What is Seismology?

Seismology is the study of earthquakes and the elastic waves that they excite in the Earth. Accordingly, seismology is often subdivided into  source and structure studies.  Source seismology – Earthquakes occur when lithospheric blocks slip against one another along surfaces known as faults. Over the past decade, we have learned that this slip can occur slowly, producing a variety of phenomena such as “silent” or “slow” earthquakes and seismic “tremor.” When the slip occurs quickly it is called an earthquake and violent ground motions can be excited; these pose a hazard to much of the world’s population. At Maryland, we are interested in understanding both the fundamental rock physics that produces the range of slip behavior, and in better characterizing earthquake sources and hazard, particularly within plate interiors.Structure seismology – Seismic waves, akin to sound waves in air, travel through the Earth and carry with them information about the temperature, pressure, density and composition in the deep interior. Because the deepest hole ever dug was only ~12 km deep, the vast majority of the Earth’s interior remains inaccessible to us. By analyzing and modeling the individual wiggles that make up a seismogram, we can infer what the interior of the Earth looks like. In particular, we can determine – with varying degrees of success and difficulty – the rigidity, bulk modulus, density, attenuation and anisotropy. These parameters can be associated with a particular composition and temperature. Seismic anisotropy, which is propagation and polarization dependence of seismic wavespeeds, is though to form in the mantle primarily through the preferential alignment of crystals that make up mantle rocks, and therefore gives us direct information on flow within the mantle.