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TitleFault parameters of the Nisqually earthquake determined form moment tensor solutions and the surface deformation from GPS and InSAR
AuthorBustin, A; Hyndman, R DORCID logo; Lambert, AORCID logo; Ristau, J; He, J; Dragert, H; Van der Kooij, M
SourceBulletin of the Seismological Society of America vol. 94, no. 2, 2004 p. 363-376,
Alt SeriesGeological Survey of Canada, Contribution Series 2003031
PublisherSeismological Society of America (SSA)
Mediapaper; on-line; digital
File formatpdf
ProvinceBritish Columbia
NTS82; 92; 93D; 93E; 93L; 102; 103A; 103B; 103C; 103F; 103G; 103H; 103I; 103J; 103K
Areasouthern British Columbia; coastal British Columbia; Pacific Ocean; Washington State; Puget Sound; Oregon; Canada; United States of America
Lat/Long WENS-134.0000 -114.0000 55.0000 40.0000
Lat/Long WENS-134.0000 -114.0000 55.0000 40.0000
Subjectsgeophysics; earthquakes; earthquake studies; earthquake mechanisms; faults; deformation; displacement; satellite imagery; subduction; subsidence; epicentres; moment measures; modelling; downgoing slab; geodesy; satellite geodesy; seismology; fault plane solutions; Nisqually earthquake; Juan de Fuca Plate; Cascadia Subduction Zone; synthetic aperture radar surveys (SAR)
Illustrationssketch maps; focal mechanisms; tables; seismograms; time series; satellite images; interferograms; digital elevation models; profiles; 3-D models; cross-sections; block diagrams
ProgramNSERC Natural Sciences and Engineering Research Council of Canada
ProgramGEOIDE Geomatics for Informed Decisions
Released2004 04 01
AbstractThe magnitude 6.8 Nisqually earthquake occurred on 28 February 2001 at a depth of 50-60 km within the subducting Juan de Fuca plate. The fault parameters are estimated from moment tensor solutions and by comparing the surface displacements from Global Positioning System (GPS) data and from satellite interferometry, with predictions from elastic deformation models. The simple deformation model calculates the coseismic surface displacements caused by an earthquake on an extensional rectangular fault in a uniform half-space. Continuous GPS stations within 200 km of the epicenter resolved horizontal displacements as great as 9 mm (210°) and vertical displacements as great as 13 mm of subsidence near the epicenter. The near-vertical displacements were also determined from a differential interferogram created from synthetic aperture radar (InSAR) data from RADARSAT, the only satellite data available for the event. A maximum vertical subsidence of approximately 20 mm is observed 30 km east of the epicenter. The GPS, InSAR, and moment tensor solutions provide a consistent solution for the rupture parameters of the Nisqually earthquake. The fault has a strike of 180° and a dip of 20° and is centered at 47.10° N and 122.67° W (4 km east and 6 km south of the epicenter) or has a strike of 360° and a dip of 70° and is centered at 47.10° N and 122.69° W (2 km east and 6 km south). The trade-off between fault area and rupture displacement is not resolved by our data, but a good fit is found with the main rupture having an area of 230 km2 and an along-strike length of 23 km and downdip width of 10 km. The rupture area is centered at a depth of 51 km with a scalar moment of 2.0 × 1019 N m and, with the given area, an average rupture displacement of 1.4 m. To refine the interpretation of the GPS and InSAR data, a 3D heterogeneous numerical model was generated having realistic shear moduli structure, a 3D model of the subducting slab, and a spherical Earth. The results are similar to those from the half-space model, but there is significant refinement with a deeper rupture center at 60 km.

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