Geodynamics of the Baikal rift zone and plate tectonics of Asia

Abstract

Abstract:We have compiled and analyzed earthquake focal solutions for the territory of Mongolia and its surroundings in order to reveal a spatial variability of stress orientation and stress regimes of the crust. According to the stress inversion results, the SHmax is turning from W-E in the eastern Mongolia to SW-NE in the Gobi Altay and the central Mongolia, and then to S-N in the western part of the region. Comparison with data derived from GPS measurements shows that directions of the strain axes revealed by the geodetic and seismological observations are generally consistent. A contradiction is found for the Bolnai zone where results of GPS estimation indicate the predominance of extension (in the SE-NW direction), whereas earthquake data for the longer period of seismic observations reveal compression. Compression in this zone is mainly due to the Tsetserleg-Bolnai earthquakes contribution; however, a part of the recent data on focal mechanisms fits an extensional stress field with the NNW orientated extension axis. These data are in accordance with some published works which suggest a transtensive field from some structural geology studies in the eastern part of the Bolnai zone.The paper is supplemented with a list of M≥4.5 earthquake fault plane solutions and unpublished focal mechanisms for some M≤4.5 earthquakes of the northern Mongolia and the southern Baikal region. GEODYNAMICS & TECTONOPHYSICS P U B L I S H E D B Y T H E I N S T I T U T E O F T H E E A R T H ' S C R U S T S I B E R I A N B R A N C H O F R U S S I A N A C A D E M Y O F S C I E N C E S R e c e n t G e o d y n a m i c s 23 N.A. Radziminovich et al.: Focal mechanisms of earthquakes and stress field of the crust in Mongolia…Аннотация: Введение. Механизмы очагов землетрясений наряду с геодезическими и другими данными слу-жат источником информации о напряженно-деформированном состоянии земной коры. Задачи оценки тек-тонического режима и скорости деформирования особенно актуальны для внутриплитных областей, харак-теризующихся высоким уровнем сейсмичности. Одной из таких областей является Монголия, на территории которой известны землетрясения с М=8.0 (рис. 1). В представляемой работе собраны и проанализированы механизмы очагов землетрясений с M≥4.5 с целью проследить пространственную изменчивость поля напря-жений земной коры.Данные. Опубликованные данные о фокальных решениях можно разделить на две группы в зависимости от применяемых для их определения методов. К первой группе относятся механизмы, полученные модели-рованием волновых форм на удаленных и региональных станциях. Вторая группа решений получена при ис-пользовании метода полярности первых вступлений волн. Данный метод широко применялся для умеренной силы землетрясений северной части Монголии и Южной Сибири, что обусловлено более плотным покрытием этого региона сейсмостанциями. Используемые для анализа в данной работе решения представлены в таб-лице (в разделе «Дополнительные материалы») и на карте (рис. 2).Методы. Для инверсии поля напряжений использовались два подхода. Для землетр...

Low Vp/Vs ratios in the crust and upper mantle beneath the Sea of Okhotsk inferred from teleseismic pMP, sMP, and sMS underside reflections from the Moho

“…A right lateral N-S trending fault system is found in Sakhalin and Hokkaido; the formation of this shear zone is thought to be associated with cessation of earlier subduction and reorganization of convergence in the late Cretaceous or Paleogene [Kimura et al, 1983]. This shear zone is thought to be the plate boundary between the North American plate (or a separate Okhotsk plate) and the proposed Amurian plate to the south [Zonenshain and Savostin, 1981], the existence of which has been further supported by regional tectonics and earthquake slip vectors [Wei and Seno, 1995] and a recent GPS study [Takahashi et al, 1999].…”

Current global plate kinematics from GPS (1995–2007) with the plate‐consistent reference frame

“…Alternatively, the Okhotsk (OKH) and Amurian (AMU) microplates are supposed in place of the North American and Eurasian plates in east Asia [Zonenshain and Savostin, 1981;Seno et al, 1996;Apel et al, 2006]. From our solution GPS2007.0, the rotation rate of the Arctic-Siberian part with respect to the main part of the North American plate is statistically insignificant: 0.016 ± 0.011°/Ma; this fact supports the presence of the North American plate in Siberia although the Bering Sea block probably moves with respect to the North American plate [Fournier and Freymueller, 2007].…”

Tectonic Process of the Sedimentary Basin Formation and Evolution in the Late Cenozoic Arc-Arc Collision Zone, Central Japan

“…The latter corresponds to the strain concentration zone along the eastern margin of Japan Sea [9]. As for the Tohoku arc, the start of eastward motion of Amur Plate at around 5 Ma [69] might have resulted in a new plate boundary along the strain concentration zone since 0.5 Ma. Moreover, [36] examined the U-Pb age data of Kurobegawa granite in the Hida mountain range and concluded that the granites were emplaced incrementally through the amalgamation of many intrusions since the late Miocene up to the latest intrusion event at 0.8 Ma, and that such magmatic intrusions caused rapid uplift and erosion of the Hida mountain range in the Quaternary.…”