Friction analysis of Costa Rica ocean sediments from ODP Hole 170-1039B, 170-1040C and 205-1253

In areas of high basement topography, a regionally extensive nannofossil chalk unit is exposed at the seafl oor on the incoming plate, whereas in regions of low basement topography, hemipelagic clay-rich sediment is exposed.

Because the entire sediment section is subducted at this margin, lithologic variation in the uppermost subducting sediments may control plate boundary fault behavior. Our laboratory experiments reveal that the chalk is frictionally strong (µ = 0.71-0.88) and characterized by velocity weakening and stick-slip behavior, notably at elevated temperature. In contrast, the hemipelagic sediment is weak (µ = 0.22-0.35) and in many cases velocity strengthening.