A Low-Power Global Positioning System-Acoustic Payload to study the subduction zones offshore the Pacific Northwest and Alaska

日本、智利和苏门答腊近海的俯冲带大地震由于地震本身及其引发的海啸造成了广泛的破坏。 一个类似类型的俯冲带断层位于太平洋西北部的卡斯卡迪亚俯冲带（CSZ）。 它最后一次破裂是在1700年，远在人口聚居区广泛建立之前。 从那时起，CSZ一直在以每年几厘米的速度在地壳中建立弹性应变。 在未来，这种储存的弹性能量可能会释放为强大的地震和海啸。 大部分的弹性应变正在海岸附近的海底积累。 通过测量这种应变在近海的缓慢积累，可以更好地了解潜在的地震和海啸风险。 通过将全球定位系统和海面平台上的声学测距系统以及海底上的声学应答器相结合，可以测量弹性应变的积累。 小型（冲浪板大小）波浪和太阳能平台现在可以取代大型船只进行大量数据收集。 然而，这需要重新设计机载电子元件，使其更小，功耗更低，这是该项目的目标。全球定位系统-声学（GPS-A）方法已适用于波浪滑翔器，这是一种遥控的波浪和太阳能海面航行器。波浪滑翔机的资金将持续到2017年，用于测量卡斯卡迪亚俯冲带三个海底地点的板块变形。 九月。2014年，我们在俄勒冈州中部近海3000米深90 Nm的地点收集了30小时的GPS和声学数据。 初步结果验证了波浪滑翔机作为卡斯卡迪亚高成本船舶的替代品，并可能在其他全球站点。 然而，我们发现，目前的全球定位系统惯性导航系统（GPS-INS）和波浪滑翔机上的计算机的功率需求约为22瓦（W）。这将数据收集限制在24-30小时内，在波浪滑翔机上的660瓦时电池组耗尽之前。 此时，GPS-A的操作必须暂停2-3天，同时太阳能电池板为车载电池充电。 我们和日本研究人员的研究表明，厘米级定位需要4-5天的GPS-A测量。 由于数据收集必须在仅约24小时后暂停，以便为电池充电3天，因此在单个站点收集累积5天的GPS-A数据需要16-20天。 加上3-5天的过境地点之间，只有三到五个GPS-A网站可以访问和测量超过3个月的夏季天气窗口在卡斯卡迪亚。 这使得几乎没有时间应急天气延误，机械故障等。 随着更多的卡斯卡迪亚近海海底地点被提议和增加，效率低下的情况被放大了。 该项目将取代现有的GPS-INS和板载CPU，采用低功耗版本，仅消耗6-8 W。 GPS-A数据可以连续收集长达5天。 当波浪滑翔机在海底站点之间运输时，船上的电池会在几天内充电。 这是一个有效的业务方法，可用于卡斯卡迪亚，阿留申群岛，并可能在其他地区。

Great subduction zone earthquakes offshore Japan, Chile, and earlier Sumatra caused extensive damage due the earthquake itself and the resulting tsunami. A similar type of subduction zone fault lies offshore the Pacific Northwest, the Cascadia Subduction Zone (CSZ). It last ruptured in 1700 long before the extensive establishment of populated communities. Since then the CSZ has been building up elastic strain in the crust at the rate of a few centimeters per year. In the future, this stored elastic energy will likely be released as a powerful earthquake and tsunami. Much of the elastic strain is accumulating the seafloor offshore the coast. By measuring the slow buildup of this strain offshore, a better understanding of the potential earthquake and tsunami risk can be established. By combining the Global Positioning System and an acoustic ranging system on a sea surface platform, and acoustic transponders on the sea floor, the elastic strain buildup can be measured. Small (surfboard-size) wave- and solar-powered platforms can now replace large ships for much data collection. However, this requires re-engineering the onboard electronic components to be smaller and lower power, which is the goal of this project. The Global Positioning System-Acoustic (GPS-A) approach has been adapted to a Wave Glider, a remotely controlled, wave- and solar-powered sea-surface vehicle. The Wave Glider is funded through 2017 to measure plate deformation at three seafloor sites in the Cascadia Subduction Zone. In Sept. 2014, we collected 30 hours of GPS and acoustic data at a 3000-m-deep site 90 Nm offshore central Oregon. Preliminary results validate the Wave Glider as a replacement for high-cost ships in Cascadia, and likely at other global sites. We found, however, the power requirements of the present GPS-Inertial Navigation System (GPS-INS) and the computer onboard the Wave Glider draw about 22 Watts(W). This limits data collection to 24-30 hours, before the 660 Watt-Hour battery bank aboard the Wave Glider is depleted. At this point, GPS-A operations must be suspended for 2-3 days, while the solar panels recharge the onboard batteries. Our research and that of Japanese researchers demonstrated that 4-5 days of GPS-A measurements are needed for centimeter-level positioning. Because data collection must be suspended after only ~24 hours to charge batteries for 3 days, it takes 16-20 days to collect the cumulative 5 days of GPS-A data at a single site. Adding 3-5 days for transiting between sites, only three to five GPS-A sites can be visited and measured over a 3 month summer weather window in Cascadia. This allows little contingency time for weather delays, mechanical problems, etc. As more seafloor sites offshore Cascadia are proposed and added, the inefficiency is magnified. This project will replace the existing GPS-INS and onboard CPU with low power versions that consume only 6-8 W. GPS-A data could then be collected continuously for up to 5 days. The onboard batteries are recharged over the few days as the Wave Glider transits between seafloor sites. This is an efficient operational approach for use in Cascadia, the Aleutians, and potentially other regions.