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He W.-G.,Lanzhou Institute of Seismology | He W.-G.,Lanzhou Base of Institute of Earthquake Science | Yuan D.-Y.,Lanzhou Institute of Seismology | Yuan D.-Y.,Lanzhou Base of Institute of Earthquake Science | And 6 more authors.
Earthquake | Year: 2012

Jintananshan north-margin fault is an important active fault at the north of Jiuquan Basin. The fault starts from the northwest of Wutongdun in the west, then passes through Changshan, Guagoushan, Yuanyangchishuiku, Dakouzi, and ends in the east of Hongdun. The main trending is near EW with length 60 km, dip is south or north, and the dip angle is 60~80 degree. The active manner of the fault is mainly thrust with leftlateral strike-slip features. According to field geomorphic investigation and trench excavation, we found strong active evidence at the west segment of the Jintananshan north-margin fault. Paleo-earthquakes have also be found there.

Zhang B.,Earthquake Research Institute of Lanzhou | Zhang B.,Lanzhou Base of Institute of Earthquake Science | He W.-G.,Earthquake Research Institute of Lanzhou | He W.-G.,Lanzhou Base of Institute of Earthquake Science | And 6 more authors.
Earthquake | Year: 2012

The northern margin of Western Qinling fault zone(NWQF) is one of the main left-lateral strike slip active faults in northeastern margin of Tibetan Plateau. Through field seismic and geological investigations, we opined that the west segment of this fault remain actively strong. Significant Holocene activity characteristics are found in Qielonggou. Trenches show that at least two Holocene paleoseismic events happened in west segment of NWQF, which shows that fault activities of NWQF still exist in the west of Tufang village, extend westward from Tufang village continually and finally terminate at the Ganjia basin.

Liu J.,Lanzhou Base of Institute of Earthquake Science | Liu J.,Lanzhou Institute of Seismology | An Z.-H.,Lanzhou Base of Institute of Earthquake Science | An Z.-H.,Lanzhou Institute of Seismology | And 6 more authors.
Earthquake | Year: 2015

Based on data of electromagnetic disturbance observation stations surrounding the epicenters of the Lushan Ms7.0 and Minxian-Zhangxian Ms6.6 earthquakes, we mainly use the original waveform comparison of electromagnetic disturbances and statistical of the electric magnetic field pulse energy, and analyze the data of electromagnetic disturbance stations before the two earthquakes. The results show that; (1) The abnormal changes in the original waveform before the two earthquakes showed mainly in the forms of frequent sudden jump and increases of pulse signal for the observed values, and waveform distortion and repeated steps before earthquakes. (2) The increased energy of the geomagnetic field pulse are recorded at the geo-electromagnetic disturbance stations before two earthquakes, which basically appeared in a few days to 2 months before the earthquake. (3) Abnormal changes in the electric component and magnetic field components are recorded before earthquake, but the magnitude of change and the abnormal time are not synchronized. From the results obtained, a tentative theoretical explanation has been presented in terms of the generation mechanism of seismic electromagnetic radiation from the two earthquakes. ©, 2015, Science Press. All right reserved.

Liu F.B.,Lanzhou Institute of Seismology | Wang A.G.,Lanzhou Institute of Seismology | Wang A.G.,Lanzhou base of Institute of earthquake Science
Applied Mechanics and Materials | Year: 2014

On July 22, 2013, an Ms6.6 earthquake occurred in Minxian-Zhangxian, Gansu Province, China, which caused serious damages. Because of the abundance and clear relationship with the main shocks, aftershocks sequences are typical types of behavior and provide useful data sets. To better understand the aftershocks triggering by static stress changes of the main earthquake, based on Okada's elastic half-space model, we used accept fault plane consistent with the source and accept fault plane as the optimal models to calculate the stress changes on aftershock focuses by the Minxian-Zhangxian 6.6 Earthquake respectively. The results show that the latter model is better than former, more than 90% of aftershocks located in NWW and SEE, the stress increased areas, which is consistent with strike of Lintan-Tanchang fault (LTF), in other words, the Coulomb static stress changes of the main shock can induce the aftershocks. © (2014) Trans Tech Publications, Switzerland.

Fan Y.-Y.,Lanzhou Base of Institute of Earthquake Science | Fan Y.-Y.,Lanzhou Institute of Seismology | Du X.-B.,Lanzhou Base of Institute of Earthquake Science | Du X.-B.,Lanzhou Institute of Seismology | And 8 more authors.
Earthquake | Year: 2015

We studied changes of geo-electric fields before and after the 2013 Lushan Ms7.0 earthquake in Sichuan Province and Minxiang-Zhangxian Ms6.6 earthquake in Gansu Province observed by the Pingliang and other stations around the epicenter. The results show that: (1) Before Lushan Ms7.0 earthquake and Minxiang-Zhangxian Ms6.6 earthquake, significant anomalies of geo-electric fields were recorded by Pingliang station. (2) Maximum entropy method was used to calculate geo-electric data observed by Pingliang, Songshan and Gufeng stations before and after the Lushan earthquake and Minxian-zhangxian earthquake, and the calculation reaults reveal that the phenomenon of increased power spectrum density (especially, anomalies of low frequency components under 4×10-3 Hz) occurred before the earthquake, and the phenomenon observed by some stations disappeared after the Minxian-Zhangxian earthquake. (3) The nearer the location is to the epicenter, the more obvious change the power spectrum density anomalies and the weaker the correlation between long polar distance and short polar distance becomes. In the primary analysis for this phenomenon, we propose that the deformation of underground medium under stations in the process of earthquake preparation may stimulate macroscopic electromagnetic radiation. ©, Science Press. All right reserved.

Rong D.-L.,Lanzhou National Observatory of Geophysics | Rong D.-L.,Lanzhou Base of Institute of Earthquake Science | Li Y.-R.,Lanzhou National Observatory of Geophysics | Li Y.-R.,Lanzhou Base of Institute of Earthquake Science
Earthquake | Year: 2011

In this paper we studied the characteristics of two seismological precursors(seismic spatial correlation length and coda Q c) associated with three moderate-strong earthquakes occurred in Gansu province, China, based on Allegre's scale-rule theory of rock fracture. The results show that an increasing trends of seismic spatial correlation length and coda Q c appeared before the three earthquakes. A power exponent relation is used to fit the increasing variation form of these two parameters.

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