Fault rupture–foundation interaction: selected case histories

The 1999 earthquakes in Turkey and Taiwan, offering a variety of case histories with structures subjected to large tectonic displacements, have refueled the interest of the earthquake engineering community on the subject. While several structures were severely damaged or even collapsed, there were numerous examples of satisfactory performance. Even more astonishingly, in specific cases the surface fault rupture was effectively diverted due to the presence of a structure. For the purpose of developing deeper insights into the main mechanisms controlling this fascinating interplay, this article documents selected field case histories of fault rupture–foundation interaction from (a) the M_w 7.4 Kocaeli (August 17) 1999 earthquake in Turkey, (b) the M_w 7.1 Düzce-Bolu (November 12) 1999 earthquake in Turkey, (c) the M_w 7.6 Chi–Chi (September 21) 1999 earthquake in Taiwan, and (d) surface faulting in Mount Etna. A subset of the case histories presented herein is analysed numerically, using the methods developed in the companion paper. It is shown that relatively “heavy” or stiff structures supported by continuous and rigid foundations may divert the fault rupture. Such structures are subjected to rigid body rotation, without substantial structural distress. In contrast, structures on structurally–resilient foundation systems or on isolated supports are prone to substantial damage.     

Sea-Ice Concentration Multivariate Assimilation for the Canadian East Coast in a Coupled Sea Ice–Ocean Model

The present study focuses on the impact of ocean state (i.e., salinity and temperature) updates on the sea-ice analysis and short-term forecast in an assimilative sea ice–ocean coupled system. A relatively simple sea-ice assimilation scheme was applied to the sea ice–ocean coupled North Atlantic Nucleus for European Modelling of the Ocean (NEMO) system with a focus on the Canadian East Coast. In this assimilation scheme the ocean state was updated directly based on the correlations between the model's sea-ice concentration and the upper ocean salinity and temperature. These correlations were based on a limited time ensemble generated by applying random perturbations to the atmospheric forcing fields. High deviations in the sea-ice conditions were found along the ice edge, implying that the sea-ice edge position is sensitive to small atmospheric forcing variations. Assimilation runs with and without ocean state updates (i.e., sea-ice concentration nudging) were conducted and compared for the winter of 2002. Both continuous and intermittent assimilation schemes were examined. In a continuous sea-ice assimilation experiment, the ocean direct update is unnecessary. When the sea-ice updates are introduced intermittently the ocean state has to be altered to accommodate them, or they will be rapidly diminished by the model's dynamics. The correlations between sea-ice concentration and ocean salinity and temperature based on the first 15 days of January were used for corrections during the entire winter season when, in addition to thermodynamic processes, dynamic processes are responsible for, and even dominate, sea-ice evolution on the Labrador and Newfoundland shelves. This was an adequate choice as was demonstrated by the results of the study which showed that the experiments with ocean state adjustments generated more accurate short-term sea-ice forecasts.     

Prior-knowledge-based spectral mixture analysis for impervious surface mapping

In this study, we developed a prior-knowledge-based spectral mixture analysis (PKSMA) to map impervious surfaces by using endmembers derived separately for high- and low-density urban regions. First, an urban area was categorized into high- and low-density urban areas, using a multi-step classification method. Next, in high-density urban areas that were assumed to have only vegetation and impervious surfaces (ISs), the vegetation–impervious model (V–I) was used in a spectral mixture analysis (SMA) with three endmembers: vegetation, high albedo, and low albedo. In low-density urban areas, the vegetation–impervious–soil model (V–I–S) was used in an SMA analysis with four endmembers: high albedo, low albedo, soil, and vegetation. The fraction of IS with high and low albedo in each pixel was combined to produce the final IS map. The root mean-square error (RMSE) of the IS map produced using PKSMA was about 11.0%, compared to 14.52% only using four-endmember SMA. Particularly in high-density urban areas, PKSMA (RMSE = 6.47%) showed better performance than four-endmember (15.91%). The results indicate that PKSMA can improve IS mapping compared to traditional SMA by using appropriately selected endmembers and is particularly strong in high-density urban areas.     

Analysis of hydrological seasonality across northern catchments using monthly precipitation–runoff polygon metrics

Abstract

Seasonality is an important hydrological signature for catchment comparison. Here, the relevance of monthly precipitation–runoff polygons (defined as scatter points of 12 monthly average precipitation–runoff value pairs connected in the chronological monthly sequence) for characterizing seasonality patterns was investigated to describe the hydrological behaviour of 10 catchments spanning a climatic gradient across the northern temperate region. Specifically, the research objectives were to: (a) discuss the extent to which monthly precipitation–runoff polygons can be used to infer active hydrological processes in contrasting catchments; (b) test the ability of quantitative metrics describing the shape, orientation and surface area of monthly precipitation–runoff polygons to discriminate between different seasonality patterns; and (c) examine the value of precipitation–runoff polygons as a basis for catchment grouping and comparison. This study showed that some polygon metrics were as effective as monthly average runoff coefficients for illustrating differences between the 10 catchments. The use of precipitation–runoff polygons was especially helpful to look at the dynamics prevailing in specific months and better assess the coupling between precipitation and runoff and their relative degree of seasonality. This polygon methodology, linked with a range of quantitative metrics, could therefore provide a new simple tool for understanding and comparing seasonality among catchments.

Editor Z.W. Kundzewicz; Associate editor K. Heal

Citation Ali, G., Tetzlaff, D., Kruitbos, L., Soulsby, C., Carey, S., McDonnell, J., Buttle, J., Laudon, H., Seibert, J., McGuire, K., and Shanley, J., 2013. Analysis of hydrological seasonality across northern catchments using monthly precipitation–runoff polygon metrics. Hydrological Sciences Journal, 59 (1), 56–72.     

Phytoplankton and periphyton production and its relation to temperature in a humic lagoon

To analyse the existence of interactive competition between phytoplankton and periphyton, we studied their photosynthesis–irradiance (P–E) response during one year in a humic lagoon. Lake production was dominated by phytoplankton, which followed seasonal changes in temperature. Periphyton primary production and algae biomass increased in winter, when phytoplankton biomass and production were lower. In this study we show that even in conditions of phytoplankton dominance, the habitat coupling between phytoplankton and periphyton can still be noticed.     

Maximum magnitudes in aftershock sequences in Taiwan

In this work, Båth’s Law, the b-value in Gutenberg–Richter Law (G–R Law) in the form of the 1/β relationship, and both the a- and b-values in the G–R Law were introduced in order to estimate maximum aftershock magnitudes of earthquake sequences in the Taiwan region. The averaged difference of magnitude between the mainshock and the maximum aftershock is 1.20, and is consistent with Båth’s Law, however, with a large uncertainty. The large uncertainty implies that the difference may result from a variable controlled by other factors, such as the aftershocks number of an earthquake sequence and magnitude threshold for mainshock. With 1/β, since 86% of the earthquake sequences with a M ⩾ 6.0 mainshock follow this relationship, the upper bound of the maximum magnitude can be estimated for an earthquake sequence with a large mainshock. The a- and b-values in the G–R Law was also considered by evaluating maximum aftershock magnitudes. As there are low residuals between the model and the observations, the results suggest that the G–R Law is a good index for maximum aftershock magnitude determinations. In order to evaluate the temporal decays of maximum aftershock magnitudes, modified Omori’s Law was introduced. Using the approaches mentioned above, the maximum magnitudes and the temporal evolution of an earthquake sequence could be modeled. Among them, the model of the G–R Law has the best fit with observations for most of earthquake sequences. It shows its feasibility. The results of this work may benefit seismic hazards mitigation in the form of rapid re-evaluations for short-term seismic hazards immediately following devastating earthquakes.     

K–Ar illite dating to constrain multiple events in shallow crustal rocks: Implications for the Late Phanerozoic evolution of NE Asia

A recently developed illite-age-analysis (IAA) approach was applied to determine the multiple events for the Chugaryeong fault belt, Korea. Each event was determined by a combined approach of the optimized illite-polytype quantification and the K–Ar age-dating of clay fractions separated from the fault clays. The Late Cretaceous to Paleogene events (76.5 ± 0.8, 69.1 ± 0.6, 59.3 ± 0.7, and 48.2 ± 0.7 Ma) were recognized by calculating the authigenic 1M/1M_d illite ages on the IAA plots of the fault clays. The Early Cretaceous ages (121.7–124.7 and 112.4 ± 1.5 Ma) were also obtained from the convergent intercepts of 100% 2M₁ illite on the IAA plots. The absence of the 2M₁ illites in the host-rock indicates that the Early Cretaceous ages represent the timings of high-T hydrothermal events of >280 °C. The 2M₁ illites in the fault clays should be pre-formed by a fluid-rock interaction under a relatively high-T subsurface condition, and be mechanically reworked into the near surface along the fault by post-tectonic events. This is the first report determining the absolute age constraints of multi-activated tectonic events from a fault. These geochronological determinations of the multiple events recorded in the Chugaryeong fault belt are crucial to establish the tectonic evolution of the Korean Peninsula since the Late Cretaceous.     

The social–ecological system framework as a knowledge classificatory system for benthic small-scale fisheries

Ostrom proposed the underpinnings of a framework for the systematic study of the governance of complex social–ecological systems. Here we hypothesize that Ostrom's social–ecological system framework can be useful to build a classification system for small-scale benthic fisheries, regarding their governance processes and outcomes. The purpose of this paper is to contribute to knowledge accumulation of benthic fisheries. To tailor the framework, we relied on discussions among experts and a systematic literature review of benthic fisheries from 1980 to 2010. This literature review helped us refine variable definitions and provide readers with illustrative reference papers. We then illustrate the approach and its potential contributions through two studies of the emergence of self-organization in Mexico and Chile. We highlight synthetic lessons from the cases and the overall approach as well as reflect on remaining challenges to the development of a social–ecological system framework as a diagnostic tool for knowledge accumulation and synthesis.     

Attribution of the Langshan Tectonic Belt: Evidence from zircon U-Pb ages and Hf isotope compositions

This study describes a previously unidentified Neoproterozoic mafic dyke emplaced in the northern flank of the Langshan Tectonic Belt. This dyke intruded into the micaquartz schist of the Zhaertaishan Group, and yielded an age of 908 ± 8 Ma. The youngest U-Pb ages of micaquartz schist from the Zhaertaishan Group in the Langshan area were 1118 ± 33 Ma,1187 ± 3 Ma and 1189 ± 39 Ma,suggesting that the depositional age of the protolith of the schist was between 908 ± 8 Ma and 1118 ± 33 Ma. In addition, 436 U-Pb age data and 155 Lu-Hf isotopic data from six samples in the Langshan Tectonic Belt and one Permian greywacke from the Wuhai area show distinct differences between the northern and southern flanks of the Main Langshan area. The U-Pb ages of the northern flank are primarily Meso-Neoproterozoic; similar ages have not been identified in the southern flank to date.Moreover, two-stage Hf model ages of the northern flank feature three age peaks at ～900 Ma,～1700 Ma and ～2600 Ma; this differs from Hf model ages of the southern flank, which feature one strong age peak at ～2700 Ma. These results suggest that the northern and southern flanks of the Main Langshan area have different geochronologic characteristics and should be divided further. Based on the U-Pb ages and Hf model ages, the northern and southern flanks of the Main Langshan area are named the North and South Langshan Tectonic Belts. Comparison of the U-Pb age and two-stage Hf model age distributions from the North Langshan Tectonic Belt, South Langshan Tectonic Belt, Alxa Block and the North China Craton(NCC) reveal that the North Langshan Tectonic Belt is similar to the Alxa Block and that the South Langshan Tectonic Belt is similar to the NCC. In addition, the zircon U-Pb age of 860 ±7 Ma commonly observed in the Alxa Block was detected in the Permian greywacke from the Wuhai area of the NCC, which suggests that the amalgamation of the North and South Langshan Tectonic belts(i.e.,the amalgamation of the Alxa Block and the NCC), occurred between Devonian and late Permian.     

Evolution of groundwater chemistry in and around Vaniyambadi Industrial Area: Differentiating the natural and anthropogenic sources of contamination

Groundwaters in the crystalline aquifers are the major source of drinking water in Vaniyambadi area of Vellore district. Geochemical methods in collaboration with statistical methods were applied in this industrial area to understand the natural and anthropogenic influences on groundwater quality. To accomplish this objective, groundwater samples were collected and analyzed for physicochemical parameters and the results showed a dominance in the order of Na⁺ > Mg²⁺ > Ca²⁺ > K⁺ and HCO₃⁻ > Cl⁻ > SO₄²⁻ > NO₃⁻ for anions and cations, respectively. In contrast to this anion dominance were changed to Cl⁻ > HCO₃⁻ > SO₄²⁻ > NO₃⁻ in samples collected near the tannery industries. Groundwater quality evaluation using TDS and TH suggested that 57% of the total samples are hard-brackish type, indicating its unsuitability for drinking purpose. Generally the water type is Na⁺Cl⁻ to Ca²⁺Mg²⁺HCO₃⁻ type with an intermediate Ca²⁺Mg²⁺Cl⁻, suggesting the mixing of fresh groundwater with tannery effluent and cation exchange. Factor analysis and bivariate plots of major ions suggests that both natural and anthropogenic inputs are equally influencing the groundwater quality. Further investigations proved that silicate weathering is the dominant geogenic source of groundwater solute content, whereas tannery effluent is the anthropogenic source. Saline water mixing index (SWMI) and Cl⁻ vs NO₃⁻ bivariate plot were employed to differentiate the tannery contamination from the other anthropogenic inputs such as agricultural fertilizers, municipal sewages, etc. This analysis shows that samples 2, 4, 8 and 9 (located within the tannery cluster) have a SWMI value greater than 1, representing the groundwater–tannery effluent mixing. This study infers that groundwater in the Vaniyambadi area is under serious threat from both natural and anthropogenic contamination. However, the controlling discharge of untreated tannery effluents must be regulated to reduce the further deterioration of this vital resource in this part of the country.