Fast and accurate earthquake location within complex medium using a hybrid global-local inversion approach
Chaoying Bai 1,2,Rui Zhao 1 and Stewart Greenhalgh 3,4 1 Department of Geophysics,College of Geology Engineering and Geomatics,Chang'an University,Xi'an 710054,China 2 Key Laboratory of Western China's Mineral Resources and Geology Engineering,Ministry of Education,Xi'an 710054,China 3 Institute of Geophysics,ETH Zürich CH 8092,Switzerland 4 Department of Physics,University of Adelaide,Adelaide SA 5005,Australia
A novel hybrid approach for earthquake location is proposed which uses a combined coarse global search and fine local inversion with a minimum search routine,plus an examination of the root mean squares(RMS) error distribution.The method exploits the advantages of network ray tracing and robust formulation of the Fréchet derivatives to simultaneously update all possible initial source parameters around most local minima(including the global minimum) in the solution space,and finally to determine the likely global solution.Several synthetic examples involving a 3-D complex velocity model and a challenging source-receiver layout are used to demonstrate the capability of the newly-developed method.This new global-local hybrid solution technique not only incorporates the significant benefits of our recently published hypocenter determination procedure for multiple earthquake parameters,but also offers the attractive features of global optimal searching in the RMS travel time error distribution.Unlike the traditional global search method,for example,the Monte Carlo approach,where millions of tests have to be done to find the final global solution,the new method only conducts a matrix inversion type local search but does it multiple times simultaneously throughout the model volume to seek a global solution.The search is aided by inspection of the RMS error distribution.Benchmark tests against two popular approaches,the direct grid search method and the oct-tree important sampling method,indicate that the hybrid global-local inversion yields comparable location accuracy and is not sensitive to modest level of noise data,but more importantly it offers two-order of magnitude speed-up in computational effort.Such an improvement,combined with high accuracy,make it a promising hypocenter determination scheme in earthquake early warning,tsunami early warning,rapid hazard assessment and emergency response after strong earthquake occurrence.
【Fund】： funded by the National Natural Science Foundation of China (No.40774020);; the Key Research Program from Ministry of Education of China (No.107137)
【CateGory Index】： P315.3
【CateGory Index】： P315.3