## 5 Results  
The sampling period of the observation stations is shown in Table 1. The analysis of the RQR corresponding to the rainfall load was conducted on relatively heavy rainfall events (cumulative rainfall >20 mm) during the sampling period. The analysis results for the stations are illustrated in Figure 4, in the left panel for each BSM displays the rainfall impact functions obtained in different periods and the average function, and simulated RQR obtained by convolution of the average rainfall impact function and rainfall are shown on the right. The vertical axes in Figure 4 display responding strains and the horizontal show the time. According to the altitude and topography in the neighboring regions of BSMs, we roughly divided them into 2 categories, plain/low terrain and hill/mountain area, and checked the responses of rainfall in different topographic conditions. Figure 4: The left panel (**a**) shows the rainfall-induced strain changes, which represent the rainfall impact functions corresponding to the rainfall events. The blocks on the base map show the distribution of discrete data of rainfall quick responses (RQRs) in a certain timespan. The darker blue area means there are more than 65% discrete data within, adding lighter ones contain more than 90% of the data, the average functions (blue circles) and continuous fitting curves (red lines) are also shown. The right panel (**b**) displays the comparison between the simulated RQR (red circles) and observed RQR (blue lines) and rainfall data (green lines). The simulated data are obtained by multiplication of the average rainfall function with the rainfall. The category of plain and low-terrain means those set in the regions of low altitude and small terrain change. JING is located at the edge of the Taipei Basin with an altitude of only 19 m. The neighboring region has a flat terrain with only one 10 m high hill approximately 100 m west of the station and without significantly large rivers passing within 500 m. Overall, there were no notable terrain effects on the borehole strainmeter observations. The results show that the rainfall impact function of JING was fairly stable, demonstrating no remarkable noise-induced residual influence on the data. The intensity of the hetero-phase noise could be effectively reduced by calculating the average. The areal strain at JING rapidly reached a peak of 8.8 nanostrain/hPa a half hour after the rain started and then descended over time. It took about 26 h to decrease the strength of responding strain to 10% of the peak value. Another low-terrain BSM was SANS, which is located in a flat terrain of the river bank on the edge of the Taipei Basin. A Creek runs northward in the east of SANS at a distance around 200 m away. The rainfall response of SANS was similar to JING. After the onset of rainfall, the response reached the maximum quickly and then reduced gradually over time. However, the rainfall decay time in SANS persisted longer than in JING, it took more than 95 h after the onset of rainfall. Constrained by the limitation of lithology and topography for installation, most of BSMs installed by CGS were located in hilly areas in the Western Foothill of Taiwan (Figure 1). Apart from the topographic relief, rivers were close to the observation stations, there were 6 BSMs sliding by a notable river crossing in the vicinity of the hill or mountain area. TAIS is a typical BSM installed in the mountainous area. It is located at a slope with an altitude of around 800 m with relatively high terrain changes. According to the results, it took 0.5-1 h to reach the maximum rainfall response and persisted to at least 178 h long after raining began. The rock formation where the borehole strainmeter installed was composed by alternations of sandstone and mudstone, Late Miocene, and was overburdened by a thick colluvium and weathering debris. Water level was recorded around 50 m beneath the ground surface.