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Wang A.-G.,Lanzhou Institute of Seismology | Wang A.-G.,Lanzhou National Observatory of Geophysics | Ma W.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute | Wu Z.-J.,Lanzhou Institute of Seismology | Wu Z.-J.,Open Laboratory of Loess Earthquake Engineering
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2011

By analyzing the simulated temperature field of frozen-soil foundation with embankment in different structures, the embankment cooling effect and some important factors and their relationship are studied. The factors include embankment structure, temperature in block-stone layer, convection Rayleigh number (Ra) and the critical Rayleigh number (Rac) of different convection patterns. The research results show that the air convection pattern of block-stone in winter is the most important key factors influencing the cooling effect of embankment, and the block-stone embankment structure in which the air convection patterns are mainly (1, 1) and (2, 1) in winter has the strongest cooling effect on frozen soil foundation.

Zhang H.,Lanzhou Institute of Seismology | Zhang H.,Lanzhou National Observatory of Geophysics | Zhang L.-P.,Institute of Earthquake Science | Feng J.-G.,Lanzhou Institute of Seismology | Feng J.-G.,Lanzhou National Observatory of Geophysics
Earthquake | Year: 2014

For the Minxian-Zhangxian MS6.6 earthquake sequence of July 22, 2013, we invert focal mechanism solutions of the mainshock event and some strong aftershocks in the sequence using the CAP (Cut and Paste)method and broadband waveforms recorded by the Tenth five-year digital seismic network. The result shows that the best double solution of the MS6.6 mainshock is 189°, 51° and 142° for strike, dip and rake angles respectively, the other nodal plane is 305°, 61° and 46°; the character of the mainshock shows thrust with a small strike-slip component and the focal depth of the mainshock is 7 km. The advantage angel of the nodal plane II which is in the NE direction of the focal mechanism solutions of 8 aftershock events is about 52°, which shows the characteristics of large thrust components. The nodal plane II has been identified to be representative of the seismogenic fault plane of the event in consideration of the local active geologic structure, the distributions of the aftershocks and the seismic intensities. The characteristics of the focal mechanism of earthquake sequence are similar with the Lintan-Tanchang fault. In conclusion, the occurrence of the Minxian-Zhangxian MS6.6 earthquake may correlated with activities of the Lintan-Tanchang fault.

Zhang H.,China Earthquake Administration | Zhang H.,Lanzhou National Observatory of Geophysics | Gao Y.,China Earthquake Administration | Shi Y.-T.,China Earthquake Administration | And 2 more authors.
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2012

The northeastern margin of Tibetan plateau is controlled jointly by several tectonic blocks and shows complicated geophysical and geological characters. In the paper, the data from Gansu Seismological Network (2001-2008) are analyzed with the seismic anisotropy analysis method in crust (SAM). 1005 shear-wave splitting parameters from 18 stations are obtained. The results show that the crustal seismic anisotropy in the northeastern margin of Tibetan plateau varies in space. The delay times of slow shear-waves show the variation characteristics of the strength of crustal seismic anisotropy and the average polarizations of fast shear-waves reflect the spacial variation characteristics of regional tectonic stress. Tt is shown that the interaction of Tibetan plateau block and Alxa block controls the region of Qilianshan-Hexi corridor active structures, where the direction of tectonic stress is the same as in Tibetan plateau block. In the southeast of Gansu active structure region, it is regarded that active faults are influential on the stress field, which shows local tectonic stress characteristics.

Guo G.-H.,Lanzhou University | Guo G.-H.,Lanzhou National Observatory of Geophysics | Zhang Z.,Guilin University of Technology | Cheng J.-W.,China Earthquake Administration | And 3 more authors.
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2015

The northeastern margin of Tibetan plateau is surrounded by the Alashan block to the north, the Tarim basin to the northwest, the Ordos block to the east, and Songpan-Garzê terrane to the south. As the northern terminus of contiguous deformation, it records far field effects of collision and convergence occurring between the Indian and Eurasian, it is still in the stages of uplift and deformation, so it is an ideal region for studying the far field effects of collision and convergence between the India and Eurasian plate. Seismic anisotropy is one of the main specialities of the Earth, which can be interpreted with the Lattice Preferred Orientation (LPO) of minerals and shape Preferred Orientation of cracks or melts caused by tectonic stress. In this study, we use the seismic data recorded by the Gansu and Ningxia Province Seismic Network from Jan. 2001 to Oct. 2010. And seismic anisotropy is obtained by using the SAM technique. The average time delay and polarization are caused by the regional structure and stress field, whereas the residual values of the splitting parameters are considered to be related to local structures such as local faults. The residual polarization of fast shear-waves suggests the strike direction of local fault. The residual delay of slow shear-waves suggests the contribution extent induced by local fault. During our data process, we take the posterior choice on earthquakes with small epicenters that is a makeshift for the regions lacking earthquakes, but is useful to increase the credibility of the analysis for fast-wave polarization. The results show that the crustal seismic anisotropy in the northeastern margin of Tibetan vary in different tectonic blocks. There are the two average polarization of fast shear-waves, which are individually at NE47.72°±21.83°and 121.65°±22.07°, and the average time delay of slow shear-waves is 2.63±1.03 ms·km-1. The first dominant polarization of fast shear-waves is almost consistent with the regional principal compressive stress due to collision between Indian and Asian plate. The second predominant polarization direction of fast shear-waves is in the NWW direction which indicates the influence by the deep fault. The delay time of slow shear-waves increases from southweastern to north eastern in the study area. The residual polarization of fast shear-waves are almost consistent with the strike of local fault, and the residual delay indicates the contribution extent induced by the local faults that means which part has a higher effect. Compared with the upper mantle anisotropy results, crust-mantle anisotropy are different in Qilian-Hexi Corrider, while they have some consistence in the southeast of Gansu. © 2015, Science Press. All right reserved.

Shao Y.,China Earthquake Administration | Shao Y.,Lanzhou National Observatory of Geophysics | Yuan D.,China Earthquake Administration | Yuan D.,Lanzhou National Observatory of Geophysics | Liang M.,China Earthquake Administration
Acta Seismologica Sinica | Year: 2015

Longling-Lancang fault zone in southwestern Yunnan is an area with strong seismicity. Multi strong earthquakes with MS≥7.0 hit the area and nearly ruptured the whole fault zone during last 100 years. This paper summarized characteristics of recent tectonic activities and calculated b value of the studied area first of all, and then combined with the distribution of historical strong earthquakes and modern small ones, the fault activity since Late Quaternary and elapse time to analyze the potential seismic risk in the future synthetically. Finally, based on the seismic gap theory, the seismic gaps in the fault zone are identified. The results show that the Longling, Yongde, Cangyuan, Lancang along the fault zone and middle-east segment of Menglian fault have a potential of moderate-strong earthquake occurrence in the future ten years. © 2015, Acta Seismologica Sinica Press. All right reserved.

Zhang X.,China Earthquake Administration | Du X.,China Earthquake Administration | Du X.,Lanzhou National Observatory of Geophysics | Zhang Y.,China Earthquake Administration | And 2 more authors.
Acta Seismologica Sinica | Year: 2016

The surface explosion occurred in Tanggu district of Tianjin on August 12, 2015 caused wide attention. This paper presented the geophysical observation response to this explosion based on the data from a number of geophysical observation stations in Beijing-Tianjin-Hebei region as well as the satellite infrared remote sensing data, and obtained the geophysical disturbances information around the point. The results showed that the response of georesistivity to the explosion near the event site is apparent, that is, the georesistivity curve declined rapidly after this event and lasted for a long time. It was also observed that the geoelectric field anomalies appeared with a small amplitude two days before and after the event, and the space electronic flow declined slightly synchronously, however, no disturbances of geomagnetic field appeared at the same period. Meanwhile, the satellite infrared brightness temperature significantly increased after the event, and lasted for several days. In addition, there was no obvious response of underground water level and deformation to the event. The results indicate that different types of observations have different responses to this event, it will be valuable for analyzing and determing the anomalies related to earthquake in the future. What is more, it is also useful for a deeper cognition for the process of Tianjin explosion. © 2016, Acta Seismologica Sinica Press. All right reserved.

Xie T.,Lanzhou National Observatory of Geophysics | Xie T.,China Earthquake Networks Center | Du X.,Lanzhou National Observatory of Geophysics | Liu J.,Lanzhou National Observatory of Geophysics | And 4 more authors.
Acta Seismologica Sinica | Year: 2013

Wavelet transform technique is applied to the analysis of geo-resistivity data observed at Chengdu and Jiangyou stations before and after Wenchuan MS8.0 earthquake in 2008 and the ionospheric magnetic field recorded by DEMETER satellite before and after the Wenchuan earthquake and the 2010 Haiti earthquake, in order to study the wavelet power spectrum of geo-resistivity and ionospheric magnetic field and its relative variation. Our analysis result suggests that (1) the wavelet power spectrum and its relative variation increased greatly at the times when the geo-resistivity of N58°E channel of Chengdu station displayed its medium-term decrease and short-term increase, the impending anomaly was recorded on the N10°E channel of Jiangyou geo-resistivity station and the wavelet power spectrum of x component of ionospheric magnetic field and its relative value increased distinctly before Wenchuan earthquake, showing typical Earth-space electromagnetic anomaly of geo-resistivity and ionospheric magnetic field; (2) The wavelet power spectrum of x and z components of ionospheric magnetic field and its relative variation also increased greatly before Haiti earthquake, similar to the increase before and after Wenchuan earthquake.

Su Q.,China Earthquake Administration | Yuan D.-Y.,China Earthquake Administration | Yuan D.-Y.,Lanzhou National Observatory of Geophysics | Xie H.,China Earthquake Administration | Xie H.,Lanzhou National Observatory of Geophysics
Dizhen Dizhi | Year: 2016

Using quantitative geomorphic factors for regional active tectonic evolution is becoming more and more popular. Qilian Mountains-Hexi Corridor which locates in the northern edge of Qinghai-Tibet plateau is the most leading edge of the plateau's northward extension. The uplift rate of all segments and the intensity of influence from tectonic activity are the important evidences to understand the uplift and extension of the plateau. Heihe River Basin is located at the northern piedmont of the western segment of Qilian Mountains, the development of the rivers is influenced by the tectonic activity of the Qilian Mountains, and the unique river morphology is important carriers of the regional tectonic uplift. Geomorphologic indexes such as hypsometric integral, geomorphologic comentropy and river longitudinal profiles were extracted by GIS tools with free access to the Shuttle Radar Topography Mission (SRTM) DEMs, and according to the different expression of the geomorphological indexes in the Heihe River Basin, we divided the drainage basin into two parts and further compared them to each other. Recent studies reveal that obvious differences exist in the landscape factors (hypsometric integral, geomorphology entropy and river profiles) in the east and west part of the Heihe Basin. The structural intensity of the west part is stronger than that of the east, for example, in areas above the main planation surface on the western part, the average HI value is 0.3378, and on the eastern part the HI value is 0.355. Accordingly, areas under the main planation surface are just on the contrary, indicating different structural strength on both sides. Similar phenomenon exists in the whole drainage basins. Furthermore, by comparing the fitting river profiles with the real river profiles, differential uplift is derived, which indicates a difference between west and east (with 754 m on the western part and 219 m on the east). Comprehensive comparison and analysis show that the lithologic factors and precipitation conditions are less influencing on the geomorphic factors of the study area, and the tectonic activities, indicated by field investigation and GPS inversion, are the most important element for geomorphic evolution and development. The variation of the geomorphologic indexes indicates different tectonic strength derived from regional structures of the Qilian Shan. © 2016, Editorial Office of Seismology and Geology. All right reserved.

Liu X.-W.,China Earthquake Administration | Liu X.-W.,Lanzhou National Observatory of Geophysics | Yuan D.-Y.,China Earthquake Administration | Yuan D.-Y.,Lanzhou National Observatory of Geophysics | And 3 more authors.
Dizhen Dizhi | Year: 2016

Qilian Shan-Hexi Corridor is located at the northeastern margin of Tibetan plateau. Series of late Quaternary active faults are developed in this region. A number of strong earthquakes even large earthquakes occurred in history and present-day. In the past, the study of active faults in the area was mostly concentrated in the northern margin fault zone of the Qilian Shan on the south side of the corridor, while the research on the interior and the north side of the corridor basin was relatively rare. We found a new fault scarp in the northern part of the Baiyanghe anticline in Jiuxi Basin in 2010. It is an earthquake surface rupture zone which has never been reported before. In this paper, we carried out palaeoearthquake trench analysis on the newly found earthquake surface rupture zone and textual research of relevant historical earthquakes data. According to the interpretation of aerial photo and satellite image and field investigation, we found the surface rupture has the length of about 5 km. The rupture shows as an arc-shaped line and is preserved intact comparably. The lower terrace and the latest flood alluvial fan are offset in addition to modern gullies. By differential GPS measurement, the height of the scarp is about 0.5~0.7 m in the latest alluvial fan and about 1.5 m in the T1 terrace. From the residual ruins along the earthquake rupture zone, we believe the surface rupture might be produced by an earthquake event occurring not long ago. In addition, the rupture zone locates in the area where the climate is dry and rainless and there are no human activities induced damages. These all provide an objective condition for the preservation of the rupture zone. The trench along the fault reveals that the surface rupture was formed about 1500 years ago, and another earthquake event might have happened before it. Based on the textural research on the historical earthquake data and the research degree in the area at present, we believe that the surface rupture is related to the Yumen earthquake in 365, Yumen Huihuipu earthquake in 1785 or another unrecorded historical earthquake event. © 2016, Editorial Office of Seismology and Geology. All right reserved.

Su Q.,China Earthquake Administration | Liang M.,Seismological Bureau of Sichuan Province | Yuan D.,China Earthquake Administration | Yuan D.,Lanzhou National Observatory of Geophysics | And 3 more authors.
Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences | Year: 2016

Active tectonics is one of the factor that impacts the geological disaster. In this paper, the control factors of the geological disasters (landslide and debris flow) in Bailongjiang drainage basin are studied. Based on SRTM-3 Digital Elevation Model, we make use of ArcGIS spatial analysis techniques and Matlab scripts to extract various geomorphic parameters in Bailongjiang drainage basin systematically, such as the macro landform information, seven fitting S-A graphics of four graded rivers. Combined with neotectonic features, active faults, lithological distribution and rainfall condition, the control factors of geodisasters are analyzed. The results show that the convex fitting S-A graphics represents that the material output is bigger than the material input; on the contrary, the concave fitting S-A graphics represents that the material output is less than the material input; among which, the material input performs mountain uplift and the concrete manifestation of material output is landslide, debris flow disaster produced in emergency. In addition, mylonitization or half mylonitization strata distribution controlled by regional tectonic movement is the essential factors for geological disasters. Affected by the comprehensive factors above, it is concluded that geological disasters usually occurs in the region that elevation changes rapidly, high relief amplitude and high slope distribution and different sub-basin topography caused by regional differences in uplift control the area where geological disasters occur frequently, that is, geological disasters occur frequently in the sub-basin where material output is bigger than material input and the sub-basin where material input is bigger than material output doesn't show the geological disasters distribution point. © 2016, Editorial Department of Earth Science. All right reserved.

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