## 4 Results  
### Results of F-K Analysis  
The non-uniform station distribution within the array can cause energy spread and leakage, which can be determined using the array response function (ARF) in the slowness domain. If the stations are evenly spaced, the ARF energy should show a two-dimensional delta function, with the maximum energy in the center and gradually decaying in all directions [21; 22]. First, we choose stations based on the array response function, which displays a two-dimensional delta shape of the energy with fewer sidelobes. Only 21 of the 89 sites in the YL array have data, and the range of depth for these 21 stations is 1000 to 3900 m. We chose eight stations with depths between 2000 and 2600 m to reduce the impact of station elevation differences on the F-K analysis. The array response function with a central frequency of 0.25 Hz was obtained (Figure 2). In order to ensure the accuracy of the F-K analysis for secondary microseisms, the ARF composed of eight stations exhibits a virtually two-dimensional delta function distribution with low energy sidelobes located far from the center. After selecting the suitable stations, we performed F-K analysis on the continuous seismic data during the TOMAS cyclone's active period. The sampling rate of the YL array was 40 points/s. We used a sliding window to analyze hourly continuous data, with each subwindow being 16,384 points (409.6 s) long and overlapping the adjacent subwindow by 50%. Each subwindow was detrended, then filtered using a Hanning window with a bandwidth of 0.1 to 0.5 Hz, the frequency band of the secondary microseisms. During the grid search of the slowness and back azimuth, the beam was formed using fourth root  
Figure 2: The array response function of YL array. stacking. We normalized the F-K calculation results through the lifetime of TOMAS, then analyzed the relationship between the TOMAS cyclone path, wind speed, ocean swell, and the seismic results (Figure 3). Figure 3: Results of F-K analysis in the range of 0.1 to 0.5 Hz at four different times during the TOMAS cyclone’s lifetime period (**a–d**). The comparison between the F-K result, the location of the cyclone center, and the swell is shown in the upper portion of 3 (**a–d**). The purple star is the location of the YL array, and the purple ray is the back azimuth from F-K. The circles are the locations of the centers of TOMAS. The back azimuth and velocity of the peak energy from F-K as a function of time are shown in the lower left part. The beginning and ending times when the F-K results have a good correlation with the cyclone are marked by the green dashed lines at 21:00 on 13 March and 03:00 on 18 March. The red dashed line marks the corresponding time of the upper portion. The lower right portion is the slowness measurement at the corresponding time of the upper portion from F-K. The P wave slowness and surface wave slowness are marked as concentric circles. On 10 March 2010, at 12:00 am, TOMAS was still in the tropical depression state (Figure 3a), with a central wind speed of only 25 km/h located north of the array. The cyclone's energy at this time was insufficient to have a significant dragging effect on the seawater along the cyclone's path, and the swell heights given by ERA5 were below 2 m. Although the peak energy of the F-K analysis has a surface wave velocity (3.59 km/s), its orientation is east-southeast rather than the direction of the cyclone TOMAS. Since there is a wide area with little land in the South Ocean, the region has high wave heights from a global perspective, and the seasonal variation in wave height is not significant. This feature makes the South Ocean one of the main sources of microseismic signals [23; 24]. The results of F-K analysis at that moment probably came from the South Ocean. On 14 March, at 11:00 am, TOMAS upgraded to typhoon level with a maximum central wind speed of 100 km/h and was the northwest of the array (Figure 3b).