Geology topics

J. Svarc

Publications and source records attributed to J. Svarc.

4 recordsLinked to original sources

USGS2008

Dislocation models of interseismic deformation in the western United States

The GPS-derived crustal velocity field of the western United States is used to construct dislocation models in a viscoelastic medium of interseismic crustal deformation. The interseismic velocity field is constrained by 1052 GPS velocity vectors spanning the ???2500-km-long plate boundary zone adjacent to the San Andreas fault and Cascadia subduction zone and extending ???1000 km into the plate interior. The GPS data set is compiled from U.S. Geological Survey campaign data, Plate Boundary Observatory data, and the Western U.S. Cordillera velocity field of Bennett et al. (1999). In the context of viscoelastic cycle models of postearthquake deformation, the interseismic velocity field is modeled with a combination of earthquake sources on ???100 known faults plus broadly distributed sources. Models that best explain the observed interseismic velocity field include the contributions of viscoelastic relaxation from faulting near the major plate margins, viscoelastic relaxation from distributed faulting in the plate interior, as well as lateral variations in depth-averaged rigidity in the elastic lithosphere. Resulting rigidity variations are consistent with reduced effective elastic plate thickness in a zone a few tens of kilometers wide surrounding the San Andreas fault (SAF) system. Primary deformation characteristics are captured along the entire SAF system, Eastern California Shear Zone, Walker Lane, the Mendocino triple junction, the Cascadia margin, and the plate interior up to ???1000 km from the major plate boundaries.

Journal of Geophysical Research B: Solid Earth↗

USGS1999

Present-day deformation across the Basin and Range Province, western United States

The distribution of deformation within the Basin and Range province was determined from 1992, 1996, and 1998 surveys of a dense, 800-kilometer- aperture, Global Positioning System network, Internal deformation generally follows the pattern of Holocene fault distribution and is concentrated near the western extremity of the province, with lesser amounts focused near the eastern boundary. Little net deformation occurs across the central 500 kilometers of the network in western Utah and eastern Nevada. Concentration of deformation adjacent to the rigid Sierra Nevada block indicates that external plate-driving forces play an important role in driving deformation, modulating the extensional stress field generated by internal buoyancy forces that are due to lateral density gradients and topography near the province boundaries.

Science↗

USGS1997

Postseismic strain following the 1989 Loma Prieta earthquake from GPS and leveling measurements

Postseismic deformation in the 5 years following the 1989 Loma Prieta earthquake has been measured with the Global Positioning System and precise leveling. Postearthquake velocities at distances greater than ∼20 km from the coseismic rupture are not significantly different from those observed in the 20 years prior to the earthquake. However, velocities at stations within ∼20 km of the rupture exceed preearthquake rates and exhibit unanticipated contraction normal to the strike of the San Andreas fault system. A combination of forward modeling and nonlinear optimization suggests that the observed postseismic deformations were caused by aseismic oblique reverse slip averaging 2.9 cm/yr on the San Andreas fault and/or the Loma Prieta rupture zone and 2.4 cm/yr reverse slip along a buried fault within the Foothills thrust belt. The best fitting sources of postseismic deformation are all located at depths of less than 15 km. We find no evidence for accelerated flow or shear below the Loma Prieta rupture in the first 5 years following the earthquake. The inferred postseismic slip is likely to have been caused by the coseismic stress change updip of the 1989 rupture.

Journal of Geophysical Research B: Solid Earth↗

USGS1997

Inflation of Long Valley caldera, California, Basin and Range strain, and possible Mono Craters dike opening from 1990-94 GPS surveys

Five years of annual Global Positioning System (GPS) surveys of a network centered on Long Valley, California, constrain displacement rates for these stations relative to a central station in the network. These observations are consistent with recent models of resurgent dome inflation in Long Valley (Langbein et al., 1995) and have sufficient signal to detect the presence of Basin and Range strain in the Long Valley region. The data also allow for the possibility of dike inflation beneath the Mono Craters; dike intrusion is consistent with the Mono Craters' recent geologic history of ash eruptions, with seismic tomography, leveling data, and geologic studies of these volcanic domes and flows.

Geophysical Research Letters↗