Geophysics and Remote Sensing

Abstract

Igneous sheet intrusions such as sills, dikes, and laccoliths are abundant in volcanic basins. Mafic intrusions are characterized by high P-wave seismic velocities in the range from 5.0 to 7.0 km/s. Velocity aureoles with a thickness comparable to the sill intrusion are commonly identified on sonic log data above and below the intrusions. Sills as thin as 10 m may be detected by conventional seismic reflection data, whereas sills with a thickness above about 40 m are resolvable. Offset-dependent tuning of sill reflections is expected due to the high velocity of the intrusions. Deep sills are difficult to image by reflection methods but can be identified from wide-angle seismic data. Sill reflections are interpreted based on characteristic features such as their high amplitudes and saucer-shaped geometries. Sill complexes are further well-suited for 3D visualization techniques. Potential field and electromagnetic data may improve the reliability of the igneous intrusion interpretation; however such data have poor resolution if sills are buried below more than a few kilometers of sediments. Andesitic and felsic intrusions and laccoliths are less abundant than sills in volcanic basins, and few well-documented geophysical interpretation studies of such intrusions or dykes are published.