Chemical diagenesis, porosity reduction, and rock strength, IODP Site U1480; influences on great earthquakes at shallow depths

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http://meetingorganizer.copernicus.org/EGU2017/EGU2017-4267.pdf
Author(s): Song, Insun; Milliken, Kitty L.; Dugan, Brandon; Bourlange, Sylvain; Colson, Tobias; Frederik, Marina; Jeppson, Tamara; Kuranaga, Mebae; Nair, Nisha; Henstock, Timothy
International Ocean Discovery Program, Expedition 362 Scientific Prospectus, College Station, TX
Author Affiliation(s): Primary:
Korea Institute of Geosciences and Mineral Resources, Daejeon, South Korea
Other:
Bureau of Economic Geology, United States
Colorado School of Mines, United States
Université de Lorraine, France
University of Western Australia, Australia
Agency for the Assessment and Application of Technology, Indonesia
University of Wisconsin at Madison, United States
Yamaguchi University, Japan
National Centre for Antarctic and Ocean Research, India
University of Southampton, United Kingdom
Volume Title: European Geosciences Union general assembly 2017
Source: Geophysical Research Abstracts, Vol.19; European Geosciences Union general assembly 2017, Vienna, Austria, April 23-28, 2017. Publisher: Copernicus GmbH on behalf of the European Geosciences Union (EGU), Katlenburg-Lindau, Germany. ISSN: 1029-7006
Note: In English
Summary: International Ocean Discovery Program (IODP) Expedition 362 drilled two sites, U1480 and U1481, on the Indian oceanic plate ∼250 km west of the Sunda subduction zone to a maximum depth of 1500 meters below seafloor (mbsf). One of the primary objectives was to understand the mechanism of great earthquakes such as the 2004 Sumatra earthquake (Mw 9.0) which showed unexpectedly shallow megathrust slip by establishing the initial and evolving properties of the North Sumatran incoming sedimentary section. Core sampling and logging from the complete sedimentary section at U1480 indicates a distinct change in sedimentation rate from a slowly deposited pelagic system to a rapidly deposited submarine fan system at late Miocene. Following burial, sediments of the Nicobar Fan underwent compaction leading to porosity reduction from 66±9% near seafloor to ∼30% at the base of the sampled Nicobar Fan section (∼1250 mbsf), representing a normal consolidation behavior. Rock strength gradually increases with depth as the sediments are mechanically compacted. Below the fan (1250-1415 mbsf), the pelagic sediments are composed of tuffaceous, calcareous, and siliceous sediments/rocks and their porosity is dependent upon lithology more than upon depth. Tuffaceous materials exhibit high porosity ranging from ∼30-60%, even higher than that of overlying layers. However, porosity of most calcareous samples is lower than 20% at the same depth. The large variation in porosity depends on the degree of cementation, which in turn is controlled by grain assemblage composition and environmental conditions such as slow sedimentation rates and locally high temperatures related to igneous activity as documented by local igneous intrusives and extrusives. The minor cementation in tuffaceous sandy sediments has retained high porosity, but strengthened their skeleton so as to bear the overburden. The low porosity in calcareous rocks is considered to come from extensive cementation rather than mechanical compaction. The rock strengthening by mechanical compaction is dependent on effective stress, and does not facilitate storage of a large amount of elastic energy at shallow depth. However, chemical diagenesis (cementation) can lead to high strength that does not necessarily arise directly from burial. This chemical diagenesis potentially influences sediment strengthening that localizes great earthquakes at shallow depths. [Copyright Author(s) 2017. CC Attribution 3.0 License: https://creativecommons.org/licenses/by/3.0/legalcode]
Year of Publication: 2017
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 07 Marine Geology and Oceanography; Diagenesis; Earthquakes; Expedition 362; Geologic hazards; Great Sumatran Fault; IODP Site U1480; IODP Site U1481; Indian Ocean tsunami 2004; International Ocean Discovery Program; Natural hazards; Seismicity; Seismotectonics; Sumatra-Andaman Islands earthquake 2004; Tectonics; Tsunamis
Coordinates: S030000 S030000 E0912000 E0912000
Record ID: 2018029933
Copyright Information: GeoRef, Copyright 2018 American Geosciences Institute. Reference includes data from European Geosciences Union, Munich, Germany