Study On Scaling Relations Of Source Parameters For Moderate And Small Earthquake

The self-similarity in earthquake phenomena has been widely manifested invarious seismological observations such as the magnitude-frequency relation, theaftershock decay rate, and the scaling relation of seismic spectrum. However, it is stillone of arguments that whether the earthquake self-similarity is ubiquitous. Theserelations between source parameters are called scaling relation. Its study is veryimportant to reveal whether the rupture mechanism of big and small earthquake hasthe same physical process, to apply the source parameters to the study of earthquakeprediction and to understand the seismicity patterns.Considering the present situation and the key issue in the study on scalingrelations of source parameters for moderate and small earthquakes, we bring forwarda more comprehensive scheme to determine the source parameters for moderate andsmall earthquakes. It includes adopting the data observered near the source,re-determining the earthquake location using double-difference earthquake locationalgorithm, testifying the model of source spectra for moderate and small earthquakes,calculating the anelastic attenuation and site response, and estimating the seismicradiated energy. Four datasets including two Dayao earthquake sequences, Qingdaoearthquake swarms, and Xinfengjiang reservoir earthquakes were selected to do theresearch on scaling relations of source parameters for moderate and small earthquakes,from two aspects such as scaling relations for static parameters and dynamicparameters.We focus on comparing the results derived from different ways in the estimatingof earthquake anelastic attenuation and site response, analysing their errors andtesting the stability of results. Moreover, for the first time, we consider theunderestimate of radiated energy due to the limited bandwidth recording and itscompensation, compare the results of radiated energy estimated using severaldifferent methods. Finally, we discuss the difference in scaling relations of sourceparameters among different kind of data (e.g., active zone vs inactive zone, tectonicearthquake vs reservoir earthquake). The major conclusions are as follows:1. The results derived from empirical Green's functions (EGF) show that displacement spectra we analyzed roll off asω^-2 above the comer frequency,favoring the Bruneω^-2 model.2. The Q values estimated from different methods for the same region arevirtually identical. In general, the Q values estimated from these data observered nearthe source have low Q₀ value and highηvalue.3. The studies of site response show that the site responses inverted by usingMoya's method are larger than that of Nakamura's method, but they have consistentshape. Nakamura's method can be used instead of Moya's method to estimate the siteresponse when we can not use the Moya's method. The site responses derived formNakamura's method are independent of the angle of incidence.4. Scaling relations for static parameters show that, in general, there is a weakrelation between seismic moment and stress drop, and the stress drop increases withincreasing seismic moment. Within the focal depth we studied, the dependence ofstress drop on focal depth is not distinct. The results of Xinfengjiang dataset show thatthe stress drops for reservoir induced earthquakes appear to have lower average stressdrops than that of tectonic earthquakes, and the variation between source dimensionsand magnitude for reservoir induced earthquakes is comparably weak.5. Limited bandwidth recording can lead to the underestimates of the radiatedseismic energy, and the increasing effect derived from energy compensation in theestimation of radiated energy is more distinct for small earthquake. The scalingrelations for dynamic parameters show that scaled energy increases clearly withincreasing seismic moment, revealing that the big earthquake is more efficient inradiating energy than small earthquake. There is no apparent relation between scaledenergy and focal depth. The values of apparent stress for Xinfengjiang reservoirearthquakes are lower obviously than other areas.