Tomographic inversion of local earthquake data from the Hengill–Grensdalur central volcano complex

• Main Authors: D. R. Toomey, G. R. Foulger
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1989
• Subjects: Grensdalur; Hengill; Iceland
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.557.534; http://community.dur.ac.uk/g.r.foulger/Offprints/ToomeyFoulger1989.pdf

We have determined the three-dimensional P wave velocity structure within the area of the Hengill-Grensdalur central volcano complex, southwest Iceland, from the tomographic inversion of 2409 P wave arrival times recorded by a local earthquake xperiment. The aperture of the 20-element seismic network utilized in the inversion permitted imaging ofa 5-km-thick rustal volume underlying a 15 x 14 km 2 area. Within this localized volume are located the underpinnings of the active Hengill volcano and fissure swarm, the extinct Grensdalur volcano, and an active high-temperature g othermal field. It was thus expected that the characteristic length scale of heterogeneity would be of the order of a kilometer. In order to image heterogeneous eismic velocity structure at this scale we paid particular attention to the fidelity of the assumed model parameterization, defined as the degree to which the parameterization can reproduce xpected structural heterogeneity. We also discuss the trade-off between the resolution of model parameters and image fidelity, compare results obtained from different parameterizations t illustrate his trade-off, and present: • synoptic means of assessing image resolution that utilizes the off-diagonal information contained within the resolution matrix. The final tomographic image presented here was determined for a parameterization with fidelity that closely matches the geologic heterogeneity observed on the surface. For this parameterization, the resolution of individual parameters i generally low; however, aquantitative analysis of resolution provides an unambiguous a sessment