Tentative Intracontinental Seismic Activity in South Siberia and Russian Far East

Overwhelming majority of minor, strong and major earthquakes in south Siberia and Russian Far East coincide with relatively narrow intracontinental zones on the boundaries of blocks and lithosphere plates. The geodynamic activity of these zones connects, besides the plate interaction, with deep lithosphere structure and anomalies of the different geophysical fields as well as with blocks’ kinematics. Authors’ located areas of the seismic centers origin and the possible manifestations of the high seismicity based on the distribution of the maximal volumes of releasing seismic energy. We established these areas, with certain care, in the northeast Altai and adjacent part of the west Sayany, in the west of the east Sayany, around the Baikal Lake and in northwest Transbaikalia, in the east of Transbaikalia between the Vitim River and upper stream of the Aldan River, and in the north of the Sakhalin Island. The majority of minor and strong, rarely major, earthquakes took place in these areas. Deep and near surface structural peculiarities influence on these areas’ geodynamics and allow establishing possible levels of seismic energy releasing. We draw areas of intensive seismic energy releasing with its calculating for each from investigated regions. They gravitate towards interblock zones, which separate crust blocks and the North Eurasian Lithosphere Plate. The fulfilled investigation allows establishing specific areas of the increased seismicity in south Siberia, Russian Far East and adjacent territories

ПРЕДОПРЕДЕЛЕННОСТЬ И СВЯЗЬ ИСТОРИЧЕСКИХ СОБЫТИЙ С ПРИРОДНЫМИ ПРОЦЕССАМИ НА ЗЕМЛЕ И В СОЛНЕЧНОЙ СИСТЕМЕ (О ЦИКЛЕ КНИГ ПО ХРОНОЛОГИИ ПРИРОДНЫХ ФЕНОМЕНОВ, ГЕОДИНАМИКЕ И ГЕЛИОГЕОДИНАМИКЕ)

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Геодивайдер 102–103° в.д. в современной структуре литосферы Центральной Азии

A quasi-linear zone of noticeable geological and geophysical changes, which coincides approximately with 102–103° E meridians, is termed by the authors as “geodivider”. Active submeridional faults are observed predominantly along the zone and coincide with its strike. Seismicity is most intensive in the central part of this zone, from the Lake Baikal to the Three Rivers Region at the Sino-Myanmar frontier. Transects with deep seismic sections and energy dissipation graphs show most sharply increasing seismic energy amounts and hypocenter depths in the western part of the geodivider which delimits (in the first approximation) the Central Asian and East Asian transitional zones between the North Eurasian, Indian and Pacific lithosphere plates. The transpression tectonic regime dominates west of the geodivider under the influence of the Hindustan Indentor pressure, and the transtension regime prevails east of it due to the Pacific subduction slab submergence and continuation. The regime change coincides with an abrupt increase in the crust thickness – from 35–40 km to 45–70 km – west of the geodivider, as reflected in the geophysical fields and metallogenic characteristics of the crust. The direction of P- and S-waves anisotropy together with the GPS data show decoupling layers of the crust and mantle in the southern part of the geodivider. According to our investigations, the 102–103° E geodivider is a regional geological-geophysical border that may be compared with the Tornquist Line, and, by its scale, with the Uralian and Appalachian fronts and some others large structures.Квазилинейная зона заметных геологических и геофизических изменений совпадает приблизительно с меридианами 102–103° в.д. Активные субмеридиональные разломы развиты в этой зоне, названной авторами геодивайдером 102–103° в.д. Наиболее интенсивная сейсмичность характеризует центральную часть геодивайдера от озера Байкал до региона Трех рек на границе Китая и Мианмар. Проведение трансектов с глубинными сейсмическими разрезами и графиками диссипации сейсмической энергии показывает преимущественно резкое возрастание объемов сейсмической энергии и глубины гипоцентров на западном крыле геодивайдера. Геодивайдер разделяет, в первом приближении, Центрально-Азиатскую и Восточно-Азиатскую транзитные зоны между Северо-Евразийской, Индийской и Тихоокеанской литосферными плитами. Тектонический режим транспрессии преобладает к западу от геодивайдера под влиянием давления Индостанского индентора, и режим транстенсии распространен к востоку от него, благодаря глубокому погружению и продолжению Тихоокеанского слэба. Смена режимов совпадает с резким увеличением мощности коры к западу от геодивайдера от 35–40 до 45–70 км, отражающимся в геофизических полях и коровых металлогенических характеристиках. Направление P- и S-волн анизотропии наряду с данными GPS показывает их несовпадение в различных слоях коры и мантии в южной части геодивайдера. По результатам наших исследований геодивайдер 102–103° в.д. представляет собой тип геолого-геофизической границы, сопоставимой с линией Торнквиста, по масштабу с Уральским и Аппалачским фронтами и с рядом других крупных структур

New Permo-Carboniferous geochemical data from central Thailand: implication for a volcanic arc model

Current ideas and models of geotectonic reconstructions of Southeast Asia are reviewed and new data on Late Carboniferous through Middle Permian tuffites and sills from central Thailand are presented in the light of the problems of Southeast Asian palaeogeography. The volcanic rocks of quartz-keratophyric to spilitic composition are associated with platform carbonates and deep basin sediments. Their geochemistry and the character of the accompanying sediments suggest the existence of a Late Palaeozoic volcanic arc separating a subduction zone in the west from a back arc basin to the east. The geotectonic frame of Southeast Asia is explained in terms of repeated accretion of volcanic arcs by the Late Palaeozoic subduction zone along the northern Tethys margin

ГЕОДИНАМИЧЕСКИЕ РЕЖИМЫ ЦЕНТРАЛЬНОЙ АЗИИ ЗАПАДНЕЕ И ВОСТОЧНЕЕ ГЕОРАЗДЕЛА 102–104°

Ample geologic and geophysical data provide the basis for distinguishing the 102–104° E geodivider in the North, Central and South Asia. The geodivider’s central part is confirmed by the data on seismicity, seismically active faults and the modern crust block structure. These data and historical and instrumentally identified earthquake epicenters were used for a more correct definition of the block boundaries and interblock zones in the central part of the geodivider and in its wings. Seismic energy is considerably increased (to 1011–1016 J) in the eastern part of the geodivider’s western wing, and rarely increased directly in the geodivider itself. Near the geodivider, a seismic energy increase is detected east of it only at the western border of the South-Eastern China Block. The authors analyzed deep seismic sections and constructed energy dissipation graphs along transects crossing the geodivider and its western wing. The analysis and the graphs show the predomination of left-lateral NW-striking slips in the north, thrusts to the east and southeast in the center, and right-lateral NE-striking slips in the south. The total seismic energy increases constantly to the west. In the central and northern segments of the geodivider’s central part and west of it, horizontal blocks displacements cause a direct influence on seismicity level increasing and changes in geodynamic regimes within the investigated territory of Central Asia. Changes in the horizontal displacement vector are accompanied by the change of tectonic strain regimes. Increased heat flow values to the east from the geodivider within the East Asian transit zone are probably related to the change of the geodynamic regimes in the same direction under the influence of the submerged Pacific slab. The data obtained by the Chinese and Russian researchers confirm delamination (stratification) processes in the Southeast Tibet crust during its interaction with the colder and thicker lithosphere of Southeast China, and displacement of its upper layers to the southeast and south, as we supposed in our earlier publications.Геораздел 102–104° в.д. выделяется по многочисленным геологическим и геофизическим при­знакам в Северной, Центральной и Южной Азии, подтверждаемым в его центральной части данными по сейсмичности, сейсмоактивным разломам и современному блоковому строению земной коры. На основании этих данных и по распространению эпицентров инструментально зафиксированных и исторических землетрясе­ний откорректированы границы блоков и межблоковых зон в центральной части геораздела и на его крыльях. Значительное возрастание объемов высвобождающейся сейсмической энергии до 1011–1016 Дж происходит в восточной части западного крыла геораздела, реже – непосредственно в нем, а к востоку от него – только на западной границе блока Юго-Восточного Китая вблизи геораздела. Проведенный авторами анализ глубинных сейсмических разрезов и графиков диссипации энергии вдоль трансектов, пересекающих геораздел и его западное крыло, показывает преобладание левосторонних сдвигов с северо-западным простиранием на севере, надвигов к востоку и юго-востоку в центре и правосторонних сдвигов с северо-восточным простиранием на юге. Общий уровень объема энергии постоянно возрастает к западу. Перемещения по горизонтали блоков в центральном и северном сегментах центральной части геораздела 102–104° в.д. и к западу от него по данным GPS оказывают непосредственное влияние на увеличение уровня сейсмичности и изменение геодинамических режимов в пределах изучаемых районов Центральной Азии. Смена направления векторов горизонтального перемещения сопровождается изменением режима тектонических напряжений. Установлено возрастание значений теплового потока к востоку от геораздела в Восточно-Азиатской транзитной зоне, предположительно связанное со сменой геодинамического режима в том же направлении под влиянием погруженного тихоокеанского слэба. Данные по сейсмической анизотропии и томографии литосферы, полученные китайскими и российскими исследователями, подтверждают процессы деламинации коры Юго-Восточного Тибета при ее взаимодействии с более холодной и мощной литосферой Юго-Восточного Китая и перемещение ее верхних слоев к юго-востоку и к югу, предполагавшееся в более ранних работах авторов

CENTRAL ASIAN GEODYNAMIC REGIMES WEST AND EAST 102–104° GEODIVIDER

Ample geologic and geophysical data provide the basis for distinguishing the 102–104° E geodivider in the North, Central and South Asia. The geodivider’s central part is confirmed by the data on seismicity, seismically active faults and the modern crust block structure. These data and historical and instrumentally identified earthquake epicenters were used for a more correct definition of the block boundaries and interblock zones in the central part of the geodivider and in its wings. Seismic energy is considerably increased (to 1011–1016 J) in the eastern part of the geodivider’s western wing, and rarely increased directly in the geodivider itself. Near the geodivider, a seismic energy increase is detected east of it only at the western border of the South-Eastern China Block. The authors analyzed deep seismic sections and constructed energy dissipation graphs along transects crossing the geodivider and its western wing. The analysis and the graphs show the predomination of left-lateral NW-striking slips in the north, thrusts to the east and southeast in the center, and right-lateral NE-striking slips in the south. The total seismic energy increases constantly to the west. In the central and northern segments of the geodivider’s central part and west of it, horizontal blocks displacements cause a direct influence on seismicity level increasing and changes in geodynamic regimes within the investigated territory of Central Asia. Changes in the horizontal displacement vector are accompanied by the change of tectonic strain regimes. Increased heat flow values to the east from the geodivider within the East Asian transit zone are probably related to the change of the geodynamic regimes in the same direction under the influence of the submerged Pacific slab. The data obtained by the Chinese and Russian researchers confirm delamination (stratification) processes in the Southeast Tibet crust during its interaction with the colder and thicker lithosphere of Southeast China, and displacement of its upper layers to the southeast and south, as we supposed in our earlier publications

The 102–103° E geodivider in the modern lithosphere structure of Сentral Asia

A quasi-linear zone of noticeable geological and geophysical changes, which coincides approximately with 102–103° E meridians, is termed by the authors as “geodivider”. Active submeridional faults are observed predominantly along the zone and coincide with its strike. Seismicity is most intensive in the central part of this zone, from the Lake Baikal to the Three Rivers Region at the Sino-Myanmar frontier. Transects with deep seismic sections and energy dissipation graphs show most sharply increasing seismic energy amounts and hypocenter depths in the western part of the geodivider which delimits (in the first approximation) the Central Asian and East Asian transitional zones between the North Eurasian, Indian and Pacific lithosphere plates. The transpression tectonic regime dominates west of the geodivider under the influence of the Hindustan Indentor pressure, and the transtension regime prevails east of it due to the Pacific subduction slab submergence and continuation. The regime change coincides with an abrupt increase in the crust thickness – from 35–40 km to 45–70 km – west of the geodivider, as reflected in the geophysical fields and metallogenic characteristics of the crust. The direction of P- and S-waves anisotropy together with the GPS data show decoupling layers of the crust and mantle in the southern part of the geodivider. According to our investigations, the 102–103° E geodivider is a regional geological-geophysical border that may be compared with the Tornquist Line, and, by its scale, with the Uralian and Appalachian fronts and some others large structures