1) model also fits the data and suggests that the velocity uncertainties should be 3-6 times larger than for the white noise model. We cannot adequately distinguish between these two noise models, nor can we rule out the possibility of a random walk signal at the lowest frequencies; these questions await the analysis of longer time series. In any case, reducing the magnitude of low-frequency colored noise is critical and appears to be best accomplished by building sites with deeply anchored and braced monuments. Otherwise, rate uncertainties estimated from continuous GPS measurements may not be improved significantly compared to those estimated from infrequent campaign-mode measurements.

Abstract. The June 28, 1992 (Mw=7.3) Landers, California, earthquake was the first earthquake to be surveyed by a continuously operating Global Positioning System (GPS) array. The coordinate time series of seven sites are evaluated for station displacements during an interval of 100 days centered on the day of the earthquake. We employ a new spatial filtering technique that removes common-mode errors from the coordinate time series. This approach provides precise estimates of site-specific displacements compared to the cumbersome method of analyzing baselines between pairs of stations. All sites indicate significant coseismic horizontal displacements of 5-65 mm with uncertainties of 1-2 mm. Horizontal displacements are in general agreement with elastic dislocation models, in particular for sites closer to the epicenter. Vertical displacements range from-13 to +7 mm with uncertainties of 2-4 mm. The observed vertical displacements in all cases show 5-10 mm more subsidence than expected from geodetic and seismic/geologic models. Significant postseismic horizontal displacements totaling 6+2 mm (10--20% of the coseismic displacement) are detected at the three sites closest to the epicenter. These displacements are modeled as a short-term exponential relaxation with a decay time of 22+10 days superimposed on a longer-term linear interseismic trend. Scaling the observed coseismic and postseismic displacements at one of the sites with the distance to the epicenter provides a measure of site strain, which agrees well with the direction and magnitude determined from more precise laser strain meter data. The time series do not show any detectable preseismic displacements.

No abstract

No abstract

It has long been recognized that New Orleans is subsiding and is therefore susceptible to catastrophic flooding. Here we present a new subsidence map for the city, generated from space-based synthetic-aperture radar measurements, which reveals that parts of New Orleans underwent rapid subsidence in the three years before Hurricane Katrina struck in August 2005. One such area is next to the Mississippi River-Gulf Outlet (MRGO) canal, where levees failed during the peak storm surge: the map indicates that this weakness could be explained by subsidence of a metre or more since their construction.

A network of 11 continuous GPS stations was constructed in Israel between 1996 and 2001 to monitor current crustal movements across the Dead Sea Fault (DSF). Analysis of the GPS measurements with respect to the ITRF2000 Reference Frame yields time series of daily site positions containing both secular and seasonal variations. Horizontal secular variations (station velocities) are evaluated with respect to the main tectonic element in the region, the DSF. We use six velocity vectors west of the DSF to define the ITRF2000 pole of the Sinai sub‐plate, and rotate the velocity field for all stations into the Sinai reference frame (SRF). The velocity vectors reveal that (1) relative station movements are less than 4 mm/yr; (2) the nine stations located west of the DSF show no statistically significant motion with respect to the SRF; and (3) the two stations located in the Golan Heights (KATZ and ELRO) and a station in Damascus, Syria (UDMC) show 1.7–2.8 mm/yr northward motion with respect to Sinai, indicating a left‐lateral motion along the DSF. Using locked‐fault models, we estimate the current slip rate across the DSF as 3.3 ± 0.4 mm/yr. If we exclude the northern sites (ELRO and UDMC), which are located adjacent to the compressional jog of Mount Hermon, our estimate increases to 3.7 ± 0.4 mm/yr. The calculated ITRF2000 Sinai, Eurasia, and Nubia poles and a published pole for Arabia allow us to calculate the current relative plate motion of Sinai‐Arabia and Sinai‐Nubia.

No abstract

No abstract