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Huang X.-L.,Chinese Academy of Geological Sciences | Huang X.-L.,Peking University | Wu Z.-H.,Chinese Academy of Geological Sciences | Zhao X.-Y.,Seismological Bureau of Yunnan Province | And 4 more authors.
Acta Geoscientica Sinica | Year: 2015

Two earthquakes of MS5.6 and MS6.1 occurred successively on May, 2014, in Yingjiang, Yunnan province. In order to determine their seismogenic structures and the regional active tectonic settings, the authors carried out field investigation of seismic intensity, remote sensing image interpretation, analysis of focal mechanism solutions and aftershock distribution. The results show that the macro-epicenters of two earthquakes were both located near the area of Malipo Village, Mengnong Township, Yingjiang County, but their seismogenic faults are different from each other. The former was associated with the NE-trending left-lateral strike-slip Xima-Panlongshan fault, whereas the latter occurred along the SN-trending right-lateral strike-slip Sudian fault. Historical seismicities were dominated by the earthquakes with magnitude 5~6 in the Yingjiang region, which clustered along the SN-trending fault. Under the combination effect of Sagaing fault and inner arc belt in western Yunnan, the north of Tengchong block bounded by Dayingjiang fault is mainly dominated by nearly SN-trending right-lateral strike slip faults, whereas the south is dominated by NE-trending left-lateral strike slip faults. The activity of nearly NS-tranding faults was relatively stronger in Late Quaternary. © 2015, Science Press. All right reserved.

Wu K.,China University of Geosciences | Wu K.,Chinese Academy of Geological Sciences | Wu Z.,Chinese Academy of Geological Sciences | Xu F.,Seismological Bureau of Yunnan Province | And 6 more authors.
Geological Bulletin of China | Year: 2016

Yongping Town in Jinggu of Yunnan Province experienced three times of strong earthquakes from October to December in 2014, which were Ms6.6, Ms5.8, Ms5.9 respectively. In order to determine the cause of this earthquake swarm in the geological structure area, the authors, based on the investigation at the surface in combination with the geological structure, intensity and the aftershock distribution and focal mechanism solution, have reached the conclusion that the macro epicenter of the earthquake swarm activity was located in the mountain area on the southeast side of Yongping basin. The seismogenic fault was the NW-trending dextral strike slip fault which had no obvious geological and geomorphological features. The southeastward migration phenomenon of the aftershocks indicates, due to the temporary block of the oblique connecting position of the rock bridge fault, there was a brief stagnation when Ms6.6 earthquake rupture propagation was spread southeastward. Nevertheless, on December 6th, after breaking through barriers, the earthquake rupture further triggered the Ms5.8 and Ms5.9 earthquakes. This shows that the earthquake swarm activity accorded with the behavior of focal rupture along the NW seismogenic fault segment rupture. The remote sensing interpretation of regional active faults indicates that the seismogenic fault lay just between Chafang NW- trending right strike- slip faults and Puwen NW-trending right strike-slip faults. The area belongs to the incoherent area of Chafang-Puwen fault zone. The authors point out that the strong earthquake swarm activities should be tectonic activities during the coalescence of Chafang-Puwen fault in the upper crust. Combined with the historical seismic data of the Simao block, it is held that the grades of all the seismic activities were less than or equal to 6.8, and the seismogenic structures were mostly NW-trending faults. These phenomena indicate that, in the present tectonic stress field, the NW-trending fault activity is more obvious relative to the NE-trending fault and belongs to the main earthquake controlling structure, which deserves much attention in furture seismic geological work. © 2016, Science Press. All right reserved.

Fu J.,Chinese Academy of Geological Sciences | Zhang K.,Sun Yat Sen University | Ma Z.,Beifang University of Nationalities | Wang S.,Chinese Academy of Geological Sciences | Wu Y.,Seismological Bureau of Yunnan Province
Earth Science Frontiers | Year: 2013

The formation of the Yellow River was one of the important geological events, which comprehensively reflects the East Asian neotectonic movement and natural environmental changes. The middle reach of the Yellow River is a key to the study of the Yellow River Evolution. In the Xiaosigou located in the northern section of the Shanxi-Shaanxi Gorge, the T5 terrace represents the prototype of the Yellow River terrace before the communication of the gorge and the T4 terrace represents the run-through of the Yellow River. In this research, we choose the typical profiles of five T5 terraces and one T4 terrance from the Sanmenxia Gorge to Xiaosigou for a systematic study. Comparing the analysis results of the overlying loess on the terraces with those of Duanjiapo typical loess on the Loess Plateau by field stratigraphy, OSL and ESR dating, and magnetic susceptibility, we make sure that the most old loess layer on the T5 and T4 terraces is S2 and S1 paleosol, respectively. From the results of loess stratigraphic sequences, it is confirmed that the two terraces were formed at 250-200 ka and 130-80 ka, respectively. From the distribution and deposition characteristics of the terraces, it is found that the tectonic activities at 250-200 ka were the main causes of the terraces of T5, when the Miniature Yellow River eroded headward from to Sanmenxia to Xiaosigou in Hejin region; while the north of Yellow River in Jin-Shaan region was formed at 130-80 ka when the Miniature Yellow cut through the Hetao Basin, resulting in the eventual formation of the current Yellow River.

Yang Y.-H.,Wuhan University | Zhu L.-B.,Wuhan University | Su Y.-J.,Seismological Bureau of Yunnan Province | Chen H.-P.,Wuhan University | And 2 more authors.
Journal of Asian Earth Sciences | Year: 2015

The traditional method to study anisotropy of the crust is utilizing Ps-converted waves on receiver functions. We try to measure the splitting parameters of Ps converted waves on seismogram directly. Ps converted waves on teleseismic seismograms will be unclear due to the interference signals such as the tail of P waves, scattering waves and noises. However, interference signals and Ps converted waves have different polarization characteristics. Through theoretical and observational studies, we found that the minimum energy method is applicable to obtain the correct splitting parameters of Ps converted waves on seismograms and the time window is relatively easily chosen. We selected triennial teleseismic records, SNR greater than 7, from 51 seismic stations operated by Earthquake Administration of Yunnan Province, which located in southeastern Tibetan plateau and Sichuan-Yunnan area. We applied a narrow filter range, 0.2-0.6. Hz, to minimize the interference of the tail of P waves, scattering waves and noises. Finally, we obtained 41 measurements from 51 seismic stations with the minimum energy method. Through the comparison with geodetic data, geophysical data and previous anisotropic studies, we conclude that the eastward extrusion of the Tibetan plateau affects the anisotropic property of the whole crust in southeastern Tibetan plateau and its surrounding areas. © 2015 Elsevier Ltd.

Hu H.,CAS Yunnan Astronomical Observatory | Han Y.,CAS National Astronomical Observatories | Su Y.,Seismological Bureau of Yunnan Province | Wang R.,CAS Yunnan Astronomical Observatory
Journal of Asian Earth Sciences | Year: 2013

During recent years huge earthquakes frequently occurred and caused surprise attack on many places of the globe. Frequent exceptional strong disasters of earthquakes remind that we must strengthen our research on cause of formation, mechanism, prediction and forecast of earthquakes, and achieve the goal of advancing the development of Earth science and mitigation of seismic disasters. The commensurability of earthquake occurrences has been studied by means of the commensurability revealed by the Titius-Bode law in the paper. The studied results show that the earthquakes basically all occur at the commensurable point of its time axis, respectively. It also shows that occurrence of the earthquakes is not accidental, showing certain patterns and inevitability, and the commensurable value is different for earthquakes occurring in different area. © 2013 Elsevier Ltd.

Zhang L.,Yunnan University | Hu Y.-L.,Yunnan University | Qin M.,Seismological Bureau of Yunnan Province | Duan Y.,Seismological Bureau of Yunnan Province | And 3 more authors.
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2015

Tengchong Volcano Area (24°40'-25°30'N, 98°15'-98°45'E) is one of the most famous and youngest volcano-active areas in China. It is located on the northeast side of the collision belt between the Indian and Euroasian plates. It is a part of Myanmar Arc seismic structure, belonging to the Himalayan strong-earthquake belt. There are 68 volcanoes distributed in the region of 90 km long in the north-south direction and 50 km wide in the east-west direction. Among them are 4 Holocene (Q4) volcanoes, 18 Late-Pleistocene (Q3) volcanoes, and 38 Early-Pleistocene (Q1) volcanoes. To study the geologic evolution and volcanic activity of the Tengchong Volcano Area, we need to investigate the variation of crustal thickness and the distribution of the Poisson's ratio in the area, as well as the detailed thickness and topography of the lithosphere. We use the seismic data observed by 9 digital broadband stations of Tengchong Earthquake-Monitoring Net from July 2007 through December 2011. The P receiver functions are used to study the crustal thickness and the Poisson's ratio in the region, while the converted phases at the Moho and the LAB in the S receiver functions are utilized to get the depths of the Moho and the LAB. To reduce the noises and remove the effect of the heterogeneity, we stack the P and S receiver functions beneath each station, respectively, to get an averaged trace of P receiver functions and an average trace of S receiver functions. Before the stacking of the weak converted phases from the Moho and the LAB, each seismic event is moveout corrected to the reference epicentral distance of 67 degree (corresponding to the ray parameter of 6.40 s/deg). Based on the IAS91 model, the receiver functions are transformed from the time domain to the depth domain. 1) The crustal thickness of Tengchong Volcanic Area ranges from 33.5 to 38.0 km. 2) The Poisson's ratio of the area mainly varies from 0.26 to 0.32. The ratio beneath 6 stations is over 0.29, which is attributed to the increase of mafic component in the crust. There may exist two magma chambers. 3) The thickness of the lithosphere ranges from 78.2 to 88.0 km. The crustal thickness of Tengchong Volcanic Area ranges from 33.5 to 38.0 km, with a feature of being thick at the north and south ends but thin in the middle (or the Moho is uplifted in the middle part). The Poisson's ratio is between 0.262 and 0.322. Six stations present high Poisson's ratio, and the crust may be partially melted in some local areas. There probably exist two magma chambers on the east side of Mazhang and the area of Tengchong-Shaba, but their scopes need further determination. The thickness of the lithosphere ranges from 78.2 to 88.0 km, being thinner than that of the surrounding area. In the center of the volcano area (i.e., the convergence between the Tengchong volcanic fault and the Yingjiang-Longchuan fault), both the crust and the lithosphere are uplifted. The lithosphere presents a dome shape obviously, caused by the extension and thinning of the lithosphere by the upwelling of the asthenosphere (or the uplift of mantle hot materials). ©, 2015, Science Press. All right reserved.

Hu H.,Chinese Academy of Sciences | Su Y.-J.,Seismological Bureau of Yunnan Province | Gao Y.-F.,Chinese Academy of Sciences | Wang R.,Chinese Academy of Sciences
Applied Geophysics | Year: 2016

The geophysical mechanism behind astronomical time–latitude residuals (ATLR) are discussed. The photoelectric astrolabe at Yunnan Observatory (YO) observed apparent synchronous anomalous ATLR before the Wenchuan M8.0 earthquake (EQ) in May 12, 2008 and the Lushan M7.0 EQ n April 20, 2013. We compared the ATLR from the YO photoelectric astrolabe and EQ data since 1976. Anomalous ATLR was observed before several strong EQs in the Yunnan Province. We believe the photoelectric astrolabe can be used to predict strong EQs and the anomalous ATLR are a potential EQ precursor. © 2016, Editorial Office of Applied Geophysics and Springer-Verlag Berlin Heidelberg.

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