Simulation of the active and quiet periods of seismicity

In this paper we simulate the repeated occurrence of strong earthquakes along a strike-slip fault by using a finite element model. The fault valve mechanism is included in the model in order to take into account the effeCt of POre fluid pressure variation. Five parameters are used to characterize the rheology of the fault, POre pressure variation, and fracture criteria. By Systematically varying these parameters and calculating a large number of models we carried out a preliminary investigation on the alternatively quiet and active periods of seismicity and their relation to model Parameters and loading conditions. Under the action of a constant-rate boundary movement, in the case of intermediate stress and pore pressure, the models display a regular quiescence-activity phenomenon with a cycle length of 1/3-1 of the recurrence pened. When the model is under high stress or high pore pressure, this phenomenon becomes irregular or inexplicit. When the model is subject to periedic boundary forces and the amplitude of force variation is not too small, it results in an alternatively quiet and active seismicity Pattern with the same Period Of the force variation.

The seismicity research in the sub-regions of Chinese mainland using strain accumula-ting and releasing model

The sub-regions are divided for the seismicity of the Chinese mainland based on the hypothesis of the active crustal blocks and the division of the active boundaries. On this result, the seismicity of each active crustal blocks are studied by calculating the accumulated and released strain of the earthquakes based on strain accumulating and releasing model, and the different seismicity stages of the sub-regions are discussed basically. Finally we have discussed the premise of the model application and the potential problems of the model results.

A STUDY ON THE ONSET AND ITS ACTIVE AND BREAK PERIODS OF SUMMER MONSOON OVER THE SOUTH CHINA SEA

Based on ECMWF reanalysis data of 1979-1993 and TBB data of GMS,an analysis on the onset and its activities of the summer monsoon over the South China Sea (SCS) is made.It is found that the mean onset date is around 16 May,the latest onset is at beginning of June.There is a marked interannual variation of the onset date.There occurs marked southwesterly wind over the SCS in the last dekad of April in some years,but it only persists for a short period,and then,the easterly flow appears again.In the beginning of June,the true onset occurs.From the end of April to the middle of May prior to the onset,strong southwesterly wind appears to the north of 15°N over the SCS,which could not be treated as the onset of the SCS summer monsoon.These strong westerlies are due to the southward propagation of cold front or the strengthening of the subtropical high in the SCS.After the onset,there are active and break periods of the southwesterly summer monsoon,the average break period is about 15 days in one year (from onset of summer monsoon to 20 August).

Rediscussion on the seismic regime network

On the basis of the past research and utilization on the windows and belts of seismic regime, the seismic regime network which has been supposed and proved in the past is set up by using the monthly frequency data of small earthquakes from 1970 to 1991 over the whole country. Through checking its function in practice, it is found that the spatial distribution of precursor information is not an isolate window or belt, but a broad precursor information field before the Ms≥7. 0 earthquakes in China and its nearby regions. According to the windows and belts in the field, synchronism and generality of initial time and place of prediction, the comprehensive prediction of activity time periods of groups of strong earthquakes and the detail method of correspondence of groups are proposed. After restrict mathematical test, 10 prediction methods for references are set forth, in which two best methods are selected as references for the whole case prediction in one to three years. Some related problems are discussed at the end of this paper.

Long-term optical flux and colour variability in quasars

We have used optical V and R band observations from the Massive Compact Halo Object （MACHO） project on a sample of 59 quasars behind the Magellanic clouds to study their long term optical flux and colour variations. These quasars, lying in the redshift range of 0.2 〈 z 〈 2.8 and having apparent V band magnitudes between 16.6 and 20.1 mag, have observations ranging from 49 to 1353 epochs span- ning over 7.5 yr with frequency of sampling between 2 to 10 days. All the quasars show variability during the observing period. The normalised excess variance （Fvar） in V and R bands are in the range 0.2% 〈 F^r 〈 1.6% and 0.1% 〈 Fnr 〈 1.5% respectively. In a large fraction of the sources, Fvar is larger in the V band compared to the R band. From the z-transformed discrete cross-correlation function analysis, we find that there is no lag between the V and R band variations. Adopting the Markov Chain Monte Carlo （MCMC） approach, and properly taking into account the correlation between the errors in colours and mag- nitudes, it is found that the majority of sources show a bluer when brighter trend, while a minor fraction of quasars show the opposite behaviour. This is similar to the results obtained from another two independent algorithms, namely the weighted linear least squares fit （FITEXY） and the bivariate correlated errors and intrinsic scatter regression （BCES）. However, the ordinary least squares （OLS） fit, normally used in the colour variability studies of quasars, indicates that all the quasars studied here show a bluer when brighter trend. It is therefore very clear that the OLS algorithm cannot be used for the study of colour variability in quasars.

Linking satellite-based spring phenology to temperate deciduous broadleaf forest photosynthesis activity

Satellite-based remote sensed phenology has been widely used to assess global climate change.However,it is constrained by uncertain linkages with photo-synthesis activity.Two dynamic threshold methods were employed to retrieve spring phenology metrics from four Moderate Resolution Imaging Spectro-radiometer(MODIS)products,including fraction of Absorbed Photosyntheti-cally Active Radiation(fAPAR),Leaf Area Index(LAI),Normalized Difference Vegetation Index(NDVI),and Enhanced Vegetation Index(EVI)for three temperate deciduous broadleaf forests in North America between 2001 and 2009.These MODIS-based spring phenology metrics were subsequently linked to the photosynthetic curves(daily gross primary productivity,GPP)measured by an eddy covariance flux tower.The 20% dynamic threshold spring onset metrics from MODIS products were closer to the photosynthesis onset metrics at the date of 2% GPP increase for NDVI and fAPAR,and closer to the date of 5%and 10% increase of GPP for EVI and LAI,respectively.The 50% dynamic threshold onset metrics were closer to the photosynthesis onset metrics at the date of 10%GPP increase for NDVI,and closer to the date of 20% GPP increase for fAPAR,LAI and EVI,respectively.These results can improve our knowledge on the photosynthesis activity status of remotely sensed spring phenology metrics.

DYNAMICS IN A CLASS OF NEURON MODELS

In this paper, we investigate the dynamics in a class of discrete-time neuron mod-els. The neuron model we discussed, defined by such periodic input-output mapping as a sinusoidal function, has a remarkably larger memory capacity than the conven-tional association system with the monotonous function. Our results show that the orbit of the model takes a conventional bifurcation route, from stable equilibrium, to periodicity, even to chaotic region. And the theoretical analysis is verified by numerical simula...