A common feature in seismic imageries of the crust and mantle is a layering pattern.Layering structures do exist in multiple scales,such as layered strata and unconformities in local and regional scales,and undulating seismic discontinuities in the crust and mantle.However,layering arti-fact also exists due to limitations in seismic processing and data coverage.There is a tendency for seis-mic stacking methods to over-map reflectors and scatters into along-isochron layers.In contrast,seis-mic tomography methods tend to under-map sub-horizontal layers with along-raypath smears and ar-tifacts of various de-mean processes.To better identify signals and artifacts in seismic imageries,it is necessary to understand the origins of various artifacts and make careful comparison between the solu-tions of different data and methods.
Seismic studies of the crustal structure beneath the Three Gorges Reservoir（TGR） region in Central China have been limited by the sparse and uneven distribution of seismic stations.To in-crease the station coverage,we made three deployments of a mobile seismologic array in the TGR re-gion during the three summers from 2008 to 2010.Here we present interpretations along a west-east profile through the central TGR region based on new seismic waveform data and a velocity model con-strained by regional earthquake data.Two strong mid-crustal reflection interfaces at depths around 10 and 20 km are seen under the TGR.The shallow reflector defines the bottom of the Zigui（秭归） basin.The new waveform data show that the amplitude of the Moho reflection is quite weak,and beneath the Moho,there is a strong reflector around 54-km depth.It is likely that in the TGR region,the Moho is a gradient rather than a sharp boundary.We speculate that the gradient Moho and the 54-km-deep re-flector in the upper mantle in the TGR region may be by-products of the Qinling（秦岭）-Dabie（大别） orogen.
The main aim of this work is to understand the distribution of minerals by obtaining a shallow velocity structure around the Karatungk（喀拉通克） region.Data were acquired in 2009 by a denser array in deploying a transportable seismometer with 4.5 Hz vertical geophone.All the P-wave arrival times are picked automatically with Akaike information criterion,and then checked man-machine interactively by short-receiver geometry.The database for local active-source tomographic in-version involves 4 241 P-wave arrival time readings from 96 shots and three quarry blasts.Checker-board tests aimed at checking the reliability of the obtained velocity models are presented.The result-ing Vp distribution slices show a complicated 3-D structure beneath this area and offer a better under-standing of three well-defined mineral deposits.Near the surface we observe a series of zones with slightly high-velocity which probably reflect potential deposits.Based on features of metallic ores we attempt to delimit their distributions and stretched directions.
We firstly detected the Earth's free toroidal oscillations excited by three large earthquakes in Japan,2011,Chile,2010 and Indonesia,2005 from the observed data of the JCZ-1 seismometer at Wuhan Seismic Station. The eigenperiods of basic modes (0T2 - 0T67 ) and first modes (1T2 ～ 1T50 ) were detected,and their error ratios were less than 0. 5% by comparing the observed eigenvalues with the theoretical eigenvalues in PREM. We supplemented some modes- 0T11,0T15 , 0T19 , 1T4 , 1T5 and 1T14 ,which were not mentioned in PREM,and also observed the spectral line multi-peak phenomenon from 0T2, 0T6 , 0T7 and 0T8 . These results show that the JCZ-1 seismometer is able to precisely observe the Earth's long period toroidal free oscillations.
