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GEODYNAMICS & TECTONOPHYSICS
PUBLISHED BY THE INSTITUTE OF THE EARTH'S CRUST SIBERIAN BRANCH OF RUSSIAN ACADEMY OF SCIENCES
2016 VOLUME 7 ISSUE 1 PAGES 23-38 ISSN 2078-502X
http://dx.doi.org/10.5800/GT-2016-7-1-0195
Focal mechanisms of earthquakes and stress field of the crust
IN MONGOLIA AND ITS SURROUNDINGS
N. A. Radziminovich1, G. Bayar2, A. I. Miroshnichenko1, S. Demberel2, M. Ulziibat2, D. Ganzorig2, A. V. Lukhnev1
1 Institute of the Earth's Crust, Siberian Branch of RAS, Irkutsk, Russia
2 Research Center of Astronomy and Geophysics of MAS, Ulaanbaatar, Mongolia
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4.5 earthquake fault plane solutions and unpublished focal mechanisms for some M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.
Key words: Mongolia; earthquake; fault plane solution; tectonic stress field; GPS measurements
Recommended by V.A. San'kov
For citation: Radziminovich N.A., Bayar G., Miroshnichenko A.I., Demberel S., Ulziibat M., Ganzorig D., Lukhnev A.V. 2016. Focal mechanisms of earthquakes and stress field of the crust in Mongolia and its surroundings. Geodynamics & Tectonophysics 7 (1), 23-38. doi:10.5800/GT-2016-7-1-0195.
Механизмы очагов землетрясений и поле напряжений Монголии и прилегающих территорий
Н. А. Радзиминович1, Г. Баяр2, А. И. Мирошниченко1, С. Дэмбэрэл2, М. Ульзибат2, Д. Ганзориг2, А. В. Лухнев1
1 Институт земной коры СО РАН, Иркутск, Россия
2 Исследовательский центр астрономии и геофизики МАН, Улан-Батор, Монголия
Аннотация: Введение. Механизмы очагов землетрясений наряду с геодезическими и другими данными служат источником информации о напряженно-деформированном состоянии земной коры. Задачи оценки тектонического режима и скорости деформирования особенно актуальны для внутриплитных областей, характеризующихся 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 напряжений 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 моделированием волновых форм на удаленных и региональных станциях. Вторая группа решений получена при использовании 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 таблице (в разделе «Дополнительные материалы») и на карте (рис. 2).
Методы. Для инверсии поля напряжений использовались два подхода. Для землетрясений основных сейсмических зон (Болнай, Гобийский Алтай, Могод и т.д.) применялась программа Win-Tensor [Delvaux, Sperner, 2003], в которой реализован метод right dihedra [Angelier, 1984]. Для получения более сглаженной по всей территории картины ориентации осей напряжений использовалась программа SATSI [Hardebeck, Michael, 2006], минимизирующая разницу между соседними «индивидуальными» стресс-тензорами для сейсмоактивных областей. Для более корректного сравнения сейсмологических данных с результатами GPS-измерений и визуализации сейсмотектонических деформаций представлены стереограммы средних фокальных механизмов [Nikitin, Yunga, 1977; Yunga, 1990].
Результаты. Полученные результаты показывают, что фокальные решения землетрясений южной, западной и восточной части Монголии однородны и представлены главным образом сдвиговыми и взбросовы-ми подвижками в очагах. Большим разнообразием кинематических типов разрывов характеризуется территория к северу от Болнайского разлома. Для непосредственно Болнайской зоны не удалось получить единого стресс-тензора. Выборка разделилась на главные толчки (Болнайское и Цэцэрлэгское землетрясения 1905 г.), состоящие из субисточников, и события, зарегистрированные в период инструментальных наблюдений. Последние показывают наличие в выборке решений, удовлетворяющих режиму растяжения. В целом, наблюдается изменение ориентации оси SHmax от направления Ю-С в западной части Монголии до ЮЗ-СВ в Гобий-ском Алтае и в центральной части страны и до широтного направления в Восточной Монголии.
Обсуждение результатов. Очевидно, что основные характеристики поля напряжений на представленной территории уже выявлены и описаны в предшествующих работах [Zhalkovskii et al., 1995; Petit et al., 1996; Delvaux et al., 1998; Melnikova et al., 2004; Melnikova, Radziminovich, 2005; San'kov et al., 2005; Gol'din, Kuchai, 2007; Radziminovich et al., 2007; Parfeevets, San'kov, 2010; San'kov et al., 2011; Parfeevets, San'kov, 2012; Rebetsky et al., 2013; Tataurova et al., 2014; Kuchai, Kozina, 2015; Karagianni et al., 2015; и др.]. Все увеличивающийся объем новых данных, с одной стороны, подтверждает сделанные ранее выводы, а с другой - позволяет выявить некоторые детали.
Результаты, полученные по сейсмологическим данным, согласуются с данными, полученными в ходе геолого-структурных работ [Parfeevets, Sankov, 2012] и GPS-измерений [Calais et al., 2003; Loukhnev et al., 2010]. Выделяется Болнайская зона, которая по геодезическим расчетам характеризуется деформацией удлинения земной коры или растяжением. Выше отмечалось, что часть фокальных механизмов соответствует такому полю напряжений. Более того, замеры трещиноватости также приводят авторов [Parfeevets, Sankov, 2012] к выводу о режиме транстенсии в восточной части Болнайской зоны, связанном, вероятно, с дивергенцией Евразийской и Амурской плит [Petit, Fournier, 2005]. Характер изменений сейсмотектонических деформаций в этом районе позволил авторам работы [Kuchai, Kozina, 2015] выделить, хоть и в широких пределах, границу Амурской плиты.
По данным о землетрясениях с M>7.0 была рассчитана скорость деформации по формуле Кострова (табл. 2). Для временного интервала в 100 лет она составила 1.12х1020 N m yr-1, что является высоким значением для внутриконтинентальных областей по сравнению с модельными значениями [Holt et al., 1995, 2000]. Очевидно, это связано с сильнейшими землетрясениями региона, произошедшими на протяжении небольшого интервала времени.
Заключение. Карта фокальных механизмов и результаты инверсии поля тектонических напряжений могут быть полезны при сейсмотектоническом и геодинамическом анализе Центральной Азии. В разделе «Дополнительные материалы» приведена компиляционная таблица механизмов очагов землетрясений с M>4.5 и ранее неопубликованные механизмы очагов землетрясений Северной Монголии и Южного Прибайкалья с M<4.5.
Ключевые слова: Монголия; землетрясение; механизм очага; поле тектонических напряжений;
GPS-измерения
On-line supplementary materials: Focal mechanisms solutions / Focal_solutions.xls
Supplementary materials explanations / Explanations.pdf
1. Introduction
Data on stress regimes and strain rates for intracon-tinental domains are of particular interest for understanding intraplate seismicity. In this respect, Mongolia is an appropriate region for research because of its location far from the plate boundaries, active tectonics, high level of seismic activity, and geodynamic position in Central Asia. It has been accepted that active deformation of the western part of Mongolia is related to the India-Eurasia collision [Tapponnier, Molnar, 1979; Zonenshain, Savostin, 1981; and others], although the stress transfer mechanism is under debate [Avouac, Tapponnier, 1993; Peltzer, Saucier, 1996; England, Molnar, 1997; and others]. The eastern part of Mongolia, which is characterized by the moderate level of seismic activity and diffusive seismicity type, might be influenced by the Pacific subduction process [Barth, Wenzel, 2010; and others]. This part is also assumed to belong to the Amurian block or plate, although the existence of this plate is doubted by some researchers [De Mets et al., 1990; Calais et al., 2003; and others]. At the same time, local mantle anomalies, such as one under the Khangay dome, whose uplift is thought to be resulting from hot mantle upwelling [Windley, Allen, 1993; Priestley et al., 2006; and others] should not be excluded from consideration.
Earthquake focal mechanisms along with geodetic and other data are important information to solve the problems concerning the mechanism and mode of the lithosphere deformation. However, much attention has been traditionally given to large earthquakes. Indeed, based on the data on largest earthquakes of Mongolia (M>7 and even M>8), the principal types of movements on the main fault zones were revealed, but these data cannot provide insight into the spatial stress variability and/or heterogeneity. These issues are essential for Mongolia since the question about the balance between local mantle dynamics and far-field forces in this region is still open.
At present, there are a lot of current stress studies based on earthquake focal mechanisms for the Central Asia, including Mongolia. Different approaches have been used to constrain the present-day stress and strain state of the crust, among which are widely used stress inversion procedures [Petit et al., 1996; Delvaux et al., 1998; Déverchère et al., 2000; San'kov, Parfeevets, 2005; Parfeevets, San'kov, 2010, 2012; Karagianni et al., 2015; and others], the method of seismotectonic deformation estimation [Zhalkovskii et al., 1995; Melniko-va et al., 2004; Melnikova, Radziminovich, 2005; San'kov et al., 2005; Gol'din, Kuchai, 2007; Radziminovich et al., 2007, 2008; San'kov et al., 2011; Tataurova et al., 2014; Kuchai, Kozina, 2015; and others], and the method of cataclastic analysis [Rebetsky et al., 2013; Leskova, Emanov, 2014; and others].
In this study, we have compiled and analyzed fault-plane solutions for M>4.5 earthquakes available for the region study since 1900 (until 1960 it concerns only large earthquakes with M>8). Furthermore, unpublished focal mechanisms for some M<4.5 earthquakes of the northern Mongolia and the southern Siberia are given in the Supplementary Materials. These solutions were not involved in the analysis due to the lower magnitude and possible hierarchical mode of the crust stress state. The main aim was to trace a spatial variability of stress orientation and stress regimes throughout the territory of Mongolia and its surroundings. For that, a stress inversion was applied to the data as well as seismotectonic deformation estimation. Then, the obtained results were compared with the geodetic measurement data for this region.
2. DATA
The published data on focal mechanisms of the Mongolian earthquakes can be categorized into two groups according to an approach to their determination, namely waveform modelling and first motion polarity methods. Different techniques of surface and body waves modelling using teleseismic records were applied to study both large and moderate earthquakes. Moreover, fault plane solutions for some large earthquakes (Fig. 1), such as the 1905 Tsetserleg-Bolnai earthquakes, the 1931 Fu Yun earthquake, the 1950 Mondy earthquake, the 1957 Gobi-Altai earthquake, the 1967 Mogod event, and the 2003 Chuya event were confirmed by the surface ruptures reports [Vosnesen-sky, 1962; Florensov, Solonenko, 1963; Okal, 1976, 1977; Khilko et al., 1985; Huang, Chen, 1986; Baljinnyam et al., 1993; Kurushin et al., 1997; Bayasgalan, Jackson, 1999; Bayasgalan et al., 2005; Schlupp, Cisternas, 2007; Ulziibat, 2006; Emanov, Leskova, 2005]. A significant part of the solutions comes from the Global Centroid-Moment-Tensor Project (former Harvard CMT Project) [http://www.globalcmt.org]. The first motion approach has been widely used for the northern part of Mongolia and the neighbouring regions of Russia due to denser seismic stations covering these regions. The main contribution to the first motion solutions of the earthquakes was made by A.V. Solonenko and co-authors [1993] who re-estimated the solutions from their earlier reports and presented the revised focal solutions in the international format (in terms of parameters of nodal planes and axes rather than cosine or sinus to the poles of the planes). Now, a regular source of information on focal solutions is the annual catalogue "Earthquakes of the Northern Eurasia" (former "Earthquakes in the USSR") published by the Russian Geophysical Survey. For the territory of China, only focal mechanisms from the world seismic agencies are taken
RUSSIA
р Mondy eq. l04.IV.1950 Mw6.9
Irkutsk
Transbaikalia
Bolnai eq. 23.VII.1905 Mw8.4
Mogod eq. 05.1.1967 Mw7.1
Ulaanbaatar
Russia
Kazakhstan
Mongolia
MONGOLIA
China
Mongolia network A Altai-Sayan network A Baikal network
CHINA
▲ Buryatia local network
Fig. 1. The map of topography, seismic networks and the largest earthquakes of the study region. Events in the pre-instrumental period of observations are shown by green transparent circles; earthquakes recorded by the regional networks are shown by red circles.
Рис. 1. Карта рельефа, сейсмических сетей и крупнейших землетрясений исследуемого региона. Зеленые прозрачные кружки - события в период доинстру-ментальных наблюдений; красные кружки - землетрясения, зарегистрированные региональными сетями.
because the regional sources of data are not readily available.
For earthquakes that occurred from 1996 to 2008, we examined both the analogous and digital seismo-grams of the Baikal, Mongolian and Altay-Sayan regional networks to constrain the focal mechanisms using polarity of Pn and Pg arrivals. A part of the solutions was published in annual issues of "Earthquakes of the Northern Eurasia"; here a list of solutions for weak earthquakes is presented. A compilation of earthquake fault plane solutions is given in Supplementary Materials.
Most of M>4.5 earthquake mechanisms were shown in the map issued in 2011 [Map of focal mechanisms..., 2011; Radziminovich et al., 2011; Sodnomsambuu et al., 2011]. This map with additions is given in Fig. 2. In the event that both first motion and CMT solutions are available, the former is preferably shown. Although the geometry and kinematic types of fault planes determined by different authors are similar in most cases, mechanisms for some earthquakes differ (Fig. 3). The most important variation case for understanding of regional seismotectonics is the 1950 Mw 6.9 Mondy earthquake. Its final solution is given in [Delouis et al., 2002]. Figure 3 also shows a rare case of focal solutions determined for an earthquake of the Transbaikalia region. This is the 2006 Mw 4.5 Balei earthquake for which the published mechanisms also vary. The fault plane solution obtained from the first motion polarities [Melnikova et al., 2011] is of reverse-fault type, whereas the seismic moment tensor inverted from the phase and amplitude spectra of body and surface waves shows a pure strike-slip motion [Barth, Wenzel, 2010]. The third available solution, which we accept as the most reliable one, was derived in [Radziminovich et al., 2012] by using the surface wave amplitude spectra along with the first motion polarities at the local stations. This focal mechanism suggests a reverse slip with a strike-slip component on NW and N-S planes that is consistent with the structural position of the source.
3. METHODS
In our study, two approaches were used to inverse the regional stress field. The first was to divide the region into the subareas corresponding to the major structural units as well as the main zones of seismicity, and to invert the focal mechanisms of the earthquakes of each subarea for stress. For inversion a program Win-Tensor [Delvaux, Sperner, 2003] was used that implements the right dihedra method [Angelier, 1984] and a dynamic rotational optimisation procedure. In this software package, the graphical right dihedra method was developed for estimating stress ratio R=(<j2-a3)/(a1-a3).
The second way was to obtain the stress field over the whole region provided by the data, since the sub-area data sampling may be incorrect and, moreover, it does not allow tracing the spatial stress variations. To meet this objective, we applied SATSI software, which is a damped inversion devised by [Hardebeck, Michael, 2006]. This method is based on the linear inversion technique [Michael, 1984] and minimizes the difference in stress between adjacent subareas where a single stress tensor was obtained. As noted by the authors of this method, damped inversion removes stress variation artifacts and resolves stress rotations more appropriate in comparison with a simple smoothed model or a moving-window inversion. For damped inversion, a scalar damping parameter that controls the relative weighting of the data misfit and the model length in the minimization should be set. To choose the damping parameter, we examined the trade-off curve between misfit and model length for a range of damping values and selected value e=0.6 (Fig. 4) that was near the corner of the trade-off curve, i.e. where both the model length and data variance were relatively small.
Probably, it is more reasonable to compare GPS strain patterns not with stress inversion results but with seismotectonic strain. For this, we visualized the averaged focal mechanism for each subarea applying the method of seismoteconic deformation described in [Nikitin, Yunga, 1977; Yunga, 1990]. Unlike the stress inversion, this approach takes into account the magnitude of earthquakes in samples; thus, a contribution of each event to the strain is determined by its magnitude. Strain patterns from GPS measurements were derived using horizontal GPS velocities within the Baikal-Mongolian network [Lukhnev et al., 2010]. Strain parameters were calculated according to the formulae taken from [Turcotte, Shubert, 1985]. Correctness of computation results was tested on the data from Tables 1 and 2, and Fig. 2 from the above mentioned paper [Lukhnev et al, 2010].
4. RESULTS
The first conclusion evidently inferred from the map is that the focal solutions of earthquakes in the southern Mongolia are rather homogeneous, whereas in the northern part they are widely variable (see Fig. 2). Indeed, the earthquakes in the major part of the Mongolian territory and the neighbouring regions of China are characterized by strike-slip and reverse movements. The strike-slip compressive stress regime (following the classification by [Delvaux et al., 1997]) with SHmax azimuth 220° was deduced for the Gobi Altai area (Table 1). The same regime was found for the Mongolian Altai, but the orientation of the SHmax here was determined as 195°. The pure strike-slip regime was
Geodynamics & Tectonophysics 2016 Volume 7 Issue 1 Pages 23-38 http://dx.doi.org/10.5800/GT-2016-7-1-0195
Seismicity
M 3.0-4.9 5.0-5.9 6.0-6.9 7.0-7.9
Since 1964 to 2010 (period of the regional networks observations)
Since 1900 to 1963
Fault plane solutions in the lower hemisphere projection
©
Results of waveform inversion and Global CMT Project 'best-double-couple' solutions
Solutions derived from first motion polarities
Aimag centers
Sainshand
Fig. 2. The map of focal mechanisms of earthquakes in Mongolia and its surroundings [Map of focal mechanisms..., 2011, with additions].
SRTM files [Jarvis et al., 2008] were used to make topography in Mercator projection, WGS 84. Seismicity data (from 1964 to 2010) were taken from the regional catalogs issued by the Baikal Division of the Siberian Branch of the Russian Geophysical Survey, the Altay-Sayan Division of the Siberian Branch of the Russian Geophysical Survey, and the Mongolian national network.
Рис. 2. Карта механизмов очагов землетрясений Монголии и сопредельных территорий [Map of focal mechanisms..., 2011, с дополнениями].
Использованы файлы SRTM [Jarvis et al., 2008] для изображения рельефа в проекции Меркатора, WGS84. Эпицентры землетрясений (1964-2010 гг.) взяты из региональных каталогов Байкальского филиала Сибирского отделения Российской геофизической службы, Алтае-Саянского филиала Сибирского отделения Российской геофизической службы и Монгольской национальной сети.
1950/04/04 1962/01/22 1966/05/10 1967/01/20
• V г * 4Л
•«"•an* —о«.,,,» мм««» 55?в. "ЯГ «KS SSSSf
1972/02/26 1972/08/31 1974/07/04 1980/12/15 1981/08/16
С ей % -vv -vv ъъх
Solonenko S?l0|neinQQ-5 n j оси TaPPonler Huang and Bavasaalan Solonenko Solonenko
etal., 1993 Doser, 1991 etal., 1993 uoser, 1991 and Molnar, Khilko Chen, 1986 etal 2005 etal., 1993 CMT etal., 1993 CMT Doser, 1991
1979 etal, 1985 istsubevent 2d subevent 1st subevent 2d subevent
1986/04/24 1986/11/04 1987/09/18 1988/06/30 1988/07/23 1999/01/29
Ъ** ©ее «С ^^
Solonenko Solonenko Solonenko Bayasgalan Solonenko Solonenko Bayasgalan Barth
etal., 1993 CMT etal., 1993 CMT etal., 1993 CMT etal., 2005 etal., 1993 CMT etal., 1993 CMT etal., 2005 CMT and Wenzel, 2010
2003/11/17 2006/01/06 f> W | (f) I
Emanov CMT Melnikova Radziminovich Barth
and Leskova,2005 etal., 2011 etal., 2012 and Wenzel, 2010
| Fig. 3. Focal mechanisms of the earthquakes with some variations in the solutions determined by different authors and with different approaches.
I Рис. 3. Механизмы очагов землетрясений, для которых имеется несколько решений, полученных разными авторами, а также с использованием различных подходов.
♦ ю
5
0.26 0 2 . 1.6
о О . .
о О
| 0.22 0 1.2
's— 1
ГО л 1
> ▼ 0.9
0.18 Л08
^ а 0.7
"О О
0.1
0 0.1 0.2 0.3 0.4 0.5 0.6
model length
Fig. 4. The trade-off curve between model length and data variance for the full range of possible values of damping parameter e. Numbers indicate values of e.
Рис. 4. График для выбора оптимального значения параметра сглаживания е. Кривая показывает соотношение между длиной модели и дисперсией данных. Числа указывают значение е.
revealed for the Mogod seismic area, named so after the 1967 Mw 7.1 earthquake. The eastern part of the studied region is poorly provided by focal mechanisms, although it is still seismically active. The available solutions, which are mainly GCMT ones and the data from
[Barth, Wenzel, 2010], show the compressive strike-slip regime with 262° of the SHmax orientation (Fig. 5).
The more complex pattern is observed in the area to the north of the Bolnai zone where the stress regime is converted from compression resulted from the India-Eurasian collision to local extension of the Baikal rift. The central part of the Baikal basin is characterized by a pure extension in the NW-SE direction, whereas earthquakes located at its southern termination have a significant strike-slip component along with normal faulting, and this gave grounds to conclude that this area is subject to transtension [Radziminovich et al, 2006]. Compression becomes stronger westward so that the Sayan Mountains are under the strike-slip field and Tuva region is under the compressive strike-slip regime.
The Bolnai area encompasses the rupture zones of the Tsetserleg-Bolnai M 8.0 earthquakes. While making inversion, we revealed that the sample contained too diverse solutions to yield a satisfactory result, so it was divided into several subsets. The 1905 mainshock subset consisting of several subevents [Schlupp, Cisternas, 2007] clearly shows the strike-slip compressional regime with SHmax azimuth 22°. As to the earthquakes recorded by the regional networks for the last 50 years, their focal mechanisms are very heterogeneous, and the low quality of the stress solution for the whole subset resulted in separating it into two opposed stress tensors fitted the data, namely compressional and ex-tensional ones (Table 1).
Table 1. Stress inversion results for different areas using the method and stress regime classification by D. Delvaux
Таблица 1. Результаты инверсии тектонических напряжений для разных районов, полученные по методу
Д. Дельво
Area N 01 02 03 R Rv F1 Q Regime
Baikal 24 76/140 01/234 14/324 0.56 0.56 16.5 B pure extensive
Bolnai 1 8 01/022 03/293 87/131 0.02 2.02 9.8 A strike-slip compressional
Bolnai 2 11 07/296 08/205 79/069 0.71 2.71 19.0 B pure compressional
Bolnai 3 8 78/216 08/085 09/354 0.36 0.36 25.6 С pure extensional
Eastern Mongolia 12 07/262 79/033 07/171 0.27 1.73 25.7 C compressive strike-slip
Goby Altai 13 00/220 12/130 78/310 0.05 2.05 15.0 B compressive strike-slip
Mongolian Altai 35 00/015 19/285 71/105 0.19 2.19 43.3 C pure compressive
Mogod 15 03/059 63/155 27/327 0.62 1.38 23.1 C pure strike-slip
Sayan 8 16/077 72/229 08/345 0.42 1.58 39.6 C pure strike-slip
Tuva 18 07/031 62/286 27/125 0.12 1.88 54.2 C compressive strike-slip
Ubsu Nur 20 07/203 46/106 43/299 0.29 2.29 75.4 C pure compressive
Note. N - number of focal solutions in a sample; cti, а2, аз - orientation (inclination/azimuth) of the principal stress axes (maximum, intermediate, and minimum compression, correspondingly); Q - tensor quality rank (from A (best) to E (worst)); R - stress ratio (ranges from 0 to 1); Rv - stress regime index; F1 - slip-shear misfit angle; Regime - stress regime. Bolnai 1 is the 1905 mainshock subset, Bolnai 2 and Bolnai 3 are the subsets representing the recent earthquakes.
Примечание. N - количество решений механизмов очагов землетрясений для данной выборки; а1, а2, аз - ориентация (угол наклона / азимут) главных осей напряжений (максимальное, среднее и минимальное сжатие, соответственно); Q - качество решения (от А (лучшее) до Е (худшее)); R - коэффициент, показывающий соотношение осей напряжений (в диапазоне от 0 до 1); Rv-показатель режима напряжений; F1 - угол между вектором скольжения и теоретическим направлением скалывания. Болнай 1 -данные по главному сейсмическому событию 1905 г.; Болнай 2 и 3 - данные по землетрясениям инструментального периода наблюдений.
85° 90° 95° 100° 105° 110° 115° 120°
grid.
Vectors give the orientations of maximum (red) and minimum (blue) compressional horizontal stress SH and Sh. An arrow length depends on the inclination to the horizon. Inversion results obtained by Tensor program (in circles) show also intermediate axis orientations (green). Names of the main active domains and the inversion results correspond to Table 1.
Рис. 5. Результаты инверсии тектонических напряжений, полученные для основных активных областей (в кружках) и в ходе линейной инверсии со сглаживанием для сетки с шагом 1°.
Векторами показана ориентация максимальных (красные) и минимальных (синие) горизонтальных напряжений сжатия SH и Sh. Длина стрелок зависит от угла наклона к горизонту. Результаты инверсии, полученные с помощью программы Tensor (в кружках), показывают также ориентацию промежуточной оси (зеленого цвета). Названия основных активных областей и результаты инверсии соответствуют данным таблицы 1.
Another complex area is the territory to the west and north from the Ubsu Nur Lake. It is subject to the S-N compression; nevertheless, diversity of focal solution types here resulted in the largest misfit angle.
The damped inversion results are more smoothed when compared to the stress tensors for subareas. It should be noted that in the outermost SW part of the region, within the China territory, SHmax suddenly becomes oriented in the SE-NW bearings. Such orientation (more precisely, NNW) of the compression axis was in one fault plane solution among others mechanisms; furthermore, the available focal solutions in this area are solitary while the method requires adjacent data. Thus, this is an artefact due to the limited data set for this area. As a whole, the results show that SHmax is turning from the W-E direction in the eastern Mongolia to NE-SW in the Gobi Altay and the central Mongolia, and then to S-N in the western part of the region (Fig. 5).
5. Discussion
The regularities revealed on the recent seismologi-cal data are generally consistent with the Late Cenozoic tectonic stress features inferred from a structural analysis of the active fault zones [Parfeevets, Sankov, 2010, 2012], as well as with the recent geodetic data. The GPS velocity field shows two main trends (Fig. 6): the NE trend within Jungaria, the Mongolian Altay, and the Great Lakes Valley, and the SE trend for the central and eastern Mongolia [Calais et al., 2003; Lukhnev et al., 2010]. The change between these trends spatially coincides with the Khangay dome and the Bolnai zone, being the northern boundary of the dome.
Figure 7 shows the strain patterns within the Baikal-Mongolia GPS network and the stereograms of average mechanisms that actually represents seismo-tectonic strain. The stereograms were obtained for the
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112
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Fig. 6. The field of GPS horizontal velocities with respect to Eurasia for 1994-2007.
Red arrows show directions and velocities (mm/yr) with 95% confidence limit; light grey arrows show vectors averaged on a 30'x30' regular grid. The map is based on the data from Table 1 in [Lukhnev et al., 2010]. 1 - abbreviated station name and velocity (mm/yr); 2 - direction and velocity with 95% confidence ellipse.
Рис. 6. Поле горизонтальных скоростей по данным GPS относительно Евразии с 1994 по 2007 г.
Направления и скорости (мм/год) с 95%-ным доверительным интервалом показаны красными стрелками; светло-серые стрелки показывают векторы скоростей, интерполированные по сетке 30'х30'. Карта базируется на данных из таблицы 1, опубликованной в [Lukhnev et al., 2010]. 1 - сокращенное название станции и скорость (мм/год); 2 - направление и скорость с 95%-ным доверительным эллипсом.
main seismic zones (like the stress inversion subareas) so that they do not coincide fully with the geodetic triangles. Nevertheless, the general features can be compared. For the southern and western areas, where strong earthquakes occurred like the 1957 M 8.3 Gobi-Altay earthquake or the 1931 M 8.0 Fu Yun earthquake in Mongolian Altay, the strain patterns obtained from GPS and seismological data are consistent, whereas the above mentioned Bolnai zone shows a contradiction. The results of GPS estimation indicate the predominance of extension (in the SE-NW direction), while compression was revealed for the longer period of seismic observations. Yet, the seismotectonic strain
shows compression that was provided mainly by the Tsetserleg-Bolnai earthquakes; however, we noted above that a part of the recent data on focal mechanisms fits an extensional stress field with the NNW oriented extension axis. The diversity of the recent focal solutions might be caused by postseismic relaxation or stress perturbation after the mainshocks or it could reflect the different scale of the considered earthquake. In addition, there is an ambiguity related to comparison between GPS and seismicity data on account of different spatial and time domains to be compared, and complexity of the rupture kinematics in case of a large earthquake.
UZUR
Fig. 7. Strain patterns within the Baikal-Mongolia GPS network.
Red and blue arrows show principal shortening and stretching strain axes derived from the GPS velocity data from Table 1 in [Lukhnev et al., 2010]. Seismotectonic strain is visualized by yellow stereograms, which are the averaged focal solutions for the main seismic zones outlined by thin black lines.
Рис. 7. Ориентация и скорость деформации земной коры в пределах Байкало-Монгольского GPS-полигона.
Оси укорочения и удлинения, установленные по данным GPS-векторов (таблица 1 [Lukhnev et al., 2010]), показаны красными и синими стрелками. Сейсмотектонические деформации показаны на стереограммах (желтый) как усредненные решения механизмов очагов землетрясений для основных сейсмических зон, оконтуренных тонкой черной линией.
However, another confirmation of the transtensive field existence in the eastern part of the Bolnai zone comes from Quaternary fault-slip data [Parfeevets, Sankov, 2012]. The extension here is supposed to be related to the divergent motions between the North Eurasia and Amurian plates [Petit, Fournier, 2005]. Changes in seismotectonic deformations in this area were also reported by O.A. Kuchai and M.E. Kozina [2015] who outlined there the boundary of the Amurian plate.
The complexity of focal solutions is also observed in the NW part of the study region. Despite this area is subjected to the S-N compression, normal fault earthquakes are rather numerous there. This area is also distinguished by the fact that seismicity is mainly con-
fined to the ridges and uplifts rather than to basins (e.g., Tuva basins, Great Lake basin, Ubsu-Nur basin). S.V. GoFdin and O.A. Kuchai [2007] explained these two observations by the block structure of the Altay-Sayan area, and, more precisely, by "the hierarchic systems of rigid and plastic blocks (rheological structure)". In other words, the basins are supposed to be aseismic rigid block; as to normal slip focal solutions found here, they are thought to occur in regions of strain shadow.
We roughly estimated the strain rate for the territory of Mongolia using the widely known KostrovNs formulae [Kostrov, 1974] as summed moment tensors of earthquakes divided by shear modulus, volume and time interval of observations. Only earthquakes with M>7.0 (the Mw 6.9 Mondy event was also included)
Table 2. Components of the seismotectonic strain rate tensor
Таблица 2. Компоненты тензора скорости
сейсмотектонической деформации
£xx 8yy Szz Sxy Syz Sxz £ij, (yr-1)
0.89 -4.04 3.13 -42.4 2.03 -3.80 10-9
Note. Elements of the symmetrical strain rate tensor obtained by summing moment tensors of earthquakes with M>7.0 and dividing the results by the time interval (100 years) and the crust volume (1200x2900x20 km). Coordinate axes x, y and z are east, north, and up, respectively. Minus and plus indicate shortening and stretching of the crust, respectively.
Примечание. Компоненты симметричного тензора скорости деформации получены путем суммирования моментов тензоров землетрясений магнитудой M>7.0 и деления результата на временной интервал (100 лет) и объем коры (1200x2900x20 км). Оси координат х, у и z - восток, север, вверх соответственно. Знаки - и + указывают на сокращение и растяжение земной коры, соответственно.
that constitute significant strain release were considered. Values of the average strain rate tensor components are shown in Table 2. The largest value is about 42x10-9 yr-1 for the horizontal shear component Sxy that exceeds the shortening rate estimated for different parts of Mongolia from GPS measurements, which ranges approximately from 3x10-9 to 25x10-9 yr-1 [Lukh-nev et al., 2010]. In case of summing only scalar seismic moments of the earthquakes, the seismic strain rate is 8.7x10-9 yr-1. For the time interval of 100 years, the seismic moment release is approximately 1.12x1020 N m yr-1. Even such rough estimates of the strain rate and seismic moment release are rather high for the in-tracontinental setting. It has been already noted by W.E. Holt and his colleagues, who reported that in the 20th century the earthquake moment release rate in Mongolia was about a factor of 4 higher than the model long-term rate [Holt et al., 1995,2000]; this is obviously due to the occurrence of several great earthquakes close in time and space. Proximity of the four earthquakes with M>8 implies a possible link between them, for example, through viscoelastic stress transfer, as was tested in [Chery et al., 2001].
6. Conclusions
In this report, we have gathered earthquake focal solutions for the territory of Mongolia and its surroundings in order to reveal a spatial variability of the stress orientation and stress regimes of the crust. Our results do not bring much change in the already published results for this territory [Zhalkovskii et al., 1995; Melnikova et al., 2004; Melnikova, Radziminovich, 2005;
San'kov et al., 2005, 2011; Gol'din, Kuchai, 2007; Par-feevets, San'kov, 2010; Rebetsky et al., 2013; Kuchai, Kozina, 2015; and others] indicating that the main characteristics of the present-day regional stress field are quite steady.
The map of focal mechanisms shows that the earthquake focal solutions in the southern and western parts of Mongolia and the neighbouring regions of China and Russia are quite uniform (strike-slip and thrust movements). The more complex pattern is observed in the area to the north from the Bolnai zone where the stress regime is thought to be converted from compression due to the India-Eurasian collision to local extension due to the Baikal rifting. The complicated picture of focal mechanisms distribution in the Altay-Sayan area may be explained by the block structure of this territory.
According to the stress inversion results, the SHmax is turning from W-E in the eastern Mongolia to NE-SW in the Gobi Altay and the central Mongolia and then to S-N in the western part of the region. The regularity can be explained by the recent geodynamics of this part of Asia.
The strain axes directions revealed by the geodetic and seismological observations are generally consistent. As for the strain rate, clustering of large earthquakes in time due to mutual triggering may be an additional factor (along with the incompleteness of seismic catalogues) that complicates the comparison of geodetic and seismic strain rate.
The data compiled and visualized in this study show the spatial gaps to be covered by earthquake focal solutions. For instance, the vast areas of the eastern part of Mongolia and Transbaikalia remains insufficiently studied that should be compensated not only 'for the sake of pure scientific interest' but mainly for seismic hazard assessment of the capital of Mongolia. Ulaanbaa-tar, the largest city at the region with population about 1,200,000 people, has recently faced with increasing the seismic activity in its vicinity. Therefore, a proper knowledge of kinematic type of active faults under the recent stress regime is strongly needed to constrain potential earthquake scenarios.
We hope that the map and the stress inversion results can be a useful tool for geodynamic and seismo-tectonic analyses of this part of Asia and it will facilitate better understanding of spatial co-existence of different stress regimes.
7. Acknowledgements
We are grateful to the reviewers for their helpful and constructive comments. We thank F.L. Zuev (Laboratory of Recent Geodynamics, Institute of the Earth's Crust), who implemented geodetical strain calculations in a program used for the paper. This work is
a result of collaboration between the Institute of the Earth's crust (Irkutsk, Russia) and the Research Center of Astronomy and Geophysics (Ulaanbaatar, Mongolia).
The reported study was funded by the Russian Foundation for Basic Research according to the research project № 16-05-00224.
8. References
Angelier J., 1984. Tectonic analysis of fault slip data sets. Journal of Geophysical Research 89 (B7), 5835-5848. http://dx.doi.org/10.1029/JB089iB07p05835.
Avouac J.P., Tapponnier P., 1993. Kinematic model of active deformation in central Asia. Geophysical Research Letters 20 (10), 895-898. http://dx.doi.org/10.1029/93GL00128.
Baljinnyam I., Bayasgalan A., Borisov B.A., Cisternas A., Dem'yanovich M.G., Ganbaatar L., Kochetkov V.M., Kurushin R.A., Molnar P., Philip H., Vashchilov Yu.Ya., 1993. Ruptures of major earthquakes and active deformation in Mongolia and its surroundings. Geological Society of America Memoirs, vol. 181. Boulder, Colorado, 64 p. http://dx.doi.org/ 10.1130/MEM181-p1.
Baljinnyam I., Monhoo D., Tsembel B., Dugarma T., Adya M., Bayaraa G., 1975. Seismicity of Mongolia. Ulaanbaatar, 105 p. (in Mongolian).
Barth A., Wenzel F., 2010. New constraints on the intraplate stress field of the Amurian plate deduced from light earthquake focal mechanisms. Tectonophysics 482 (1-4), 160-169. http://dx.doi.org/10.1016Zj.tecto.2009.01.029.
Bayasgalan A., Jackson J.A., 1999. A re-assessment of the faulting in the 1967 Mogod earthquakes in Mongolia. Geophysical Journal International 138 (3), 784-800. http://dx.doi.org/10.1046/j.1365-246x.1999.00907.x.
Bayasgalan A., Jackson J., MacKenzi D., 2005. Lithosphere rheology and active tectonics in Mongolia: relations between earthquake source parameters, gravity and GPS measurements. Geophysical Journal International 163 (3), 1151-1179. http://dx.doi.org/10.1111/j.1365-246X.2005.02764.x.
Calais E., Vergnolle M., San'kov V., Lukhnev A., Miroshnitchenko A., Amarjargal S., Deverchere J., 2003. GPS measurements of crustal deformation in the Baikal-Mongolia area (1994-2002): implications on current kinematics of Asia. Journal of Geophysical Research 108 (B10), 2501. http://dx.doi.org/10.1029/2002JB002373.
Chery J., Carretier S., Ritz J.-F., 2001. Postseismic stress transfer explains time clustering of large earthquakes in Mongolia. Earth and Planetary Science Letters 194 (1-2), 277-286. http://dx.doi.org/10.1016/S0012-821X(01) 00552-0.
De Mets C., Gordon R.G., Argus D.F., Stein S., 1990. Current plate motions. Geophysical Journal International 101 (2), 425-478. http://dx.doi.org/10.1111/j.1365-246X.1990.tb06579.x.
Delouis B., Deverchere J., Melnikova V., Radziminovitch N., Loncke L., Larroque C., Ritz J.-F., San'kov V., 2002. A reappraisal of the 1950 (Mw 6.9) Mondy earthquake, Siberia, and its relationship to the strain pattern at the southwestern end of the Baikal rift zone. Terra Nova 14 (6), 491-500. http://dx.doi.org/10.1046/j.1365-3121.2002. 00445.x.
Delvaux D., Kuchai O.A., Zhalkovsky N.D., Sankov V.A., Melnikova V.I., Radziminovitch N.A., Petit C., Van der Meer R., Hendriks B.W.H., Dehandshutter B., 1998. Seismotectonics and neotectonics of the Altai-Sayan belt. In: Active tectonic continental basins. Interaction between structural and sedimentary processes. International Conference organized at the occasion of the end of INTAS Project 134, April 30 - May 2, 1998, Gent, Belgium: Abstract volume. University of Gent, Belgium, p. 63.
Delvaux D., Moyes R., Stapel G., Petit C., Levi K., Miroshnichenko A., Ruzhich V., Sankov V., 1997. Paleostress reconstruction and geodynamics of the Baikal region, Central Asia, Part 2. Cenozoic rifting. Tectonophysics 282 (1-4), 1-38. http://dx.doi.org/10.1016/S0040-1951(97)00210-2.
Delvaux D., Sperner B., 2003. Stress tensor inversion from fault kinematic indicators and focal mechanism data: the TENSOR program. In: D. Nieuwland (Ed.), New insights into structural interpretation and modelling. Geological Society, London, Special Publications, vol. 212, p. 75-100. http://dx.doi.org/10.1144/GSL.SP.2003.212.01.06.
Deverchere J., Radziminovitch N., Calais E., Deschamps A., Melnikova V., Petit C., Sankov V., 2000. Seismicity of the Baikal rift and central Mongolia: seismic potential, seismogenic thickness, segmentation, and rheological properties of the lithosphere. In: Seismology in Siberia at the Millenium boundary. Materials of the international geophysical conference, 27-29 September, 2000. Novosibirsk, p. 294-298.
Doser D.I., 1991. Faulting within the western Baikal rift as characterized by earthquake studies. Tectonophysics 196 (1-2), 87-107. http://dx.doi.org/10.1016/0040-1951(91)90291-Y.
EmanovA.A., Leskova E.V., 2005. Structure of the aftershock process of the Chuya earthquake (Gorny Altai). Russian Geology and Geophysics 46 (10), 1053-1060.
England P., Molnar P., 1997. The field of crustal velocity in Asia calculated from quaternary rates of slip on faults. Geophysical Journal International 130 (3), 551-582. http://dx.doi.org/10.1111/j.1365-246X.1997.tb01853.x.
Florensov N.A., Solonenko V.P. (Eds.), 1963. The Gobi-Altai earthquake. Publishing House of Academy of Sciences of USSR, Moscow, 424 p. (in Russian) [Гоби-Алтайское землетрясение / Ред. Н.А. Флоренсов, В.П. Солоненко. М.: Изд-во АН СССР, 1963. 424 с.].
Gol'din S.V., Kuchai O.A., 2007. Seismic strain in the Altai-Sayan active seismic area and elements of collisional geodynamics. Russian Geology and Geophysics 48 (7), 536-557. http://dx.doi.org/10.1016Zj.rgg.2007.06.005.
Hardebeck J., Michael A., 2006. Damped regional-scale stress inversions: Methodology and examples for southern California and the Coalinga aftershock sequence. Journal of Geophysical Research 111 (B11), B11310. http://dx.doi. org/10.1029/2005JB004144.
Holt W.E., Chamot-Rooke N., Le Pichon X., Haines A.J., Shen-Tu B., Ren J., 2000. Velocity field in Asia inferred from Quaternary fault slip rates and Global Positioning System observations. Journal of Geophysical Research 105 (B8), 19185-19209. http://dx.doi.org/10.1029/2000JB900045.
Holt W.E., Li M., Haines A.J., 1995. Earthquake strain rates and instantaneous relative motion within central and east Asia. Geophysical Journal International 122 (2), 569-593. http://dx.doi.org/10.1111/j.1365-246X.1995.tb07014.x.
Huang J., Chen W.-P., 1986. Source mechanisms of the Mogod earthquake sequence of 1967 and the event of 1974 July 4 in Mongolia. Geophysical Journal of the Royal Astronomical Society 84 (2), 361-379. http://dx.doi.org/ 10.1111/j.1365-246X.1986.tb04360.x.
Jarvis A., Reuter H.I., Nelson A., Guevara E., 2008. Hole-filled seamless SRTM data V4, International Centre for Tropical Agriculture (CIAT). Available from: http://srtm.csi.cgiar.org (last accessed 03.03.2016).
Karagianni I., Papazachos C.B., Scordilis E.M., Karakaisis G.F., 2015. Reviewing the active stress field in Central Asia by using a modified stress tensor approach. Journal of Seismology 19 (2), 541-565. http://dx.doi.org/10.1007/ s10950-015-9481-4.
Khilko S.D., Kurushin R.A., Kochetkov V.M., Misharina L.A., Melnikova V.I., Gileva N.A., Lastochkin S.V., Baljinnyam I., Monkhoo D., 1985. Earthquakes and foundations of seismic zoning in Mongolia. Nauka, Moscow, 224 p. (in Russian) [Хилько С.Д., Курушин Р.А., Кочетков В.М., Мишарина Л.А., Мельникова В.И., Гилева Н.А., Ласточкин С.В., Балжинням И., Монхоо Д. Землетрясения и основы сейсмического районирования Монголии. М.: Наука, 1985. 224 с.].
Khromovskikh V.S., Solonenko V.P., Kurushin R.A., Zhilkin V.M., 1975. Macroseismic data on the earthquakes of Eastern Sayan, southern Pribaikalye and northern Mongolia. Specific features of the distribution of the intensity of ground shaking. In: Seismotectonics and Seismicity of the Southeastern part of the Eastern Sayan. Nauka, Novosibirsk, p. 28-42 (in Russian) [Хромовских В.С., Солоненко В.П., Курушин Р.А., Жилкин В.М. Макросейсмические сведения о землетрясениях Восточного Саяна, Южного Прибайкалья и Северной Монголии. Особенности распределения интенсивности сотрясения при землетрясениях // Сейсмотектоника и сейсмичность юго-восточной части Восточного Саяна. Новосибирск: Наука, 1975. С. 28-42].
Kostrov V.V., 1974. Seismic moment and energy of earthquake, and seismic flow of rock. Izvestiya Acad. Sci. USSR, Physics of Solid Earth, Engl. Transl. (10), 23-44.
Kuchai O.A., Kozina M.E., 2015. Regional features of seismotectonic deformations in East Asia based on earthquake focal mechanisms and their use for geodynamic zoning. Russian Geology and Geophysics 56 (10), 1491-1499. http://dx.doi.org/10.1016/j.rgg.2015.09.011.
Kurushin R.A., Bayasgalan A., Ulzybat M., Enhtuvshin B., Molnar P., Bayarsayhan C., Hudnut K.W., Lin J., 1997. The surface rupture of the 1957 Gobi-Altay, Mongolia, earthquake. Geological Society of America Special Paper, vol. 320. Geological Society of America, Boulder, Colorado, 144 p. http://dx.doi.org/10.1130/0-8137-2320-5.!.
Leskova E.V., EmanovA.A., 2014. Some properties of the hierarchical model reproducing the stress state of the epicen-tral area of the 2003 Chuya earthquake. Izvestya, Physics of the Solid Earth 50 (3), 393-402. http://dx.doi. org/10.1134/S1069351314030057.
Lukhnev A.V., San'kov V.A., Miroshnichenko A.I., Ashurkov S.V., Calais E., 2010. GPS rotation and strain rates in the Baikal-Mongolia region. Russian Geology and Geophysics 51 (7), 785-793. http://dx.doi.org/10.1016/j.rgg.2010. 06.006.
Map of focal mechanisms of earthquakes in Mongolia, 2011. The map coordinators: N. Radziminovich, S. Demberel; Authors: Bayaraa G., Ulzibat M., Ganzorig D., Erdenezul D., Munkhoo D., Tsembel B., Adiya M., Selenge L., Melnikova V., Radziminovich Ya. Research Centre of Astronomy & Geophysics of the Mongolian Academy of Sciences (RCAG), Ulaanbaatar, 2011.
Melnikova V.I., Radziminovich N.A., Adyaa M., 2004. Mechanisms of earthquake foci and seismotectonic deformations of the Mongolia region. In: V.I. Dzhurik, T. Dugarmaa (Eds.), Complex geophysical and seismological investigations in Mongolia. Research Centre of Astronomy and Geophysics of the Mongolian Academy of Sciences, Ulaanbaatar; Institute of the Earth's Crust SB RAS, Irkutsk, p. 165-170.
Melnikova V.I., Radziminovitch N.A., 2005. Focal mechanisms and seismotectonic deformations in Mongolian region. In: Proceedings of the 2d International Symposium "Active geophysical monitoring of the lithosphere of the Earth". Novosibirsk, p. 326-329.
Mel'nikova V.l., Radziminovich Ya.B., Gileva N.A., Radziminovich N.A., Papkova A.A., 2011. The January 6, 2006, Balei earthquake as a reflection of the present tectonic activity of the east Trans-Baikal region. Doklady Earth Sciences 437 (2), 552-556. http://dx.doi.org/10.1134/S1028334X11040222.
Michael A.J., 1984. Determination of stress from slip data: Faults and folds. Journal of Geophysical Research 89 (B13), 11517-11526. http://dx.doi.org/10.1029/JB089iB13p11517.
Misharina L.A., 1972. Stresses in earthquake foci of the Mongoli-Baikal folded zone. In: Fields of Elastic Stresses of the Earth and Focal Mechanisms of Earthquakes. Nauka, Moscow, p. 161-171 (in Russian) [Мишарина Л.А. Напряжения в очагах землетрясений Монголо-Байкальской зоны // Поле упругих напряжений Земли и механизм очагов землетрясений. М.: Наука, 1972. С. 161-171].
Moskvina A.G., 1978. Mechanism and parameters of the January 5, 1967 Mogod earthquake and its aftershocks. lzvestiya AN SSSR, seriya Fizika Zemli (1), 3-17 (in Russian) [Москвина А.Г. Механизм и параметры очага Могодского землетрясения 5 января 1967 г. и его афтершоков // Физика Земли. 1978. № 1. С. 3-17].
Nikitin L.V., Yunga S.L., 1977. Methods of theoretical determinations of tectonic strain and stress in seismically active regions. lzvestiya AN SSSR, seriya Fizika Zemli (11), 54-67 (in Russian) [Никитин Л.В., Юнга С.Л. Методы теоретического определения тектонических деформаций и напряжений в сейсмоактивных областях // Известия АН СССР, серия Физика Земли. 1977. № 11. С. 54-67].
Okal E., 1976. A surface-wave investigation of the rupture mechanism of the Gobi-Altay (December 4, 1957) earthquake. Physics of the Earth and Planetary Interiors 12 (4), 319-328. http://dx.doi.org/10.1016/0031-9201(76) 90027-3.
Okal E.A., 1977. The July 9 and 23, 1905, Mongolian earthquakes: a surface wave investigation. Earth and Planetary Science Letters 34 (2), 326-331. http://dx.doi.org/10.1016/0012-821X(77)90018-8.
Parfeevets A.V., San'kov V.A., 2010. Late Cenozoic fields of the tectonic stresses in Western and Central Mongolia. lzvestiya, Physics of the Solid Earth 46 (5), 367-378. http://dx.doi.org/10.1134/S1069351310050010.
Parfeevets A.V., V.A. San'kov, 2012. Late Cenozoic tectonic stress fields of the Mongolian microplate. Comptes Rendus Geoscience 344 (3-4), 227-238. http://dx.doi.org/10.1016Zj.crte.2011.09.009.
Peltzer G., Saucier F., 1996. Present-day kinematics of Asia derived from geologic fault rates. Journal of Geophysical Research 101 (B12), 27943-27956. http://dx.doi.org/10.1029/96JB02698.
Petit C., Déverchère J., Houdry F, Sankov V.A., Melnikova V.l., Delvaux D., 1996. Present-day stress field changes along the Baikal rift and tectonic implication. Tectonics 15 (6), 1171-1191. http://dx.doi.org/10.1029/96TC00624.
Petit C., Fournier M., 2005. Present-day velocity and stress fields of the Amurian plate from thin-shell finite-element modelling. Geophysical Journal International 160 (1), 357-369. http://dx.doi.org/10.1111/j.1365-246X.2004. 02486.x.
Priestley K., Debayle E., McKenzie D., Pilidou S., 2006. Upper mantle structure of eastern Asia from multimode surface waveform tomography. Journal of Geophysical Research 111 (B10), B10304. http://dx.doi.org/10.1029/2005 JB004082.
Radziminovich N.A., Demberel S., Bayaraa G., 2011. Map of the focal mechanisms of earthquakes in Mongolia. In: Abstracts of the IX Joint Russian-Mongolian Conference, Irkutsk, 10-12 Oct., 2011, p. 27-28.
Radziminovitch N.A., Melnikova V.l., Adyaa M., Ankhtsetseg D., Selenge L., Bayar G., 2007. Recent stress and strain state of the crust of the northern Mongolia and southern Baikal regions from focal solutions. In: Extended abstract volume of the Conference commemorating the 50th anniversary of the 1957 Gobi-Altay earthquake, 25 July -8 August, 2007, Ullanbaatar, Mongolia. Ulaanbaatar, p. 195-200.
Radziminovitch N.A., Melnikova V.l., Miroshnitchenko A.l., 2008. Stress field and seismotectonic strain of the earth crust of the northern Mongolia and southern Baikal region from focal solutions. In: Abstracts of the 3rd World Stress Map Conference, 15-17 October 2008, GFZ Potsdam, Germany, p. 104.
Radziminovitch N.A., Melnikova V.l., San'kov V.A., Levi K.G., 2006. Seismicity and seismotectonic deformations of the crust in the Southern Baikal basin. lzvestiya, Physics of the Solid Earth 42 (11), 904-920. http://dx.doi.org/ 10.1134/S1069351306110048.
Radziminovich Ya.B., Mel'nikova V.l., Seredkina A.l., Gileva N.A., Radziminovich N.A., Papkova A.A., 2012. The Balei earthquake of 6 January 2006 (Mw=4.5): A rare case of seismic activity in eastern Transbaikalia. Russian Geology and Geophysics 53 (10), 1100-1110. http://dx.doi.org/10.1016/j.rgg.2012.08.010.
Rebetsky Yu.L., Kuchai O.A., Marinin A.V., 2013. Stress state and deformation of the Earth's crust in the Altai-Sayan mountain region. Russian Geology and Geophysics 54 (2), 206-222. http://dx.doi.org/10.1016/j.rgg.2013.01.011.
San'kov V.A., Lukhnev A.V., Radziminovich N.A., Mel'nikova V.l., Miroshnichenko A.l., Ashurkov S.V., Calais E., Déverchére J., 2005. A Quantitative estimate of modern deformations of the Earth's crust in the Mongolian block (based on GPS-geodesy and seismotectonic data). Doklady Earth Sciences 403A (6), 946-949.
San'kov V.A., Parfeevets A.V., 2005. Late cenozoic stressed state of active fault zones in western Mongolia and Tuva. Doklady Earth Sciences 403A (6), 852-855.
San'kov V.A., Parfeevets A.V., Lukhnev A.V., Miroshnichenko A.I., Ashurkov S.V., 2011. Late Cenozoic geodynamics and mechanical coupling of crustal and upper mantle deformations in the Mongolia-Siberia mobile area. Geotectonics 45 (5), 378-393. http://dx.doi.org/10.1134/S0016852111050049.
Schlupp A., Cisternas A., 2007. Source history of the 1905 great Mongolian earthquakes (Tsetserleg, Bolnay). Geophysical Journal lnternational 169 (3), 1115-1131. http://dx.doi.org/10.1111/j.1365-246X.2007.03323.x.
Sodnomsambuu D., Radziminovich N., Gangaadorj B., Munkhuu U., Davaasuren G., Danzansan E., Radziminovich Y., Melnikova V., Battsetseg B., 2011. Focal mechanisms of earthquakes in Mongolia. Abstract #S11B-2206 presented at 2011 Fall Meeting, AGU, San Francisco, Calif., 5-9 Dec.
Solonenko A.V., Solonenko N.V., Melnikova V.l., Kozmin B.M., Kuchai O.A., Sukhanova S.S., 1993. Strains and displacements in earthquake foci of Siberia and Mongolia. In: Seismicity and seismic zoning of northern Eurasia, vol. 1. UIPE, Moscow, p. 113-122 (in Russian) [Солоненко А.В., Солоненко Н.В., Мельникова В.И., Козьмин Б.М., Кучай О.А., Суханова С. С. Напряжения и подвижки в очагах землетрясений Сибири и Монголии // Сейсмичность и сейсмическое районирование Северной Евразии. Вып. 1. М.: ОИФЗ РАН, 1993. C. 113-122].
Tapponier P., Molnar P., 1979. Active faulting and Cenozoic tectonics of the Tien Shan, Mongolia and Baikal region. Journal of Geophysical Research 84 (B7), 3425-3459. http://dx.doi.org/10.1029/JB084iB07p03425.
Tataurova A.A., Kozina M.E., Kuchai O.A., 2014. The block structure of the Altay-Sayan region revealed by seismological data. In: Abstracts of the Symposium with invited international participants "Faulting in the lithosphere and concomitant processes: tectonophysical analysis", August, 11-16, 2014, Irkutsk, Institute of the Earth's crust, p. 34.
Turcotte D., Shubert G., 1985. Geodynamics: Geological Applications of Continuum Physics. Mir, Moscow, Vol. 1, 376 p.; Vol. 2, 360 p. (in Russian) [Теркот Д., Шуберт Дж. Геодинамика: Геологические приложения физики сплошных сред. М.: Мир, 1985. Т. 1. 376 с.; Т. 2. 360 с.].
Ulziibat M., 2006. The 2003 Chuya Sequence (North Altay range): Tectonic Context and Seismological Study. Ph.D. Thesis, Université de Nice-Sophia Antipolis, 172 p.
Vvedenskaya A.V., Balakina L.M., 1960. Method and results of the determination of stresses acting in the foci of earthquakes of Pribaikalie and Mongolia. In: Seismology Board Bulletin, Issue 10. Problems of Seismotectonics of the Pribaikalie and Adjacent Territories. Publishing House of the USSR Acad. Sci., Moscow, p. 73-84 (in Russian) [Введенская А.В., Балакина Л.М. Методика и результаты определения напряжений, действующих в очагах землетрясений Прибайкалья и Монголии // Бюллетень Совета по сейсмологии. № 10. Вопросы сейсмотектоники Прибайкалья и смежных территорий. М.: Изд-во АН СССР, 1960. С. 73-84].
Voznesensky A.V., 1962. Investigation of the Region of the Hangay Earthquakes of 1905 in northern Mongolia. Materials from the department of Physical Geographical Society of the USSR, vol. 1. Leningrad, 50 p. (in Russian) [Вознесенский А.В. Исследования в области Хангайских землетрясений 1905 г. в Северной Монголии // Материалы отделения физической географии Географического общества СССР. Вып. 1. Л., 1962. 50 с.].
Windley B.F., Allen M.B., 1993. Mongolian plateau: Evidence for a late Cenozoic mantle plume under central Asia. Geology 21 (4), 295-298. http://dx.doi.org/10.1130/0091-7613(1993)021<0295:MPEFAL>2.3.C0;2.
Yunga S.L., 1990. Methods and results of studies of seismotectonic deformations. Nauka, Moscow, 191 p. (in Russian) [Юнга С.Л. Методы и результаты изучения сейсмотектонических деформаций. М.: Наука, 1990. 191 с.].
Zhalkovskii N.D., Kuchai O.A., Muchnaya V.l., 1995. Seismicity and some characteristics of the state of stress of the Earth's crust in the Altai-Sayan region. Geologiya i Geofizika (Russian Geology and Geophysics) 36 (10), 20-30 (in Russian) [Жалковский Н.Д., Кучай О.А., Мучная В.И. Сейсмичность и некоторые характеристики напряженного состояния земной коры Алтае-Саянской области // Геология и геофизика. 1995. Т. 36. № 10. С. 20-30].
Zonenshain L.P., Savostin L.A., 1981. Geodynamics of the Baikal rift zone and plate tectonics of Asia. Tectonophysics 76 (1-2), 1-45. http://dx.doi.org/10.1016/0040-1951(81)90251-1.
Radziminovich, Natalia A., Candidate of Geology and Mineralogy, Senior Researcher
Institute of the Earth's Crust, Siberian Branch of RAS
128 Lermontov street, Irkutsk 664033, Russia
Tel.: 89642160520; И e-mail: nradzim@crust.irk.ru
Радзиминович Наталья Анатольевна, канд. геол.-мин. наук, с.н.с. Институт земной коры СО РАН 664033, Иркутск, ул. Лермонтова, 128, Россия Тел.: 89642160520; И e-mail: nradzim@crust.irk.ru
Bayar Gangaadorj, Researcher
Research Center of Astronomy and Geophysics of MAS
Ulaanbaatar 210351, Mongolia
e-mail: bayart@rcag.ac.mn
Баяр Гангаадорж, научный сотрудник Исследовательский центр астрономии и геофизики МАН 210351, Улан-Батор, Монголия e-mail: bayart@rcag.ac.mn
Miroshnichenko, Andrei I., Candidate of Geology and Mineralogy, Senior Researcher Institute of the Earth's Crust, Siberian Branch of RAS 128 Lermontov street, Irkutsk 664033, Russia Tel.: +7(3952)429534; e-mail: mai@crust.irk.ru
Мирошниченко Андрей Иванович, канд. геол.-мин. наук, с.н.с. Институт земной коры СО РАН 664033, Иркутск, ул. Лермонтова, 128, Россия Тел.: (3952)429534; e-mail: mai@crust.irk.ru
Demberel Sodnomsambuu, Director, Professor Research Center of Astronomy and Geophysics of MAS Ulaanbaatar 210351, Mongolia e-mail: demberel@rcag.url.mn
Дэмбэрэл Содномсамбуу, директор, профессор Исследовательский центр астрономии и геофизики МАН 210351, Улан-Батор, Монголия e-mail: demberel@rcag.url.mn
Ulziibat Monkhoo, Head of the Seismological Department of RCAG Research Center of Astronomy and Geophysics of MAS Ulaanbaatar 210351, Mongolia e-mail: ulzibat@rcag.url.mn
Ульзибат Монхо, начальник отдела сейсмологии Исследовательский центр астрономии и геофизики МАН 210351, Улан-Батор, Монголия e-mail: ulzibat@rcag.url.mn
Ganzorig Davaasuren, Researcher
Research Center of Astronomy and Geophysics of MAS
Ulaanbaatar 210351, Mongolia
e-mail: ganzorig@rcag.url.mn
Ганзориг Даваасурен, научный сотрудник Исследовательский центр астрономии и геофизики МАН 210351, Улан-Батор, Монголия e-mail: ganzorig@rcag.url.mn
Lukhnev, Andrei V., Candidate of Geology and Mineralogy, Senior Researcher
Institute of the Earth's Crust, Siberian Branch of RAS
128 Lermontov street, Irkutsk 664033, Russia
Tel.: +7(3952)429534; e-mail: loukhnev@crust.irk.ru
Лухнев Андрей Викторович, канд. геол.-мин. наук, с.н.с. Институт земной коры СО РАН 664033, Иркутск, ул. Лермонтова, 128, Россия Тел.: (3952)429534; e-mail: loukhnev@crust.irk.ru
