Applications Of Seismic Array Technology In Seismologic Researches

Benefit form the building of digital seismic networks and the Internet sharing,a great deal of seismology data is available.It would advantage us not only in numbers, but also in quality.With special analysis methods for these seismic arrays,we can get more details of seismic signals,which infer more structures in the Earth.In this research,we analysis data from networks include GRSN,FNET,ORFEUS,CDSN and etc to solve several problems:the rupture process of the Kokoxili earthquake,the waveform mixing of the Sumatra earthquake,the fine structure of the 410km discontinuity beneath the south Europe,and the S velocity anomalies of the lowermost mantle beneath the western Pacific.Long strike-slip co-seismic rupture zone(＞400km)has been observed after the 14^thNovember,2001 Kokoxili earthquake.The rupture speed of this earthquake has been determined to exceed the shear wave velocity in the crust.Based on the results of field investigations and INSAR reevaluations,we used an improved back projection method to image the rupture process of this earthquake.As a result,the rupture process of the Kokoxili earthquake can be divided with rupture velocity 2.3km/s,5.5km/s,4.3km/s and 4.1km/s in 4 segments.Rupture started at sub-Rayleigh wave speed and became supershear when it approached the main Kunlun fault at the south Bukadabanfeng.The 4 segments divided with rupture speed can correspond well with the fault segments,which is Taiyanghu segment,the two parts of the Kusaihu segment and the Kunlun Pass segment.It seems that the mechanism of sub-Rayleigh rupture transferring to supershear can be explained with the surface touching of the fault.In the Sumatra earthquake,the long series of P wave train mixing with PP phase bring us a lot of trouble.We use a stacking method divide the mixing phases.To check the method,we calculated a group of synthetic seismograms and applied the dividing method on them.In result,the divided phases were clear,and the reconstructed seismograms fit well with the input seismograms.Using this method, we divided P waveforms from the wave train of the 28^thMar,2005 Nias earthquake and the 26^thDecember,2004 Sumatra earthquake.Further researches shows that the huge rupture zone of the Sumatra earthquake still affect the result,but the effect is acceptable.As an application,we divided the P waveform form 17^thJuly,2007 Java earthquake to get the actual extended time of the event.Using this we can get this parameter rapidly and actually even for large events.The May 18,1998,earthquake in south Italy(Mw5.4)produced a strong topside reflection off the 410-km discontinuity which was recorded on a multitude of seismic arrays throughout the south Europe.Data from GRSN and ORFEUS networks provide a detailed look at the 410-km structure.The salient features of the data set are(1) amplitude of P410 is 1/2 that of P phase in distance 16°～14°;(2)P410 match P phase together at distance 14°;(3)amplitude of P410 is 2/3 that of P phase in distance 14°～11°;(4)P410 die away rapidly in distance 11°～10.5°;(5)P410 disappears when distance little than 10.5°.These features are best modeled by a 20km thick 410-km model which contains a 50%part of linear gradient and a 50%part of velocity jump. The model is similar with a mineralogical model for Olivineα-βtransition.In the last part of the article,we observed the lowermost mantle beneath the western pacific with seismic wave trains.We calculated the ScS-S residuals from CDSN data,and found strong S velocity abnormal(-3s)in the southwestern part of the research area,where the northeastern part is a weak abnormal area.We use 2D finite-difference programs to calculate some synthetics with 3 typical mantle models: mantle plumes with -3%S velocities,the edge of mantle plumes with -3%S velocities in the right half,and a -30%ULVZ in the bottom of the mantle.Comparing the synthetics with the data,we considered that the source of the S abnormal can be explained that the area is in the edge of the Pacific mantle Plume.