Application And Study Of Digital Seismic Data

The application and study of digital seismic data is of great importance not onlyin theory but also in practice. Now seismology has undergone a technologicalrevolution. The development of a new generation of seismometers and digitalrecording systems with very broad bandwidth and high dynamic range, modernmonitoring system can capture all spectrum seismic wave include strong motion andsmall motion. Shanghai seismic array monitoring systems have seismic array, seismicnetwork and Sheshan seismic station of China Digital Seismic Network(CDSN). It isvery important to solve daily seismic monitoring and basis study and applicationstudy of geophysics using those seismic data.In this paper, Shanghai seismic array calibration, Frequency-Wavenumber(F-K)technique and application in Shanghai seismic array, small-scale heterogeneitiesbelow the Shanghai array from seismic wavefield fluctuations of West-North events,seismic magnitude and earth free oscillation excitated by the Indian Ocean earthquakeare studied using the broadband digital from Shanghai seismic array and CDSN.Some new research results are obtained as follows.1. Shanghai seismic array calibrationIn this paper, Shanghai seismic array calibration picture are figured from thestudy of its recording many teleseismic earthquakes in the globe range. At that time,the calibration pointed out the velocity asymmetry below the array and calibrated theevents location results and would improve the precision of location results in thefuture.2. F-K technique and its application in Shanghai seismic arrayWe are to discuss the theoretical foundation of F-K algorithm and introduce itsapplication as well. The various waves with different velocities and frequencies canbe recognized and separated by means of the F-K technique. However, inconsequence of its defect as such, it remains the problem on how to improve theprecision of its results. In this paper, we are to study some aspects: adding the secondphase to improve the location precision using F-K technique; F-K analysisdemonstrating the stability of this analysis for determining azimuth and slowness forearthquakes and instability for noise or ground motion and this method able torecognize the seismic phase; Compared with the difference of three component andthe different phase of the same events using F-K analysis; improving the amplitude of pdp using the velocity spectrum analysis method.3. Small-scale heterogeneities below Shanghai seismic array from teleseismic Pcodas waveThe data from the archives of Shanghai seismic array provide waveforms fromQinghai-Xizang earthquakes that are suitable for the study of the small-scaleheterogeneities under array. Based on the analysis of P codas of 6 events there isevidence for scattered arrivals which are generated in the upper lithosphere below theShanghai Sheshan region. Residual seismograms displaying locally generatedwavefield fluctuations can be determined and interpreted.4. The magnitude error by using seismic energyShanghai seismic array has recorded many earthquakes since its operation. It isnecessary whether the magnitude enjoys correct value. In this paper, the fact that weget the Shanghai seismic array magnitude is almost equal to the NEIC magnitude, inthe wake of which we make an analysis of the reason of error by using seismic energy.5. Detecting earth-free oscillation using synthetically the long periodseismometer, gravimeter and strain gaugeEarth free oscillation did not get along in China although observed in the worldin 1960. The majority of seismologists studied earth free oscillation using gravimeterand strain gauge in the world. In this paper, we are to detect first earth free oscillationusing synthetically the long period seismometer, gravimeter and strain gauge.Spherical and toroidal modes of the earth free oscillation are excitated by theearthquake in the India Ocean on Dec.26th 2004. More modes are extracted thanbefore.