International Geologiical Congress - Oslo 2008

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STP-02 Deducing nature and magnitude of paleoearthquakes: Finding paleoevents and quantifying them - Part 2

 

Paleoseismic evidence for reverse fault activity in relationship with a phreatomagmatic eruption in 1970 at Deception Island (West-Antarctica)

 

Raúl Pérez-López, Fundación CEU San Pablo (Spain)
Miguel Ángel Rodríguez-Pascua, IGME (Spain)
Marta Bejar, Universidad Complutense de Madrid (Spain)
José Jesús Martínez-Díaz, Universidad Complutense de Madrid (Spain)
Jorge Luis Giner-Robles, Fundación CEU San Pablo (Spain)
Pablo Gabriel Silva, Universidad de Salamanca (Spain)
Pilar Villamor, Institute of Geológical and Nucleal Sciences (New Zealand)
José Manuel González-Casado, Universidad Autónoma de Madrid (Spain)
 

 

Plotting the world's spatial distribution of the instrumental seismicity and overlapping with the major volcanic activity on the Earth's surface, clearly it exhibits a relationship. However, studies of tectonic earthquakes triggered by volcanic eruptions are scarce. This work addresses the presence of a superficial rupture scarp in relationship with the phreatomagmatic eruption occurred in 1970 at Deception Island, West Antarctica. We have analyzed previous aerial photographs (1968) to the last eruption (1970) where the fault scarp does not appear. In addition, we have analysed a high resolution satellite image (64 x 64 cm; Quickbird, 2003) where the fault scarp was mapped. This information was relevant to determine the scarp morphology, fluvial network spatial and temporal variations and uplifted fluvial terraces. This geomorphic evidence indicates fault activity between 1968 and 2003. Accordingly and during the austral summer of 2007, we carried out a field campaign with the purpose to perform several trenches across the fault scarp (hereafter, the Maria Fault). This analysis shows a reverse fault movement through 1 km of superficial rupture with 20 cm of vertical throw. This segment is bounded by a glacier to the east and the inner bay (port Foster) to the west tip of the fault rupture. This fault activity affected to the pyroclastic volcano sedimentary sequence of the 1970's eruption, being later affected by erosion processes. By comparison with the seismic instrumental database of IRIS catalogue (1960-2003), one small earthquake (M = 5.4) occurred at the summer of 1970, near to the fault scarp and the phreatomagmatic crater (800 m). The location error of the epicentre is about 15 km. Therefore, three tectonic and volcanic interaction models are discussed: (1) Reverse small-moderate earthquake, ranging between M 5 and 6 and triggered by the 1970`s eruption, (2) Reactivation of a previous superficial fault as a consequence of a dike injection and/or magma migration in relationship with the eruptive process between 1967 and 1970 and (3) Aseismic fault creep activity post-earthquake, being this a volcanic earthquake in relationship with the phreatomagmatic 1970's eruption

 

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