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Gonzalez-Garcia, JJ, Prawirodirdjo L, Bock Y, Agnew D.  2003.  Guadalupe Island, Mexico as a new constraint for Pacific plate motion. Geophysical Research Letters. 30   10.1029/2003gl017732   AbstractWebsite

[1] We use GPS data collected on Isla de Guadalupe and in northern Baja California, Mexico, to estimate site velocities relative to Pacific plate motion. The velocities of all three geodetic monuments on Guadalupe fit a rigid Pacific plate model with residuals of 1 mm/yr. Using the Guadalupe data and data from five IGS stations on the Pacific plate ( CHAT, KOKB, KWJ1, MKEA, and THTI) we estimate an angular velocity for this plate that is consistent with other recently-published estimates. Our results indicate that Isla de Guadalupe lies on the Pacific plate, and that GPS data collection on the island usefully constrains Pacific plate motion and rigidity.

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Anderson, G, Agnew DC, Johnson HO.  2003.  Salton trough regional deformation estimated from combined trilateration and survey-mode GPS data. Bulletin of the Seismological Society of America. 93:2402-2414.   10.1785/0120030014   AbstractWebsite

The Salton Trough in southeastern California, United States, has one of the highest seismicity and deformation rates in southern California, including 20 earthquakes M 6 or larger since 1892. From 1972 through 1987, the U.S. Geological Survey (USGS) measured a 41-station trilateration network in this region. We remeasured 37 of the USGS baselines using survey-mode Global Positioning System methods from 1995 through 1999. We estimate the Salton Trough deformation field over a nearly 30-year period through combined analysis of baseline length time series from these two datasets. Our primary result is that strain accumulation has been steady over our observation span, at a resolution of about 0.05 mustrain/yr at 95% confidence, with no evidence for significant long-term strain transients despite the occurrence of seven large regional earthquakes during our observation period. Similar to earlier studies, we find that the regional strain field is consistent with 0.5 +/- 0.03 mustrain/yr total engineering shear strain along an axis oriented 311.6degrees +/- 23degrees east of north, approximately parallel to the strike of the major regional faults, the San Andreas and San Jacinto (all uncertainties in the text and tables are standard deviations unless otherwise noted). We also find that (1) the shear strain rate near the San Jacinto fault is at least as high as it is near the San Andreas fault, (2) the areal dilatation near the southeastern Salton Sea is significant, and (3) one station near the southeastern Salton Sea moved anomalously during the period 1987.95-1995.11.

Agnew, DC, Wyatt FK.  2014.  Dynamic strains at regional and teleseismic distances. Bulletin of the Seismological Society of America. 104:1846-1859.   10.1785/0120140007   AbstractWebsite

We develop formulas for the size of dynamic strains caused by seismic waves from an earthquake of given magnitude and distance. These formulas include peak strain, peak dissipated power, and total dissipated energy, and they are applicable at regional and teleseismic distances. The formulas are fits to data from 89 large (6.5 <= M-w <= 9.0) shallow earthquakes, with source distances between 500 and 16,000 km, recorded between 1977 and 2013 by three long-base laser strainmeters at Pinon Flat Observatory in southern California; these strainmeters provide uniquely well-calibrated measurements of tensor strain. The residuals to the fits suggest that strain values can usually be predicted to within a factor of 2. These data also show that the strain tensor can be substantially different from that expected for plane waves: in particular, the extension perpendicular to the back azimuth, which should be zero, is always 20% or more of the extension along that azimuth. How much the strains resemble those for plane waves depends on their path, perhaps because inhomogeneities along different paths produce different amounts of multipathing. The observed strains are systematically 10%-30% larger at nearby laser strainmeter sites in the Salton trough, suggesting local amplification from inhomogeneous crustal structure.