We find at fast- and intermediate-spreading seafloor that their ridge-parallel bathymetric profiles between two neighboring fracture zones, excluding the part of the seafloor inward to fracture zone valley, are predominantly upward concave. The temporal evolution of the bathymetric profiles is characterized by (i) rapid growth of the middle deflection to about 200 m relative to the ends for the first few millions of years and (ii) a steady state afterwards. We show that these characteristics and the upward-concave sense of bending can be reasonably explained as the flexure of a thin elastic plate cooling and contracting from the top. The best-fitting model needs only about 10 % of the thermal bending moments computed based on the half-space cooling model. Our finding suggests that the classical models for how thermal strain accumulates in oceanic lithosphere are overly simplistic.