Seccia, Danilo
(2012)
Deep geometry of subduction below the Andean
belt of Colombia as revealed by seismic
tomography, [Dissertation thesis], Alma Mater Studiorum Università di Bologna.
Dottorato di ricerca in
Geofisica, 24 Ciclo. DOI 10.6092/unibo/amsdottorato/4290.
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Abstract
In this study new tomographic models of Colombia were calculated. I used the seismicity recorded by
the Colombian seismic network during the period 2006-2009. In this time period, the improvement of
the seismic network yields more stable hypocentral results with respect to older data set and allows to
compute new 3D Vp and Vp/Vs models. The final dataset consists of 10813 P- and 8614 S-arrival
times associated to 1405 earthquakes. Tests with synthetic data and resolution analysis indicate that
velocity models are well constrained in central, western and southwestern Colombia to a depth of 160
km; the resolution is poor in the northern Colombia and close to Venezuela due to a lack of seismic
stations and seismicity.
The tomographic models and the relocated seismicity indicate the existence of E-SE subducting Nazca
lithosphere beneath central and southern Colombia. The North-South changes in Wadati-Benioff zone,
Vp & Vp/Vs pattern and volcanism, show that the downgoing plate is segmented by slab tears E-W
directed, suggesting the presence of three sectors. Earthquakes in the northernmost sector represent
most of the Colombian seimicity and concentrated on 100-170 km depth interval, beneath the Eastern
Cordillera. Here a massive dehydration is inferred, resulting from a delay in the eclogitization of a
thickened oceanic crust in a flat-subduction geometry. In this sector a cluster of intermediate-depth
seismicity (Bucaramanga Nest) is present beneath the elbow of the Eastern Cordillera, interpreted as
the result of massive and highly localized dehydration phenomenon caused by a hyper-hydrous oceanic
crust. The central and southern sectors, although different in Vp pattern show, conversely, a continuous,
steep and more homogeneous Wadati-Benioff zone with overlying volcanic areas. Here a "normalthickened"
oceanic crust is inferred, allowing for a gradual and continuous metamorphic reactions to
take place with depth, enabling the fluid migration towards the mantle wedge.
Abstract
In this study new tomographic models of Colombia were calculated. I used the seismicity recorded by
the Colombian seismic network during the period 2006-2009. In this time period, the improvement of
the seismic network yields more stable hypocentral results with respect to older data set and allows to
compute new 3D Vp and Vp/Vs models. The final dataset consists of 10813 P- and 8614 S-arrival
times associated to 1405 earthquakes. Tests with synthetic data and resolution analysis indicate that
velocity models are well constrained in central, western and southwestern Colombia to a depth of 160
km; the resolution is poor in the northern Colombia and close to Venezuela due to a lack of seismic
stations and seismicity.
The tomographic models and the relocated seismicity indicate the existence of E-SE subducting Nazca
lithosphere beneath central and southern Colombia. The North-South changes in Wadati-Benioff zone,
Vp & Vp/Vs pattern and volcanism, show that the downgoing plate is segmented by slab tears E-W
directed, suggesting the presence of three sectors. Earthquakes in the northernmost sector represent
most of the Colombian seimicity and concentrated on 100-170 km depth interval, beneath the Eastern
Cordillera. Here a massive dehydration is inferred, resulting from a delay in the eclogitization of a
thickened oceanic crust in a flat-subduction geometry. In this sector a cluster of intermediate-depth
seismicity (Bucaramanga Nest) is present beneath the elbow of the Eastern Cordillera, interpreted as
the result of massive and highly localized dehydration phenomenon caused by a hyper-hydrous oceanic
crust. The central and southern sectors, although different in Vp pattern show, conversely, a continuous,
steep and more homogeneous Wadati-Benioff zone with overlying volcanic areas. Here a "normalthickened"
oceanic crust is inferred, allowing for a gradual and continuous metamorphic reactions to
take place with depth, enabling the fluid migration towards the mantle wedge.
Tipologia del documento
Tesi di dottorato
Autore
Seccia, Danilo
Supervisore
Dottorato di ricerca
Scuola di dottorato
Scienze matematiche, fisiche ed astronomiche
Ciclo
24
Coordinatore
Settore disciplinare
Settore concorsuale
Parole chiave
subduction seismic tomography
URN:NBN
DOI
10.6092/unibo/amsdottorato/4290
Data di discussione
28 Marzo 2012
URI
Altri metadati
Tipologia del documento
Tesi di dottorato
Autore
Seccia, Danilo
Supervisore
Dottorato di ricerca
Scuola di dottorato
Scienze matematiche, fisiche ed astronomiche
Ciclo
24
Coordinatore
Settore disciplinare
Settore concorsuale
Parole chiave
subduction seismic tomography
URN:NBN
DOI
10.6092/unibo/amsdottorato/4290
Data di discussione
28 Marzo 2012
URI
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