Image Analysis of Drill Core Samples from the Hikurangi Subduction Margin, New Zealand

Abstract:

The Hikurangi subduction margin hosts the shallowest and most accessible slow slip events (SSEs) on earth. To better characterize the structure and materials that contribute to SSEs, the International Ocean Discovery Program (IODP) Expeditions 372 and 375 have explored a transect of the source region of SSEs by logging, coring, and installing observatories [Wallace et al., 2019]. Core samples have been recovered from the incoming plate (Sites U1520 & U1526), frontal thrust region (Site U1518), and the upper plate just above the source region of SSEs (Site U1519). Site U1520 was cored to 1052 meters below the seafloor (mbsf) containing siliciclastic trench sediments in the uppermost section, and pelagic carbonates and volcaniclastics in the lower section. The volcaniclastics conglomerates, which start around 850 mbsf, are highly heterogeneous and are suspected to contribute to SSEs in the region [Barnes et al., 2020].

In this study, we have conducted image analysis on the core samples recovered from Site U1520 to further characterize the heterogeneity of the volcaniclastic materials from the incoming plate. Using MATLAB and Python, we quantitatively characterize the heterogeneity in terms of degree of cementation and grain size, and correlate them with shipboard composition and physical properties datasets. This information could potentially help us learn more about how heterogeneous lithologies could contribute and eventually be linked to define the location, magnitude and mechanism of SSEs.