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Outline
The frequency band of oceanic microseismic peaks lies outside the velocity flat response range of borehole short-period seismometers. This study employs a transfer function to restore the oceanic microseismic peaks recorded by low-noise short-period seismometers and uses these restored peaks as the signal source for calculating the installation azimuth angles of borehole short-period seismometers. To investigate the impact of preprocessing parameters on the qualification rate of the calculated installation azimuth angles of downhole short-period seismometers, six sets of filters with different bandwidths were first applied to preprocess 24 hours of continuous data. The continuous data were then divided into five different time lengths. Subsequently, the installation azimuth angles of the borehole short-period seismometers were calculated using a correlation method. Finally, the installation azimuth angles with an average correlation coefficient greater than 0.995 for both the east-west (EW) and north-south (NS) components, and with an angle between the EW and NS components not exceeding 1.2°, were selected. The results show that the most qualified azimuth angles were obtained when the data were preprocessed with a filter bandwidth of 0.2 to 0.6 Hz and a duration of 300 s. Moreover, the number of qualified azimuth angles was significantly higher during the period of 19:00 to 06:00 than during 07:00 to 16:00. A comparison of the Earth's background noise before and after the correction of the installation azimuth angles of surface and borehole short-period seismometers revealed that the EW and NS components did not coincide before correction but were perfectly aligned after correction, thereby validating the effectiveness of using a filter bandwidth of 0.2 to 0.6 Hz and a duration of 300 s for azimuth angle calculation. This set of preprocessing parameters can also be applied to the azimuth correction calculation of borehole very broadband seismometers and the alignment error testing of surface seismometers.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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