Anatoly Ischuk - Academia.edu (original) (raw)

Papers by Anatoly Ischuk

Geosciences, Apr 26, 2024

GNSS derived velocity vectors for stations located throughout Central Asia. All vectors are calcu... more GNSS derived velocity vectors for stations located throughout Central Asia. All vectors are calculated and presented in the International Terrestrial Reference Frame 2008 (ITRF08).

International Journal of Geophysics, Aug 27, 2018

In summer of 2015 we had completed a geophysical survey complemented by borehole drilling near th... more In summer of 2015 we had completed a geophysical survey complemented by borehole drilling near the right-bank slope of the Rogun Dam construction site, Tajikistan. These data were first processed and then compiled within a 3D geomodel. The present paper describes the geophysical results and the 3D geomodel generated for an ancient mass movement located immediately downstream from the construction site. The geophysical survey included electrical and seismic profiles and ambient vibration measurements as well as earthquake recordings. The electrical and seismic data were processed as tomographic sections, the ambient vibrations as horizontal-to-vertical spectral H/V ratios, and the earthquake data mainly in terms of standard spectral ratios. By estimating the average shear wave velocities of the subsurface, we computed the local soft layer thickness from the resonance frequencies revealed by the H/V ratios. Three seismic stations had been installed for ten days along a profile crossing the intermediate plateau. Standard spectral ratios inferred from ten processed earthquake measurements confirmed the presence of a thick soft material layer on the plateau made of weathered rocks, colluvium, and terrace deposits, which produce a medium-level amplification at about 2 Hz. The 3D geomodel was first built on the basis of new topographic data, satellite imagery, and a geological map with two sections. Then, the various electrical resistivity and seismic refraction tomographies were inserted in the geomodel. The soft layer thickness information and borehole data were represented in terms of logs in the model. The site is crossed by the Ionakhsh Fault that could be modeled on the basis of the geological inputs and of a lateral resistivity gradient found on one electrical profile along the steep lower slope. The integrated interpretation of all results reveals that probably only a relatively small part of the ancient giant mass movement is really exposed to slope instability phenomena.

EGU General Assembly Conference Abstracts, Apr 1, 2017

The terminal stage of subduction sets in when the continental margin arrives at the trench and th... more The terminal stage of subduction sets in when the continental margin arrives at the trench and the opposite forces of the sinking slab and buoyant continent extend and ultimately sever the subducted lithosphere. This process, although common in geological history, is short-lived, and therefore rarely observed. The deep seismicity under the Hindu Kush (Central Asia), including the 2015 M w 7.5 event, is a rare case that testifies to this process. Here, we use new seismological data to create a high resolution picture of slab break-off and infer its dynamics. High precision earthquake locations and tomographic images show subduction of continental crust down to ∼180 km. A large dataset of source mechanisms indicates sub-vertical extension in the entire slab but a strain rate analysis showed that the deeper seismogenic portion of the slab, below the subducted crust, extends at higher rates (∼40 km/Ma). Most M w > 7 earthquakes between 1983-2015, relocated relative to our new well-constrained earthquake catalog, cluster in a small volume below 180 km, and indicate shearing on an overturned interface. A slip model for the latest 2015 M w 7.5 event suggests that it ruptured into a seismic gap on this interface. From this configuration we conclude that a horizontal slab tear develops along-strike of the Hindu Kush seismic zone at the base of the subducted continental crust. Below the subducted crust, the deepest and also largest earthquakes (180-265 km) are likely associated with deformation in the mantle lithosphere. From the seismicity distribution and the rupture mechanisms we further deduce that the dominant deformation mechanism in this deeper portion of the slab changes along-strike from simple to pure shear. The fastest detachment rates and largest earthquakes occur during the simple shear dominated stage. Earthquakes in the upper part (60-180 km), above the rapidly extending slab, might be triggered by processes related to the subduction of crustal rocks.

Advancing Culture of Living with Landslides, 2017

The ongoing construction and further operation of the Rogun HPP in one of the most seismically ac... more The ongoing construction and further operation of the Rogun HPP in one of the most seismically active regions of Central Asia can cause activation of dangerous processes along the slopes adjacent to the dam and reservoir. Among the gravitational mass displacements recorded near the major hydroelectric facilities, the old right-bank landslide located downstream the hydrosystem is worth of special consideration. Possible landslide activation triggered by earthquakes and/or flooding may cause collapse of unstable masses with adverse consequences for the major HPP facilities. The complex geological and tectonic conditions of the construction area, the great height of the earth-fill Rogun dam, as well as large-scale man-made impacts on the slopes surrounding major HPP facilities, including the filling of the reservoir, require a profound analysis of slope stability downstream from the dam with assessment of possible landslide risk scenarios. This report describes the main results of the comprehensive studies, calculations and dynamic modeling of stability of the right-bank landslide-prone slope, which suggest that the potentially unstable mass of strongly weathered rocks with the volume from 2 to 5 × 106 m3 on a steep part of the slope may fully or partially collapse in case of combination of strong seismic action (PGA > 0.3 g) and of precipitation. In case of synchronous collapse of about five-million m3 of unstable rocks, the blockage of the Vakhsh River by a landslide dam is inevitable, with risk of flooding of the tunnels and consequential disturbance of normal functioning of the HPP.

Engineering Geology, Nov 1, 2009

Earthquake-triggered landslides are a major geological hazard in Central Asia. In July 1949, the ... more Earthquake-triggered landslides are a major geological hazard in Central Asia. In July 1949, the M7.4 Khait earthquake triggered many hundreds of landslides in a mountainous region near the southern limit of the Tien Shan Mountains, central Tajikistan. These landslides involved widespread rock-slope failure as well as large numbers of flowslides in loess that mantles the steep slopes of the region. In the Yasman valley hundreds of loess landslides coalesced to form a massive loess flow (est. vol. 245 Mm 3) that travelled up to 20 km on a slope of only 2°. In an adjacent valley, the Khait landslide involved transformation of an earthquake-triggered rockslide into a very rapid flow by the entrainment of saturated loess into its movement. It travelled 7.41 km over a vertical distance of 1421 m with an estimated average velocity of 30 m/s. We estimate its volume as 75 Mm 3 , an order of magnitude less that previously published estimates. The Khait landslide was simulated using DAN. The number of casualties due to earthquake-triggered landslides in the epicentral region was considerable. Approximately 4000 people were killed in the Yasman valley loess flow as 20 villages (kishlaks) were overwhelmed. In the Khait landslide alone we estimate ca. 800 people lost their lives when the villages of Khait and Khisorak were overrun by rapidly moving debris. Our data indicates that a total of approximately 7200 people were killed by earthquake-triggered landslides in the epicentral region of the Khait earthquake and that, in terms of loss of life, the 1949 Yasman valley loess flow was one of the most destructive landslides in recent history.

. Central Asian countries, which include Kazakhstan, the Kyrgyz Republic, Tajikistan, Turkmenista... more . Central Asian countries, which include Kazakhstan, the Kyrgyz Republic, Tajikistan, Turkmenistan, and Uzbekistan, are known to be highly exposed to natural hazards, particularly earthquakes, floods, and landslides. With the aim of enhancing financial resilience and risk-based investment planning to promote disaster and climate resilience in Central Asia, the European Union, in collaboration with the World Bank and the GFDRR, launched a regional program for “Strengthening Financial Resilience and Accelerating Risk Reduction in Central Asia” (SFRARR). Within this framework, a consortium of national and international scientific institutions was established and tasked with developing a regionally consistent multi-hazard and multi-asset probabilistic risk assessment. The overall goal was to improve scientific understanding on local perils and to provide local stakeholders and governments with up-to-date tools to support risk management strategies. However, the development of a comprehensive risk model can only be done on the base of an accurate hazard evaluation, the reliability of which depends significantly on the availability of local data and direct observations. This paper describes the preparation of the input data sets required for the implementation of a probabilistic earthquake model for the Central Asian countries. In particular, it discusses the preparation of a new regional earthquake catalog harmonized between countries and homogenized in moment magnitude (Mw), as well as the preparation of a regional database of selected active faults with associated slip rate information to be used for the construction of the earthquake source model. The work was carried out in collaboration with experts from the local scientific community, whose contribution proved essential for the rational compilation of the two harmonized datasets.

Bulletin of the Seismological Society of America, 2017

A seismic hazard evaluation in terms of 5% damped peak ground acceleration and spectral accelerat... more A seismic hazard evaluation in terms of 5% damped peak ground acceleration and spectral acceleration was carried out for the Arabian Peninsula using a probabilistic approach. For this purpose, a revised earthquake catalogue extending from 19 AD to 2015 AD was utilized, including all available earthquakes with magnitude greater than 4.0. The seismic hazard assessment was conducted in the framework of the logic-tree approach to take into account epistemic uncertainties associated with input parameters [seismic source model, recurrence parameters, maximum magnitude, and ground-motion prediction equations (GMPEs)]. A novel seismic source model consisting of 57 seismic zones is proposed as an alternative included in the modeled logic tree. The recurrence parameters were computed mainly using the doubly bounded exponential distribution. Horizontal ground motion in terms of geometric mean acceleration was computed for different spectral periods utilizing GMPEs borrowed from tectonic environments comparable to those surrounding the Arabian Peninsula. The 5% damped seismic hazard values at bedrock conditions were calculated for return periods of 475, 975, and 2475 years. Additionally, uniform hazard spectra for important population centers in the Arabian Peninsula are provided. The highest seismic hazard values were observed along the Zagros, the East Anatolian Fault, and the Gulf of Aqaba-Dead Sea Fault. The provided maps could be used to design the Unified Gulf Building Code.

General Assembly European Geosciences Union (Vienna, Austria 2013), Apr 1, 2013

ABSTRACT The Pamir - Hindu Kush orogenic system is surely one of the least studied corners along ... more ABSTRACT The Pamir - Hindu Kush orogenic system is surely one of the least studied corners along the India-Eurasia collisional belt despite featuring several tectonically unique features. The lack of modern geophysical data from the region left the deep processes and structures that cause and host the unique intermediate depth earthquakes here mostly in the dark. To shed light on some of these processes we image the seismic velocity structure in the upper mantle and transition zone. We implemented a tomographic inversion for P-wave velocities based on teleseismic earthquakes recorded at temporal and permanent seismic stations within the study region. Our study is mainly based on the temporary seismic deployments from the TIPAGE (Tien Shan Pamir Geodynamic Project), FERGHANA and TIPTIMON (Tien Shan Pamir Monitoring Program) projects. Within the framework of these projects, 40, 20 and 25 mostly broadband stations were deployed from mid-2008 to mid-2010 and from June 2012 onwards within Tajikistan and Kyrgyzstan. These data were complemented by a similar number of permanent stations covering in the course most of central Asia. We measured so far more than 30,000 phase arrivals from approx. 700 earthquakes occurring at epicentral distances between 20 to 180 degree. This data set is inverted simultaneously for velocity anomalies and station corrections. To account for the large variations of crustal thickness beneath the study region, we implemented a newly determined Moho model for the Pamir and surroundings, which is based on receiver function analysis. The resulting tomographic model extends to depths of approximately 500 km and covers the area between 67 to 79 degree East and 36 to 44 degree North. We will present preliminary P wave velocity images based on the currently available data set.

Disaster education in schools can raise awareness among students, teachers, and parents, leading ... more Disaster education in schools can raise awareness among students, teachers, and parents, leading to more accurate risk perception and better understanding of protective measures. For a disaster education curriculum to be effective, particularly in the context of earthquakes, the curriculum must be science-based. For example, to prepare for earthquakes, it is crucial to understand the physical processes that cause them. This is particularly important in communities that hold a fatalistic attitude towards earthquakes where instructing students to "drop, cover, and hold on" during an earthquake will not be effectively practiced if community members have no scientific knowledge of earthquakes. Unfortunately, most teachers lack the knowledge, resources and expertise required for teaching a science-based earthquake education curriculum. Our paired teaching approach is one way to support school teachers in bringing earthquake science into their classrooms.

We have installed 20 new Global Positioning System (GPS) markers in the West Pamir and the Tajik ... more We have installed 20 new Global Positioning System (GPS) markers in the West Pamir and the Tajik Depression and measured 25 markers once a year between 2013 and 2016 in survey mode. The stations are positioned along two dense NW-SE oriented profiles with an average spacing of 5-10 km. The profiles cross the Darvaz and the Vakhsh/Ilyak fault and thus monitor the recent slip of these two profiles, which are expected to accommodate the gravity-driven westward extrusion of the West Pamir into the Tajik Depression. Some of the stations include millimeter to centimeter offsets potentially caused by the 2015 Mw7.2 Sarez, Pamir, earthquake.

Geophysical Research Letters, 2018

Geodetically derived velocities from Central Asia show that Northern Afghanistan, the Tajik Pamir... more Geodetically derived velocities from Central Asia show that Northern Afghanistan, the Tajik Pamir, and northwestern Pakistan all move northward with comparable large velocities toward Eurasia. Steep velocity gradients, hence high strain rates, occur only across the Main Pamir Fault zone and with lesser magnitude between the northernmost Hindu Kush and the south and southeast margins of the Tajik Depression. Localized shortening is not apparent on any active India-Hindu Kush crustal boundary; hence, crustal convergence between India and Eurasia in Central Asia is absorbed primarily on the northern and western margins of the Pamir. This concentrated strain on the Pamir margins is consistent with one, geometrically complex, interface between subducting Asian lithosphere and the Pamir. That interface might curve westward such that the Hindu Kush seismic zone is a continuation of the Pamir seismic zone, or alternatively, Hindu Kush earthquakes might occur in convectively unstable mantle lithosphere mechanically detached from surface faults. Plain Language Summary Using Global Positioning System (GPS) measurements of surface velocities, we find that much of the relative motion between India and Eurasia in Central Asia is accommodated on a single crustal boundary on the north side of the Pamir, wrapping around the eastern and southern margins of the Tajik Depression.

NATO Science Series, 2006

Journal of Geophysical Research: Solid Earth, 2019

The Cenozoic convergence between India and Asia has created Earth's thickest crust in the Pamir-T... more The Cenozoic convergence between India and Asia has created Earth's thickest crust in the Pamir-Tibet Plateau by extreme crustal shortening. Here we study the crustal structure of the Pamir and western Tian Shan, the adjacent margins of the Tajik, Tarim, and Ferghana Basins, and the Hindu Kush, using data collected by temporary seismic experiments. We derive, compare, and combine independent observations from P and S receiver functions. The obtained Moho depth varies from~40 km below the basins to a double-normal thickness of 65-75 km underneath the Pamir and Hindu Kush. A Moho doublet-with the deeper interface down to a depth of~90 km-coincides with the arc of intermediatedepth seismicity underneath the Pamir, where Asian continental lower crust delaminates and rolls back. The crust beneath most of the Central and South Pamir has a low V p /V s ratio (<1.70), suggesting a dominantly felsic composition, probably a result of delamination/foundering of the mafic rocks of the lower crust. Beneath the Cenozoic gneiss domes of the Central and South Pamir, which represent extensional core complexes, the V p /V s ratios are moderate to high (~1.75), consistent with the previously observed, midcrustal low-velocity zones, implying the presence of crustal partial melts. Even higher crustal average V p /V s ratios up to 1.90 are found in the sedimentary basins and along the Main Pamir Thrust. The ratios along the latter-the active thrust front of the Pamir-may reflect fluid accumulations within a strongly fractured fault system.