Seafloor observatories to monitor slow slip phenomena

Abstract:

We present an overview of existing autonomous and cabled observatories that allow to monitor slow slip phenomena, examples of observations and new instruments that will be deployed in the near future or are under development. Pore-fluid pressures recorded by CORK borehole observatories are able to detect elastic strain caused by seismic events. Data from two instrumented boreholes at the toe of the subduction prism off Nicoya Peninsula, Costa Rica, show that also strain related to slow slip phenomena can be detected. Slow slip events were not only detected as transient pore-pressure signals, but also as relative uplift detected by the difference of absolute seafloor pressure measurements. CORK 1364A off Vancouver Island will be connected to Ocean Networks Canada's NEPTUNE cabled ocean observatory, in summer 2016. At the same time, the CORK Observatory, which currently only measures seafloor and formation pressures, will be augmented by downhole tiltmeters, a borehole broadband seismometer, and a temperature string. This comprehensive suite of instruments sending high-resolution real-time data will be used to study offshore subduction processes which may include slow slip phenomena if they are detectable. Additionally, we are working on a new use of broadband seismometers. It turns out that their mass-position data is well suited to detect seafloor tilt signals at much longer periods than the regular instrument response. We are comparing mass-position derived tilt information to data from a newly developed seafloor accelerometer and tiltmeter prototype. We anticipate that the new instrument will allow us to monitor seafloor deformation autonomously or cabled over long periods of time. Cabled ocean observatories as the US Cabled Array and the Canadian NEPTUNE observatory, are interesting research platforms that allow enhanced observations not only by providing real-time data, but also by allowing resolution, data rates, and lengths of time-series that are otherwise difficult to achieve.