E. A. Rogozhin

Tectonic setting and geological manifestations of the 2003 Altai earthquake

Geological and geomorphic manifestations of the source of the earthquake that occurred in the southern Gorny Altai on September 27, 2003, are described. This earthquake, the strongest over the entire history of seismological observations, caused damage to buildings and structures in the Chuya and Kurai basins and was accompanied by exposure of its source at the surface with formation of a system of seismic ruptures trending in the northwestern direction. The linear zone of seismic rupture was traced for more than 70 km on the northern slopes of the North Chuya and South Chuya ranges, and a developed network of related splays was found. The secondary (gravitational and vibrational) seismic dislocations were expressed as downfalls, landslides, and gryphons in the pleistoseist zone. These dislocations occur over an area of approximately 90 × 25 km2 that broadly coincides with the region of quakes having intensities of IX–VII. The paleoseismogeological investigations performed in the source region of the 2003 earthquake have shown that seven seismic events with M = 7.0–8.0 occurred in its source over the last 5000 years with a 500-to 900-year recurrence period. The study of the tectonic setting of the earthquake source in the Gorny Altai has allowed northward tracing of the main seismically active zones of the Mongolian and Gobi Altai, where earthquakes with a magnitude M > 7.0 occurred repeatedly, in particular, during the 20th century, and combination of all mountain systems of the Greater Altai into a common high-magnitude seismotectonic province.

Major Earthquakes of the Southern Gornyi Altai in the Holocene

The paper describes geological and geomorphological features of ancient major earthquakes that occurred in the Holocene in the zone of the Altai earthquake of September 27, 2003 (southern Gornyi Altai). Fossil earthquakes occurred in the regions of the Northern and Southern Chuya ridges and Chuya and Kurai basins; their sources reached the surface and formed systems of coseismic ruptures oriented SE-NW or E-W. Secondary (gravitational and vibrational) paleoseismic deformations were represented by rockfalls, landslides, and gryphons in near-field zones of these paleoevents. They were spread in an area of about 2000–2500 km2 coinciding, on the whole, with the position of source zones. Paleoseismogeological investigations showed that, apart from earthquakes of the 20th and 21st centuries, eight seismic events with magnitudes M = 7.0–8.0 occurred in the region over the last 8500 years. Ancient strong earthquakes that produced the observed paleoseismic ruptures occurred approximately 230–300, 1000, 1700, 2300, 3500, 4500, 5200, and 8500 years ago. Therefore, the recurrence interval averaged 1400 yr for earthquakes with a magnitude of about 7.0 and 2100 yr for events with a magnitude of about 7.5.

Deep structure of the Racha earthquake source zone from seismic tomography data

The Racha earthquake of 1991 was the strongest of the earthquakes recorded in the Caucasus. It was studied by an international epicentral expedition. Unique data gathered by this expedition included records of aftershocks whose swarm was very intense. A 3-D velocity model is obtained from analysis of these data by the method of local earthquake tomography. The ancient crystalline basement and the sedimentary-volcanic Mesozoic-Cenozoic cover could be identified from cross sections of the P wave field. The eastern and western boundaries of an uplift in the basement of the Dzirulskii Massif are delineated. Linear low velocity heterogeneities correlating with the active Kakheti-Lechkhumi fault zone and two Trans-Caucasian linear fault zones are discovered in the basement. The cloud of aftershock hypocenters is shown to correlate with a reflector coinciding with the cover-basement interface.

Seismotectonics of the transitional region from the Baikal Rift Zone to orogenic rise of the Stanovoi range

This paper is based on the data obtained during the field study of active faults carried out in 2005–2006 in the Chita and Amur oblast and South Yakutia in connection with detailed seismic demarcation of the projected East Siberia-Pacific Ocean pipeline route. The comprehensive geomorphic and geophysical fieldwork was focused on paleoseismogeology and accompanied by trenching in the zones of reactivated faults. These works allowed us to specify the available information on the present-day structure, seismotectonic regime, and potential seismic hazard of the conjugation of the Baikal Rift Zone and the arched-block rise of the Stanovoi Ridge.

The structure and contemporary activity of the Intramoesian fault in northeastern Bulgaria obtained through a complex of new geological-geophysical methods

The structure of the Intramoesian fault is studied for the purpose of estimating its contemporary activity. The fault is known in the territory of Romania and Bulgaria, but it is insufficiently studied both from the geological point of view on the surface and from the geophysical point of view, from which the pattern of its deep structure can be inferred. The fault zone is the key structure for the solution of the problem of estimating the seismic hazard of the region, since the latest studies of this territory indicate the existence of traces of relatively young tectonic processes. According to some concepts the Intramoesian fault sets bounds to the tectonic plate, which is subducted under the Carpathian fold system in the region of the Vrancea Mountains. The paper under consideration presents the results of the field study of the southeastern, the Bulgarian, part of the fault with the application of a complex of geological-geomorphological and geophysical methods. On this basis, the structural segmentation of the fault is carried out and the specific features of its intersection with the disjunctives of another structural orientation are inferred. The data, which determine the degree of its geological and seismic activity, are also discussed.

Tectonic position and geological manifestations of the 2006 olyutor earthquake in Koryakia

The results of seismotectonic study of the epicentral zone of the major earthquake in northern Kamchatka oblast are presented. Primary and secondary surface seismic dislocations were revealed. The exposed seismic source as a complex system of seismic faults up to 140 km in total length was found and mapped in detail. The system consists of three en echelon arranged NE-oriented segments about 16, 45, and 75 km long. The general strike of the fault system coincides with the orientation of the ridges in the Koryak Highland. The kinematics of the longest northeastern segment is reverse faulting of the southeastern wall combined with right-lateral strike-slip faulting. The maximum vertical and horizontal separations are 3 and 1.5 m, respectively. Vibration fractures, griffons, landslides, and rockfalls were revealed and documented as secondary seismic dislocations. The indications of paleoseismic dislocations were studied and documented as well. The age of paleoseismic events was determined with radiocarbon method from soil samples. The seismic source is confined to the boundary of the North American and Bering Sea lithospheric plates and exhibits its internal structure for a long distance. Seismic events testify to recent geological activity of the zone of interaction between the lithospheric plates. The collected data provide insights into the structure of the seismic source and its tectonic setting at the active continental margin of Asia.

Deep structure of the Moscow Aulacogene in the western part of Moscow

Geological and geomorphological studies of the Moscow Aulacogene in the western part of Moscow suburbs have been conducted. This deep structure has been studied by microseismic sounding. The resulting section presents the faults which frame the Teplostanskii Graben in the south (Ramenskii or Butovskii, expressed on the surface as a ledge in the relief) and in the north (Pavlovo-Posadskii, being traced on the surface as a series of lineaments and the valley of Setun’ River). The position of the surface Archean-Lower Proterozoic crystalline basement within the limits of the graben and within the limits of buried elevated blocks (Krasnogorskii and Tumsk-Shaturskii) frame it in the north and south, respectively. Additionally, another fault has been identified in the central part of the graben: the Solntsevskii fault, which has a north-western course and which separates the deflection of the basement in two blocks that are sunken in a slightly different degree. The low-velocity horizons of the Riphean-Vendian complex which make up the graben at depths of 2 to 4.5 km have been found. Down to depths of 15 km, as a component of the upper crust, the graben is underlain by a high-velocity material which also forms the upper part of the section of the crystalline basement in the neighboring elevated block. A low-velocity block of the lithosphere is located in the larger (northern) part of the graben deeper (down to 40 km) beneath the zones of Pavlovo-Posadskii and Solntsevskii faults; in the southern part there is a high-velocity block. In the fault zones framing the graben in the north and south, the surface layer and soil displays a flow of juvenile hydrogen and helium which exceeds several tenfold the background values. According to the collected data, the Teplostanskii Graben has roots traceable through the entire crust and penetrating into the upper mantle.

Archaeoseismological studies and structural position of the medieval earthquakes in the South of the Issyk-Kul depression (Tien Shan)

We carried out archaeoseismological studies in the Southern Issyk-Kul region (Kyrgyz Tien Shan) and obtained radiocarbon datings of the collected samples. These data suggest that the sources of strong earthquakes have occurred in this territory in the 11th and (probably) 16th centuries. These earthquakes had magnitude M ≥ 7 and seismic intensity of at least I ≥ 9. The sources of these earthquakes were associated with the local adyr (piedmont) faults—components of the Pre-Terskei border fault. Our results demonstrate considerable underestimation of the seismic hazard for the South Issyk-Kul region in the latest Seismic Zoning Map of Kyrgyz Republic (2012), which should be taken into account in the construction of the new seismic zoning map for Kyrgyzstan.

March 11, 2011 M 9.0 Tohoku earthquake in Japan: Tectonic setting of source, macroseismic, seismological, and geodynamic manifestations

The results of interpretation of seismological, geological, geophysical, geodetic, and macroseismic data on the source zone of the catastrophic Tohoku earthquake with M = 8.8–9.0 (from different estimates), which occurred March 11, 2011 off the eastern coast of Honshu Island, are reported. Consideration of the seismotectonic features of the Western Pacific; the distribution of epicenters and hypocenters of the main shock, fore- and aftershocks; the solution of focal mechanisms of the strongest shocks; and the data on directions of lateral and vertical displacement of the island surface makes it possible to contour the source region, reconstruct the structure of the source in the subsurface, and estimate the deformation of the lithosphere resulted from this great seismic event.

Seismic monitoring of industrial objects: Problems and solutions

Using the example of safety provision problems of hydraulic engineering structures (HESs), the seismic monitoring experience is analyzed (parameters of states of objects, equipment and schemes for fulfilling seismic observations) and, based on this, it is proposed to modify existing industrial monitoring practices. The efficiency of the different kinds of the HES monitoring performed by the united seismic equipment with an expanded dynamic range is shown. Innovative instrumental solutions for recording seismic signals are described.