Waveform-matching reverse time migration for local earthquakes

With the increasing use of passive seismic data, developing seismic reflection imaging methods based on passive data is of considerable practical significance. This study presents a waveform-matching reverse time migration for the primary reflected data from local earthquakes. In order to mitigate inconsistencies in frequency band and energy across earthquakes of different magnitudes, we first establish reference seismic waveform with standardized dominant frequency and magnitude. A matching operator is derived for each event by matching its waveforms with the reference waveform. This operator is then applied via convolution to all waveforms, producing standardized seismic waveforms with consistent wavelet features. The reshaped waveforms are then subjected to reverse time migration using an impedance imaging condition for primary reflections. To suppress strong energy interference near the hypocenters, both illumination compensation and three-dimensional smoothed spherical mask centered on each source are used. Numerical tests using both simple two-layer model and fault-containing model demonstrate that the new method is robust and effective. The reverse time migration of primary reflected data of local earthquakes accurately images underground impedance boundaries such as stratum interfaces and fault planes, showing its promise for future application in seismically active fault zones.