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 experiment. The aperture
of the 20-element seismic network utilized in the inversion permitted
imaging of a 5-km-thick crustal volume underlying a 15-14 km2 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 geothermal 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
seismic 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 expected structureal
heterogeneity. We also discuss the trade-off between the resolution
of model parameters and image fidelity, compare results obtained
from different parameterizations to illustrate this trade-off, and
present a synoptic means of assesing 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 is generally low; however, a quantitative analysis of
resolution provides an unambiguous assessment of well-resolved volumes.
Within the better resolved regions of the model the averaging volumes
are 1-2 km and 2-4 km in vertical and horizontal extent, respectively.
Results of tomographic inversion image three distinct bodies of anomalously
high velocity, two of these extend from near the surface to a depth
of about 3 km. These high-velocity volumes are located directly beneath
the surface expressions of the extinct Grensdalur volcano and the
extinct Husmuli basalt shield. The third high-velocity structure
occurs in the depth range of 3-4 km but does not extend to the surface.
These three high-velocity bodies are interpreted to be solidified
magmatic intrusions. Relatively low velocities underlay limited portions
of the trace of the present accretionary axis and a low-velocity
body is imaged in the roots of the active Hengill volcano. The volume
of lower velocities located beneath the surface expression of the
Hengill volcano is interpreted to be a region of partial melt.
%0 Journal Article
%1 toomey_foulger:1989
%A Toomey, D. R.
%A Foulger, G. R.
%D 1989
%J Journal of Geophysical Research
%K geophysics seismology
%N B12
%P 17497--17510
%R 10.1029/JB094iB12p17497
%T Tomographic inversion of local earthquake data from the Hengill-Grensdalur
central volcano complex, Iceland
%U http://dx.doi.org/10.1029/JB094iB12p17497
%V 94
%X 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 experiment. The aperture
of the 20-element seismic network utilized in the inversion permitted
imaging of a 5-km-thick crustal volume underlying a 15-14 km2 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 geothermal 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
seismic 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 expected structureal
heterogeneity. We also discuss the trade-off between the resolution
of model parameters and image fidelity, compare results obtained
from different parameterizations to illustrate this trade-off, and
present a synoptic means of assesing 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 is generally low; however, a quantitative analysis of
resolution provides an unambiguous assessment of well-resolved volumes.
Within the better resolved regions of the model the averaging volumes
are 1-2 km and 2-4 km in vertical and horizontal extent, respectively.
Results of tomographic inversion image three distinct bodies of anomalously
high velocity, two of these extend from near the surface to a depth
of about 3 km. These high-velocity volumes are located directly beneath
the surface expressions of the extinct Grensdalur volcano and the
extinct Husmuli basalt shield. The third high-velocity structure
occurs in the depth range of 3-4 km but does not extend to the surface.
These three high-velocity bodies are interpreted to be solidified
magmatic intrusions. Relatively low velocities underlay limited portions
of the trace of the present accretionary axis and a low-velocity
body is imaged in the roots of the active Hengill volcano. The volume
of lower velocities located beneath the surface expression of the
Hengill volcano is interpreted to be a region of partial melt.
@article{toomey_foulger:1989,
abstract = {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 experiment. The aperture
of the 20-element seismic network utilized in the inversion permitted
imaging of a 5-km-thick crustal volume underlying a 15-14 km2 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 geothermal 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
seismic 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 expected structureal
heterogeneity. We also discuss the trade-off between the resolution
of model parameters and image fidelity, compare results obtained
from different parameterizations to illustrate this trade-off, and
present a synoptic means of assesing 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 is generally low; however, a quantitative analysis of
resolution provides an unambiguous assessment of well-resolved volumes.
Within the better resolved regions of the model the averaging volumes
are 1-2 km and 2-4 km in vertical and horizontal extent, respectively.
Results of tomographic inversion image three distinct bodies of anomalously
high velocity, two of these extend from near the surface to a depth
of about 3 km. These high-velocity volumes are located directly beneath
the surface expressions of the extinct Grensdalur volcano and the
extinct Husmuli basalt shield. The third high-velocity structure
occurs in the depth range of 3-4 km but does not extend to the surface.
These three high-velocity bodies are interpreted to be solidified
magmatic intrusions. Relatively low velocities underlay limited portions
of the trace of the present accretionary axis and a low-velocity
body is imaged in the roots of the active Hengill volcano. The volume
of lower velocities located beneath the surface expression of the
Hengill volcano is interpreted to be a region of partial melt.},
added-at = {2012-09-01T13:08:21.000+0200},
author = {Toomey, D. R. and Foulger, G. R.},
biburl = {https://www.bibsonomy.org/bibtex/226a574dbbd337915ef724cd4065bf480/nilsma},
doi = {10.1029/JB094iB12p17497},
interhash = {500353e61c678fb62cea1ccdbeb8ac5f},
intrahash = {26a574dbbd337915ef724cd4065bf480},
issn = {0148-0227},
journal = {Journal of Geophysical Research},
keywords = {geophysics seismology},
month = dec,
number = {B12},
pages = {17497--17510},
timestamp = {2021-02-09T13:26:58.000+0100},
title = {Tomographic inversion of local earthquake data from the Hengill-Grensdalur
central volcano complex, Iceland},
url = {http://dx.doi.org/10.1029/JB094iB12p17497},
volume = 94,
year = 1989
}