利用人工爆破资料研究福建一维P波速度结构和地震定位

Data from controlled explosions provide a unique advantage to study velocity models as the source locations are precisely known. A series of explosion were conducted in Fujian Province in 2010-2012. In this study, we hand-picked first Pg and Pn arrivals and secondary Pg arrivals from the explosion seismograms recorded at provincial stations. Using a joint inversion method, we inverted for a new 1-D P-wave velocity model, Fujian explosion model (FJEM). The FJEM model shows a 45% improvement in fitting the travel-time data over the current routine model. Similar velocity models inverted from subsets of explosion data suggest a relative stable and simple velocity structure in Fujian province. Relocations of the explosions suggest that the traditional South China model has small horizontal location errors (average 0. 52±0. 45 km), but errors in depth are significant (average 4. 7±1. 2 km), while the FJEM model has similar horizontal location capability but much smaller errors in depth (average 1. 3±1. 1 km). Synthetic tests using real earthquake bulletins show similar results for the South China model: (1) for earthquakes in the interior of Fujian with good azimuthal coverage, the horizontal mislocation is small; (2) the horizontal mislocations for earthquakes along the coast and in Taiwan Strait with poor azimuthal coverage can be very large; and (3) mislocations in depth can be large regardless station distribution, which have strong trade-off with origin time errors. Essentially, the horizontal location is largely affected by station azimuthal coverage and much less by the reference model. But the improved FJEM model not only is closer to the real Earth (fit data better) but also can reduce depth mislocation. We propose that South China model be replaced and the FJEM model be used in routine earthquake locations in Fujian and perhaps neighboring regions as well.