome of a probabilistic assessment. Copyright © 2009 John Wiley & Sons, Ltd.     

Modeling storm surges associated with super typhoon durian in South China Sea

Super typhoon Durian struck the central Philippines on November 30, 2006 and southern coast of Vietnam on December 5, 2006. The reported maximum wind exceeded 250 km/h, and the central pressure was 904 hPa during the peak of the system. The typhoon brought colossal damage, both in terms of lives and in terms of properties to the Philippines and Vietnam while Thailand and Malaysia were slightly affected. The energy from the high-velocity wind and central pressure drop resulted in the generation of storm surges along the coastal region of the Philippines including its surrounding islands as well as parts of southern Vietnam. In this paper, a numerical 2D model is used to study the oceanic response to the atmospheric forcing by 2006 super typhoon Durian in the coastal regions of the Philippines and Vietnam. The initial study of this model aims to provide some useful insights before it could be used as a coastal disaster prediction system in the region of South China Sea (SCS). The atmospheric forcing for the 2D model, which includes the pressure gradient and the wind field, is generated by an empirical asymmetrical storm model. The simulated results of storm surges due to typhoon Durian at two locations lie in the range of observed data/estimates published by the Joint Typhoon Warning Centre (JTWC).     

Long-term simulations of the sulfur concentrations over the China, Japan and Korea: A model comparison study

Three comprehensive acid deposition models were used to simulate the sulfur concentrations over northeast Asia over the period covering entire year of 2002, and discussed the aggregated uncertainties and discrepancies of the three models. The participating models are from the countries participating in the project of Longrange Transboundary Air Pollutants in Northeast Asia (LTP): China, Japan and Korea. The Eulerian Model-3/CMAQ (by China), Regional Air Quality Model (RAQM, by Japan), and Comprehensive Acid Deposition Model (CADM, by Korea) were employed by each country with common emissions data established by the administrative agencies of China, Japan and Korea. The episodic simulation results between 1 to 15, March 2002 are also presented, during which aircraft measurements were carried out over the Yellow sea. The episodic results show both a wide short-term variability in simulations against measurements, and maximum concentration differences of 3～5 times among the three models, requiring that further attention before confidence among the three models can be claimed for short-term simulations. However, the year-long cumulative simulations showed almost the same general features, with lower aggregated uncertainties between the three models, produced by the long term integration over northeast Asia.     

Aquifer Treatment of Sea Water to Remove Natural Organic Matter Before Desalination

An investigation of a sea water reverse osmosis desalination facility located in western Saudi Arabia has shown that aquifer treatment of the raw sea water provides a high degree of removal of natural organic matter (NOM) that causes membrane biofouling. The aquifer is a carbonate system that has a good hydraulic connection to the sea and 14 wells are used to induce sea water movement 400 to 450 m from the sea to the wells. During aquifer transport virtually all of the algae, over 90% of the bacteria, over 90% of the biopolymer fraction of NOM, and high percentages of the humic substance, building blocks, and some of the low molecular weight fractions of NOM are removed. Between 44 and over 90% of the transparent exopolymer particles (TEP) are removed with a corresponding significant reduction in concentration of the colloidal fraction of TEP. The removal rate for TEP appears to be greater in carbonate aquifers compared to siliciclastic systems. Although the production wells range in age from 4 months to 14 years, no significant difference in the degree of water treatment provided by the aquifer was found.     

Competing space and place identity with landscape change analysis using Web GIS through Singapore historical maps (1828–2015)

The investigation of historical maps is fundamental to understanding the dynamics of landscape changes. In this study, we propose Web GIS tools as a way to compare historical maps efficiently for knowledge production. A key impetus of this article is to contribute to the ongoing efforts to broaden the appeal of ‘mixed‐methods research’ by bridging the epistemological and methodological gaps between GIS and qualitative methodologies in knowledge production. This article proposes a new visualization method for historical landscape change analysis by comparing multiple maps simultaneously with the mash‐up of Web GIS. Based on the analysis of exterior facts represented on the maps, four developmental footprints were investigated, namely, surviving place identity, disappeared place identity replaced by new identity, waning place identity overlapped with new identity, and waning identity by disconnected spatial relationships. To this end, the study argues that Web GIS applications have more potential in spatial knowledge production than traditional desktop GIS.     

Structure and peculiarities of the seismic regime in the source zone of the Takoe earthquake on September 1, 2001 (M W 5.2)

The Takoe earthquake (M _W 5.2) occurred between two en-echelon segments of the active Aprelovskii fault on September 1, 2001, and was accompanied by an earthquake swarm, which was successfully recorded by a local network of digital seismic stations located on the southern part of Sakhalin Island. Modern methods were applied to relocate the parameters of the sources for the earthquake swarm event and significantly specify their spatial distribution and relations to the structural-geological features of the complex system of interacting faults. New data on the correlation between the source mechanism and the modern geodynamic setting in the southern part of Sakhalin were obtained.