Publication: Descomposición fractal en subdominios morfotectónicos del mapa de lineamientos morfológicos en la isla Decepción
(Shetland del Sur, Antártida)
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2007
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Instituto Geológico y Minero de España
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Abstract
La isla Decepción (Archipiélago de las Shetland del Sur, Antártida) es una de las áreas sismo-volcánicas más activas de la Antártida. El último y reciente período eruptivo en 1967, 1969, 1970, y la elevada frecuencia de los terremotos de baja magnitud así lo evidencian. La isla se encuentra en un marco geodinámico complejo que establece SO-NE y NNO-SSE como direcciones de control tectónico más relevantes; sin embargo, se desconoce como afecta la compleja organización geométrica de las redes de fracturas y fallas en la distribución del volcanismo y la sismicidad en la isla. Para estudiar tal efecto, en este trabajo se confecciona una cartografía 1:25.000 de los lineamientos morfológicos sobre la isla, a partir de una síntesis bibliográfica, del análisis morfométrico del relieve y del procesado de imágenes aéreas, que ulteriormente es validada mediante comparación con un modelo de fracturación de la isla. Con el objeto de encontrar una estructura en los patrones de lineamientos sobre este mapa se ha analizado si se comporta con características fractales en agregación y ocurrencia. La agregación de lineamientos ha sido caracterizada según un modelo de Levy-Lee de exponente D, detectándose tres comportamientos en la distribución azimutal de la dimensión fractal: D<1,5, D≈1,5, y D>1,5, que diferencian seis sectores sobre la isla. La ocupación espacial de las fracturas ha sido caracterizada mediante la estimación de la dimensión fractal de recubrimiento Do, lo que ha permitido distinguir las áreas en las que éstos tienden a distribuirse uniformemente (mayores valores de Do≈1,62 en el NE de la isla) de las que lo hacen limitadamente (valores más bajos de Do≈1,39 en la zona SW). La evaluación conjunta de disposición geográfica de las zonas con características fractales de agregación y ocurrencia semejantes ha permitido establecer una subdivisión en zonas en las que la morfología de los patrones de los lineamientos morfotectónicos se comporta de forma semejante. La comparación de esta zonificación con la tipología del volcanismo y/o actividad reciente acontecida en su interior permite establecer una posible relación entre el tipo de actividad volcánica y la complejidad del patrón en el que ocurre.
The Deception Island (Archipelago of the Shetland of the South, Antártida) is an active seismo-volcanic area in the Antarctic continent. The last and recent eruptive period in 1967, 1969, 1970, and the high frequency of low magnitude earthquakes demonstrate it. The island is in a complex geodynamic setting that establishes SO-NE and NNO-SSE the more important directions of tectonic control, however is not known how the complex geometric organization of fracture networks and faults affects in the distribution of the volcanism and the seismicity in the island. In order to study such effect, in this work a 1:25000 map of the morphologic lineaments is prepared, from a bibliographical synthesis, morphometric analysis of the relief and aerial image processing. The result is validated by means of comparison with a fracturation model of the island. In order to find an structure in the lineament patterns on this map their fractal aggregation and occurrence have been analyzed. The aggregation has been characterized according to a model of Levy-Lee with exponent D, detecting three behaviours in the azimuthal distribution of the fractal dimension: D<1,5, D = 1,5, and D>1.5, that allow to differentiate six sectors on the island. The space occupation of the fractures has been characterized by means of the estimation of the fractal covering dimension Do which allowed to distinguish the areas in which these tend to distribute uniformly (greater values of Do = 1,62 in NE of the island) or clustered (lower values of Do = 1,39 in zone SW). The joint evaluation of geographic disposition of the zones with similar fractal aggregation and occurrence characteristics has allowed establishing a subdivision in zones where the morphology of the lineament patterns bucket of similar way. The comparison of this zoning with the volcanism typology and/or recent activity allows to establish a possible relation between the type of volcanic activity and the complexity of the pattern in which it happens.
The Deception Island (Archipelago of the Shetland of the South, Antártida) is an active seismo-volcanic area in the Antarctic continent. The last and recent eruptive period in 1967, 1969, 1970, and the high frequency of low magnitude earthquakes demonstrate it. The island is in a complex geodynamic setting that establishes SO-NE and NNO-SSE the more important directions of tectonic control, however is not known how the complex geometric organization of fracture networks and faults affects in the distribution of the volcanism and the seismicity in the island. In order to study such effect, in this work a 1:25000 map of the morphologic lineaments is prepared, from a bibliographical synthesis, morphometric analysis of the relief and aerial image processing. The result is validated by means of comparison with a fracturation model of the island. In order to find an structure in the lineament patterns on this map their fractal aggregation and occurrence have been analyzed. The aggregation has been characterized according to a model of Levy-Lee with exponent D, detecting three behaviours in the azimuthal distribution of the fractal dimension: D<1,5, D = 1,5, and D>1.5, that allow to differentiate six sectors on the island. The space occupation of the fractures has been characterized by means of the estimation of the fractal covering dimension Do which allowed to distinguish the areas in which these tend to distribute uniformly (greater values of Do = 1,62 in NE of the island) or clustered (lower values of Do = 1,39 in zone SW). The joint evaluation of geographic disposition of the zones with similar fractal aggregation and occurrence characteristics has allowed establishing a subdivision in zones where the morphology of the lineament patterns bucket of similar way. The comparison of this zoning with the volcanism typology and/or recent activity allows to establish a possible relation between the type of volcanic activity and the complexity of the pattern in which it happens.