Short-term Anomaly Research Articles

Adding Practitioner Scholars to Our Faculties

Adding Practitioner Scholars to Our Faculties

Some results of modeling D-D seismogenic pattern by the fracture model experiment of large-scale rock samples (I)

Using the natural limestone samples taken from the field with dimension of 500 mm×500 mm×1 000 mm, the D-D (dilatancy-diffusion) seismogeny pattern was modeled under the condition of water injection, which observes the time-space evolutionary features about the relative physics fields of the loaded samples from deformation, formation of microcracks to the occurrence of main rupture. The results of observed apparent resistivity show: 1 The process of the deformation from microcrack to main rupture on the loaded rock sample could be characterized by the precursory spatial-temporal changes in the observation of apparent resistivity; 2 The precursory temporal changes of observation in apparent resistivity could be divided into several stages, and its spatial distribution shows the difference in different parts of the rock sample; 3 Before the main rupture of the rock sample the obvious “tendency anomaly” and “short-term anomaly” were observed, and some of them could be likely considered as the “impending earthquake” anomaly precursor of apparent resistivity. The changes and distribution features of apparent resistivity show that they are intrinsically related to the dilatancy phenomenon of the loaded rock sample. Finally, this paper discusses the mechanism of resistivity change of loaded rock sample theoretically.

Study on the decision method of short-term and impending precursory anomaly of earth resistivity (in Chinese) : Earthquake (Beijing), 1, 1994, pp 88–96

Study on the decision method of short-term and impending precursory anomaly of earth resistivity (in Chinese) : Earthquake (Beijing), 1, 1994, pp 88–96

A reinterpretation of the precursory seismic b-value anomaly from fracture mechanics

SUMMARY A new model is presented which can explain the major temporal fluctuations in seismic b-value in terms of the underlying physical processes of time-varying applied stress and crack growth under conditions of constant strain rate. The model predicts two minima in the b-value, separated by a temporary maximum of inflexion point; a corollary being that a single broad maximum would be expected in scattering attenuation. These fluctuations in b-value are consistent with reported ‘intermediate-term’ and ‘short-term’ earthquake precursors separated by a period of seismic quiescence. We present preliminary results from controlled laboratory experiments and report recent field observations both of which are consistent with the predicted form, and in particular exhibit the distinctive, second short-term anomaly which reaches a value bc= 0.5 during the critical phase.

Significance of a δ13C anomaly near the Devonian/Carboniferous boundary at the Muhua section, South China

The Muhua section of Guizhou Province, South China is one of three candidates for the Devonian/Carboniferous international boundary stratotype1. Although palaeontological and stratigraphical data have been published2,3, no stable isotope study has previously been made. Detailed δ13C and δ18O analyses from the Muhua section reveal a significant short-term δ13C negative anomaly of 8–9‰ at the base of the Siphonodella crenulata conodont zone. This is the first δ13C negative anomaly found near the Devonian/Carboniferous boundary, and is similar to δ13C anomalies reported from the Permian/Triassic, Cretaceous/Tertiary, and Precambrian/Cambrian boundaries4,5. We suggest, therefore, that the δ13C anomaly at Muhua section provides evidence for major rapid changes in ocean–atmospheric chemistry, and may reflect an important event in geological history.