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Anderson, JG, Rockwell TK, Agnew DC.  1989.  Past and possible future earthquakes of significance to the San Diego region. Earthquake Spectra. 5:299-335. Abstract
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Astiz, L, Shearer PM, Agnew DC.  2000.  Precise relocations and stress change calculations for the upland earthquake sequence in southern California. Journal of Geophysical Research-Solid Earth. 105:2937-2953.   10.1029/1999jb900336   AbstractWebsite

We relocate earthquakes that occurred near the 1988 (M-L = 4.7) and the 1990 (M-L = 5.5) Upland, California, earthquakes to map the fault geometry of the poorly defined San Jose fault and to test the static:Stress triggering hypothesis for this sequence. We adopt the L1 norm, waveform cross-correlation method of Shearer [1997] to obtain precise relocations for 1573 events: between 1981 and 1997 in the Upland area. To limit computation time, we only perform waveform cross correlation on 60 of the nearest neighbors of leach relocated event. Our final relocations show two linear features. The first is imaged,by the locations of the initial month of aftershocks of the 1988 Upland earthquake, which delineate a fault with a,dip angle of similar to 45 degrees between 7 and 9 km depth, consistent with the mainshock focal mechanism. The second linear feature is a plane, dipping at about 74 degrees from 2 to 9 km depth, which is illuminated by both the 1988:and 1990 Upland sequences, in agreement with the inferred location of the San Jose fault at depth. However, below 9 km the event locations become more diffuse, giving rise to two different interpretations of the fate of the San Jose fault at depth. One possibility is that the fault shallows at depth, consistent with our relocations: but not with the focal mechanism of a M-L = 4.7 deep aftershock. Alternatively, the. fault may be offset at depth by the more shallow dipping fault strand broken during the 1988 earthquake, Using these inferred fault geometries, we compute stress changes resulting from slip during the mainshocks to test whether the relocated aftershocks are consistent with the:hypothesis that more aftershocks occur where the change in static Coulomb failure stress is positive (on faults optimally oriented for failure). This requires an extension of previous models of changes in the failure stress to three dimensions and arbitrary fault orientation. We find that patterns of change in Coulomb failure stress differ little between the different fault geometries: all are nearly symmetric about the fault and so do not match the aftershock distribution, in which most of the off-fault events occur to one side of the fault plane.

Agnew, DC, Jones LM.  1991.  Prediction Probabilities from Foreshocks. Journal of Geophysical Research-Solid Earth and Planets. 96:11959-11971.   10.1029/91jb00191   AbstractWebsite

When any earthquake occurs, the possibility that it might be a foreshock increases the probability that a larger earthquake will occur nearby within the next few days. Clearly, the probability of a very large earthquake ought to be higher if the candidate foreshock were on or near a fault capable of producing that very large mainshock, especially if the fault is towards the end of its seismic cycle. We derive an expression for the probability of a major earthquake characteristic to a particular fault segment, given the occurrence of a potential foreshock near the fault. To evaluate this expression, we need: (1) the rate of background seismic activity in the area, (2) the long-term probability of a large earthquake on the fault, and (3) the rate at which foreshocks precede large earthquakes, as a function of time, magnitude, and spatial location. For this last function we assume the average properties of foreshocks to moderate earthquakes in California: (1) the rate of mainshock occurrence after foreshocks decays roughly as t-1, so that most foreshocks are within three days of their mainshock, (2) foreshocks and mainshocks occur within 10 km of each other, and (3) the fraction of mainshocks with foreshocks increases linearly as the magnitude threshold for foreshocks decreases, with 50% of the mainshocks having foreshocks with magnitudes within three units of the mainshock magnitude (within three days). We apply our results to the San Andreas, Hayward, San Jacinto, and Imperial faults, using the probabilities of large earthquakes from the report of the Working Group on California Earthquake Probabilities (1988). The magnitude of candidate event required to produce a 1% probability of a large earthquake on the San Andreas fault within three days ranges from a high of 5.3 for the segment in San Gorgonio Pass to a low of 3.6 for the Carrizo Plain.

Johnson, HO, Agnew DC, Wyatt FK.  1994.  Present-Day Crustal Deformation in Southern California. Journal of Geophysical Research-Solid Earth. 99:23951-23974.   10.1029/94jb01902   AbstractWebsite

The effects of laterally homogeneous mantle electrical conductivity have been included in steady. Using an extensive set of precise geodetic measurements, we have developed a detailed picture of present-day deformation rates in southern California. This large set of measurements, amounting to nearly 2000 repeated distance measurements over the period 1973 to 1991, comes from the U.S. Geological Survey's Geodolite trilateration program, involving their combined Anza, Joshua Tree, and Salton networks. Building on previous results from these data, we are able to present the deformation field as estimates of the rate of horizontal strain accumulation in small four-station subnetworks of the overall 89-station network.; Using this technique, the spatial details of the 18-year average strain rate field can be determined. By correlating these spatial details with the tectonics of the region we are able to understand better how deformation is partitioned across this highly complex margin between the Pacific and North American tectonic plates. Some of the more interesting findings of this study are that (1) the vast majority of strain rate estimates show a pattern of nearly pure shear as would be expected in a transcurrent environment, (2) the fastest accumulation of surface strain in southern California is along the San Jacinto Fault west of the Salton Sea, not along the San Andreas Fault, (3) strain accumulation rate along the length of the San Jacinto Fault increases toward the southeast as the fault enters the Imperial Valley, (4) a large area near the southern end of the Salton Sea, where the San Andreas Fault meets the Brawley Seismic Zone, is undergoing areal dilatation, which is in part consistent with the formation of crust at a spreading center, and (5) deformation at the transition zone between the San Andreas Fault and the Eastern California Shear Zone also appears to be the result of crustal spreading.

Agnew, DC, Berger J, Farrell WE, Gilbert JF, Masters G, Miller D.  1986.  Project IDA: a decade in review. EOS Trans. AGU. 67:203-212. Abstract
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