Identifying parameters of advanced soil models using an enhanced transitional Markov chain Monte Carlo method

Acta Geotechnica - Parameter identification using Bayesian approach with Markov Chain Monte Carlo (MCMC) has been verified only for certain conventional simple constitutive models up to now. This...     

Relative energy zero ratio-based approach for identifying pulse-like ground motions

Pulse-like ground motions are capable of inflicting significant damage to structures. Efficient classification of pulse-like ground motion is of great importance when performing the seismic assessment in near-fault regions. In this study, a new method for identifying the velocity pulses is proposed, based on different trends of two parameters: the short-time energy and the short-time zero crossing rate of a ground motion record. A new pulse indicator, the relative energy zero ratio(REZR), is defined to qualitatively identify pulse-like features. The threshold for pulse-like ground motions is derived and compared with two other identification methods through statistical analysis. The proposed procedure not only shows good accuracy and efficiency when identifying pulse-like ground motions but also exhibits good performance for classifying records with high-frequency noise and discontinuous pulses. The REZR method does not require a waveform formula to express and fit the potential velocity pulses; it is a purely signal-based classification method. Finally, the proposed procedure is used to evaluate the contribution of pulse-like motions to the total input energy of a seismic record, which dramatically increases the seismic damage potential.     

Latest Middle Miocene fauna and flora from Kumkol Basin of northern Qinghai-Xizang Plateau and paleoenvironment

We report 7 mammalian and 16 pollen species from the top of the Shimagou Formation in Kumkol Basin of northern Qinghai-Xizang Plateau, whose age is latest Middle Miocene(about 12.5 Ma). We erect a new species of fossil rodent,Spermophilinus kumkolensis sp. nov. The micromammalian fauna from the Kumkol Basin shares high similarities with contemporary faunas from Europe and northern China, indicating the existence of active zoogeographic exchange between Europe and northern Asia. Trees are dominant in pollen fossils, and herbs and shrubs are minorities. Broadleaved Quercus and Fagus predominate in tree pollens. The flora reconstructed by pollens displays a mixture of evergreen broadleaved forest and dry and warm steppe landscape. Compared to the modern vegetation in Yunnan region, the latest Middle Miocene flora in the Kumkol Basin represents a distinct vertical distribution. The ecotypes of the latest Middle Miocene fauna and flora in the Kumkol Basin,as a whole, are markedly different from those of modern animals and vegetation, the past climate being more suitable than today.     

Comparison of the effects of soil moisture and El Niño on summer precipitation in eastern China

Science China Earth Sciences - The effects of spring soil moisture over the vast region from the lower and middle reaches of the Yangtze River valley to North China (YRNC) and El Niño on the...     

Throat aurora observed by DMSP/SSUSI in a global view

Throat aurora was defined based on the ground observations near local noon and has been suggested to be the ground signature of an indentation on the subsolar magnetopause. A global view of the auroral oval with throat aurora will be critical for inferring global processes at the magnetopause, but it has never been achieved. Using imaging spectrograph observations from Defense Meteorological Satellite Program satellites, for the first time, here we show typical throat auroras in a global view and reveal some important observational facts as follows.(1) The throat auroras can be as long as ～8 degrees in latitudinal direction,which is hardly to be fully seen in the ground-based camera.(2) The plasma flows and field aligned currents associated with throat aurora show consistences with previous radar observations, which have been suggested to be the observational evidence of magnetopause reconnection.(3) Most importantly, we confirmed that the electron and ion precipitations associated with throat aurora are always spatially separated, i.e., electrons in the east and ions in the west. The observational results not only establish a new picture of the aurora oval near local noon, but also provide important support to a conceptual model of throat aurora.     

Dynamic performance analysis of a seismically isolated bridge under braking force

In order to study the dynamic performance of seismically isolated bridges under the most unfavorable loads in the longitudinal direction,a dynamic equation for vehicle braking in the longitudinal direction is established.A four or fiveorder Runge-Kutta method is adopted to obtain the time-history response of a wheel set under braking force.The quadratic discretization method is then used to transform this time-history into a braking and bending force time-history of a structural fixed node,and a dynamic response analysis of the seismically isolated bridge under the vehicle’s braking force is carried out using ANSYS,a universal finite element analysis software.According to the results,seismic isolation design results in a more rational distribution of braking force among piers;the influence of the initial braking velocity on the vehicle braking force is negligible;the location where the first wheel set leaves the bridge is the most unfavorable parking location;a seismic isolation bridge bearing constructed according to typical design methods enters into a yield stage under the braking force, while the shearing force at the bottom of the pier declines as the isolation period is extended;the design requirements can be met when the yield displacement of the seismic isolation bearing is less than 5 mm and the yield strength is greater than the braking force.     

2007年宁洱6.4级地震序列精定位

Five mobile digital seismic stations were set up by the Earthquake Administration of Yunnan Province near the epicenter of the main shock after the Ning’er M6.4 earthquake on June 3, 2007. In this paper, the aftershock sequence of the Ning’er M6.4 earthquake is relocated by using the double difference earthquake location method. The data is from the 5 mobile digital seismic stations and the permanent Simao seismic station. The results show that the length of the aftershock sequence is 40km and the width is 30km, concentrated obviously at the lateral displacement area between the Pu’er fault and the NNE-trending faults, with the majority occurring on the Pu’er fault around the main shock. The depths of aftershocks are from 2km to 12km, and the predominant distribution is in the depth of 8～10km. The mean depth is 7.9km. The seismic fault dips to the northwest revealed from the profile parallel to this aftershock sequence, which is identical to the dip of the secondary fault of the NE-trending Menglian-Mojiang fault in the earthquake area. There are more earthquakes concentrated in the northwest segment than in the southeast segment, which is perhaps related to the underground medium and faults. The depth profile of the earthquake sequence shows that the relocated earthquakes are mainly located near the Pu’er fault and the seismic faults dip to the southwest, consistent with the dip of the west branch of the Pu’er fault. In all, the fault strike revealed by earthquake relocations matches well with the strike in the focal mechanism solutions. The main shock is in the top of the aftershock sequence and the aftershocks are symmetrically distributed, showing that faulting was complete in both the NE and SW directions.