Duncan Agnew's faceDuncan Carr Agnew, Professor

Courses Taught

Research Interests

Continuous Crustal Deformation

The deformation of the crust is what drives the earthquake cycle, but this deformation is (except at the time of earthquakes) so gradual as to be very difficult to measure. Together with Frank Wyatt, I have for some time been studying how best to make such measurements, and what the best ones mean. Most of the data come from Piñon Flat Observatory (PFO), at which there is a unique collection of precise instruments for measuring crustal motion and other geophysical quantities. We have recently added another instrument (a long-base laser strainmeter) at Durmid Hill, just off the southern end of the San Andreas Fault (the section which is, by general consent, closest to failure). Some recent results from these instruments include:

Long-term Crustal Deformation

Beginning from this interest in continuous crustal deformation measurement, I, like many other geophysicists, have become interested in using the Global Positioning System (GPS) to study long-term motion in different parts of southern California. Themap of southern California shows the field areas, as well as the locations of the observatories referred to in the previous section. A major interest has been the area offshore (see the papers by Larson et al. and Feigl et al. in the list below), since measurements of crustal motion in this area are the only way to quantify the seismic hazard. I have also been surveying a detailed network in the area of the San Jacinto fault zone near PFO, to understand its reponse to applied stresses.

In the last few years, the use of continuous GPS (pioneered by the SOPAC project at Scripps, established by Yehuda Bock), has provided measurements of much higher time resolution; a current interest, especially given the current densification of this network in Los Angeles, is in understanding the errors of the technique: something for which the strainmeter data provide useful "ground truth".

Instrumentation

Having had a long-term involvment in the operation of the low-frequency part of the Project IDA seismic net, I remain interested in how to develop instruments to record earth motion, especially at low frequencies.

Tides and Earth Rotation

I have pursued some research into earth tides and the effects of the oceans on them; most recently, with the aim of using these as a calibration signal for in situ instruments.

Research Unit Affiliations

Selected Publications

1994: Wyatt, F.K., Agnew, D,C., Gladwin, M. "Continuous measurements of crustal deformation for the 1992 Landers earthquake sequence." Bull. Seismol.Soc. Amer, 84: 768-779.

1993: Feigl, K.L., Agnew, D.C., Bock, Y., Dong, D., Donnellan, A., Hager, B.H., Herring, T.A., Jackson, D.D., Jordan, T.H., King, R.W., Larsen, S., Larson, K.M., Murray, J.H., Shen, Z., Webb, F.H. "Space geodetic measurement of crustal deformation in central and southern California, 1984\-1992." J. Geophys. Res., 98: 21,677-21,712.

1993: Larsen, S., Agnew, D. C., Hager, B., "Strain accumulation in the Santa Barbara Channel: 1970-1988," J. Geophys. Res., 98: 2119-2133.

1992: Agnew, D. C. "The time-domain behavior of power-law noises." Geophys. Res. Lett., 19: 333-336.

1991: Agnew, D. C., Jones, L. M. "Prediction probabilities from foreshocks." J. Geophys. Res., 96: 11959-11971.

1991: King, N. E., and Agnew, D. C., "How large is the retrograde annual wobble?". Geophys. Res. Lett., 18: 1735-1738.

1989: Rojstaczer, S., Agnew, D. C. "The influence of formation material properties on the response of water levels in wells to earth tides and atmospheric loading." J. Geophys. Res., 94 12,403-12,411.

Contact Information

Duncan Carr Agnew
IGPP 0225
University of California, San Diego
La Jolla, CA 92093-0225

fax: (619) 534-5332
internet: dagnew@ucsd.edu
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Last Revised: 29 November 1996