Strain accumulation in southern California, 1973–1980

Abstract

Frequent surveys of seven trilateration networks in southern California over the interval 1973–1980 suggest that a regional increment in strain may have occurred in 1978–1979. Prior to 1978 and after late 1979 the strain accumulation has been predominantly a uniaxial north‐south compression. This secular trend was interrupted sometime in 1978–1979 by an increment in both north‐south and east‐west extension in five of the seven networks. The onset of this change appears to have occurred first in the networks farthest south. The changes occurred without any unusual seismicity within the networks, but the overall seismicity in southern California was unusually low prior to and has been unusually high since the occurrence. The average principal strain rates for the seven networks in the 1973–1980 interval are 0.17 μstrain/yr north‐south contraction and 0.08 μstrain/yr east‐west extension. Although the observed increment in strain could be related to unidentified systematic error in the measuring system, a careful review of the measurements and comparisons with three other measuring systems reveal no appreciable cumulative systematic error.

Slip rate of the western Garlock fault, at Clark Wash, near Lone Tree Canyon, Mojave Desert, California

“…Geodetic data (Fig. 2D) indicate that the Garlock region is currently dominated by northwest-trending, right-lateral strain rather than by northeasttrending, left-lateral strain (Savage et al, 1981(Savage et al, , 1990(Savage et al, , 2001Gan et al, 2000;Miller et al, 2001;Peltzer et al, 2001). Present-day, northwest-oriented, right-lateral shear has been documented at rates of 9-11 mm/yr north of the Garlock fault (Dixon et al, 2000;Meade and Hager, 2005) and ~7-15 mm/yr south of the Garlock fault (Sauber et al, 1986(Sauber et al, , 1994Meade and Hager, 2005).…”

“…It has been interpreted (1) as a conjugate shear to the San Andreas fault (Hill and Dibblee, 1953) that helps to accommodate convergence at the major restraining bend in the San Andreas fault in southern California (Stuart, 1991), (2) as a transform fault accommodating extension in the Basin and Range (Davis and Burchfi el, 1973), and (3) as a structure accommodating block rotation in the northeastern Mojave (Humphreys and Weldon, 1994;Guest et al, 2003). In contrast to all three geologic models, geodetic data suggest that the region surrounding the Garlock fault is dominated by northwestoriented, right-lateral shear and that very little left-lateral strain is accumulating on the Garlock fault (Savage et al, 1981(Savage et al, , 1990(Savage et al, , 2001Gan et al, 2000;McClusky et al, 2001;Miller et al, 2001;Peltzer et al, 2001).…”

Correlation of Changes in Gravity, Elevation, and Strain in Southern California

“…1), and the results of surveys through 1980 have been reported by Savage et al (2). The strain data that we report derived from the surveys of Savage et al (2) but differ slightly because we analyzed only localized subsets of the lines that make up the Tehachapi and Cajon networks (8). Uncertainties associated with the areal-strain data are approximately 0.3 part per million (ppm) (1 standard deviation), in comparison with observed changes as large as 2 ppm.…”

“…Although temporal anomalies in many of these quantities have been reported (2)(3)(4), the relations between the various anomalies are not well understood because, in general, the measurements that define them lack spatial or temporal coincidence. We present the results from gravity, elevation, and areal-strain surveys near Tejon Pass, California (Fig.…”

“…For applications in ophthalmology, the short penetration depth of CO2 laser radiation (-10 p.m at 10.6 p.m) is advantageous, since a significant local effect can be achieved in ocular tissues without damaging underlying or neighboring structures. Carbon dioxide lasers have been used for scleral dissection, in filtering procedures for glaucoma (1), and as a photocautery to seal fibrovascular fronds and retinal tears at the time of vitrectomy (2). It has been suggested that CO2 laser radiation could be used in a vitrectomy to "vaporize" regions of vitreous (3)(4)(5) and thus avoid the traction on adjacent structures evident when me-11 MARCH 1983 10.…”