HR: 15:15h
AN: S43C-04 INVITED     [Abstracts]
TI: The Aysen (Southern Chile) 2007 Seismic Swarm: Volcanic or Tectonic Origin?
AU: * Comte, D
EM: dcomte@dgf.uchile.cl
AF: Depto. de Geofisica Universidad de Chile, Blanco Encalada 2002, Santiago, SA 2777, Chile
AU: Gallego, A
EM: agallego@ufl.edu
AF: Dept. of Geological Sciences University of Florida, 241 Williamson Hall, Gainesville, FL 32611, United States
AU: Russo, R
EM: rrusso@ufl.edu
AF: Dept. of Geological Sciences University of Florida, 241 Williamson Hall, Gainesville, FL 32611, United States
AU: Mocanu, V
EM: mocanu@gg.unibuc.ro
AF: Dept. of Geology and Geophyics University of Bucharest, 6 Traian Vuia Str., Bucharest, RO 70139, Romania
AU: Murdie, R
EM: Ruth.Murdie@ctbto.org
AF: CTBTO, P.O. Box 1200, Vienna, VI 1400, Austria
AU: VanDecar, J
EM: jvandecar@hotmail.com
AF: DTM, Carnegie Inst. Of Washington, 5200 Broad Branch Rd., Washington, DC 20015, United States
AB: The Aysen seismic swarm began January 23, 2007, with a magnitude 5.2 (USGS) earthquake and, after an apparent decrease in activity, continued with a magnitude 5.6 event on February 26. The swarm is characterized by numerous felt earthquakes of small to moderate magnitude, located at crustal depths beneath the Aysen Canal, a prominent fiord of the Chilean littoral. The region is characterized by the subduction of an active oceanic spreading ridge: the Chile Ridge, the divergent Nazca-Antarctic plate boundary, is currently subducting beneath continental South America along the Chile Trench at approximately 46.5°S, forming a plate triple junction in the vicinity of the Taitao Peninsula, somewhat south and west of the swarm. Also, the Liquine-Ofqui dextral strike- slip fault traverses the Aysen Canal in the vicinity of the swarm. This fault has been interpreted as a 1000 km long dextral intra-arc strike-slip fault zone, consisting of two major strands which extend north from the Chile Margin triple junction. The Liquiñe-Ofqui system is marked by several pull-apart basins along its trace through the area. Seismic activity along the Liquiñe-Ofqui fault zone has been poorly studied to date, largely because teleseismic events clearly related to the fault have been few, and southern hemisphere seismic stations are lacking. However, we deployed a dense temporary broad-band seismic network both onland and on the islands in the Aysen region, which allowed us to capture the initial phases of the swarm on some 20 stations, and to determine the background seismicity patterns in this area for the two years preceding the swarm. The swarm could be caused by several processes: the spatial and depth distribution of the events suggests that they are well correlated with reactivation of the southern end of the Liquiñe-Ofqui fault, as defined by geologic studies and onshore gravity data collected in southern Chile. The swarm may be related to formation of new volcanic center between Volcan Hudson (last erupted 1991) and Volcan Maca. Given uncertainties in the event locations, the 2007 seismic swarm could also result from a combination of tectonic motions on the Liquiñe-Ofqui fault system and magmatic arc activity. The two earthquakes with magnitudes over 5 and the numerous felt earthquake of the swarm clearly indicate that seismic hazard estimations in this previously quiescent region must be re-estimated.
DE: 7200 SEISMOLOGY
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Seismology [S]
MN: 2007 Joint Assembly