Frictional properties of sediments entering the Costa Rica subduction zone offshore the Osa Peninsula; implications for fault slip in shallow subduction zones

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doi: 10.1186/1880-5981-66-72
Author(s): Namiki, Yuka; Tsutsumi, Akito; Ujiie, Kohtaro; Kameda, Jun
Author Affiliation(s): Primary:
Kyoto University, Department of Geology and Mineralogy, Division of Earth and Planetary Sciences, Kyoto, Japan
University of Tsukuba, Japan
Hokkaido University, Japan
Volume Title: Earth, Planets and Space
Source: Earth, Planets and Space, 66(1). Publisher: Terra Scientific Publishing Company (TERRAPUB), Tokyo, Japan. ISSN: 1343-8832
Note: In English. This article is part of the series "New perspective of subduction zone earthquake", edited by Gaku Kimura, Juichiro Ashi, Masataka Kinoshita, Christie Rowe, and David Shelly. 40 refs.; illus., incl. sketch map
Summary: We examined the frictional properties of sediments on the Cocos plate offshore the Osa Peninsula, Costa Rica, and explored variations in the intrinsic frictional properties of the sediment inputs to the Costa Rica subduction zone. Sediment samples were collected at Site U1381A during the Integrated Ocean Drilling Program Expedition 334, and include hemipelagic clay to silty clay material (Unit I) and pelagic silicic to calcareous ooze (Unit II). The frictional properties of the samples were tested at a normal stress of 5 MPa under water-saturated conditions and with slip velocities ranging from 0.0028 to 2.8 mm/s for up to 340 mm of displacement. The experimental results reveal that the steady-state friction coefficient values of clay to silty clay samples are as low as ∼0.2, whereas those of silicic to calcareous ooze samples are as high as 0.6 to 0.8. The clay to silty clay samples show a positive dependence of friction on velocity for all tested slip velocities. In contrast, the silicic to calcareous ooze samples show a negative dependence of friction on velocity at velocities of 0.0028 to 0.28 mm/s and either neutral or positive dependence at velocities higher than 0.28 mm/s. Given the low frictional coefficient values observed for the clay to silty clay samples of Unit I, the décollement at the Costa Rica Seismogenesis Project transect offshore the Osa Peninsula likely initiates in Unit I and is initially very weak. In addition, the velocity-strengthening behavior of the clay to silty clay suggests that faults in the very shallow portion of the Costa Rica subduction zone are stable and thus behave as creeping segments. In contrast, the velocity-weakening behavior of the silicic to calcareous ooze favors unstable slip along faults. The shallow seismicity occurred at a depth as shallow as ∼9 km along the Costa Rica margin offshore the Osa Peninsula (Mw 6.4, June 2002), indicating that materials characterized by velocity-weakening behavior constitute the fault zone at the depth of the seismicity. Fault slip nucleating along a fault in Unit II would be a likely candidate for the source of the shallow earthquake event. Copyright 2014 The Author(s) and Namiki et al.; licensee Springer.
Year of Publication: 2014
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 16 Structural Geology; Central America; Clastic sediments; Clay minerals; Cocos Plate; Costa Rica; Costa Rica Seismogenesis Project; Depth; Displacements; Dynamic loading; East Pacific; Expedition 334; Fault zones; Faults; Friction; Hemipelagic environment; IODP Site U1381; Integrated Ocean Drilling Program; Interfaces; Loading; Marine environment; Mechanical properties; Middle America Trench; North Pacific; Northeast Pacific; Ooze; Osa Peninsula; Pacific Ocean; Pore pressure; Pore water; Sediments; Seismicity; Shallow depth; Sheet silicates; Silicates; Slip rates; Subduction zones; X-ray diffraction data
Coordinates: N082543 N082543 W0840928 W0840929
Record ID: 2015009317
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data supplied by Springer Verlag, Berlin, Federal Republic of Germany