Characterization of site-specific GPS errors using a short-baseline network of braced monuments at Yucca Mountain, southern Nevada

We use a short-baseline network of braced monuments to investigate site-specific GPS effects. The network has baseline lengths of ∼10, 100, and 1000 m. Baseline time series have root mean square (RMS) residuals, about a model for the seasonal cycle, of 0.05–0.24 mm for the horizontal components and 0.20–0.72 mm for the radial. Seasonal cycles occur, with amplitudes of 0.04–0.60 mm, even for the horizontal components and even for the shortest baselines. For many time series these lag seasonal cycles in local temperature measurements by 23–43 days. This could suggest that they are related to bedrock thermal expansion. Both shorter-period signals and seasonal cycles for shorter baselines to REP2, the one short-braced monument in our network, are correlated with temperature, with no lag time. Differences between REP2 and the other stations, which are deep-braced, should reflect processes occurring in the upper few meters of the ground. These correlations may be related to thermal expansion of these upper ground layers, and/or thermal expansion of the monuments themselves. Even over these short distances we see a systematic increase in RMS values with increasing baseline length. This, and the low RMS levels, suggests that site-specific effects are unlikely to be the limiting factor in the use of similar GPS sites for geophysical investigations

Crustal loading near Great Salt Lake, Utah

Two sites of the BARGEN GPS network are located ∼30 km south of Great Salt Lake (GSL). Lake-level records since mid-1996 indicate seasonal water elevation variations of ∼0.3 m amplitude superimposed on a roughly “decadal” feature of amplitude ∼0.6 m. Using an elastic Green's function and a simplified load geometry for GSL, we calculate that these variations translate into radial crustal loading signals of ±0.5 mm (seasonal) and ±1 mm (decadal). The horizontal loading signals are a factor of ∼2 smaller. Despite the small size of the expected loading signals, we conclude that we can observe them using GPS time series for the coordinates of these two sites. The observed amplitudes of the variations agree with the predicted decadal variations to <0.5 mm. The observed annual variations, however, disagree; this difference may be caused by some combination of local precipitation-induced site motion, unmodeled loading from other nearby sources, errors in the GSL model, and atmospheric errors

Global Positioning System constraints on fault slip rates in the Death Valley region, California and Nevada

We estimated horizontal velocities at 15 locations in the vicinity of Yucca Mountain, Nevada, from Global Positioning System surveys conducted between 1991 and 1996. We used these velocity estimates to infer slip rates on two major Quaternary faults within the eastern California shear zone (ECSZ), the Hunter Mountain and Death Valley faults. The sum of slip rates across the two faults is well determined at 5 ± 1 mm/yr (1-σ). Between 3 to 5 mm/yr of this motion appears to be accommodated along the Death Valley fault, implying 30–50 m of strain accumulation over the next 10,000 yr. If so, there is potential for 5 to 10 M_(w) 6.5–7.5 earthquakes during this period, a finding consistent with paleoseismological studies of the fault zone. Yucca Mountain, which lies 50 km east of the ECSZ, is the proposed location for the disposal of high-level nuclear waste in the United States

Radio-Size Estimates of SN 1993J

Supernova 1993J (SN 1993J) in M81, now classified as Type IIb, is a strongly emitting radio supernova whose size can be resolved and whose growth can be monitored with the technique of very long baseline interferometry (VLBI). The results could provide important information about the circumstellar matter and the degree of asymmetry of the explosion. For several models of the emission of the radio supernova, we report estimates of its angular sizes 29 and 36 days after explosion at the wavelengths of 3.6 and 1.3 cm, respectively. These results, which correspond to our first epochs in an ongoing effort to determine the supernova structure and its growth, slightly favor an optically thick uniform disk model, given the recently derived Cepheid distance to M81 and the estimated maximum supernova expansion speed. Further VLBI observations, combined with the expansion-speed data, may yield an independent estimate of the distance to M81.This work was supported in part by the Spanish DGICYT grant PB89-009 and in part by NSF grant AST 9303527. We thank Kurt Weiler for a very careful review of this paper and N. Renzetti and P. Wolken for their extraordinary efforts in arranging for our use of the DSN antenn

Subcontinental-scale crustal velocity changes along the Pacific–North America plate boundary

Transient tectonic deformation has long been noted within approx100 km of plate boundary fault zones and within active volcanic regions, but it is unknown whether transient motions also occur at larger scales within plates. Relatively localized transients are known to occur as both seismic and episodic aseismic events, and are generally ascribed to motions of magma bodies, aseismic creep on faults, or elastic or viscoelastic effects associated with earthquakes. However, triggering phenomena and systematic patterns of seismic strain release at subcontinental (~1,000 km) scale along diffuse plate boundaries have long suggested that energy transfer occurs at larger scale. Such transfer appears to occur by the interaction of stresses induced by surface wave propagation and magma or groundwater in the crust, or from large-scale stress diffusion within the oceanic mantle in the decades following clusters of great earthquakes. Here we report geodetic evidence for a coherent, subcontinental-scale change in tectonic velocity along a diffuse ~1,000-km-wide deformation zone. Our observations are derived from continuous GPS (Global Positioning System) data collected over the past decade across the Basin and Range province, which absorbs approximately 25 per cent of Pacific–North America relative plate motion. The observed changes in site velocity define a sharp boundary near the centre of the province oriented roughly parallel to the north-northwest relative plate motion vector. We show that sites to the west of this boundary slowed relative to sites east of it by ~1 mm yr^(-1) starting in late 1999

Efectos a corto y largo plazo de la administración de calcitonina y calcio sobre el calcio, magnesio y fósforo inorgánico en sangre en la osteoporosis posmenopáusica

This paper studies the effects of the administration of calcitonin (CT) and Ca on post menopausal osteoporosis, immediately (short-term) and after three months (long-term) of treatment, on total and ionic calcium (Ca), magnesium (Mg), inorganic phosphorus (Pi), calcitonin (CT) and parathyroid hormone (PTH) in plasma. The short-term results show a decrease in total and ionic Ca and Pi four hours after the beginning of the treatment; at seven hours, only Pi varies. A decrease in the total and ionic Ca was observed after three months of CT treatment (long-term effects). No hormonal (PTH and CT) variations were found either in the short or the long-term. However, the PTH/CT ratio decreased significantly during the experiment and this may be an important factor in explaining the long-term Ca variations