Study On The Seismic Wave Application In Determination The Yield Of Underground Nuclear Explosion And Rupture Process Of Natural Earthquake

Seismic wave can be generated when underground nuclear explosion or earthquake occurs,therefore,study on the informations which brings by seismic wave become one of the main content of seismology.Based on the theory and the characteristic of seismic wave,we can analysis and interpretation of seismograms which is the effective way to determine the source paramaters of underground nuclear explosion and the rupture process of natural earthquake.Both the yield and burial depth are two important parameters of an underground nuclear explosion test,the accurately estimations has great significance for reasonable evaluation of nuclear power and can test the credibility of the seismological monitoring inspection.Traditional yield estimation methods are based on amplitudes or magnitudes in which the relationship between amplitudes or magnitudes and yield,however,at local and regional distances,the waveforms such as body phases Pn,Pg,Sn and short period surface Lg,which used to estimate the yield has high complexity and easily affected by the source and path inhomogeneity,in the meantime,as a consequence of the direct-wave variability,multistation averaging is necessary to reduce the amplitude scatter,all of these factors can cause errors in source size and explosion yield estimation if they are not accounted for properly.In order to avoid the impact of these factors mentioned above,we establish a new method that can simultaneously estimate the burial depth and yield by using the recoeds at a single station to fit the regional coda amplitudes of the full wave train,building on the characteristic of the coda-wave which has stable waveform features and not as sensitive to the undesirable effects of source radiation pattern and path heterogeneity.Based on the single-scattering model and definition of coda envelopes of single regional phase,we construct an analytical expressions of coda envelopes at local and regional distance which modeled by using source spectral function,geometric spreading,site response,transfer function and coda shape function.Furthermore,we generalize the method to multiple phases and explain the effects of propagation,sites and the direct phase-to-coda transfer function,thus,analysis,select and verify each parameter of theory coda amplitudes by using the regional waveform data records in northeast China.Then,we obtain the stable amplitude envelopes from which the regional phases are apparently shown.And on this basis,perform a grid search to compare the theory coda envelopes for variable yield and burial depth with the actual waveform recording of events,find out the best fitting range,and obtain the estimations of five North Korean nuclear tests.The results shows that the yields increase from 0.6±0.2kt to 3.0±1.5kt and then 10.0±2.0kt,decrease to 8.0±2.0kt and finally increase to 11.0±2.0kt,according their origin time.In the meantime,the first test has a shallow burial depth of 150± 100m,for the second one,the depth is estimated to be 350± 100m,while both third and fourth tests have very similar depths of 500±200m,then decrease to 500± 150m in the fifth test.The results are below the yield-burial depth line and consistent with the previous findings,which can prove the reliability and also shows that by using coda envelopes at a single station can simultaneously obtain the estimations of yield and burial depth.Rupture process is a vital part of earthquake seismology,which provides the detail informations about the source process of main earthquake,the shake map of hypocentral region,the useful references to evaluate the effect of earthquake and to estimate the spatial and temporal distribution of aftershocks,and it's helpful to earthquake resistance and disaster mitigation.The static coulomb stress change calculated after the great earthquake,is an effective method for study the stress change of source region,and gives the judgment of earthquake triggering and the distribution of aftershocks.We utilize a finite-fault inversion which developed in the wavelet domain,and perform a joint inversion of far-field broadband body waves and surface waves records to discuss the rupture processes of September,17,2015,Mw8.3 Illapel earthquake and February,27,2010 Maule Mw8.8 earthquake in Chile.The results consistent with the previous findings,which imply that two events are thrust earthquakes,the rupture processes and the distribution of major slips are rather simple and concentered.The results indicate that the average rake,average slip,average rupture velocity and moment tensor for the 2015 Illapel earthquake are 107°,2.43m,1.82km/s and 3.28×1021Nm,respectively,and with a peak slip of 8m which located in 75km(along strike)and 8km in depth,and most of energy released after 104s;the distribution of major slips are concentered on the north of the epicenter,.The average rake,average slip,average rupture velocity and moment tensor for the 2010 Maule earthquake are 109°,4.95m,1.90km/s and 1.86x1022Nm,respectively,and with a peak slip of 12.5m which located in 100km(along strike)and 21km in depth,and most of energy released after 121s;and our joint inversion clearly evidences a bilateral propagation of rupture,extending on both sides of the epicenter.Furthermore,the 2015 Illapel Mw8.3 earthquake generates a larger tsunami,on account of the larger shallow slip.Based on the rupture distribution,we calculate the static coulomb stress change for the two events and shows that both of them makes an increase in the average stress,furthermore,the increased stress in source region of the 2015 Illapel earthquake which caused by the 2010 Maule event is 0.01-0.15bar,that may indicate a promotion from the 2010 Maule earthquake leading to the 2015 Mw8.3 Illapel earthquake.