SEISMO-GEOLOGY: SEEING THE EARTH WITH TWO EYES OPEN

In order to wring greater detail from information we gather about the Earth, it is necessary to combine data and insights garnered from a broad suite of geologic sub-disciplines. Nowhere is this integrating trend clearer than in seismology, which has long been our main avenue of understanding tectonics at depth. Improved resolution and technical skills allow geologists to track surface structures into the upper mantle routinely. The limits of inferences based on seismology follow from our ability to determine primarily current Earth structure and details of seismic rupture at depth. The latter problem is important for active tectonics, state of stress in slabs, and rheology; Earth structure entails distribution of seismic velocities, attenuation, and anisotropy, derived from essentially two observables, travel time and waveforms. Viable interpretations of these observations depend heavily on surface geology, petrology, and mineral physics. Seismic velocities and combinations thereof, bulk sound velocity, Poisson's ratio, and other parameters derived from travel times through the Earth are frequently related to crustal and upper mantle compositions, and geologic observations made in the field or in the lab play a crucial role in this process. Seismic anisotropy observations are linked to observed petrofabrics in crustal and upper mantle rocks and lab synthetics to determine aspects of crustal deformation or upper mantle flow. Rheology and thermal state can be derived from observations of seismic attenuation and corresponding experiments in petrology and mineral physics that allow interpretation. Given their "snap-shot" nature, seismic structural imaging often provides the "final state" structure to be attained by any tectonic models - conceptual or numerical - purporting to show the sequence of events that occurred in an area of interest. Examples of these links will be explored during this presentation.