Seismotectonic deformation and crustal stress pattern have been studied comprehensively in major seismogenic structures of the Kharaulakh sector of the Verkhoyansk fold system and adjacent parts of the Chersky seismotectonic zone. The study focuses on neotectonic structures, deep structure, and systems of active faults, as well as tectonic stress fields inferred by tectonophysical analysis of Late Cenozoic faults and folds. The results, along with geological and geophysical data, reveal main strain directions and structural patterns of crustal stress and strain in the Arctic segment of the Eurasia–North America plate boundary. The area is a junction of mid-ocean and continental structures evolving in a mixed setting of extension, compression, and their various combinations. The rotation pole of the two plates is presumably located near Buor-Khaya Bay. In this case, extension is expected to act currently upon the neotectonic structures north of the bay and compression to control those in the south and southeast. This inference is consistent with the identified zoning of stress and strain in the Kharaulakh sector.

Abstract:The paper presents results of seismogeological studies of active faults bordering the Upper Kerulen basin, one of the largest intermountain basins of the Khentei upland. Morphometric and trenching methods were applied to estimate the main parameters of seismogenic dislocations and associated Holocene palaeoearthquakes (540-2810, 3170-3720, and 7480-9220 years ago). The maximum palaeoearthquake magnitude (7.5) characterizes the seismic capacity of the potential focal area (PFA) confined to the Kerulen fault. The new data show the need to revise the potential seismicity concepts of the southern Khentey area and to make appropriate changes in the general seismic zoning maps. The relationship between the dislocations and the modern topography features, as well as deformation of the subsurface sediments in the studied mine openings give evidence of thrusting under the sub-lateral to northwestern subhorizontal compression.Key words: Khentei; Kerulen seismogenic structure; morphometry; trenching; absolute age of a paleoearthquake Аннотация: Представлены результаты сейсмогеологических исследований активных разломов, ограничи-вающих Верхнекеруленскую впадину -одну из крупнейших межгорных впадин Хэнтейского нагорья. Мор-фометрией и тренчингом определены основные параметры сейсмогенных дислокаций и связанных с ними трех палеоземлетрясений, произошедших в течение голоцена (в интервалах 540-2810, 3170-3720 и 7480-9220 лет назад). Максимальная магнитуда палеоземлетрясений (7.5) характеризует сейсмический потенциал приуроченной к Керуленскому разлому зоны вероятных очагов землетрясений (зоны ВОЗ).

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The Gunzhin Fault is a tectonic structure in the southern Hentiyn arched uplift (central Mongolia). A fragment of this fault, exposed by two paleoearthquakes, is traced northeastward for ~25 km from the northern periphery of Ulaanbaatar. The first comprehensive seismogeological studies here were aimed at determining the seismic potential of seismogenic structures on the basis of the dislocation parameters. Judging by the strain amplitudes and length, earthquakes with a magnitude of >7.0 might be generated here. The paleoearthquake was dated by the radiocarbon method at 7800–4667 B.C. Seismogenic zones with a high seismic potential were identified in central Mongolia for the first time. Dextral strike-slip faults were observed here among active NE-trending faults, suggesting the presence of E–W compressive stress.

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