Another area of interest is the physics of the earthquake process, including studies of crustal deformation and "slow" earthquakes in the near field as well as general study of source kinematics using far-field data. The investigators are interested not only in shallow earthquakes but also in the underlying mechanisms of intermediate- and deep- focus seismic events. Additionally, by using deformation and other related data, departmental investigators work on the mechanisms of volcanic eruptions.

Instrumentation devleopment and deployment has always been a strength at DTM. The Department played a lead role in the design of a new broadband seismometer for use in conjunction with the national program in lithospheric seismology. The Department currently owns twenty broadband portable digital seismographs.

DTM possesses unique data sets for innovative studies in seismology. Since 1970, the seismology group has operated a small worldwide network of broadband, high-dynamic-range seismometer stations in seismically active regions, including Iceland, Peru, and Japan. These instruments provide high-quality data for the study of body waves having frequencies of up to several hertz, and of surface waves having periods to 100 seconds or more, for the tens of thousands of events which have occurred over the last 25 years. The high dynamic range provides on-scale recordings for study of both very large and very small earthquakes. In addition, DTM scientists have deployed Sacks-Evertson dilatometers (strainmeters) in Iceland, Japan, Peru, China, and along the San Andreas fault (California). These instruments, also broadband with high dynamic range, are sensitive to seismic waves. But they can also detect long-term, crustal movements throughout the period range. They are thus ideal for studying crustal deformation and the earthquake process. Both instruments--the broadband seismometer and the strainmeter--were designed at DTM. In addition, DTM has an extensive library of data from standard global digital networks.

Laboratory Studies
(I. Selwyn Sacks, Paul G. Silver)

A laboratory program for studying the seismic properties of rocks, undertaken jointly with the Geophysical Laboratory. The group seeks to answer such questions as the relation between attenuation of seismic waves and the degree of partial melting of rocks appropriate for the mantle. Other areas of interest include the relation between phase transitions and deep-focus earthquakes, the nature of the 660-km discontinuity, the D" region at the base of the mantle, and the characteristics of strain-induced anisotropy in upper and lower mantle materials.

Planetary Evolution
(Sean C. Solomon)

Geological, geophysical, and geochemical studies of magnetism, tectonics, and chemical evolution of the terrestrial planets. Tools include imaging and other experimental observations from recent spacecraft missions to the planets. Topics of current research include the history and resurfacing and outgassing on Venus, the nature and evolution of the lithosphere on Venus and Mars, the formation and structural and magmatic evolution of large volcanoes on the terrestrial planets, the nature of mantle-lithosphere interaction on Venus, and an exploration of the factors affecting differences in the tectonic evolution of Venus and Earth. This work is linked strongly to the research on solar system formation and to the broad efforts of the Department to understand the formation and evolution of the planet most acessible to detailed investigation--the Earth.

Postdoctoral Fellows and Associates

Natalia Gómez Pérez
Maureen Long
Thomas Ruedas
Alex Song
Wen-che Yu