Tilt Corrections for Normal Mode Observations on Ocean Bottom Seismic Data, an example from the PI-LAB experiment

Abstract

Earth's normal modes are fundamental observations used in global seismic tomography to understand Earth structure. Land seismic station coverage is sufficient to constrain the broadest scale Earth structures. However, 70% of Earth's surface is covered by the oceans, hampering our ability to observe variations in local mode frequencies that contribute to imaging small-scale structures. Broadband ocean bottom seismometers can record spheroidal modes to fill in gaps in global data coverage. Ocean bottom recordings are contaminated by signals from complex interactions between ocean and solid Earth dynamics at normal mode frequencies. We present a method for correcting tilt on broadband ocean bottom seismometers by rotation. The correction improves the ability of some instruments to observe spheroidal modes down to 0S4. We demonstrate this method using 15 broadband ocean bottom seismometers from the PI-LAB array. We measure normal mode peak frequency shifts and compare with 1-D reference mode frequencies and predictions from 3-D global models. Our measurements agree with the 3-D models for modes between 0S14 - 0S37 with small but significant differences. These differences likely reflect real Earth structure. This suggests incorporating ocean bottom normal mode measurements into global inversions will improve models of global seismic velocity structure.

Seismicity Properties of the Chain Transform Fault Inferred Using Data From the PI‐LAB Experiment

“…The goal was to determine what makes a plate "plate-like" (Fischer et al, 2010(Fischer et al, , 2020Rychert et al, 2020). The data from the experiment also provided an opportunity to study a range of other phenomena, including, for instance, constraining local sediment properties (Agius et al, 2018;Saikia et al, 2020), imaging the mantle transition zone (Agius et al, 2021), determining 1D oceanic attenuation structure (Saikia et al, 2021a), tracking infragravity waves in the ocean (Bogiatzis et al, 2020), developing better corrections to improve normal mode measurements for seafloor data (Harmon et al, 2022), tidal triggering at the MAR (Leptokaropoulos et al, 2021), and TF seismicity on the nearby Romanche (Hicks et al, 2020) and the Chain TFs. Our study focuses on the Chain TF, which is characterized by a narrow 0-20 Myr old rupture zone, stretching over 300 km in roughly the east-west direction between two ridge spreading axes, slipping at a full spreading rate of ∼30 mm/yr.…”