Soil characteristics in Doon Valley (north west Himalaya, India) by inversion of H/V spectral ratios from ambient noise measurements

Past and recent observations have shown that the local site conditions significantly affect the behavior of seismic waves and its potential to cause destructive earthquakes. Thus, seismic microzonation studies have become crucial for seismic hazard assessment, providing local soil characteristics that can help to evaluate the possible seismic effects. Among the different methods used for estimating the soil characteristics, the ones based on ambient noise measurements, such as the H/V technique, become a cheap, non-invasive and successful way for evaluating the soil properties along a studied area. In this work, ambient noise measurements were taken at 240 sites around the Doon Valley, India, in order to characterize the sediment deposits. First, the H/V analysis has been carried out to estimate the resonant frequencies along the valley. Subsequently, some of this H/V results have been inverted, using the neighborhood algorithm and the available geotechnical information, in order to provide an estimation of the S-wave velocity profiles at the studied sites. Using all these information, we have characterized the sedimentary deposits in different areas of the Doon Valley, providing the resonant frequency, the soil thickness, the mean S-wave velocity of the sediments, and the mean S-wave velocity in the uppermost 30 m.

Diseño de un modelo geológico-geotécnico 3D de la Vega Baja del Río Segura (Alicante, SE España)

Los modelos geológico-geotécnicos permiten al ingeniero comprender mejor las condiciones reinantes en un determinado lugar, además de identificar los principales problemas geotécnicos y hacer más realista la estimación de propiedades del suelo. En este trabajo se presenta la metodología empleada para el diseño de un modelo geológico-geotécnico tridimensional de la Vega Baja del Río Segura que consta de cuatro zonas caracterizadas por sus propiedades geotécnicas y su problemática asociada. El modelo resulta fundamentalmente de gran utilidad para la planificación de investigaciones preliminares de obras civiles.

Comparison among monitoring strategies to assess water flow dynamic and soil hydraulic properties in agricultural soils

Irrigated agriculture is usually performed in semi-arid regions despite scarcity of water resources. Therefore, optimal irrigation management by monitoring the soil is essential, and assessing soil hydraulic properties and water flow dynamics is presented as a first measure. For this purpose, the control of volumetric water content, θ, and pressure head, h, is required. This study adopted two types of monitoring strategies in the same experimental plot to control θ and h in the vadose zone: i) non-automatic and more time-consuming; ii) automatic connected to a datalogger. Water flux was modelled with Hydrus-1D using the data collected from both acquisition strategies independently (3820 daily values for the automatic; less than 1000 for the non-automatic). Goodness-of-fit results reported a better adjustment in case of automatic sensors. Both model outputs adequately predicted the general trend of θ and h, but with slight differences in computed annual drainage (711 mm and 774 mm). Soil hydraulic properties were inversely estimated from both data acquisition systems. Major differences were obtained in the saturated volumetric water content, θs, and the n and α van Genuchten model shape parameters. Saturated hydraulic conductivity, Ks, shown lower variability with a coefficient of variation range from 0.13 to 0.24 for the soil layers defined. Soil hydraulic properties were better assessed through automatic data acquisition as data variability was lower and accuracy was higher.

Evaluating the Effectiveness of Post Fire Emergency Rehabilitation Treatments on Soil Degradation and Erosion Control in Semi-Arid Mediterranean Areas of the Spanish South East

In this study, we seeded a native plant species and applied a mulch of chopped wood originating from the same burned area to avoid the establishment of invasive species. We evaluated four treatments: (1) seeding, (2) mulch, (3) seeding and mulch, and (4) control. Our objective was to increase plant recovery and to minimize the soil erosion and degradation. The study was conducted in Alicante, Spain in Torremanzanas forest of the semi-arid Mediterranean bioclimatic area after the wildfire of November, 2002. During three years of monitoring, we find that combined treatment: seeding and mulch increased the post fire plant recovery 20% approximately more than the rest of treatments and the control plots. We also found that seven months after treating mulch and seeding and mulch treatments presented a gain of soil: +5.18 to + 5.24 mm while the seeding treatment and control plots presented soil loss rates of: −0.48 to −0.49 mm. In addition, mulch treatment significantly decreased soil compaction to the half, and increased the infiltration capacity to 40 ml.mn−1 more than in plots without mulch, as well as increased the soil respiration to the double compared with no mulch plots. Work in progress confirms the positive effect of chopped wood as mulching treatment with or without seeding on the soil protection against soil erosion, and the amelioration of bio-physical properties after wildfires in the Mediterranean semi-arid burned areas.