A new empirical estimator of coseismic landslide displacement for Zagros Mountain region (Iran)

Earthquake-induced landslides are responsible worldwide for significant socioeconomic losses and historically have a prominent position in the list of natural hazards affecting the Iran plateau. As a step toward the development of tools for the assessment and the management of this kind of hazard at regional scale, an empirical estimator of coseismic displacements along potential sliding surfaces was obtained through a regression analysis for the Zagros region, a mountainous Iranian region subjected to earthquake-induced landslides. This estimator, based on the Newmark’s model, allows to evaluate the expected permanent displacement (named ‘‘Newmark displacement’’) induced by seismic shaking of defined energy on potential sliding surface characterized by a given critical acceleration. To produce regression models for Newmark displacement estimators, a data set was constructed for different critical acceleration values on the basis of 108 accelerometric recordings from 80 Iranian earthquakes with moment magnitudes between 3.6 and 7. The empirical estimator has a general form, proposed by Jibson (Eng Geol 91:209–218, 2007), relating Newmark displacement to Arias intensity (as parameter representing the energy of the seismic forces) and to critical acceleration (as parameter representing the dynamic shear resistance of the sliding mass). As an example of application, this relation was employed to provide a basic document for earthquake-induced landslide hazard assessment at regional scale, according to a method proposed by Del Gaudio et al. (Bull Seismol Soc Am 93:557–569, 2003), applied to the whole Iranian territory, including Zagros region. This method consists in evaluating the shear resistance required to slopes to limit the occurrence of seismically induced failures, on the basis of the Newmark’s model. The obtained results show that the exposure to landslide seismic induction is maximum in the Alborz Mountains region, where critical accelerations up to *0.1 g are required to limit the probability of seismic triggering of coherent type landslides within 10% in 50 years

Attenuation relation of Arias intensity for Zagros Mountains region (Iran)

Arias intensity is considered a shaking parameter suitable for characterizing earthquake impact on ground stability. Within the framework of a study aimed at providing tools for the assessment of hazards related with earthquake induced slope failures, Arias intensity attenuation relations were determined for the Zagros Mountains region, an active tectonic belt elongated NW-SE in the western and south-western part of Iran. The calculation of relation coefficients was based on strong-motion data of earthquakes located in the Zagros area and recorded by Iranian stations managed by BHRC (Building and Housing Research Center of Iran). Five models of attenuation relation were considered and their coefficients were estimated through a least square regression analysis. The relations obtained were then applied to a data sample different from that used for regression and the RMS (Root Mean Square) of residuals was examined in order to compare effectiveness of different relations in probabilistic estimates. Furthermore a comparison made with attenuation relations obtained *Manuscript Click here to view linked References 2 for the Alborz and central part of Iran showed significant differences possibly related to structural differences

Application of a time probabilistic approach to seismic landslide hazard estimates in Iran

Iran is a country located in a tectonic active belt and is prone to earthquake and related phenomena. In the recent years, several earthquakes caused many fatalities and damages to facilities, e.g. the Manjil (1990), Avaj (2002), Bam (2003) and Firuzabad-e-Kojur (2004) earthquakes. These earthquakes generated many landslides. For instance, catastrophic landslides triggered by the Manjil Earthquake (Ms = 7.7) in 1990 buried the village of Fatalak, killed more than 130 peoples and cut many important road and other lifelines, resulting in major economic disruption. In general, earthquakes in Iran have been concentrated in two major zones with different seismicity characteristics: one is the region of Alborz and Central Iran and the other is the Zagros Orogenic Belt. Understanding where seismically induced landslides are most likely to occur is crucial in reducing property damage and loss of life in future earthquakes. For this purpose a time probabilistic approach for earthquake-induced landslide hazard at regional scale, proposed by Del Gaudio et al. (2003), has been applied to the whole Iranian territory to provide the basis of hazard estimates. This method consists in evaluating the recurrence of seismically induced slope failure conditions inferred from the Newmark's model. First, by adopting Arias Intensity to quantify seismic shaking and using different Arias attenuation relations for Alborz - Central Iran and Zagros regions, well-established methods of seismic hazard assessment, based on the Cornell (1968) method, were employed to obtain the occurrence probabilities for different levels of seismic shaking in a time interval of interest (50 year). Then, following Jibson (1998), empirical formulae specifically developed for Alborz - Central Iran and Zagros, were used to represent, according to the Newmark's model, the relation linking Newmark's displacement Dn to Arias intensity Ia and to slope critical acceleration ac. These formulae were employed to evaluate the slope critical acceleration (Ac)x for which a prefixed probability exists that seismic shaking would result in a Dn value equal to a threshold x whose exceedence would cause landslide triggering. The obtained ac values represent the minimum slope resistance required to keep the probability of seismic-landslide triggering within the prefixed value. In particular we calculated the spatial distribution of (Ac)x for x thresholds of 10 and 2 cm in order to represent triggering conditions for coherent slides (e.g., slumps, block slides, slow earth flows) and disrupted slides (e.g., rock falls, rock slides, rock avalanches), respectively. Then we produced a probabilistic national map that shows the spatial distribution of (Ac)10 and (Ac)2, for a 10% probability of exceedence in 50 year, which is a significant level of hazard equal to that commonly used for building codes. The spatial distribution of the calculated (Ac)xvalues can be compared with the in situ actual ac values of specific slopes to estimate whether these slopes have a significant probability of failing under seismic action in the future. As example of possible application of this kind of time probabilistic map to hazard estimates, we compared the values obtained for the Manjil region with a GIS map providing spatial distribution of estimated ac values in the same region. The spatial distribution of slopes characterized by ac < (Ac)10 was then compared with the spatial distribution of the major landslides of coherent type triggered by the Manjil earthquake. This comparison provides indications on potential, problems and limits of the experimented approach for the study area. References Cornell, C.A., 1968: Engineering seismic risk analysis, Bull. Seism. Soc. Am., 58, 1583-1606. Del Gaudio V., Wasowski J., & Pierri P., 2003: An approach to time probabilistic evaluation of seismically-induced landslide hazard. Bull Seism. Soc. Am., 93, 557-569. Jibson, R.W., E.L. Harp and J.A. Michael, 1998: A method for producing digital probabilistic seismic landslide hazard maps: an example from the Los Angeles, California, area, U.S. Geological Survey Open-File Report 98-113, Golden, Colorado, 17 pp

A time probabilistic approach to seismic landslide hazard estimates in Iran

Understanding where seismically induced landslides are most likely to occur is crucial in land use planning and civil protection actions aimed at reducing property damage and loss of life in future earthquakes. For this purpose an approach proposed by Del Gaudio et al. [1] has been applied to the whole Iranian territory to provide the basis to assess location and temporal recurrence of conditions of seismic activation of slope failures, according to the Newmark's model [2]. Following this approach, occurrence probabilities for different levels of seismic shaking in a time interval of interest (50 years) were first obtained through a standard hazard estimate procedure. Then, empirical formulae in the form proposed by Jibson et al. [3] and calibrated for the main seismogenic Iranian regions were used to evaluate the slope critical acceleration (Ac)x for which a prefixed probability exists that, under seismic shakings, Newmark's displacement DN exceeds a threshold×corresponding to landslide triggering conditions. The obtained (Ac)x values represent the minimum slope resistance required to limit the probability of landslide seismic triggering within the prefixed value. A map reporting the spatial distribution of these values gives comparative indications on regional different exposure of slopes to shaking capable of inducing failures and provides a reference for hazard estimate at local scale. The obtained results show that the exposure to landslide seismic induction is maximum in the Alborz Mountains region, where critical accelerations up to ∼0.1 g are required to limit the probability of seismic triggering of coherent type landslides within 10% in 50 years

Crack evolution in damage stress thresholds in different minerals of granite rock

Crack evolution in a rock depends on the mineralogy, microstructure and fabric of specific rock type. This study aims to investigate how mineralogy and grain shape affect the microcrack initiation and propagation of granite rock, which contains plagioclase, quartz, k-feldspar, biotite and amphibole, during uniaxial compression loading. Physico-mechanical properties and microcrack features such as linear microcrack density (LMD) and microcrack type were investigated. By acoustic emission (AE) measurements, damage stress thresholds were identified. Then, crack characteristics of a fresh sample were compared with the samples that were loaded until damage threshold stresses. The results demonstrate that at an early stage of loading, pre-existing microcracks growth and LMD of intergranular crack increase. In the elastic phase, all microcracks types increase at the same rate. When the loading reaches to the strength limit of the sample, the total LMD reduced, because cracks start to coalesce and form new and large transgranular microcrack. Investigating crack propagation in mineral shows that at first, microcrack generates in biotite and at last in quartz. Plagioclase has the highest LMD and microcracks usually formed within the cleavage plane, but alteration and inclusions of tiny minerals can drastically change the LMD and orientation of microcracks. Biotite can terminate or let the microcrack to pass through the crystal based on the orientation of the microcrack plane and cleavage microcrack within the mineral. Furthermore, crystals with an aspect ratio higher than two have higher LMD. By getting close to the uniaxial compression strength, more microcracks appear close to the grain boundary which increases the circularity of the grain.Shahram Ghasemi, Mashalah Khamehchiyan, Abbas Taheri, Mohammad Reza Nikudel, Ahmad Zalool

Effects of high temperature processes on physical properties of silica sand

High temperature processes may alter soil properties, creating potential risks of subsidence, erosion and other hazards. Soils may be exposed to high temperatures during some aggressive contaminant remediation processes as well as natural events such as fires. Characterising the effects of high temperatures on soil properties is essential to understanding the potential hazards that may arise after exposure. Thermal treatment and smouldering remediation were carried out on silica sand used here as a simple soil. Changes observed in physical properties were associated with the treatment type and exposure temperature. Particle, minimum and maximum densities were independent of heat treatment type and temperature. In contrast, particle size distribution, mineralogy, capillary rise, and hydraulic conductivity were linked to treatment type and exposure temperature with the most substantial changes associated with smouldering remediation. Changes in colour and mass loss with increasing temperature suggest changes within the crystal structure of the silica sand beyond loss of moisture content within the pore space and dehydration of iron deposits from goethite to hematite. Based on these observations, exposure to high temperature processes and the complex geo-chemical reactions during smouldering remediation can have significant effects on soil properties. Monitoring after exposure is advisable to determine the severity of exposure and any mitigation measures that may be necessary

Re-examination of the spatial distribution of landslides triggered by the Manjil-Iran 1990 earthquake

The Iranian Plateau, one of the most seismically active regions of the world, has a long history of catastrophic earthquakes. One of the recent destructive events that affected good part of Iran, was the large magnitude (MS =7.7, MW=7.3, Mb =6.4) Manjil earthquake of June 20, 1990, 21:00:10.9 UT. It completely destroyed 700 villages in the Sefidrud river valley and also the cities of Rudbar, Manjil and Loshan, killing more than 40,000 people, injuring 60,000 and rendering 500,000 homeless. Many landslides were triggered by the earthquake and some of them were catastrophic causing numerous fatalities and damage to infrastructure. In this paper the spatial distribution of 51 major landslides triggered by the Manjil earthquake is examined to assess the susceptibility to seismically induced landsliding of an area located in the middle of Alborz mountain range in the northern part of Iran. The study area, which covers 310 km2 is characterized by high relief (including elevations ranging between 1960 and 160 meters a.s.l.) and generaly steep slopes. From the lithological point of view, the study area contains Eocene age volcanic tuffs and andesites, Alborz magmatic assemblage (Karaj Formation, Eocene) consisting of porphyritic and nonporphyritic, andesitic and andesite-basaltic compositions, rhyodacites, calcareous and non-calcareous pyroclastics such as tuffs and agglomerates, limestone, shale and sandstone (Shamshak Formation), unconsolidated, poorly sorted Quaternary deposits. In this study, topographic data with a 30 m resolution and a digital representation of, geology, relevant geotechnical parameters and seismic shaking (Arias intensity) were ingested into a GIS. Then, using regional attenuation relations, Newmark's permanent-deformation (sliding-block) analysis was applied to estimate coseismic landslide displacements and to predict spatial probability of slope-failures. The modelled displacements were compared with the inventory of landslides triggered by the Manjil earthquake to test the reliability of the identification of the zones susceptible to earthquake-induced landslides. The results show that only 40 percent of major landslides were located in areas where the estimated Newmark displacement is larger than the value (10 cm) generally considered as a critical threshold for slope failure: these landslides are found on steeper slopes made of tuffs, agglomerates and limestones. The remaining 60 percent of landslides (with estimated Newmark displacement below the critical value) were found on shallower slopes mostly including Quaternary deposits and interbedded shales and sandstones (Shamshak Formation), and closely associated with the drainage network. Different causes of the apparent discrepancies between the calculated Newmark displacements and landslide triggering are analysed by examining the influence of the uncertainties in geotechnical parameters, possibility of liquefaction failure, as well as the role of factors like topographic, and lithologic shaking amplification, delayed failure following alteration of hydrogeological conditions, and river erosion

Artificial microcracking of granites subjected to salt crystallization aging test

Salt crystallization-induced decay of Vardavard granodiorite and Shirkouh monzogranite, two Iranian building stones, were assessed with two non-destructive methods: saturation-buoyancy technique and P- and S-wave velocity measurement. Moreover, polarized and fluorescence microscopy studies were used to evaluate the behavior of the studied stones at microscopic scale against a salt crystallization aging test. The aging test extended pre-existing microcracks and generated new ones. Intracrystalline microcracking was the most predominant microcrack type for both samples. Fine-grained Vardavard granodiorite experienced higher intercrystalline microcracking than coarse-grained Shirkouh monzogranite. The microcracking mechanism of feldspars substantially depends on their alteration degree and microstructural precursors. When a growing microcrack reaches a biotite, it propagates within the crystal if the growing microcrack coincides with the cleavage plane; otherwise, it propagates as an intercrystalline one. The increase in maximum microcrack length of the samples was higher than the increase in their mean microcrack length. Low-strength Vardavard granodiorite showed higher microcrack width after the aging test. Dry weight loss in low-strength Vardavard granodiorite was more pronounced than in high-strength Shirkouh monzogranite. Dry unit weight decreased at a higher rate than saturated unit weight with the increase of effective porosity. The reduction in ultrasonic wave velocities and the increment in effective porosity and water absorption were more pronounced for Vardavard granodiorite, indicating a higher degree of decay, i.e., higher microcrack generation, enlargement, and widening. Shirkouh monzogranite, which has large-sized crystals and pores, wider initial microcracks, high tensile strength, and low effective porosity and microcrack density, was more durable than Vardavard granodiorite