Publications

Export 7 results:
Sort by: Author [ Title  (Asc)] Type Year
A B C [D] E F G H I J K L M N O P Q R S T U V W X Y Z   [Show ALL]
D
Fialko, Y, Sandwell D, Agnew D, Simons M, Shearer P, Minster B.  2002.  Deformation on nearby faults induced by the 1999 Hector Mine earthquake. Science. 297:1858-1862.   10.1126/science.1074671   AbstractWebsite

Interferometric Synthetic Aperture Radar observations of surface deformation due to the 1999 Hector Mine earthquake reveal motion on several nearby faults of the eastern California shear zone. We document both vertical and horizontal displacements of several millimeters to several centimeters across kilometer-wide zones centered on pre-existing faults. Portions of some faults experienced retrograde (that is, opposite to their long-term geologic slip) motion during or shortly after the earthquake. The observed deformation likely represents elastic response of compliant fault zones to the permanent co-seismic stress changes. The induced fault displacements imply decreases in the effective shear modulus within the kilometer-wide fault zones, indicating that the latter are mechanically distinct from the ambient crustal rocks.

Agnew, DC, Hodgkinson K.  2007.  Designing compact causal digital filters for low-frequency strainmeter data. Bulletin of the Seismological Society of America. 97:91-99.   10.1785/0120060088   AbstractWebsite

For the strainmeter component of the Plate Boundary Observatory, filters are needed to produce low-frequency series (5-minute samples) from the higher-frequency (1 Hz) data generated by the instruments. We present design methods for finding filters that are efficient, causal, and compact. We use standard methods for generating symmetric finite impulse response filters, followed by root finding, selection of roots, and reconstruction of the weights, using procedures that make these processes numerically stable. The final filters show appropriate performance even in the presence of large teleseismic signals, but introduce unavoidable artifacts for strain data from large local earthquakes.

Agnew, DC.  1986.  Detailed Analysis of Tide-Gauge Data - A Case-History. Marine Geodesy. 10:231-255. AbstractWebsite
n/a
Bock, Y, Agnew DC, Fang P, Genrich JF, Hager BH, Herring TA, Hudnut KW, King RW, Larsen S, Minster JB, Stark K, Wdowinski S, Wyatt FK.  1993.  Detection of Crustal Deformation from the Landers Earthquake Sequence Using Continuous Geodetic Measurements. Nature. 361:337-340.   10.1038/361337a0   AbstractWebsite

THE measurement of crustal motions in tectonically active regions is being performed increasingly by the satellite-based Global Positioning System (GPS)1,2, which offers considerable advantages over conventional geodetic techniques3,4. Continuously operating GPS arrays with ground-based receivers spaced tens of kilometres apart have been established in central Japan5,6 and southern California to monitor the spatial and temporal details of crustal deformation. Here we report the first measurements for a major earthquake by a continuously operating GPS network, the Permanent GPS Geodetic Array (PGGA)7-9 in southern California. The Landers (magnitude M(w) of 7.3) and Big Bear (M(w) 6.2) earthquakes of 28 June 1992 were monitored by daily observations. Ten weeks of measurements, centred on the earthquake events, indicate significant coseismic motion at all PGGA sites, significant post-seismic motion at one site for two weeks after the earthquakes, and no significant preseismic motion. These measurements demonstrate the potential of GPS monitoring for precise detection of precursory and aftershock seismic deformation in the near and far field.

Barbour, AJ, Agnew DC.  2012.  Detection of Seismic Signals Using Seismometers and Strainmeters. Bulletin of the Seismological Society of America. 102:2484-2490.   10.1785/0120110298   AbstractWebsite

Using data from borehole and long-base strainmeters and from borehole and surface seismometers, we compare the seismic-wave detection capability of strainmeters and seismometers. We use noise spectra to determine the relative signal-to-noise ratios (SNRs) on different sensors, as a function of the phase velocity and frequency of a signal. For the instruments we analyze, signals with frequencies from 10(-3) to 10 Hz and phase velocities typical of (or higher than) surface and body waves will have lower SNRs on the strainmeters than on broadband seismometers. At frequencies from 0.1 to 10 Hz the borehole (short-period) seismometers have better SNRs than strainmeters for typical phase velocities; at lower frequencies strainmeter data signals would have higher SNRs.

Agnew, DC, Sieh KE.  1978.  Documentary Study of Felt Effects of Great California Earthquake of 1857. Bulletin of the Seismological Society of America. 68:1717-1729. AbstractWebsite
n/a
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.