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Titel |
Seismic structure of the Carboneras fault region, SE Spain from ambient noise analysis and laboratory measurements |
VerfasserIn |
Christina Kelly, Andreas Rietbrock, Daniel Faulkner, Nicholas Harmon |
Konferenz |
EGU General Assembly 2013
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 15 (2013) |
Datensatznummer |
250076750
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Zusammenfassung |
The Carboneras fault in southeastern Spain is a left-lateral strike-slip fault forming part
of the trans-Alboran shear zone. Detailed mapping has revealed a complex fault
structure, including a number of high-strain fault gouge bands. The geology of the
surrounding area varies widely, with metamorphic basement rocks, sedimentary
basins, and areas of igneous intrusion within a 50 km2 area. Preliminary results are
presented, building towards an integrated geological and seismological structure of the
region.
A temporary network of 24 seismometers, including 10 regional broadband 3T, and
arrays of ESPDs/6TDs across sections of the fault was deployed in 2010-2011.
Ambient seismic noise recorded on this network is used to image the subsurface
in the area. Cross-correlations of ambient seismic noise are calculated between
stations and approximate to the Green’s functions between each station-station
pair. Short-period surface wave dispersion curves are estimated for each raypath
from the Green’s functions using frequency time analysis. The suite of determined
dispersion curves are then used to obtain velocity maps for various periods, relating to
different depths. The data are then also used to obtain 1D to 3D velocity-depth models.
Sensitivity kernals show that depths down to 8-10km are sampled. An average
1D velocity model over the area, to fit the average dispersion curve, suggests a
shallow surface layer of 0.5 km with velocities of 1.5 kms-1 or less. This model
suggests a velocity jump to 2.5 kms-1 below this until 2 km depth, followed by a
velocity of 3.3 kms-1 until  7km depth and a velocity of  3.95 kms-1 below
this.
The observed 3D velocity structure correlates well with mapped surface geology of the
area. Metamorphic basement rocks and areas dominated by igneous intrusion are observed as
relatively high-velocity areas. Major sedimentary basins in the area appear to exhibit lower
velocities. Different rock types correspond to lateral changes in velocity of the order of 1
kms-1.
Seismic velocities of rocks in the Carboneras fault area are further investigated
through laboratory experiments to provide a higher resolution view of the fault
structure. Samples used are from the Carboneras micaschist, from which the fault
gouge is derived. Ultrasonic P and S waves are pulsed through the samples. The
signals from uniaxial and triaxial experiments are analysed. The effects of differential
stress and and confining pressure on velocity and attenuation properties are studied.
Velocities determined from S-wave laboratory experiments at various confining
pressures are compared to those obtained at various depths from Green’s function
analysis. |
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