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D. Lange J. Cembrano A. Rietbrock C. Haberland T. Dahm K. Bataille 《Tectonophysics》2008,455(1-4):14-24
A temporal seismic network recorded local seismicity along a 130 km long segment of the transpressional dextral strike-slip Liquiñe-Ofqui fault zone (LOFZ) in southern Chile. Seventy five shallow crustal events with magnitudes up to Mw 3.8 and depths shallower than 25 km were observed in an 11-month period mainly occurring in different clusters. Those clusters are spatially related to the LOFZ, to the volcanoes Chaitén, Michinmahuida and Corcovado, and to active faulting on secondary faults. Further activity along the LOFZ is indicated by individual events located in direct vicinity of the surface expression of the LOFZ. Focal mechanisms were calculated using deviatoric moment tensor inversion of body wave amplitude spectra which mostly yield strike-slip mechanisms indicating a NE–SW direction of the P-axis for the LOFZ at this latitude. The seismic activity reveals the present-day activity of the fault zone. The recent Mw 6.2 event near Puerto Aysén, Southern Chile at 45.4°S on April 21, 2007 shows that the LOFZ is also capable of producing large magnitude earthquakes and therefore imposing significant seismic hazard to this region. 相似文献
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Jos Cembrano Alain Lavenu Peter Reynolds Gloria Arancibia Gloria Lpez Alejandro Sanhueza 《Tectonophysics》2002,354(3-4)
The southern Andes plate boundary zone records a protracted history of bulk transpressional deformation during the Cenozoic, which has been causally related to either oblique subduction or ridge collision. However, few structural and chronological studies of regional deformation are available to support one hypothesis or the other. We address along- and across-strike variations in the nature and timing of plate boundary deformation to better understand the Cenozoic tectonics of the southern Andes.Two east–west structural transects were mapped at Puyuhuapi and Aysén, immediately north of the Nazca–South America–Antarctica triple junction. At Puyuhuapi (44°S), north–south striking, high-angle contractional and strike-slip ductile shear zones developed from plutons coexist with moderately dipping dextral-oblique shear zones in the wallrocks. In Aysén (45–46°), top to the southwest, oblique thrusting predominates to the west of the Cenozoic magmatic arc, whereas dextral strike-slip shear zones develop within it.New 40Ar–39Ar data from mylonites and undeformed rocks from the two transects suggest that dextral strike-slip, oblique-slip and contractional deformation occurred at nearly the same time but within different structural domains along and across the orogen. Similar ages were obtained on both high strain pelitic schists with dextral strike-slip kinematics (4.4±0.3 Ma, laser on muscovite–biotite aggregates, Aysén transect, 45°S) and on mylonitic plutonic rocks with contractional deformation (3.8±0.2 to 4.2±0.2 Ma, fine-grained, recrystallized biotite, Puyuhuapi transect). Oblique-slip, dextral reverse kinematics of uncertain age is documented at the Canal Costa shear zone (45°S) and at the Queulat shear zone at 44°S. Published dates for the undeformed protholiths suggest both shear zones are likely Late Miocene or Pliocene, coeval with contractional and strike-slip shear zones farther north. Coeval strike-slip, oblique-slip and contractional deformation on ductile shear zones of the southern Andes suggest different degrees of along- and across-strike deformation partitioning of bulk transpressional deformation.The long-term dextral transpressional regime appears to be driven by oblique subduction. The short-term deformation is in turn controlled by ridge collision from 6 Ma to present day. This is indicated by most deformation ages and by a southward increase in the contractional component of deformation. Oblique-slip to contractional shear zones at both western and eastern margins of the Miocene belt of the Patagonian batholith define a large-scale pop-up structure by which deeper levels of the crust have been differentially exhumed since the Pliocene at a rate in excess of 1.7 mm/year. 相似文献
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Kinematic analysis of fault slip data for stress determination was carried out on Late Miocene to Quaternary rocks from the fore arc and intra-arc regions of the Chilean Andes, between 33° and 46° south latitudes. Studies of Neogene and Quaternary infilling (the Central Depression), as well as plutonic rocks of the North Patagonian Batholith along the Liquiñe–Ofqui Fault Zone, have revealed various compressional and/or transpressional states of stress. In the Pliocene, the maximum compressional stress (σ1) was generally oriented east–west. During the Quaternary, the deformation was partitioned into two coeval distinctive states of stress. In the fore arc zone, the state of stress was compressional, with σ1 oriented in a N–S to NNE–SSW direction. In the intra-arc zone the state of stress was transpressional with σ1 striking NE–SW. Along the coast, in one site (37°30′S) the Quaternary strain deformation is extensional, with an E–W direction, which can be explained by a co-seismic crustal bending readjustment. 相似文献
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D. Legrand S. Barrientos K. Bataille J. Cembrano A. Pavez 《Continental Shelf Research》2011,31(3-4):154-161
A seismic swarm of more than 7200 earthquakes occurred in Aysen Fjord, southern Chile, from January to June 2007. It started suddenly on 23 January 2007 with an earthquake of magnitude Mw=5.3, followed by five earthquakes with magnitudes increasing from Mw=5.2 to 6.2 within three months. Two large earthquakes of magnitudes Mw=6.1 and 6.2 occurred on 02 and 21 April 2007, respectively. The latest earthquake generated landslides that induced a tsunami within the fjord, killing 10 people. This swarm has been examined using international seismic catalogues and seismicity located with a local seismic network; in particular its double tectonic and volcanic origin has been explored. All the focal mechanisms are compatible with the long- and short-term tectonics of the Liquiñe-Ofqui Fault Zone, a major intra-arc fault system of the Patagonian fjord land. The space, time, and size distributions of these earthquakes, that occurred within an active volcanic area revealed by the presence of several Holocene monogenetic volcanoes, may be explained both by fluid-induced (magma and/or hydrothermal fluids) activity combined with tectonic activity. The co-existence of these two tectonic and volcanic phenomena is a good example of retroactive links between fluids and tectonic fractures. 相似文献
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J. Cembrano G. Gonzlez G. Arancibia I. Ahumada V. Olivares V. Herrera 《Tectonophysics》2005,400(1-4):105-125
Upper crustal strike-slip duplexes provide an excellent opportunity to address the fundamental question of fault zone development and strain partitioning in an evolving system. Detailed field mapping of the Mesozoic Atacama fault system in the Coastal Cordillera of Northern Chile documents the progressive development of second- and third-order faults forming a duplex at a dilational jog between two overstepping master faults: the sinistral strike-slip, NNW-striking, Jorgillo and Bolfin faults. These are constituted by a meter-wide core of foliated S-C ultracataclasite and cataclasite, flanked by a damage zone of protocataclasite, splay faults and veins. Lateral separation of markers along master faults is on the order of a few kilometers. Second-order, NW-striking, oblique-slip subsidiary fault zones do not show foliated ultracataclasite; lateral sinistral separations are in the range of 10 to 200 m with a relatively minor normal dip-slip component. In turn, third-order, east–west striking normal faults exhibit centimetric displacement. Oblique-slip (sinistral–normal) fault zones located at the southern termination of the Bolfin fault form a well-developed imbricate fan structure. They exhibit a relatively simple architecture of extensional and extensional-shear fractures bound by low displacement shear fractures. Kinematic analysis of fault slip data from mesoscopic faults within the duplex area, document that the NW-striking and the EW-striking faults accommodate transtension and extension, respectively. Examination of master and subsidiary faults of the duplex indicates a strong correlation between total displacement and internal fault structure. Faults started from arrays of en echelon extensional/extensional-shear fractures that then coalesced into throughgoing strike-slip faults. Further displacement leads to the formation of discrete bands of cataclasite and ultracataclasite that take up a significant part of the total displacement. We interpret that the duplex formed by progressive linkage of horsetail-like structures at the southern tip of the Bolfin fault that joined splay faults coming from the Jorgillo and Coloso faults. The geometry and kinematics of faults is compared with that observed in analog models to gain an insight into the kinematic processes leading to complex strike-slip fault zones in the upper crust. 相似文献
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