Passive Sources and Diffracted Points Imaging Using Combinational Cross-Correlation Imaging Condition

Abstract

Time-reversal imaging is a critical technique for characterizing natural earthquakes and artificial sources. Traditional time reversal methods sum the extrapolated wavefields of different receivers to suppress artifacts and obtain images of the sources. Multiplication-based time-reversal imaging uses the product of extrapolated wavefields to provide source images with fewer artifacts and higher resolutions. However, although multiplication among wavefields efficiently suppresses the artifacts, sources with weaker energy are also suppressed. We combined the two imaging algorithms and proposed a combinational cross-correlation reverse time migration (CcRTM) to image multiple sources. First, the receivers were divided into several groups and independently extrapolated in reverse time. Then, n receivers were selected each time, and the geometric mean between the receiver wavefields was calculated. In the third step, images of multiple sources were obtained using the arithmetic mean of all geometric mean results with different receiver combinations. Compared with multiplication-based source location methods, our method retains the root in the geometric mean to preserve the amplitude ratio between the sources. CcRTM can be applied to image diffractions by considering subsurface small-scale diffractors as secondary sources enabling the detection of anomalies smaller than the wavelength limit. To suppress the reflection energy, we introduced an excitation time to restrict the imaging time. Synthetic and field examples demonstrated the accuracy and efficiency of the proposed imaging method.