MRI: Offshore Earthquake Monitoring at Subduction Zones Using Autonomous Underwater Vehicles and High-Speed Optical Telemetry For Data Retrieval

MRI：使用自主水下航行器和高速光学遥测数据检索在俯冲带进行近海地震监测

• 批准号: 1532035
• 负责人: John Collins
• 金额: $ 92.32万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-08-15 至 2021-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1532035&HistoricalAwards=false
• 关键词: MRI; Offshore; Earthquake; Monitoring; Subduction

The earth's subduction zones, where one tectonic plate overrides another, are the sites of the planet's largest and most dangerous earthquakes. Recent examples are the 2004 magnitude 9.1 Sumatra and the 2010 magnitude 9 Tohoku, Japan earthquakes. In addition to massive destruction brought about by ground shaking, both of these earthquakes generated devastating tsunamis. These events are a reminder that fault motion in our planet's largest earthquakes happens offshore under the continental shelf, a region that is challenging to monitor. The scarcity of seismic instrumentation in the source regions of these great earthquakes has limited the seismological community's ability to answer fundamental scientific questions and to evaluate hazards in real-time. Sustained offshore monitoring of subduction zones would not only lead to improved understanding of these faults but also potentially allow the identification of increased short-term risk. Extensive foreshock sequences located far offshore preceded both the 2010 Tohoku event and the recent 2014 magnitude 9 Pisagua Chile earthquake. These sequences demonstrated that there are detectable time periods on the scale of weeks when subduction zones are more likely to produce a large rupture. To fully understand this basic fault behavior and possibly utilize an understanding of it to reduce risk, rapid access to high quality seismic data from offshore directly above the great earthquakes is needed. The seismological community routinely deploys seismographs offshore, but data access requires ship-based instrument recovery, a lengthy and expensive task that may not be possible or desirable during a potential foreshock sequence. Seismology is a fast moving science: earthquakes are detected within seconds, magnitude estimates are tweeted within minutes, fault planes are determined within hours, and research articles are often submitted within weeks of a major earthquake. The full potential of offshore seismic data can only be realized if these data are rapidly ingested into data centers. Recent advances at Woods Hole Oceanographic Institution in optical telemetry and marine robotics, coupled with the availability of commercial off-the-shelf low-power seismic sensors, data loggers and atomic clocks offer the capability for multi-year deployments of arrays of ocean-bottom seismographs (OBS) that are capable of delivering high-frequency, accurately-timed seismic data to shore with data latencies of hours to days without OBS recovery. This project will develop such a system by integrating a WHOI-designed optical modem capable of telemetry rates of 20 Mbits/second with an OBS and with a long-range (up to 286 nautical miles) REMUS Autonomous Underwater Vehicle (AUV). These proven rates allow telemetry of a week of high-rate (100 Hz) seismic data on 4 channels (ground motion and pressure) in minutes (or a year of data in less than 2 hours). Moreover, accurate timing is critical for earthquake location but OBS lack the benefit of GPS timing. The optical link will also allow measurement of the offset of the OBS clock relative to a GPS-synchronized time signal carried by the AUV to a precision of ~1 microsecond. These technologies will make possible multi-year deployments of OBS arrays with on-demand data offload and clock-check without the need for annual recovery/re-deployment cruises, saving hundreds of thousands of dollars per experiment. This capability will be particularly suitable for the dense near-shore arrays needed to monitor subduction zones.

地球俯冲带是一个板块覆盖另一个板块的地方，是地球上最大、最危险的地震发生的地点。最近的例子是 2004 年苏门答腊岛 9.1 级地震和 2010 年日本东北部 9 级地震。除了地面震动造成大规模破坏外，这两次地震还引发了毁灭性的海啸。这些事件提醒我们，地球上最大的地震中的断层运动发生在大陆架下的近海，这是一个难以监测的区域。这些大地震震源区缺乏地震仪器，限制了地震界回答基本科学问题和实时评估灾害的能力。对俯冲带进行持续的海上监测不仅可以增进对这些断层的了解，而且有可能识别增加的短期风险。在 2010 年东北地震和最近的 2014 年智利皮萨瓜 9 级地震之前，远海地区发生了广泛的前震序列。这些序列表明，存在可检测到的几周尺度的时间段，此时俯冲带更有可能产生大的破裂。为了充分了解这种基本断层行为并可能利用对其的了解来降低风险，需要从大地震正上方的海上快速获取高质量的地震数据。 地震界通常在海上部署地震仪，但数据访问需要船基仪器恢复，这是一项漫长而昂贵的任务，在潜在的前震序列期间可能是不可能或不理想的。地震学是一门快速发展的科学：地震可以在几秒钟内检测到，震级估计可以在几分钟内发布到推特上，断层面可以在几小时内确定，研究文章通常会在大地震发生后的几周内提交。 只有将海上地震数据快速纳入数据中心，才能充分发挥这些数据的潜力。伍兹霍尔海洋研究所在光学遥测和海洋机器人技术方面的最新进展，加上商用现成的低功率地震传感器、数据记录器和原子钟的可用性，为海底阵列的多年部署提供了能力地震仪 (OBS) 能够将高频、精确定时的地震数据传输到岸上，数据延迟数小时到数天，而无需 OBS 恢复。该项目将通过将 WHOI 设计的遥测速率为 20 Mbits/s 的光学调制解调器与 OBS 和远程（长达 286 海里）REMUS 自主水下航行器 (AUV) 集成来开发这样的系统。这些经过验证的速率允许在几分钟内遥测 4 个通道（地震动和压力）上一周的高速率 (100 Hz) 地震数据（或在不到 2 小时内遥测一年的数据）。此外，准确的授时对于地震定位至关重要，但OBS缺乏GPS授时的优势。光学链路还可以测量 OBS 时钟相对于 AUV 携带的 GPS 同步时间信号的偏移，精度可达约 1 微秒。这些技术将使 OBS 阵列的多年部署成为可能，并具有按需数据卸载和时钟检查功能，而无需每年进行恢复/重新部署巡航，从而每次实验节省数十万美元。这种能力将特别适合监测俯冲带所需的密集近岸阵列。