Damage Characteristic Of Ground Motion And Theoretical Method Of Earthquake Early Warning

For the key scientific issues in the earthquake early warning(EEW)and the emergency processing field,the researches of the basic theory of EEW and damage characteristic of ground motion on structures were carried out.The specific contents were as follows:based on a large number of strong ground motion records,the high-precision theoretical method to detect and pick P,S phases using initial records was obtained.For the estimation uncertainties in the earthquake magnitudes and ground motion parameters,we proposed the initial characteristic parameters of early warning significance and established the relevant laws between typical EEW characteristic parameters and source parameters and ground motion parameters,respectively,in addition,the corresponding EEW theory and method were derived.Meanwhile,the causal relationships between ground motion parameters and building damage were studied to link input records directly to measures of damage.Through the researches,we proposed the theory and method for EEW of high-precision and established the relationships between ground motions and building damage,by quickly predicting the early disaster from the earthquake warning,this paper can provide a scientific basis for the establishment of a more reasonable and accurate earthquake emergency response system(including emergency warning and disaster assessment).The main work and achievements are as follows:(1)On the basis of the strong ground motion records of the 2008 Ms8.0 Wenchuan earthquake and the building collapse ratios(CRs)on a large scale,the fragility relationships between the CRs of 20 targeted districts and 4 ground motion parameters(the peak ground acceleration PGA,peak ground velocity PGV,peak spectrum acceleration PSA,spectrum intensity SI)were obtained,and based on which the damage criteria were proposed.In addition,we developed an effective method for estimating building damage classifications,which could effectively eliminate the deviation in the design forces for structures.The predicted collapse ratios CRRS corresponding to the PGA for the Wenchuan earthquake were computed based on the seismic coefficient kR of the revised "Code for Seismic Design of Buildings".If we assumed that buildings were built according to the improved Seismic Fortification Criterion,the predicted CRRS for the targeted districts would be significantly lower compared with the actual damage they sustained,where most of the CRRS were below 30%except for Bajiao,Qingping and Wolong,with 34%,54%and 43%,respectively.(2)We proposed a set of auto-fast combination algorithms to detect and pick P and S waves for EEW by single-station in real-time.On the basis of the proposed polarization filter functions,we combined the preliminary detection of the revised STA/LTA method in terms of the adjustment coefficient ? with the kurtosis-AIC function to refine the signal and lock on the arrival time with a higher degree of accuracy.We tested our techniques to the main-shock and aftershocks of the Ms8.0 Wenchuan earthquake,where 1398 acceleration records were treated.The detection rates of P wave and S wave were 91%and 85%while the automatic picks deviated from the manual picks by-0.021 ±0.068-sec for P onsets and-0.025±0.169-sec for S onsets,respectively.The results of the proposed detection algorithms were shown to perform well and can be applied for the early warning of impending earthquakes occurred with diverse focal mechanisms,complicated propagation processes and site effects,which could fulfill the requirements of accuracy,speediness,effectiveness for EEW by single station.(3)We proposed a theoretical method of fast-accurate magnitude estimation for EEW by single-station.Based on the proposed magnitude predication method in terms of the squared displacement integral(ID2),and by selecting the average ground motion period(?c)and the peak displacement amplitude(Pd)as comparisons,we established the regression relationships between these 3 parameters and magnitudes using the acceleration records of 43 aftershocks of the Ms8.0 Wenchuan earthquake,in addition the magnitude estimation formulas were derived accordingly.By comparing the differences between the estimated magnitudes and catalogue magnitudes,the proposed method of ID2 was of the highest accuracy among the investigated parameters.Furthermore,aiming at large earthquakes,i.e.the Wenchuan Ms8.0 main-shock,we investigated the applicability of the initial parameters to correlate the magnitude using 3-second and the proposed parameter ID2 was relatively more accurate.Then with the evolutionary estimation of ID2 as a function of the time window,we showed that the proposed regression relationships can be extended to large earthquakes,that the saturation effect could be removed by the use of time windows around 6-second with ID2.(4)We proposed a theoretical method of fast-accurate site ground motions estimation for EEW by single-station.Based on the proposed parameter of first 3-second P wave spectral intensity S1(3s),the aftershocks of the 2008 Ms8.0 Wenchuan earthquake were used to compare the relationships between the proposed first 3-second P wave spectral intensity SI(3s),the peak displacement amplitude Pd and the squared velocity integral IV2 and 3 ground motion parameters(the peak ground acceleration PGA,peak ground velocity PGV and spectral intensity SI),in addition the corresponding ground motion estimation formulas were derived.The comparison results showed that the proposed SI(3s)method was more accurate in estimating peak ground acceleration PGA,thus more suitable for the EEW models that use acceleration parameter.Aiming at large magnitude earthquakes,i.e.the Wenchuan main-shock,we put forward to introduce a correction coefficient to revise the characteristic parameter in advance,thus the accurate-fast estimation for the following ground motions of large earthquakes could be achieved where the underestimation was also mitigated to a certain extent.(5)Based on the proposed EEW theory and method generated from the strong ground motion dataset,the further analysis and verification were carried out on the basis of the ground motion simulation theory.A new idea and route for the research of EEW by means of numerical earthquake simulations was presented,and the feasibility and rationality of which were verified.It would provide a new research method for the EEW.By the simulative methodology of 3D ground motion,we established the comprehensive earthquake evaluation 3D model among the typical faults and underground structures,based on which the ground motion simulation on whole process including the seismic source-propagation path-site condition was obtained.With the simulated 240 seismic waves,we tested the applicability of the proposed magnitude estimation parameter,the squared displacement integral(ID2)and the ground motion estimation parameter,the first 3-second P wave spectral intensity SI(3s).According to the established relationship between ID2 and magnitude as well as the relationships between SI(3s)and PGA,PGV,SI using theoretical seismic waves,the consistency illustrated that the equations deduced from the aftershocks of the Wenchuan earthquake were also appropriate for the simulated seismic waves.