T21D-2868
Hydrogeological and Seismic Responses to Incoming Materials at the Non-Accreting Margin, Offshore the Osa Peninsula, Costa Rica
Tuesday, 15 December 2015
Poster Hall (Moscone South)
Robert N Harris1, Jun Kameda2, Mayuko Shimizu3, Kohtaro Ujiie4, Akito Tsutsumi5, Minoru Ikehara6, Masaoki Uno7, Asuka Yamaguchi8, Yohei Hamada9, Yuka Namiki5 and Gaku Kimura8, (1)Oregon State University, Corvallis, OR, United States, (2)The University of Tokyo, Tokyo, Japan, (3)JAEA Japan Atomic Energy Agency, Toki, Japan, (4)University of Tsukuba, Tsukuba, Japan, (5)Kyoto University, Kyoto, Japan, (6)University of Kochi, Kochi, Japan, (7)Tohoku University, Sendai, Japan, (8)University of Tokyo, Bunkyo-ku, Japan, (9)JAMSTEC Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan
Abstract:
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).
