This electronic supplement contains tables showing station parameters, including location and depth, as well as our calculated orientation for the H1 component of the broadband sensors. Our analysis assumes the use of a left-handed coordinate system, whereby the H1 component is nominally north, and the H2 component is 90° clockwise from H1, unless explicitly stated otherwise.
Table S1 [Plain Text Comma-separated Values; 21 KB]. Instrument type, H1 orientation, uncertainty, number of data, and number of unique earthquakes used in the final calculation for all Cascadia Initiative (CI) ocean-bottom seismometer (OBS). The table also includes specific mention of cases in which the standard calculation was not used. Data selection criteria were occasionally adapted to specific stations based on the background noise levels and environmental conditions, particularly at shallow stations. Column 12 indicates whether we excluded the highest-frequency (35 and 40 mHz) results to improve the signal. A “0” means that these measurements were excluded, a “1” means they were included. Column 13 states the specific cross-correlation threshold utilized.
Table S2 [Plain Text Comma-separated Values; 7 KB] Orientation data for the Ocean Seismic Network (OSN) and phase 2 deployment for Plume-Lithosphere Undersea Mantle Experiment (PLUME2) networks considered in the main article. The Laske et al. (1994) results for the PLUME2 network were presented by Rychert et al. (2013) and not recalculated for this study.
Laske, G., G. Masters, and W. Zurn (1994). Frequency-dependent polarization measurements of long-period surface waves and their implications for global phase-velocity maps, Phys. Earth Planet. In. 84, 111–137.
Rychert, C., G. Laske, N. Harmon, and P. Shearer (2013). Seismic imaging of melt in a displaced Hawaiian plume, Nature Geosci. 6, 657–660, doi: 10.1038/ngeo1878.
[ Back ]