ALBERT

Description: In this work, we present the seismic catalogue compiled for Central Asia (Kazakhstan, Kyrgyzstan, Tajikistan, Uzbekistan and Turkmenistan) in the framework of the Earthquake Model Central Asia (EMCA) project. The catalogue from 2000 B.C. to 2009 A.D. is composed by 33,034 earthquakes in the MLH magnitude (magnitude by surface waves on horizontal components widely used in practice of the former USSR countries) range from 1.5 to 8.3. The catalogue includes both macroseimic and instrumental constrained data, with about 32,793 earthquake after 1900 A.D. The main sources and procedure used to compile the catalogues are discussed, and the comparison with the ISC-GEM catalogue presented. Magnitude of completeness analysis shows that the catalogue is complete down to magnitude 4 from 1959 and to magnitude 7 from 1873, whereas the obtained regional b value is 0.805.

Description: Within the framework of the EMCA - Earthquake Model Central Asia - project, the cities of Bishkek (Kyrgyzstan) and Dushanbe (Tajikistan) were selected for building monitoring using measurements of seismic noise to obtain the dynamical properties of the buildings. Eight buildings of different construction types, date of construction and building height, both, Soviet-era and recently constructed buildings, were instrumented for a period of a few hours. In this study, an overview of the experiment is given, including a short description of each monitored building’s structure and the performed installation. Preliminary results for a representative Soviet-era residential building in Dushanbe are presented. Modal analysis is performed using the Frequency Domain Decomposition (FDD) method to estimate the natural frequencies and the mode shapes. The wave propagation velocities in the two directions along the building axes are determined by an interferometric approach. Although the experimental set-up was not the optimal, valuable information about the dynamical characteristics of the buildings were still obtained.

Description: In this work, the development of an on-site early warning system for Bishkek (Kyrgyzstan) is outlined. Several low cost sensors equipped with MEMS accelerometers are installed in eight buildings distributed within the urban area. The different sensing units communicate each other via wireless links and the seismic data are streamed in real-time to the data center using internet. Since each single sensing unit has computing capabilities, software for data processing can be installed to perform decentralized actions. In particular, each sensing unit can perform event detection task and run software for on-site early warning. If a description for the vulnerability of the building is uploaded in the sensing unit, this piece of information can be exploited to introduce the expected probability of damage in the early-warning protocol customized for a specific structure.

Description: Central Asia is one of the most exposed regions in the world to landslide hazard. The large variability of local geological materials, together with the difficulties in forecasting heavy precipitation locally and in quantifying the level of ground shaking, call for harmonized procedures to better quantify the hazard and the negative impact of slope failures across the Central Asian countries. As a first step towards a quantitative landslide hazard and risk assessment, a landslide susceptibility analysis at regional scale has been carried out, by benefitting of novel seismic hazard outcomes reached in the frame of Earthquake Model Central Asia (EMCA) project. By combining information coming from diverse potential factors, it is possible to detect areas where a potential for landslides exists. Initial results allow the identification of areas that are more susceptible to landslides with a level of accuracy greater than 70%. The presented method is, therefore, capable of supporting land planning activities at the regional scale in places where only scarce data are available.

Description: It is well known that variability in the surface geology potentially leads to the modification of earthquake-induced ground motion over short distances. Although this effect is of major importance when seismic hazard is assessed at the urban level, it is very often not appropriately accounted for. In this paper, we present a first attempt at taking into account the influence of the shallow geological structure on the seismic hazard assessment for Bishkek, Kyrgyzstan, using a proxy (Vs30) that has been estimated from in situ seismic noise array analyses, and considering response spectral ratios calculated by analyzing a series of earthquake recordings of a temporary seismic network. To highlight the spatial variability of the observed ground motion, the obtained results are compared with those estimated assuming a homogeneous Vs30 value over the whole urban area. The seismic hazard is evaluated in terms of peak ground acceleration (PGA) and spectral acceleration (SA) at different periods (frequencies). The presented results consider the values obtained for a 10% probability of exceedance in 50 years. The largest SA estimated considering a rock site classification of the area (0.43 g) is observed for a period of 0.1 s (10 Hz), while the maximum PGA reaches 0.21 g. When site effects are included through the Vs30 proxy in the seismic hazard calculation, the largest SA, 0.67 g, is obtained for a period of 0.3 s (about 3.3 Hz). In terms of PGA, in this case the largest estimated value reaches 0.31 g in the northern part of the town. When the variability of ground motion is accounted for through response spectrum ratios, the largest SA reaches a value as high as 1.39 g at a period of 0.5 s. In general, considering site effects in the seismic hazard assessment of Bishkek leads to an increase of seismic hazard in the north of the city, which is thus identified as the most hazardous part within the study area and which is more far away from the faults.

Description: Central Asia is one of the seismically most active regions in the world. Its complex seismicity due to the collision of the Eurasian and Indian plates has resulted in some of the world’s largest intra-plate events over history. The region is dominated by reverse faulting over strike slip and normal faulting events. The GSHAP project (1999), aiming at a hazard assessment on a global scale, indicated that the region of Central Asia is characterized by peak ground accelerations for 10% probability of exceedance in 50 years as high as 9 m/s 2 . In this study, carried out within the framework of the EMCA project (Earthquake Model Central Asia), the area source model and different kernel approaches are used for a probabilistic seismic hazard assessment (PSHA) for Central Asia. The seismic hazard is assessed considering shallow (depth 〈 50 km) seismicity only and employs an updated (with respect to previous projects) earthquake catalog for the region. The seismic hazard is calculated in terms of macroseismic intensity (MSK-64), intended to be used for the seismic risk maps of the region. The hazard maps, shown in terms of 10% probability of exceedance in 50 years, are derived by using the OpenQuake software [Pagani et al. 2014], which is an open source software tool developed by the GEM (Global Earthquake Model) foundation. The maximum hazard observed in the region reaches an intensity of around 8 in southern Tien Shan for 475 years mean return period. The maximum hazard estimated for some of the cities in the region, Bishkek, Dushanbe, Tashkent and Almaty, is between 7 and 8 (7-8), 8.0, 7.0 and 8.0 macroseismic Intensity, respectively, for 475 years mean return period, using different approaches. The results of different methods for assessing the level of seismic hazard are compared and their underlying methodologies are discussed.

Description: During the past centuries, many cities in Central Asia have suffered significant damages caused by earthquakes. A crucial step towards preparedness for future events, the definition of the optimal engineering designs for civil structures and the mitigation of earthquake risks involves the accomplishment of site response studies. To accurately identify local variations of the site response at different locations within the cities, earthquakes recorded by seismic networks as well as measurements of the seismic noise can be used for estimating the resonance frequencies and for evaluating the expected level of ground motion at each site. Additionally, the measurements can help identifying site specific features like more-dimensional resonances and directional effects. This information can be complemented with array measurements of ambient seismic noise in order to estimate local shear-wave velocity profiles, an essential parameter for evaluating the dynamic properties of soil, and to characterize the corresponding sediment layers at each site. The present study gives an overview on the progressive development of the seismic zonation studies in the frame of EMCA carried out in several cities in Central Asia.

Description: Rapidly expanding urban areas in Central Asia are increasingly vulnerable to seismic risk; but at present, no earthquake early warning (EEW) systems exist in the region despite their successful implementation in other earthquake-prone areas. Such systems aim to provide short (seconds to tens of seconds) warnings of impending disaster, enabling the first risk mitigation and damage control steps to be taken. This study presents the feasibility of a large scale cross-border regional system for Central Asian countries. Genetic algorithms are used to design efficient EEW networks, computing optimal station locations and trigger thresholds in recorded ground acceleration. Installation of such systems within 3 years aims to both reducing the endemic lack of strong motion data in Central Asia that is limiting the possibility of improving seismic hazard assessment, and at providing the first regional earthquake early warning system in the area.

Description: One of the key parameters for earthquake source physics is stress drop since it can be directly linked to the spectral level of ground motion. Stress drop estimates from moment-corner frequency analysis have been shown to be extremely variable, and this to a much larger degree than expected from the between-event ground motion variability. This discrepancy raises the question whether classically determined stress drop variability is too large, which would have significant consequences for seismic hazard analysis. We use a large high-quality dataset from Japan with well-studied stress drop data to address this issue. Non-parametric and parametric reference ground motion models are derived and the relation of between-event residuals for JMA equivalent seismic intensity and peak ground acceleration with stress drop is analyzed for crustal earthquakes. We find a clear correlation of the between-event residuals with stress drops estimates; however, while the island of Kyushu is characterized by substantially larger stress drops than Honshu, the between-event residuals do not reflect this observation, leading to the appearance of two event families with different stress drops levels yet similar range of between-event residuals. Both the within-family and between-family stress drop variations are larger than expected from the ground motion between-event variability. A systematic common analysis of these parameters holds the potential to provide important constraints on the relative robustness of different groups of data in the different parameter spaces and to improve our understanding on how much of the observed source parameter variability is likely to be true source physics variability.

Description: We propose a P-wave based procedure for the rapid estimation of the radiated seismic energy, and a novel relationship for obtaining an energy-based local magnitude (MLe) measure of the earthquake size. We apply the new procedure to the seismic sequence that struck central Italy in 2016. Scaling relationships involving seismic moment and radiated energy are discussed for the Mw 6.0 Amatrice, Mw 5.9 Ussita and Mw 6.5 Norcia earthquakes, including 35 ML 〉4 aftershocks. The Mw 6.0 Amatrice earthquake shows the highest apparent stress, and the observed differences among the three main events highlight the dynamic heterogeneity with which large earthquakes can occur in central Italy. Differences between estimates of MLe and Mw allows identification of events which are characterized by a higher proportion of energy being transferred to seismic waves, providing important real-time indications of earthquakes shaking potential.