Hydrogeological and seismic responses to incoming materials at the non-accreting margin, offshore the Osa Peninsula, Costa Rica

Author(s): Harris, R. N.; Kameda, J.; Shimizu, Mayuko; Ujiie, K.; Tsutsumi, A.; Ikehara, M.; Uno, M.; Yamaguchi, Asuka; Hamada, Y.; Namiki, Y.; Kimura, G.
Author Affiliation(s): Primary:
Oregon State University, Corvallis, OR, United States
Other:
University of Tokyo, Japan
Japan Atomic Energy Agency, Japan
University of Tsukuba, Japan
Kyoto University, Japan
University of Kochi, Japan
Tohoku University, Japan
Japan Agency for Marine-Earth Science and Technology, Japan
Volume Title: AGU 2015 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2015; American Geophysical Union 2015 fall meeting, San Francisco, CA, Dec. 14-18, 2015. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: The relationship between temperature and the updip limit of seismicity has been demonstrated for accretionary margins where the incoming sediment is thick relative to basement relief (e.g., Oleskevich et al., JGR 1999). Here we show an example offshore the Osa Peninsula where this relationship does not appear to hold. At this non-accreting margin, the incoming sediment thickness is thin and the basement relief is substantial. The MW 6.4, 16 June 2002, Osa, Costa Rica earthquake occurred along the plate interface, 25 km landward of the trench at a depth of approximately 5-10 km (Arroyo et al., G3, 2014). Two-dimensional thermal models indicate that the temperature at this position is approximately 70-90°C (Harris et al., G3, 2010), and is cooler than the reported correlation between temperature and the updip limit of seismicity. We estimate the incoming fluid budget based on the 100 m section from the Costa Rica Seismogenesis Project reference site (IODP Exp. 334 Site U1381) using porosity and bulk mineral assemblage based on X-ray diffraction analysis of core samples. The porosity (76%) combined with the water content in smectite (∼40 vol.%) and biogenic silica (∼24 vol.%), leads to a total sedimentary water influx estimate of 6.9 m3/yr per m of trench length. The dehydration source term is calculated with respect to silica diagenesis and clay diagenesis using the thermal model. Peak mineral dehydration occurs at temperatures of approximately ∼100°C, 40-30 km landward of the trench and 5-10 km landward of the shallowest seismicity (Arroyo et al., G3, 2014). These results suggest that in this region the presence of subducting bathymetric relief may be more important in influencing the updip extent of seismicity than the thermal regime. This interpretation is consistent with the observed patchy seismicity (Bilek et al. Geology, 2003) and emphasizes the importance of frictional heterogeneities along the subduction thrust (Bilek and Lay, GRL, 2002).
Year of Publication: 2015
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; 19 Geophysics, Seismology; Central America; Costa Rica; Costa Rica Seismogenesis Project; Earthquakes; East Pacific; Expedition 334; IODP Site U1381; Integrated Ocean Drilling Program; Marine sediments; North Pacific; Northeast Pacific; Osa Peninsula; Osa earthquake 2002; Pacific Ocean; Sediments; Seismicity; Seismotectonics; Tectonics
Coordinates: N082543 N082543 W0840928 W0840929
Record ID: 2016046939
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