Aigulak Focal Area as a Result of the Impact of the 2003 Chuya Earthquake on Gorny Altai

Deev E.V., Panin A.V., Solomina O.N., Bricheva S.S., Borodovskiy A.P., Entin A.L., Kurbanov R.N.

Deev E., Dublyansky Y., Kokh S., Scholz D., Rusanov G., Sokol E., Khvorov P., Reutsky V., Panin A.

Deev E.V., Krzhivoblotskaya V.E., Borodovskiy A.P., Entin A.L.

A system of 22 km long surface rupture produced by paleoearthquakes has been mapped for the first time along the Kubadru Fault which delineates the Kokorya Basin in the north. The ruptures morphology record reverse and right-lateral strike-slip geometry of the Kubadru Fault. The ruptures pattern represent a combined effect of four paleoearthquakes, including three events in the past 1.4 kyr. The magnitudes of the earthquakes could range from 6.7 to 7.6. The revealed structure of the Kubadru Fault Zone consists of counter-dipping reverse faults. Motions on two reverse fault systems maintained thrusting of the Kurai Range on the basin sediments and caused the growth of a foreberg between the basin and the range.

Korzhenkov A.M., Deev E.V., Pozdnyakova N.I.

Structural and geomorphological studies were carried out in the foothills of the Kurai Range in southeast Gorny Altai. It is shown that the structure of the Kurai Fault Zone here is governed by north-dipping reverse faults and thrusts, along which the Kurai Range thrusts onto deposits of the Chuya and Kurai depressions. They are feathered by south-dipping backthrusts. Displacements along these fault systems lead to growth of forbergs in front of the range front and separation of smaller negative morphostructures from the Chuya and Kurai depressions. Numerous fault scarps have been revealed along the faults, which are outlets of seismic sources of paleoearthquakes to the surface. For a number of scarps, in addition to the vertical component, the strike-slip component of displacements is also read in the relief. Some fault scarps have an age of a few hundred years and arose in the sources of paleoearthquakes with minimal magnitude: MW = 6.7–7.3.

Emanov A.F., Emanov A.A., Fateev A.V.

Abstract —The 2003 Chuya earthquake aftershocks are studied using the data obtained during experiments with dense networks of stations. Density maps of the foci of more than 50,000 aftershocks are compared with the day surface faults and the block structure and tectonics of the focal area. The large shearing strain caused by the Chuya earthquake is accompanied by a spatially intermittent aftershock structure stretching along it. The density maps of long-lasted aftershocks differ in structure from the maps of seismic activity in the initial aftershock area. The study has revealed a relationship between the block structure of the epicentral area and the structure of the aftershock process. The nodes of the intersection of faults with the aftershock area are characterized by reduced aftershock activity. The aftershock process is only partly confined to the block-separating faults. In many cases, the aftershock process is shifted relative to these faults or wanders from them.

Rogozhin E.A., Ovsychenko A.N., Larkov A.S.

The paper considers the results of a study of modern strong earthquakes (1991 Racha, 2006 Olyutor, 2003 Altai, and 2011–2012 Tuva) according to a single methodological plan. The need for such studies is dictated by constantly increasing requirements on the accuracy of predicting hazardous natural impacts. Analysis of the seismotectonic conditions of the locations of sources of strong earthquakes made it possible to identify geological structures and thus form an idea of the morphotectonic criteria for identifying potential sources in other regions. Modern earthquakes have continued the development of different-scale tectonic structures directly expressed in the modern relief. These activated structures form regular combinations inscribed in morphostructures of different scales. The displacements during modern earthquakes continue the development of morphostructures traced throughout the Middle Pleistocene–Holocene. The size and number of morphostructures involved in seismic activation are directly related to the magnitude of an event and reflect the specific hierarchical level of seismogenesis. In order to assess the seismic hazard, it is important that the presence or absence of pronounced active faults on the surface does not directly reflect the level of seismic hazard.

Makarov P.V., Khon Y.A.

A new autosoliton view is developed for the seismic process. In physical terms, faults correspond to stationary autosolitons, and inter- and intrafault deformation disturbances are traveling autosolitons. Slow dynamics reveals itself only on large time scales because slow autosoliton disturbances, as a rule, have velocities 4–7 orders of magnitude lower than the sound velocity. It is shown that, in the loaded strong medium, slow autowave and autosoliton disturbances are generated by short dynamic actions (pulses) at interfaces. In real geomaterials, these are block boundaries and various-scale faults. Dynamic movements of structural elements cause the deformation autowaves and autosolitons to propagate from the interfaces into blocks and along faults. Velocities of such deformation autowaves and autosolitons are low and proportional to velocities of the related movements of structural elements in the geomedium. Propagating in structural elements that are in a certain stress-strain state, deformation autowaves and autosolitons can be taken as small disturbances of the existing fields of the stress-strain state. A mathematical model is represented for the geomaterial treated as a nonequilibrium randomly inhomogeneous medium. Special features of the generation and propagation of deformation autosolitons in such media are studied.

Makarov P.V., Smolin I.Y., Khon Y.A., Eremin M.O., Bakeev R.A., Peryshkin A.Y., Zimina V.A., Chirkov A., Kazakbaeva A.A., Akhmetov A.Z.

In the autosoliton view, the complete mathematical model of the seismic process taken as the deformation and fracture process of a loaded geomedium combines dynamic equations of solid mechanics and specific constitutive equations for geomedium rheology. These equations describe both the conventional stress-strain evolution due to the stress wave propagation with sound velocities, which are governed by special features of constitutive equations, and slow dynamics of the loaded strong medium. Numerical investigation is given to the generation of deformation autosolitons, front structure, and propagation of intra- and interfault deformation disturbances. Slow deformation disturbances in real geomedium elements are numerically modeled.

Vysotsky E.M., Novikov I.S., Lunina O.V., Agatova A.R., Nepop R.K.

A 48 km long zone of surface deformation produced by the Ms = 7.3 intracontinental earthquake of 2003 in Gorny Altai is studied in its five segments between the Aktru and Irbistu rivers, where ruptures show the greatest offsets and distinct structural patterns. A total of 554 coseismic ruptures of five slip geometry types are analyzed in terms of length, orientation, and relative percentage. The rupture patterns are discussed with reference to previously published evidence and compared with other strike-slip zones worldwide.

Turova I., Deev E., Pozdnyakova N., Entin A., Nevedrova N., Shaparenko I., Bricheva S., Korzhenkov A., Kurbanov R., Panin A.

• Kurai Fault Zone has generated five M w = 6.6–7.6 earthquakes for the past 6.5 ka. • Kurai Range is stepping over the basins along the main north-dipping reverse faults. • Paleoseismic slip occurred as backthrusting on south-dipping pinnate reverse faults. • The backthrusting maintains the growth of forebergs in front of the Kurai Range. • Geoelectrical data made it possible to trace faults to a depth of 50 m. The Kurai Fault Zone (KFZ) is one of the most hazardous seismogenic structures in the Gorny Altai (Russia). The KFZ have generated five paleoearthquakes with M w = 6.6–7.6 and ESI 2007 shaking intensities of VIII to XI. The ultimate event, presumably in the second half of the 18th century, was preceded by four paleoearthquakes approximately 1.3, 3.2, 5.8, and 6.3 ka ago. The morphology of fault scarps , trenching results, deformation features in Neogene sediments, as well as electric resistivity surveys, reveal reverse slip mechanisms. All earthquakes were sourced by south-dipping backthrusts with respect to the main north-dipping reverse and thrust faults along which the Kurai Range is stepping over the two basins. The backthrusting maintains the growth of forebergs in front of the Kurai Range. Narrow basins limited by reverse faults separate forebergs from the Chuya and Kurai basins. Joint interpretation of geological (including trenching) and geophysical (ERT and GPR) data reveals the resistivity structure of the area with seismogenic faults traceable to depths of 40–50 m. The KFZ model, with the reconstructed relationships between the intramontane basins and the flanking mountains, as well as the structural control of large earthquakes, makes good reference for other worldwide regions of current and past seismicity in compressional settings. Assessment of probable magnitudes and recurrence of earthquakes within the KFZ is of special importance in view of the future deployment of the gas pipeline from Russia to China.

Kuzmin Y.O.

Topical problems of the formation of slow deformation waves and their connection with recent geodynamic (deformational) processes are discussed. It is shown that the term “diffusion of stresses (displacements, strains)” is ill defined from the standpoint of physics of transfer phenomena because in the case of diffusion, mass transfer takes place, whereas the wave processes transfer energy. It is noted that the existing models describing the “diffusion of stresses” are solved based on the mathematical formalism of heat conduction theory which relies on the phenomenon of energy transfer. It is demonstrated that applying the term “wave” to the “stress diffusion” processes is untenable because in the classical sense, wave processes describe undamped (sustained, continuous) oscillations propagating in a homogeneous medium at constant velocity. The processes describing the “diffusion of stresses” form strongly damped oscillations whose propagation velocity substantially decreases with time. As a mechanism corresponding to the wave canonical concepts, a model of autowave deformation processes is proposed that implement the relay-race transfer and successive re-initiation of deformation activity from a fault to a fault or from one activated segment of a fault to another segment. Problematic issues of identifying the slow deformation waves are discussed, and the recommendations are proposed for constructing a network of observation points for the in situ measurements of spatiotemporal migration of the Earth’s surface deformations. It is substantiated that the existence of slow deformation waves does not explain the entire observed spatiotemporal spectrum of recent movements of the Earth’s surface.

Deev E.V.

The conducted paleoseismological and archaeoseismological studies reveal three zones of concentration of the ancient and historical earthquakes in Gorny Altai which are related to the Kurai Fault zone, Katun, and South Terekta faults. The surface ruptures are detected within the Kurai Fault zone, which were formed in the epicentral zones of the paleoearthquakes that occurred 6500, 5800, 3200, and 1300 years ago and had magnitudes Mw = 6.7–7.6. The recurrence period of the paleoearthquakes is 700 to 2600 years. The detected secondary seismogenic deformations indicate that an epicentral zone of the paleoearthquake with an age of less than 12.5 ka (Mw = 7.2–7.6, intensity I = 10–11), the traces of earthquakes and their clusters with M ≥ 5–5.5 and I ≥ 6–7, which occurred about 150 and 90 ka ago, in the intervals of 38–19 ka ago (with a recurrence period of about 2 ka), and 19–12.5 ka ago are related to the southern part of the Katun Fault. The earthquake of I ≥ 5–6 which damaged the constructions of the Chultukov Log 1 burial mound in the period from IV century B.C. to the beginning of I century A.D. is associated with the northern part of the Katun Fault. In the zone of the South Terekhta Fault, the seismogenic displacements that occurred in VII–VIII centuries A.D. (Mw = 7.4–7.7, I = 9–11) and about 16 ka ago (M ≥ 7, I = 9–10) are revealed. The latter triggered the formation of a landslide-dammed lake which was destroyed by the earthquake about 6 ka ago (M ≥ 7, I = 9–10). Secondary paleoseismic deformations of the ancient earthquakes (M ≥ 5–5.5, I ≥ 6–7) are recorded in the sediments of the Uimon Basin with an age of 100–90 ka and about 77 ka. These results should be taken into account in designing a gas pipeline in the People’s Republic of China, building infrastructure for tourism, and elaborating the seismic zoning maps for the territory of the Russian Federation.

Deev E.V., Turova I.V., Borodovskiy A.P., Zolnikov I.D., Oleszczak L.

ABSTRACTPalaeoseismological and archaeoseismological studies in the Kurai fault zone, along which the Kurai Range is thrust onto Cenozoic deposits of the Chuya intramontane basin, led to the identification of a long reverse fault scarp 8.0 m high. The scarp segments are primary seismic deformations of large ancient earthquakes. The scarp’s morphology, results of trenching investigations, and deformations of Neogene deposits indicate a thrusting of the piedmont plain onto the Kurai Range, which is unique for the Gorny Altai. Similarly for Northern Tien Shan, we explain this by the formation of both a thrust transporting the mountain range onto the depression and a branching thrust dislocation that forms the detected fault scarp. In a trench made in one of the scarp segments, we identified the parameters of the seismogenic fault – a thrust with a 30° dipping plane. The reconstructed displacement along the fault plane is 4.8 m and the vertical displacement is 2.4 m, which indicates a 7.2–7.6 magnitude of the...

Vetrov E.V., Buslov M.M., De Grave J.

Abstract Results of apatite fission track dating have been summarized and correlated with stratigraphic, geoelectrical, tectonic, and geomorphological data. The average regional rate of rock denudation in southeastern Gorny Altai is reflected in three thermotectonic events: (1) Late Cretaceous–Early Paleogene tectonic activity with a denudation rate of ~200 m/Myr, related to the distant impact of the Mongol–Okhotsk orogeny; (2) Middle Paleogene–Early Neogene stabilization with peneplanation; and (3) Neogene–Quaternary “stepwise” tectonic activity with a denudation rate of ≤270 m/Myr, related to the distant impact of the Indo-Eurasian collision. We present results of study of the evolution of regional tectonic processes and topography over the last 100 Myr by analysis of digital and shaded elevation models and apatite fission track dating.

Seminsky К.Z.