1. A method for prestack time migration, including velocity calibration and trend fitting (“iDEPTHing”) before curved-my prestack time migration, comprising: a. editing seismic velocities, including at least one of honoring geologic trends existing in a survey area, using envelopes of vertical trends based on rock properties and using computed envelopes; b. computing lateral trends of RMS velocities derived from seismic data by geostatistical variogram modeling; c. preparing scale factors from well (hard) data and seismic (soft) data wherein the well (hard) data include at least one of checkshot data and up-scaled and bulk-shifted sonic logs; d. calibrating RMS velocities, including applying interpolated scale factors to RMS velocities wherein the interpolation is a function of the lateral trends; and e. curved-ray prestack time migration using interpolated calibrated RMS velocities, wherein the interpolation is a function of the lateral trends.