System software for interactive human–computer data processing based on the IASP91 Earth model was designed. An interactive data processing system for visualizing earthquake data was designed and implemented via the Intel Fortran platform. The system reads and processes broadband seismic data acquired by field stations, mainly including the reading and import of raw data, pre-processing, identification of seismic phases and inter-correlation traveltimes picking. In the data processing step, shortcomings have been improved and functions have been gradually refined and enhanced, making it easier and faster to process data. It has already processed more than 1000 large seismic events received by the station from 2013 to 2018. The practical application shows that the human–computer interaction system is easy to operate, accurate, fast and flexible, and is an effective tool for processing seismic data.
We used the ray tracing technique based on the IASP91 Earth model to calculate the travel times in order to identify the phases. This technique can calculate the travel times for the seismic phases in the conventional travel time tables. The waveform data received from the stations in the Guangxi area are selected for analysis and discussion. The outcomes of the numerical modeling and its use demonstrate that there is good agreement in terms of the absolute differences between the calculated and theoretical travel times from the ISAP91 tables. The relative residuals are determined directly from the actual arrival times picking during the correlation analysis, and the validity of the travel time method for picking seismic phases by correlation analysis can be demonstrated.
The hypocenter parameters of an earthquake may give us an insight into the Earth’s structure and tectonic processes. Among the hypocenter parameters, the focal depth is normally more difficult to estimate than the earthquake location (latitude and longitude). We propose to use the pPKIKP-PKIKP arrival time intervals for estimating the focal depth. We analyze the sensitivity of the pPKIKP-PKIKP arrival time interval to the earthquake depth. We measure the pPKIKP-PKIKP arrival time interval on seismograms (the vertical component), and invert the time interval data set using the simulated annealing inversion algorithm. We illustrate the inversion approach on two teleseismic earthquakes which have shallow and deep focal depths, and demonstrate that the approach is indeed appropriate to the shallow and deep event. We can obtain a reliable estimate on focal depth, even though the seismic station is sparse or in a remote part of the epicenter.
Since PKIKP is a teleseismic phase with small angle arrived at station, almost vertical to the surface, it is an important phase for establishing the earth’s structure interior, including its derived phases reflected from discontinuity boundaries at the 410 km and 660 km in the upper mantle transitional zone. In this paper, based on the IASP91 Earth velocity model and raytracing technique, the kinematic characteristics of the PKIKP and its derived phases are numerically simulated and analyzed. The results show that the arrivals of the pairs of P4PKIKP and PKIKPP4, pP4PKIKP and pPKIKPP4, P6PKIKP and PKIKPP6, pP6PKIKP and pPKIKPP6 derived from PKIKP are coincided each other, respectively, enhancing the energies for phase identification. The phases pPKIKP, pPKIKPP4, and pPKIKPP6 arrivals are parallel to each other and phases PKIKP, PKIKPP4, and PKIKPP6 arrivals also are parallel to each other for the events with different source depths, and that the time differences between PKIKPP4 and PKIKP, PKIKPP6 and PKIKP always parallel each other and independent of the source depth. When the velocity discontinuity of the upper mantle transitional zone is inclined toward the increasing epicenter distance direction, the travel time of phases PKIKPP4 or PKIKPP6 will increase with distance increasing; Conversely, the travel time will decrease with distance increasing.
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