應用於短週期海底地震儀之低角度平衡裝置設計

Abstract

海底地震儀於水下獨立作業時，由於海床的不平整以及水流等擾動，使得感震器的姿態難以掌握。任何感震器對於傾角皆存在一定敏感度，過大的傾角會降低感測器的表現，尤其是信號的振幅。因此，多數的海底地震儀皆有搭載平衡裝置，校正角度為360°。然而，根據我們先前部署的經驗，確保感震器於海床保持水平姿態，並不需要過高的校正角度。因此，在本研究中我們基於低角度的假設，設計出全新概念的平衡機構。我們也透過振動平台測試，確保新型設計不會對地動信號造成影響。在控制方面，除了原有的週期性檢查外，我們還嘗試在系統中加入臨界值監控，目的是將信號品質最佳化。基於全新的平衡裝置，我們整合出一地震儀原型 CH01，並將其與信號品質良好的寬頻地震站進行共站比對。儘管雜訊水平不如預期，但在區域地震觀測方面仍具有一定水準。研究最後，我們也對淺海型 OBS 的未來發展提出幾個論點。現階段，為了符合成本效益，淺海型 OBS 應朝繫泊式方向發展，並需考量目標佈放的環境與時長，提出更完善的設計。未來應整合OBS系統並實際進行水下測試，以確保裝置的穩定性和可靠性。

Ocean Bottom Seismometers (OBS) face significant challenges in maintaining proper sensor orientation due to uneven seabeds and water currents during underwater operations. Since all seismic sensors are sensitive to tilt, excessive tilt can degrade their performance, particularly in signal amplitude. Consequently, most OBS are equipped with leveling devices that offer 360° correction angles. However, our previous deployment experiences indicate that such extensive correction angles are unnecessary. In this study, we propose a novel leveling device based on a low-angle hypothesis, aiming to reduce complexity and cost while maintaining functionality. We conducted vibration platform tests to ensure that the new design does not interfere with ground motion signals. Additionally, we incorporated threshold monitoring into the system alongside traditional periodic checks to optimize signal quality. Using the new leveling device, we assembled a prototype seismometer, CH01, and compared its performance with that of high-quality broadband seismic stations. Despite higher-than-expected noise levels, CH01 demonstrated satisfactory performance in regional earthquake observations. Finally, to achieve cost-effectiveness, we suggest that shallow-water OBS should be designed as moored systems. Future research should focus on optimizing the assembly process of the leveling device, conducting comprehensive tests, and performing actual underwater tests to ensure device stability and reliability. Considerations of deployment environments and durations will be essential for refining the design and improving the overall performance of the OBS system.