Abstract
X-ray computed tomography (XCT) is an advanced imaging technique that has been increasingly used in the past years because it can provide valuable information on internal structures of a rock sample in a non-invasive manner. The maximum resolution of lab-based XCT facilities is ~0.5 μm, which might be sufficient to capture macropores in some rocks (i.e., sandstone), but will result in underestimation of porosity in clay-rich sediments containing micro-and nano-scale pores. Furthermore, such high-resolution XCT facilities are quite expensive and not ubiquitous. In this study, we introduce a new methodology based on the K-means clustering algorithm to process of low-resolution XCT images, illustrating its capability through porosity analysis of drillcores obtained during Integrated Ocean Drilling Program (IODP) expedition 343. The cation exchange capacity (CEC) of the squeezed samples of the same cores was also measured and used to correct shipboard measurements of Moisture and Density (MAD) porosity for the effect of the water bound in the interlayer clay particles, thereby calculating interstitial porosity. The results indicate that the porosities estimated by our method are in agreement with these MAD_derived interstitial porosities in several cores acquired from the overthrusted sediments above the Japan trench plate boundary. Also, considering interstitial porosity as a realistic measurement of porosity, the results show that our semi-automatic method improves estimations compared with a manual thresholding segmentation, as the latter suffers from user subjectivity.
Highlights
25 In March 2011, the Mw ~9 Tohoku-oki earthquake, one of the largest seismic events ever recorded, occurred across a megathrust fault in the west of the Japan trench (Fig. 1)
X-ray computed tomography (XCT) is an advanced imaging technique that has been increasingly used in the past years because it can provide valuable information on internal structures of a rock sample in a non-invasive manner
We introduce a new 15 methodology based on the K-means clustering algorithm to process of low-resolution XCT images, illustrating its capability through porosity analysis of drillcores obtained during Integrated Ocean Drilling Program (IODP) expedition 343
Summary
25 In March 2011, the Mw ~9 Tohoku-oki earthquake, one of the largest seismic events ever recorded, occurred across a megathrust fault in the west of the Japan trench (Fig. 1). The seismogenic region of the plate boundary between the Eurasian plate and subducting Pacific Plate was broken such that an unprecedented coseismic slip of about 50 to 60 m occurred over the shallow part of the megathrust (Fujiwara et al, 2011; Lay et al, 2011; Tanikawa et al, 2013; Chester et al, 2013; Sun; 2017) This devastating earthquake stressed the need for more detailed studies on the fault zone behavior and 30 the main causes of this event. Porosity is a fundamental property of rocks that can help to understand tectonic processes and fault zone behavior as it can serve as an indicator of Coseismic volumetric strain and fluid pressure anomaly around the fault zone (Wang & Barbour, 2017) It is a critical parameter for studying pore pressure, sediment compaction, and effective stresses, including their evolution due to 40 thermal (fluid) pressurization ( Sibson, 1973; Lachenbruch, 1980), which play an important role in rupture initiation and fault slip (Moore & Saffer, 2001; Saffer & Bekins, 2006). It comes as no surprise that several methods have been developed to estimate porosity in the past decades, including laboratory measurements (e.g., MAD and mercury intrusion porosimetry) and well-logging to imaging techniques
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