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Abstract
Microseismic monitoring systems using local location techniques tend to be timely, automatic and stable. One basic requirement of these systems is the automatic picking of arrival times. However, arrival times generated by automated techniques always contain large picking errors (LPEs), which may make the location solution unreliable and cause the integrated system to be unstable. To overcome the LPE issue, we propose the virtual field optimization method (VFOM) for locating single-point sources. In contrast to existing approaches, the VFOM optimizes a continuous and virtually established objective function to search the space for the common intersection of the hyperboloids, which is determined by sensor pairs other than the least residual between the model-calculated and measured arrivals. The results of numerical examples and in-site blasts show that the VFOM can obtain more precise and stable solutions than traditional methods when the input data contain LPEs. Furthermore, we discuss the impact of LPEs on objective functions to determine the LPE-tolerant mechanism, velocity sensitivity and stopping criteria of the VFOM. The proposed method is also capable of locating acoustic sources using passive techniques such as passive sonar detection and acoustic emission.
Highlights
Passive location techniques, in which signals travel from a source whose location is estimated to sensors whose positions are known, is widely used in different areas
P-wave arrival times can be accurately picked for relatively high signal-to-noise ratio signals, such as the STA/LTA method[20] and the higher order statistics method[21]; reliable picking of the S-wave is still problematic for local events in which the P coda overlaps with the S-wave[16]
We developed a novel method to locate single-source events from arrival times contaminated by large picking errors (LPEs)
Summary
In which signals travel from a source whose location is estimated to sensors whose positions are known, is widely used in different areas. Because of the characteristics of the received signals, the microseismic source location techniques in local monitoring operations generally use P-wave or S-wave or both arrival times to locate sources. Practical applications have reported that sensors are likely to be triggered by S-waves but are wrongly assigned P-wave velocities[22] These cases illustrate that the arrival times of both P- and S-waves may contain large picking errors (LPEs), especially when using automated picking programs. The existing picking-based source location algorithms typically utilize forward modelling and iterative estimation techniques to determine the optimal location by globally minimizing a predefined objective function in the three-dimensional solution space[26]. By maximizing a continuously differentiable objective function (the so-called virtual field), the VFOM can be introduced into standard monitoring systems
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