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doi:10.2204/iodp.proc.344.106.2013

Mid-slope Site U1380¹

R.N. Harris, A. Sakaguchi, K. Petronotis, A.T. Baxter, R. Berg, A. Burkett, D. Charpentier, J. Choi, P. Diz Ferreiro, M. Hamahashi, Y. Hashimoto, K. Heydolph, L. Jovane, M. Kastner, W. Kurz, S.O. Kutterolf, Y. Li, A. Malinverno, K.M. Martin, C. Millan, D.B. Nascimento, S. Saito, M.I. Sandoval Gutierrez, E.J. Screaton, C.E. Smith-Duque, E.A. Solomon, S.M. Straub, W. Tanikawa, M.E. Torres, H. Uchimura, P. Vannucchi, Y. Yamamoto, Q. Yan, and X. Zhao²

Background and objectives

A primary objective of Integrated Ocean Drilling Program (IODP) Expedition 344 was to understand the processes that generate earthquakes along the subduction thrust at erosive plate margins. Fundamental to this objective is determining the nature of the upper plate seaward of the seismogenic zone. Site U1380 is located in the upper plate seaward of the seismogenic zone.

Site U1380 is located on the middle slope of the Costa Rica margin along seismic Line BGR99-7 at common midpoint 2350 (Figs. F1, F2). At Site U1380, the margin consists of a 550 m thick section of slope sediments overlying upper plate framework rock. This site was selected for a number of reasons. First, interplate earthquakes and geodetic measurements indicate that this site is seaward of the updip extent of seismicity and that the plate interface is not locked. Second, the seismic section shows that this site is above the seaward edge of high-amplitude landward-dipping reflectors. Third, this site is on the flank of a local high in framework rock that minimizes drilling time through the overlying sediment. Hole U1380A was drilled during IODP Expedition 334 as an alternative to Site U1378 when drilling conditions prevented further progress. During Expedition 334, at ~480 mbsf, poor drilling conditions necessitated terminating Hole U1380A prior to reaching the framework rock (Expedition 334 Scientists, 2012c). The primary goals for revisiting this site were to determine the nature, composition, and physical properties of the upper plate framework rock; to understand the nature of the landward-dipping seismic reflectors; and to estimate the state of stress.

¹ Harris, R.N., Sakaguchi, A., Petronotis, K., Baxter, A.T., Berg, R., Burkett, A., Charpentier, D., Choi, J., Diz Ferreiro, P., Hamahashi, M., Hashimoto, Y., Heydolph, K., Jovane, L., Kastner, M., Kurz, W., Kutterolf, S.O., Li, Y., Malinverno, A., Martin, K.M., Millan, C., Nascimento, D.B., Saito, S., Sandoval Gutierrez, M.I., Screaton, E.J., Smith-Duque, C.E., Solomon, E.A., Straub, S.M., Tanikawa, W., Torres, M.E., Uchimura, H., Vannucchi, P., Yamamoto, Y., Yan, Q., and Zhao, X., 2013. Mid-slope Site U1380. In Harris, R.N., Sakaguchi, A., Petronotis, K., and the Expedition 344 Scientists, Proc IODP, 344: College Station, TX (Integrated Ocean Drilling Program). doi:10.2204/​iodp.proc.344.106.2013

² Expedition 344 Scientists’ addresses.

Publication: 11 December 2013
MS 344-106

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