Fig. 1. Development timeline of DFSS passive imaging technology

Fig. 2. Sketch of extracting empirical Green's function using ambient noise ^[35]

Fig. 3. Record section of (a) active-source cross-correlation functions and (b) NCFs ^[59]; (c) Comparison of (top) active-source cross-correlation function and (bottom) NCF

Fig. 4. (a) The dispersion curve of segments along the Taihe Road^[21]; (b) The S-wave velocity profile along the Taihe Road

Fig. 5. The waveform and dispersion spectra after the TSI method ^[69]. (a)-(c) NCFs of 3 segments. The black line represents the raw NCF, and the red line represents the denoised NCF; (d)-(f) are the dispersion spectra of the denoised waveforms shown in (a)-(c). In (d)-(f), red circles represent the maximum energy at each frequency, and the red line indicates the extracted dispersion curve

Fig. 6. The illustration of reflection/transmission coefficient ratio and the observed frequency dependency^[22]. (a) A two-dimensional background shear velocity model with a simplified rectangular fault in the center; (b) 2.5 Hz cross-correlation record section, the waveforms of the two symmetrical channels are plotted in white lines, with the red portion of the waveform used to measure R and T; (c) R/T measurements at symmetric channel pairs at different distances from the fault; (d) and (e) are similar to (b) and (c) respectively but for the frequency of 4.5 Hz

Fig. 7. Site amplification profile and near-surface shear velocity model^[78]. (a) The red line shows averaged site amplification, the blue line shows V_s30 computed from the velocity model in (b); (b) The three-layer shear velocity model from ambient noise imaging; (c) Log-log relationship between the V_s30 and site amplification (blue crosses) with the best fitted k shown in the black line

Fig. 8. Typical passive signal waveforms and temporal and spatial distributions ^[91]. (a) Icequake wave recorded by channel 281; (b) LFE waveform. (c) Temporal distributions for icequakes (light blue) per hour and LFEs (dark blue) per minute and the local air temperature (black curve), the time of AGE is marked with a red arrow, the inset picture shows a window of 20 min with an AGE (red line) and following LFEs (black lines), the air temperature is denoted with a black curve; (d) Spatial distribution for icequakes (light blue) and LFEs (dark blue)

Fig. 9. 2D V_s profile constructed from 1D V_s models obtained from 181 sub-arrays of 1 km length ^[98]

Fig. 10. A conceptual lunar fiber seismic network ^[104]. (The base station provides space and power for the (DAS) interrogator, data processing unit, and telecommunicating system, the cables can be deployed by a lunar rover)