Thud! Ring! Seismic Response What causes a seismic response? 1. Changes in bulk-rock velocity or density Lithology (e.g., sandstone, shale, limestone, salt) Slide 3 What causes a seismic response? It is changes in the velocity and/or density of the rock with fluid in the pore space Several factors effect the velocity and density of bulk-rock The most common factor is lithology e.g., sandstones generally have different velocity and density values than shales or limestone. Consider the last time you struck a hammer or pick against a rock If you struck a dense limestone, the hammer would bounce back rapidly and the sound would have a high pitched ring However, if your hammer struck a less dense shale, it would only yield a low pitched ‘thud’ The frequency of the sound you hear when your hammer strikes a rock is proportional to the density of that rock Limestone Ring! Thud! Shale Courtesy of ExxonMobil L 13 - Seismic Attributes