Geology topics

Tim J. Wright

Publications and source records attributed to Tim J. Wright.

4 recordsLinked to original sources

USGS2023

Rapid pre-explosion increase in dome extrusion rate at La Soufrière, St. Vincent quantified from synthetic aperture radar backscatter

The extrusion rate of a lava dome is a critical parameter for monitoring silicic eruptions and forecasting their development. Satellite radar backscatter can provide unique information about dome growth during a volcanic eruption when other datasets (e.g., optical, thermal, ground-based measurements, etc.) may be limited. Here, we present an approach for estimating volcanic topography from individual backscatter images. Using data from multiple SAR sensors we apply the method to the dome growth during the 2021 eruption at La Soufrière, St. Vincent. We measure an average extrusion rate of 1.8 m 3 s −1 between December 2020 and March 2021 before an acceleration in extrusion rate to 17.5 m 3 s −1 in the 2 days prior to the explosive eruption on 9 April 2021. We estimate a final dome volume of 19.4 million m 3 , extrapolated from the SAR sensors, with approximately 15% of the total extruded volume emplaced in the last 2 days. A possible explanation for the acceleration in extrusion rate could be the combined emptying of a conduit and reservoir of older material before the ascent of gas-rich magma in April 2021.

La Soufrière, Saint Vincent↗

USGS2019

Illuminating subduction zone rheological properties in the wake of a giant earthquake

Deformation associated with plate convergence at subduction zones is accommodated by a complex system involving fault slip and viscoelastic flow. These processes have proven difficult to disentangle. The 2010 M w 8.8 Maule earthquake occurred close to the Chilean coast within a dense network of continuously recording Global Positioning System stations, which provide a comprehensive history of surface strain. We use these data to assemble a detailed picture of a structurally controlled megathrust fault frictional patchwork and the three-dimensional rheological and time-dependent viscosity structure of the lower crust and upper mantle, all of which control the relative importance of afterslip and viscoelastic relaxation during postseismic deformation. These results enhance our understanding of subduction dynamics including the interplay of localized and distributed deformation during the subduction zone earthquake cycle.

Science Advances↗

USGS2004

Constraining the slip distribution and fault geometry of the M w 7.9, 3 November 2002, Denali fault earthquake with Interferometric Synthetic Aperture Radar and Global Positioning System data

The M w 7.9, Denali fault earthquake ( DFE ) is the largest continental strike-slip earthquake to occur since the development of Interferometric Synthetic Aperture Radar (In SAR ). We use five interferograms, constructed using radar images from the Canadian Radarsat-1 satellite, to map the surface deformation at the western end of the fault rupture. Additional geodetic data are provided by displacements observed at 40 campaign and continuous Global Positioning System ( GPS ) sites. We use the data to determine the geometry of the Susitna Glacier fault, thrusting on which initiated the DFE , and to determine a slip model for the entire event that is consistent with both the In SAR and GPS data. We find there was an average of 7.3 ± 0.4 m slip on the Susitna Glacier fault, between 1 and 9.5 km depth on a 29 km long fault that dips north at 41 ± 0.7° and has a surface projection close to the mapped rupture. On the Denali fault, a simple model with large slip patches finds a maximum of 8.7 ± 0.7 m of slip between the surface and 14.3 ± 0.2 km depth. A more complex distributed slip model finds a peak of 12.5 ± 0.8 m in the upper 4 km, significantly higher than the observed surface slip. We estimate a geodetic moment of 670 ± 10 × 10 18 N m ( M w 7.9), consistent with seismic estimates. Lack of preseismic data resulted in an absence of In SAR coverage for the eastern half of the DFE rupture. A dedicated geodetic In SAR mission could obviate coverage problems in the future.

Bulletin of the Seismological Society of America↗

USGS2003

Source model for the Mw 6.7, 23 October 2002, Nenana Mountain earthquake (Alaska) from InSAR

The 23 October 2002 Nenana Mountain Earthquake (M w ∼ 6.7) occurred on the Denali Fault (Alaska), to the west of the M w ∼ 7.9 Denali Earthquake that ruptured the same fault 11 days later. We used 6 interferograms, constructed using radar images from the Canadian Radarsat-1 and European ERS-2 satellites, to determine the coseismic surface deformation and a source model. Data were acquired on ascending and descending satellite passes, with incidence angles between 23 and 45 degrees, and time intervals of 72 days or less. Modeling the event as dislocations in an elastic half space suggests that there was nearly 0.9 m of right-lateral strike-slip motion at depth, on a near-vertical fault, and that the maximum slip in the top 4 km of crust was less than 0.2 m. The Nenana Mountain Earthquake increased the Coulomb stress at the future hypocenter of the 3 November 2002, Denali Earthquake by 30–60 kPa.

Alaska↗