Characteristics and interpretation of the seismic signal of a field-scale landslide dam failure experiment

Outburst floods caused by breaches of landslide dams may cause serious damages and loss of lives in downstream areas; for this reason the study of the dynamic of the process is of particular interest for hazard and risk assessment. In this paper we report a field-scale landslide dam failure experiment conducted in Nantou County, in the central of Taiwan.The seismic signal generated during the dam failure was monitored using a broadband seismometer and the signal was used to study the dam failure process.We used the short-time Fourier transform(STFT) to obtain the time–frequency characteristics of the signal and analyzed the correlation between the power spectrum density(PSD) of the signal and the water level. The results indicate that the seismic signal generated during the process consisted of three components: a low-frequency band(0–1.5 Hz), an intermediate-frequency band(1.5–10 Hz) and a highfrequency band(10–45 Hz). We obtained the characteristics of each frequency band and the variations of the signal in various stages of the landslide dam failure process. We determined the cause for the signal changes in each frequency band and its relationship with the dam failure process. The PSD sediment flux estimation model was used to interpret the causes of variations in the signal energy before the dam failure and the clockwise hysteresis during the failure. Our results show that the seismic signal reflects the physical characteristics of the landslide dam failure process. The method and equipment used in this study may be used to monitor landslide dams and providing early warnings for dam failures.     

Spatial patterns and storage composition of woody debris in a natural secondary forest dominated by <Emphasis Type="Italic">Pinus tabulaeformis</Emphasis> on Loess Plateau,China

Woody debris (WD) is an important part of natural Pinus tabulaeformis mixed stands, and it affects the forest ecosystem stability and development. The WD spatial patterns are especially important structural characteristics that can provide insights into forest dynamics. In this paper, the WD storage, WD spatial patterns and WD associations among the main species were examined in the natural secondary forest on Loess Plateau in northwest China. Data were collected in a 1 ha (100 m × 100 m) permanent plot, and all the trees with a diameter at breast height of more than 3 cm were measured and stem-mapped. Ripley’s K functions from the spatial-point-pattern-analysis method were used to analyze the spatial distribution and associations. The results showed that: (1) The total storage of WD was 10.73 t/ha, fallen wood was the main source of WD, and the majority diameters were greater than 20 cm, and in intermediate levels of decay; (2) The overall spatial pattern was closely related to the spatial scale, which exhibited an aggregated pattern on a small scale, and a random pattern on a large scale. The spatial patterns of coarse woody debris also gradually transitioned from an aggregated pattern in fine scales to a random pattern in broader spatial scales, which matched the overall spatial pattern. The spatial intensity was gradually decreased with the increasing diameters, and increased with the decomposition classes; (3) The WD of Pinus tabulaeformis species was negatively associated with Betula platyphylla and Populus davidiana on a small scale but positively associated with these species on a large scale. The spatial pattern and interspecies relations were the results of long-term interactions between the natural secondary forest community and the surrounding natural environment. These findings would provide a scientific basis for the sustainable management and protection of natural secondary forest ecosystems on Loess Plateau.     

A novel model to assess soil productivity in the dry-hot valleys of China

Accurate evaluation of soil productivity has been a long-standing challenge. Although numerous models for productivity assessment exist, most are cumbersome to use and require substantial parameter inputs. We developed a new empirical soil productivity model based on field investigations of soil erosion, soil physicochemical properties, and crop yields in the dry-hot valleys (DHVs) in China. We found that soil pH, and organic matter and available potassium contents significantly affected crop yields under eroded conditions of the DHVs. Moreover, available potassium content was the key factor affecting soil productivity. We then modified an existing soil productivity model by adding the following parameters: contents of effective water, potassium, organic matter, and clay, soil pH, and root weighting factor. The modified soil productivity model explained 63.5% of the crop yield. We concluded that the new model was simple, realistic, and exhibited strong predictability. In addition to providing an accurate assessment of soil productivity, our model could potentially be applied as a soil module in comprehensive crop models.     

Geomorphologic map of the 1<Superscript>st</Superscript> Mutnaya River,Southeastern Kamchatka,Russia

The Kamchatka Peninsula–situated in the Pacific “Ring of Fire”–has 29 active and over 400 extinct volcanoes. Since it is situated in the northeastern extremity of Russia, in subarctic climate, the volcanic landforms are overprinted by the 446 glaciers. This research focuses on the 1^stMutnaya catchment which drains the southern slopes of two active volcanoes: Avachinsky and Koryaksky. Those volcanoes are a permanent threat for the cities of Petropavlovsk and Elizovo, which are the 2 of 3 cities of the peninsula. Hence, most of the studies carried out in the area dealt with the natural hazards and only few focus on landscape evolution. Thus, the purpose of this study was to elaborate a cartographic approach which integrates classic geomorphology with state of the art GIS and remote sensing techniques. As result, different landforms and related processes have been analysed and included in the first general geomorphologic map of the 1^stMutnaya catchment.     

Limit equilibrium method (LEM) of slope stability and calculation of comprehensive factor of safety with double strength-reduction technique

When the slope is in critical limit equilibrium(LE) state, the strength parameters have different contribution to each other on maintaining slope stability. That is to say that the strength parameters are not simultaneously reduced. Hence, the LE stress method is established to analyze the slope stability by employing the double strengthreduction(DSR) technique in this work. For calculation model of slope stability under the DSR technique, the general nonlinear Mohr–Coulomb(M–C) criterion is used to describe the shear failure of slope. Meanwhile, the average and polar diameter methods via the DSR technique are both adopted to calculate the comprehensive factor of safety(FOS) of slope. To extend the application of the polar diameter method, the original method is improved in the proposed method. After comparison and analysis on some slope examples, the proposed method's feasibility is verified. Thereafter, the stability charts of slope suitable for engineering application are drawn. Moreover, the studies show that:(1) the average method yields similar results as that of the polardiameter method;(2) compared with the traditional uniform strength-reduction(USR) technique, the slope stability obtained using the DSR techniquetends to be more unsafe; and(3) for a slope in the critical LE state, the strength parameter φ, i.e., internal friction angle, has greater contribution on the slope stability than the strength parameters c, i.e., cohesion.     

Long-term statistics of extreme tsunami height at Crescent City

Historically, Crescent City is one of the most vulnerable communities impacted by tsunamis along the west coast of the United States, largely attributed to its offshore geography. Trans-ocean tsunamis usually produce large wave runup at Crescent Harbor resulting in catastrophic damages, property loss and human death. How to determine the return values of tsunami height using relatively short-term observation data is of great significance to assess the tsunami hazards and improve engineering design along the coast of Crescent City. In the present study, the extreme tsunami heights observed along the coast of Crescent City from 1938 to 2015 are fitted using six different probabilistic distributions, namely, the Gumbel distribution, the Weibull distribution, the maximum entropy distribution, the lognormal distribution, the generalized extreme value distribution and the generalized Pareto distribution. The maximum likelihood method is applied to estimate the parameters of all above distributions. Both Kolmogorov-Smirnov test and root mean square error method are utilized for goodness-of-fit test and the better fitting distribution is selected. Assuming that the occurrence frequency of tsunami in each year follows the Poisson distribution, the Poisson compound extreme value distribution can be used to fit the annual maximum tsunami amplitude, and then the point and interval estimations of return tsunami heights are calculated for structural design. The results show that the Poisson compound extreme value distribution fits tsunami heights very well and is suitable to determine the return tsunami heights for coastal disaster prevention.     

Impacts of Coastal SST Variability on the East Asian Summer Monsoon

The impacts of the seasonal and interannual SST variability in the East Asia coastal regions （EACRSST） on the East Asian summer monsoon （EASM） have been examined using a regional climate model （PδRCM9） in this paper. The simulation results show that the correlation between the EACRSST and the EASM is strengthened after the mid-1970s and also the variability of the EACRSST forcing becomes much more important to the EASM interannual variability after the mid-1970s. The impacts of the EACRSST on the summer precipitation over each sub-region in the EASM region become weak gradually from south to north, and the temporal evolution features of the summer precipitation differences over North and Northeast China agree well with those of the index of EASM （IEASM） differences.
The mechanism analyses show that different EACRSST forcings result in the differences of sensible and latent heat flux exchanges at the air-sea interface, which alter the heating rate of the atmosphere. The heating rate differences induce low level air temperature differences over East Asia, resulting in the differences of the land-sea thermal contrast （LSTC） which lead to 850 hPa geopotential height changes. When the 850 hPa geopotential height increases over the East Asian continent and decreases over the coast of East China and the adjacent oceans during the weakening period of weakens consequently. On the contrary, the EASM enhances during the strengthening period of the LSTC.     

The Spatial and Temporal Characteristics of Pc3 Geomagnetic Activity over Canada in 2000, as a Guide to Planning the Times of Aeromagnetic Surveys

Geomagnetic activity affects aeromagnetic surveys. Geomagnetic variations are quite complex and can be quantified in different ways. A measure of geomagnetic activity that is useful for planning aeromagnetic surveys is the Pc3 pulsation index developed by the Australian Space Weather Agency. Purposeful to developing guidelines for planning aeromagnetic surveys in Canada, we study the variations in Pc3 index amplitude over Canada in 2000. This study shows distinct patterns associated with the sub-auroral zone, the auroral zone, and the polar cap. Average Pc3 index activity is higher during the months of February, July, September, and November in the auroral and sub-auroral zones. The station in the polar cap exhibits maximum activity near midday during the summer months. Detailed analysis of a magnetic storm shows that Pc3 index amplitude during the beginning of the solar storm is least important at the polar cap. The mean Pc3 index also relates to solar wind parameters such as the solar wind velocity and the vertical polarity of the interplanetary magnetic field. Analysis of the morning maximum of the Pc3 index observed in the auroral zone can be used to develop guidelines for planning aeromagnetic surveys in Canada and other areas of the world affected by auroral zones.     

A GIS framework for evaluating the implications of urban road network failure due to earthquakes: Bucharest (Romania) case study

Through this paper we propose and test a GIS framework that addresses the issue of seismic risk due to urban road network failure. The approach relies on full GIS integration, on Monte Carlo simulations for generating potentially disrupted network configurations, considering also the damage probability due to direct earthquake implications, and on traffic considerations (both in typical and post-earthquake situations). The damage probability can be obtained using fragility functions for critical structures like bridges and tunnels or by determining empirically the possibility of affected buildings to generate debris leading to road obstruction. Multiple performance indicators such as travel time and distance under various conditions are combined, in order to quantify the risks inflicted by dysfunctionalities in the emergency intervention process. The framework considers at the same time temporal and spatial dimensions, being able to cope with traffic dynamics or reconfigurable network configurations. The ArcGIS Network Analyst Module is used for model integration, and full city scale analysis is performed in order to test the capabilities. Bucharest (capital of Romania) is selected for the case study; this 2 million inhabitant city is one of the most endangered in Europe, due to earthquakes that occur in the Vrancea Area, at intermediate depth, with moment magnitudes > 7, but also due to the vulnerable building stock. Beside this, it is one of Europe’s top cities when it comes to traffic congestion. The results of the study provide initial insights on the deficiencies of the city’s road network and connectivity limitations, showing the high impact of road obstructions and traffic congestion on intervention times, for ambulances and firefighters, in case of an earthquake.     

Ichnology of Bhuban and Boka Bil Formations,oligocene-miocene deposits of Manipur Western Hill,Northeast India

Oligocene-Miocene deposits of Bhuban and Boka Bil Formations, Surma Group, Manipur Western Hill consist of well preserved ichnofossil assemblages. These formations are represented by eight lithofacies such as Massive sandstone (Sm), Rippled marked argillaceous sandstone (Sr), Wavy laminated sandstone-siltstone-silty shale (Sw), Laminated shale (Fl), Massive mudstone (Fm), Trough cross-bedded sandstone (St), Lenticular laminated sandstonesiltstonesilty shale (Sll) and Laminated to massive sandstone-siltstone (Ssc). Fifteen ichnospecies were identified, which further categories into Skolithos, Cruziana, and Skolithos/Cruziana ichnofacies. Overall distribution pattern and behavioural nature of the ichnoassemblage and sedimentological attributes suggests that the sediments of Bhuban and Boka Bil Formations were deposited under frequent fluctuating sea level, moderate to strong energy condition, subtidal to lower intertidal environment, rich in organic nutrients.