[S-CG45] Science of slow-to-fast earthquakes

[SCG45-37] Two years of calibrated seafloor pressure data from the Hikurangi margin – can vertical secular strain be resolved?

★Invited Papers

*Erik K Fredrickson¹、Laura Wallace²、Spahr Webb³、D Randolph Watts⁴、Meng (Matt) Wei⁴、Ahyoung Ku⁴ (1.University of Texas at Austin Institute for Geophysics (UTIG)、2.GEOMAR Helmholtz Centre for Ocean Research、3.Lamont Doherty Earth Observatory、4.University of Rhode Island)

キーワード：seafloor geodesy, absolute pressure, seafloor pressure, ocean circulation

We present seafloor pressure data from the first two years of an ongoing marine seismogeodetic experiment in the Hikurangi subduction zone. For the time interval considered, nearby coastal GNSS show no significant transient motion, which suggests that no slow slip deformation has occurred in the offshore and presents an opportunity to observe the secular strain signal from ongoing convergence. Ordinary absolute pressure observations suffer from an effect known as instrumental drift – a long-period sensor-produced signal that obscures real long-period phenomena. To overcome this, our pressure instruments make use of the “A-0-A” calibration method to remove the drift from our observations, making them sensitive to real long-period signals. The observed drift rates for our sensor network are as large as 20 hPa/yr, much greater than the expected ~1 hPa/yr secular strain signal. Even with the drift removed, pressure signals from the ocean circulation remain an issue, for which we take two approaches. First, we correct the observations with synthetic bottom pressure predictions from the global ocean circulation models GLORYS and ECCO2, which exhibit good coherence at periods greater than 30 days. Second, we use direct observations of water column properties from CPIES instruments that are in the network as part of the broader experiment. To date, only partial data have been recovered from the CPIES, so we will have to wait until the end of the entire experiment for a full comparison between the seafloor pressure and oceanographic observations. Together, these datasets highlight the challenges of observing such subtle signals, but also showcase the promise for multi-year, multi-instrument sensor networks for addressing interdisciplinary science targets in the marine environment.