Statistical analysis and long-term prediction of seismicity for linear zones

The model of the Poisson point process is too vague for earthquake locations in space and time: earthquakes tend to cluster in middle distances and to repulse in large ones. The Poisson point model with variable density makes it possible to describe the tendency for clustering but does not reveal the periodicity of clusters. The author proposes the point-process model where locations of points are determined not by densities of point distribution, but by densities of interpoint differences distribution. In the model, a latent periodicity is revealed and used for prediction of a point process. In 1983, the point-process model prediction was made for the Kuril Islands for 1983–1987 and two signs of danger in time and location were determined. Then they were confirmed by strong earth-quakes. In 1989, a similar prediction was made for North Armenia. The Spitak earthquake in 1988 is clearly seen from the data of previous earthquakes.     

Geology, coal quality, and resources of the Antaramut–Kurtan–Dzoragukh coal field, north-central Armenia

The Antaramut–Kurtan–Dzoragukh (AKD) coal deposit is a previously unrecognized coal field in north-central Armenia. Coal has been known to exist in the general vicinity since the turn of the century, but coal was thought to be restricted to a small (1 km²) area only near the village of Antaramut. However, through detailed field work and exploratory drilling, this coal deposit has been expanded to at least 20 km², and thus renamed the Antaramut–Kurtan–Dzoragukh coal field, for the three villages that the coal field encompasses. The entire coal-bearing horizon, a series of tuffaceous sandstones, siltstones, and claystones, is approximately 50 m thick. The AKD coal field contains two coal beds, each greater than 1 m thick, and numerous small rider beds, with a total resource of approximately 31,000,000 metric tonnes. The coals are late Eocene in age, high volatile bituminous in rank, relatively high in ash yield (approximately 40%, as-determined basis) and moderate in sulfur content (approximately 3%, as-determined basis). The two coal beds (No. 1 and No. 2), on a moist, mineral-matter-free basis, have high calorific values of 32.6 MJ/kg (7796 cal/g) and 36.0 MJ/kg (8599 cal/g), respectively. Coal is one of the few indigenous fossil fuel resources occurring in Armenia and thus, the AKD coal field could potentially provide fuel for heating and possibly energy generation in the Armenian energy budget.     

Influence of earthquakes on the stability of slopes

Earthquakes are a major trigger for instability of natural and man-made slopes. Often the instability of slopes due to an earthquake causes more destruction and kills more people than the actual earthquake itself. A comparison is made between different methodologies to analyze the potential stability of slopes during earthquakes. Theoretically, it seems simple to calculate the stability of a slope during an earthquake. In reality, however, the stability is influenced by so many parameters that are either not known or which influence is so poorly known that a decent estimation of stability cannot be made. Offshore the situation is worse because proper data required for stability calculations are even less available than onshore. On- and offshore, erosion and weathering create continuously slopes that may become unstable during a future earthquake, offshore also sedimentation creates continuously new slopes. Another fundamental problem in stability analysis is the complicated and largely unknown behavior of seismic waves in three-dimensions in natural materials. The lack of accurate data and the unknown behavior of seismic waves in three-dimensions make estimations of slope stability during an earthquake unreliable.     

Seismic quiescence before the M 7, 1988, Spitak earthquake, Armenia

A detailed analysis of the 35  yr of seismicity between 1962 and 1997 using a gridding technique shows that the M 7, Spitak earthquake of 1988 December 7 was preceded by a quiescence anomaly that started at approximately 1984±0.5, and lasted about 5±0.5  yr, up to the main shock. This quiescence anomaly had a radius of about 20±3  km, estimated from circular areas with 75 per cent rate decrease, centred at the point of maximum significance of the anomaly. The quiescence was clearly present in the aftershock volume during the 5  yr before the 1988 main shock, but its statistically strongest expression was located 30  km NW of the epicentre. This anomaly fulfills the association rules between precursory quiescence anomalies and main shocks, even for a tight definition, and is therefore proposed as a case of precursory quiescence. The largest value of the standard deviate Z , found by random selection of samples by gridding, was Z =14 for a time window of T _w=3  yr, using a sample size of N =300 events. This makes this anomaly the strongest observed so far, and it is the first documented in an environment of continental collision. There are no false alarms exceeding in significance the precursor. The Armenian earthquake catalogue used for this study had 4600 earthquakes with M ≥ M _min=2.2 in the area bounded by 39.5° to 42°N/42.5° to 47°E. From the point of view of homogeneous reporting this is the best catalogue we have analysed so far. The limits of the data used and the density of the grid are dictated by the data, and have no influence on the results. The choice of free parameters does not influence the results significantly within the following limits: 100≤ N ≤500, 2≤ T _w≤7, 2.2≤ M _min≤2.8.     

Applying landscape-ecological concept and GIS modelling for assessing and mapping of ecological situation of mountainous landscapes (on the case of Syunik marz,Armenia)

Regional landscape-ecological studies have acquired a special topicality as they assure efficient environmental conservation and sustainable use of natural resources. A landscape-ecological analysis was performed based on four basic integral indices: (1) ecological potential, (2) ecological stability, (3) ecological load and (4) ecological tension. The values of basic integral indices of the landscape-ecological analysis were calculated as sums of respective factors expressed in scores and multiplied by their significance reflecting coefficients. In agreement with that rule, a formula was derived of calculation of basic indices of landscape-ecological analysis. Subsequently, those factors were integrated by ‘Model Builder’ in ArcGIS applying ‘Weighted Sum’ functions. Finally, through geographic information systems modelling, maps of basic indices of landscape-ecological analysis were produced. In conclusion – ecological potential, stability, load and tension are best indicators for the assessment of the landscape-ecological situation of the studied territory.     

Tectonic and seismic conditions for changes in spring discharge along the Garni right lateral strike slip fault (Armenian Upland)

Abstract

This study presents the relationship between local seismicity and springs discharge, in which the microseismicity modifies the state of stress of the aquifer matrix and these modifications of the local stress control the aquifer behaviour from an example of a basaltic reservoir crossed by a seismic fault.

Along the right-lateral Garni seismic wrench fault, the distribution in space and time of more than 500 micro-earthquakes has been studied providing a pattern of stress distribution. Together with this tectonic survey, the hydrographs of springs issuing from an aquifer located in basaltic lava flows and crossed by the fault have been gauged for 4 years. According to its tectonic, geologic and hydrodynamic properties, the reservoir has been divided in to several parts. The hydrological behaviour of the reservoir and of each of its parts has been modelled, based on the rainfall and hydrodynamic properties of the basaltic reservoir and of nearby reservoirs.

The model allows us to define the ‘normal behaviour’ of the springs, when their discharge is not affected by an earthquake. Anomalies to the normal hydrometric curves are defined, and correlated to small (M < 3.5) earthquakes along the Garni fault. We propose that the circulation of underground water in the area around the fault depends largely on the fracture pattern of the basalts and the aquifer basement, as pointed out from field observations. Changes in spring discharges are explained by variations in the state of stress around the Garni fault, induced by the alternation of elastic strain and stick-slip movement on the fault, and by creep far from the fault. A model of stress distribution is proposed which explains changes in fracture charateristics before and after earthquakes. © Elsevier, Paris     

Heterogeneous response of hydrogeological systems to the Izmit and Düzce (Turkey) earthquakes of 1999

At four sites in Turkey and Armenia the physico-chemical properties of thermal and mineral waters were monitored continuously during the Izmit and Düzce earthquakes that occurred along the North Anatolian fault in August and November 1999. The epicentral distances between the moment magnitude (M_w) 7.6 Izmit earthquake and the monitoring locations were 313, 488, 1,161, and 1,395 km. At the most distant site, the specific electrical conductivity of mineral water from a flowing artesian well dropped co-seismically and postseismically by 7%. No changes were observed at the other sites, although the estimated earthquake strains and peak ground accelerations are much higher. A similar pattern was observed after the Düzce earthquake, which happened three months after the Izmit event. The response of a hydrogeological system seems to depend on the site characteristics rather than on the nature of the earthquake. A hydrogeological model for the sensitive observation site farthest from the Izmit earthquake explains the observations in terms of a changed mixing ratio between two fluid components. Passing seismic waves may trigger a local pore-pressure increase according to the mechanism of advective overpressure. The preconditions for this mechanism, free gas bubbles in the aquifer in combination with a trap for rising bubbles, is probably not fulfilled by the other groundwater systems. Electronic Publication     

Seismic Hazard Assessment in Armenia

An evaluation of seismic hazard assessment in the territory of Armenia is presented in this work. The catastrophic M = 7.0 Spitak earthquake in 1988 revealed the drawbacks of the acting seismic zoning map. Two seismic hazard maps have been compiled in NSSP RA during 1991–1996. The deterministic approach was applied in the first one and the probabilistic in the second one. Both maps were compiled on the basis of the same database. Comparison between the maps shows good correlation. This revised version was published online in June 2006 with corrections to the Cover Date.