Geology topics

James Foster

Publications and source records attributed to James Foster.

4 recordsLinked to original sources

USGS2013

The utility of atmospheric analyses for the mitigation of artifacts in InSAR

The numerical weather models (NWMs) developed by the meteorological community are able to provide accurate analyses of the current state of the atmosphere in addition to the predictions of the future state. To date, most attempts to apply the NWMs to estimate the refractivity of the atmosphere at the time of satellite synthetic aperture radar (SAR) data acquisitions have relied on predictive models. We test the hypothesis that performing a final assimilative routine, ingesting all available meteorological observations for the times of SAR acquisitions, and generating customized analyses of the atmosphere at those times will better mitigate atmospheric artifacts in differential interferograms. We find that, for our study area around Mount St. Helens (Amboy, Washington, USA), this approach is unable to model the refractive changes and provides no mean benefit for interferogram analysis. The performance is improved slightly by ingesting atmospheric delay estimates derived from the limited local GPS network; however, the addition of water vapor products from the GOES satellites reduces the quality of the corrections. We interpret our results to indicate that, even with this advanced approach, NWMs are not a reliable mitigation technique for regions such as Mount St. Helens with highly variable moisture fields and complex topography and atmospheric dynamics. It is possible, however, that the addition of more spatially dense meteorological data to constrain the analyses might significantly improve the performance of weather modeling of atmospheric artifacts in satellite radar interferograms.

Journal of Geophysical Research B: Solid Earth↗

USGS2011

Slow slip event at Kilauea Volcano

Early in the morning of 1 February 2010 (UTC; early afternoon 31 January 2010 local time), continuous Global Positioning System (GPS) and tilt instruments detected a slow slip event (SSE) on the south flank of Kilauea volcano, Hawaii. The SSE lasted at least 36 hours and resulted in a maximum of about 3 centimeters of seaward displacement. About 10 hours after the start of the slip, a flurry of small earthquakes began (Figure 1) in an area of the south flank recognized as having been seismically active during past SSEs [Wolfe et al., 2007], suggesting that the February earthquakes were triggered by stress associated with slip [Segall et al., 2006].

Hawai'i↗

USGS2008

Magmatically triggered slow slip at Kilauea Volcano, Hawaii

We demonstrate that a recent dike intrusion probably triggered a slow fault-slip event (SSE) on Kilauea volcano's mobile south flank. Our analysis combined models of Advanced Land Observing Satellite interferometric dike-intrusion displacement maps with continuous Global Positioning System (GPS) displacement vectors to show that deformation nearly identical to four previous SSEs at Kilauea occurred at far-field sites shortly after the intrusion. We model stress changes because of both secular deformation and the intrusion and find that both would increase the Coulomb failure stress on possible SSE slip surfaces by roughly the same amount. These results, in concert with the observation that none of the previous SSEs at Kilauea was directly preceded by intrusions but rather occurred during times of normal background deformation, suggest that both extrinsic (intrusion-triggering) and intrinsic (secular fault creep) fault processes can lead to SSEs.

Hawaii↗

USGS2005

Global Positioning System measurements on the island of Hawai`i: 1997 through 2004

This report summarizes GPS data and observations collected between 1997 and 2004 on the island of Hawai‘i with static surveying and continuously recording instruments. On Kīlauea, the long-term deformation field is dominated by steady southeastern velocities of more than 6 cm/year and uplift of about 2 cm/yr at stations on the south flank (with respect to a fixed Pacific Plate). Superimposed on this steady signal are transient displacements associated with magmatic intrusions, earthquakes, and aseismic slip events. The largest of these was the January 30, 1997 dike intrusion and eruption. GPS instruments near Kīlauea’s summit also record numerous additional short-term fluctuations associated with variations in magma reservoir pressure and geometry. From mid-1997 through 2001, the dominant signal at the summit was deflationary, with maximum subsidence of ~5 cm/yr south of Kīlauea caldera. However, inflation of the magma system was observed from late 2001 to May 2002, and from mid-2003 through 2004. The east rift zone eruption continued at the Pu‘u ‘O‘o vent during the entire period of this report. Mauna Loa Volcano, which most recently erupted in 1984, showed low rates of contraction across the summit caldera and southeasterly motion of the southeast flank from 1997 until May 2002. Reinflation started abruptly in May 2002. Inflation contin ued through 2004, but at highly variable rates. Extension rates on a baseline across the summit caldera slowed in October 2002 and increased again starting in mid-2003. The most dramatic change during the inflation period, however, was a significant increase in extension rate on longer baselines, from the northwest to southeast flanks, in July 2004. GPS measurements on Hualalai volcano show no significant motion relative to the Pacific Plate.

Hawai'i↗