Spatio-temporal characteristics of acoustic emission during the deformation of rock samples with compressional and extensional en-echelon faults

The spatio-temporal characteristics of acoustic emission (AE) during the deformation of rock samples with compressional and extensional en-echelon faults have been studied. The results show that the pre-existing structure can significantly influence the patterns of AE spatial distribution. With increasing of differential stress, AE events firstly cluster around the two ends of pre-existing faults inside the jog and then along the line joining the two ends. The biggish AE events often occur around one end repeatedly. The image of AE clusters indicates the direction and the area of the fracture propagation. The direction of the macroscopic fracture in extensional and compressional jogs is perpendicular and parallel to the direction of axial stress, respectively. The weakening process before the fracturing of jog area is remarkable, and one of the typical precursors for the instability is that the cumulative frequency of AE events increases exponentially. After the fracturing of the jog the frequency and releasing strain energy of AE events decrease gradually. During the friction period, there is no precursory increasing of AE activity before the big stick-slip events. The change of b value in jog shows a typical change of decreasing tendentiously returning quickly before the instability. The decrease of b value occurs in the process of stress increasing and sometime goes down to the weakening stage, and the quick increase b values appears in a short time just before the instability. The comparative analysis shows that the difference in b value due to the different structures is larger than b value variation caused by increase of the differential stress. For the same sample, the temporal sequence of AE is strongly affected by the mechanical state, and the high loading velocity corresponds to the high release rate of strain energy and low b value. Due to its lower failure strength, the broken area is sensitive to small changes in differential stress. Therefore, it offers a potential explanation for the phenomena of precursory window or sensitive point and separation of seismic source and precursors.

Research on the multifractal characteristics of the temporal-spatial distribution of earthquakes over New Zealand area

Using the Hill estimator, general multifractal characteristics of events in the New Zealand area have been dis-cussed. Results show that the spatial distribution of shallow events has apparent clustering characteristics, inde-pendent of the threshold magnitude; but for deep events these characteristics are not clear. While the time interval distribution has obvious clustering characteristics both for deep and shallow events, although with a different scal-ing range, the Hill estimates tend to indicate that the time interval distribution has a unifractal rather than a multifractal nature. All above reveal that the seismicity nature for shallow and deep events is apparently different.

Study on the method for comprehensive discrimination of small earthquakes

In the paper, we apply the theory of modern digital signal processing to analysis 3-component digital seismic data recorded in Datong area of Shanxi Province by digital seismographs developed by the Institute of Geophysics, CSB in November 1999 and study the auto-discrimination of the recorded digital seismic signals. The result shows that the method for comprehensive discrimination in connection with ratios between average values of long-time and shorttime signals, spectral analysis, and wavelet analysis can be used to auto-discrimination of seismic signals through alternate man-computer processing. Many ML>2.0 earthquakes were discriminated better.

Anisotropy of the upper mantle in Chinese mainland and its vicinity

In order to deepen the understanding of the spatial change images of upper mantle media for strain strength and polarization direction, anisotropy and shear wave splitting, anisotropy and strain, strain and the tectonic process, based on the theory on the characteristics of shear wave splitting parameters in the presence of two weak azimuthal anisotropic layers and observations concerned, and using signal identification methods with high precision, the results for 136 earthquakes are obtained. The pictures of anisotropy strength and polarization direction beneath twenty stations are got. Combining the results existed previously, the characteristics and origin of the upper mantle anisotropy are discussed.

Argument on the magnitude-frequency relation

The complexity of seismicity and the relation of magnitude and frequency are discussed in this paper on the basis of nonlinear dynamics and multifractal theory. We argue that seismic active systems normally have multifractal characteristics, either for the spatial-temporal distribution or the intensity distribution of events. In the view of multifractal theory the nonlinear characteristics of the magnitude-frequency relation are discussed and the formulation is revised. Also, one example of the variance of bq estimated based on the recent New Zealand catalogue is enumerated.

Study on Correlation and Quantiative Error Estimation Method Among the Splitting Shear Wave Identification Methods

Based on the propagation characteristics of shear wave in the anisotropic layers,thecorrelation among several splitting shear-wave identification methods hasbeen studied.Thispaper puts forward the method estimating splitting shear-wave phases and its reliability byusing of the assumption that variance of noise and useful signal data obey normaldistribution.To check the validity of new method,the identification results and errorestimation corresponding to 95% confidence level by analyzing simulation signals have beengiven.